This document describes a revised protocol for the TCP-based convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The protocol revision is based on implementation issues in the original TCPCL Version 3 and updates to the Bundle Protocol contents, encodings, and convergence layer requirements in Bundle Protocol Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7 bundles as its service data unit being transported and provides a reliable transport of such bundles. Several new IANA registries are defined for TCPCLv4 which define some behaviors inherited from TCPCLv3 but with updated encodings and/or semantics.
This Internet-Draft will expire on June 17, 2018.
This document describes the TCP-based convergence-layer protocol for Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to- end architecture providing communications in and/or through highly stressed environments, including those with intermittent connectivity, long and/or variable delays, and high bit error rates. More detailed descriptions of the rationale and capabilities of these networks can be found in "Delay-Tolerant Network Architecture" [RFC4838].
An important goal of the DTN architecture is to accommodate a wide range of networking technologies and environments. The protocol used for DTN communications is the revised Bundle Protocol (BP) [I-D.ietf-dtn-bpbis], an application-layer protocol that is used to construct a store-and- forward overlay network. As described in the Bundle Protocol specification [I-D.ietf-dtn-bpbis], it requires the services of a "convergence- layer adapter" (CLA) to send and receive bundles using the service of some "native" link, network, or Internet protocol. This document describes one such convergence-layer adapter that uses the well-known Transmission Control Protocol (TCP). This convergence layer is referred to as TCPCL.
The locations of the TCPCL and the BP in the Internet model protocol stack (described in [RFC1122]) are shown in Figure 1. In particular, when BP is using TCP as its bearer with TCPCL as its convergence layer, both BP and TCPCL reside at the application layer of the Internet model.
The format of protocol data units of the Bundle Protocol, as those are defined elsewhere in [RFC5050] and [I-D.ietf-dtn-bpbis]. This includes the concept of bundle fragmentation or bundle encapsulation. The TCPCL transfers bundles as opaque data blocks.
Mechanisms for locating or identifying other bundle nodes within an internet.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This section contains definitions that are interpreted to be specific to the operation of the TCPCL protocol, as described below.
A TCPCL node refers to either side of an negotiating or in-service TCPCL Session. For most TCPCL behavior, the two nodes are symmetric and there is no protocol distinction between them. Some specific behavior, particularly during negotiation, distinguishes between the connecting node and the connected-to node. For the remainder of this document, the term "node" without the prefix "TCPCL" refers to a TCPCL node.
A TCP connection refers to a transport connection using TCP as the transport protocol.
A TCPCL session (as opposed to a TCP connection) is a TCPCL communication relationship between two bundle nodes. The lifetime of a TCPCL session is bound to the lifetime of an underlying TCP connection. Therefore, a TCPCL session is initiated after a bundle node establishes a TCP connection to for the purposes of bundle communication. A TCPCL session is terminated when the TCP connection ends, due either to one or both nodes actively terminating the TCP connection or due to network errors causing a failure of the TCP connection. For the remainder of this document, the term "session" without the prefix "TCPCL" refers to a TCPCL session.
The session parameters are a set of values used to affect the operation of the TCPCL for a given session. The manner in which these parameters are conveyed to the bundle node and thereby to the TCPCL is implementation dependent. However, the mechanism by which two bundle nodes exchange and negotiate the values to be used for a given session is described in Section 4.2.
Transfer refers to the procedures and mechanisms (described below) for conveyance of an individual bundle from one node to another. Each transfer within TCPCLv4 is identified by a Transfer ID number which is unique only to a single direction within a single Session.
A TCPCL session is idle while the only messages being transmitted or received are KEEPALIVE messages.
A TCPCL session is lively while any messages are being transmitted or received.
The TCPCL uses numeric codes to encode specific reasons for individual failure/error message types. This limits the expressiveness of TCPCL error encodings, but simplifies the encoding of errors and allows an application policy to attempt recovery from expected 'failure' modes (e.g. if a Session cannot be established with USE_TLS disabled because of a Contact Failure shutdown, a re-attempt can be made with USE_TLS enabled).
The service of this protocol is the transmission of DTN bundles via the Transmission Control Protocol (TCP). This document specifies the encapsulation of bundles, procedures for TCP setup and teardown, and a set of messages and node requirements. The general operation of the protocol is as follows.
First, one node establishes a TCPCL session to the other by initiating a TCP connection in accordance with [RFC0793]. After setup of the TCP connection is complete, an initial contact header is exchanged in both directions to set parameters of the TCPCL session and exchange a singleton endpoint identifier for each node (not the singleton Endpoint Identifier (EID) of any application running on the node) to denote the bundle-layer identity of each DTN node. This is used to assist in routing and forwarding messages (e.g. to prevent loops).
Once the TCPCL session is established and configured in this way, bundles can be transferred in either direction. Each transfer is performed by an initialization (XFER_INIT) message followed by one or more logical segments of data within an XFER_SEGMENT message. The choice of the length to use for segments is an implementation matter, but each segment must be no larger than the receiving node's maximum receive unit (MRU) (see the field "Segment MRU" of Section 4.1). The first segment for a bundle MUST set the 'START' flag, and the last one MUST set the 'end' flag in the XFER_SEGMENT message flags.
If multiple bundles are transmitted on a single TCPCL connection, they MUST be transmitted consecutively. Interleaving data segments from different bundles is not allowed. Bundle interleaving can be accomplished by fragmentation at the BP layer or by establishing multiple TCPCL sessions.
A feature of this protocol is for the receiving node to send acknowledgments as bundle data segments arrive (XFER_ACK). The rationale behind these acknowledgments is to enable the sender node to determine how much of the bundle has been received, so that in case the session is interrupted, it can perform reactive fragmentation to avoid re-sending the already transmitted part of the bundle. For each data segment that is received, the receiving node sends an XFER_ACK message containing the cumulative length of the bundle that has been received. The sending node MAY transmit multiple XFER_SEGMENT messages without necessarily waiting for the corresponding XFER_ACK responses. This enables pipelining of messages on a channel. In addition, there is no explicit flow control on the TCPCL layer.
Another feature is that a receiver MAY interrupt the transmission of a bundle at any point in time by replying with a XFER_REFUSE message, which causes the sender to stop transmission of the current bundle, after completing transmission of a partially sent data segment. Note: This enables a cross-layer optimization in that it allows a receiver that detects that it already has received a certain bundle to interrupt transmission as early as possible and thus save transmission capacity for other bundles.
For sessions that are idle, a KEEPALIVE message is sent at a negotiated interval. This is used to convey node liveliqness information during otherwise message-less time intervals.
Finally, before sessions close, a SHUTDOWN message is sent to the session peer (see Section 6.1). After sending a SHUTDOWN message, the peer can not initiate any further transfers and the session enters a closing-down phase. After receiving a SHUTDOWN message and when no transfers are in-progress (i.e. have pending or unacknowledged segments), the receiving peer can close the session without chance of lost transfers. A SHUTDOWN message can also be used to refuse a session setup by a peer (see Section 4.2). It is an implementation matter to determine whether or not to close a TCPCL session while there are no transfers queued or in-progress.
There are specific messages for sending and receiving operations (in addition to session setup/teardown). TCPCL is symmetric, i.e., both sides can start sending data segments in a session, and one side's bundle transfer does not have to complete before the other side can start sending data segments on its own. Hence, the protocol allows for a bi-directional mode of communication. Note that in the case of concurrent bidirectional transmission, acknowledgment segments MAY be interleaved with data segments.
The following figure depicts the protocol exchange for a simple session, showing the session establishment and the transmission of a single bundle split into three data segments (of lengths "L1", "L2", and "L3") from Node A to Node B.
Note that the sending node MAY transmit multiple XFER_SEGMENT messages without necessarily waiting for the corresponding XFER_ACK responses. This enables pipelining of messages on a channel. Although this example only demonstrates a single bundle transmission, it is also possible to pipeline multiple XFER_SEGMENT messages for different bundles without necessarily waiting for XFER_ACK messages to be returned for each one. However, interleaving data segments from different bundles is not allowed.
No errors or rejections are shown in this example.
For bundle transmissions to occur using the TCPCL, a TCPCL session MUST first be established between communicating nodes. It is up to the implementation to decide how and when session setup is triggered. For example, some sessions MAY be opened proactively and maintained for as long as is possible given the network conditions, while other sessions MAY be opened only when there is a bundle that is queued for transmission and the routing algorithm selects a certain next-hop node.
To establish a TCPCL session, a node MUST first establish a TCP connection with the intended peer node, typically by using the services provided by the operating system. Destination port number 4556 has been assigned by IANA as the Registered Port number for the TCP convergence layer. Other destination port numbers MAY be used per local configuration. Determining a peer's destination port number (if different from the registered TCPCL port number) is up to the implementation. Any source port number MAY be used for TCPCL sessions. Typically an operating system assigned number in the TCP Ephemeral range (49152--65535) is used.
If the node is unable to establish a TCP connection for any reason, then it is an implementation matter to determine how to handle the connection failure. A node MAY decide to re-attempt to establish the connection. If it does so, it MUST NOT overwhelm its target with repeated connection attempts. Therefore, the node MUST retry the connection setup only after some delay (a 1-second minimum is RECOMMENDED), and it SHOULD use a (binary) exponential backoff mechanism to increase this delay in case of repeated failures. In case a SHUTDOWN message specifying a reconnection delay is received, that delay is used as the initial delay. The default initial delay SHOULD be at least 1 second but SHOULD be configurable since it will be application and network type dependent.
The node MAY declare failure after one or more connection attempts and MAY attempt to find an alternate route for bundle data. Such decisions are up to the higher layer (i.e., the BP).
Once a TCP connection is established, each node MUST immediately transmit a contact header over the TCP connection. The format of the contact header is described in Section 4.1.
After receiving the contact header from the other node, either node MAY also refuse the session by sending a SHUTDOWN message. If session setup is refused, a reason MUST be included in the SHUTDOWN message.
Once a TCP connection is established, both parties exchange a contact header. This section describes the format of the contact header and the meaning of its fields.
A four-octet field that always contains the octet sequence 0x64 0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII (and UTF-8).
A one-octet field value containing the value 4 (current version of the protocol).
A one-octet field of single-bit flags, interpreted according to the descriptions in Table 1.
A 16-bit unsigned integer indicating the interval, in seconds, between any subsequent messages being transmitted by the peer. The peer receiving this contact header uses this interval to determine how long to wait after any last-message transmission and a necessary subsequent KEEPALIVE message transmission.
A 64-bit unsigned integer indicating the largest allowable single-segment data payload size to be received in this session. Any XFER_SEGMENT sent to this peer SHALL have a data payload no longer than the peer's Segment MRU. The two nodes of a single session MAY have different Segment MRUs, and no relation between the two is required.
A 64-bit unsigned integer indicating the largest allowable total-bundle data size to be received in this session. Any bundle transfer sent to this peer SHALL have a Total bundle data payload no longer than the peer's Transfer MRU. This value can be used to perform proactive bundle fragmentation. The two nodes of a single session MAY have different Transfer MRUs, and no relation between the two is required.
Together these fields represent a variable-length text string. The EID Length is a 16-bit unsigned integer indicating the number of octets of EID Data to follow. A zero EID Length SHALL be used to indicate the lack of EID rather than a truly empty EID. This case allows an node to avoid exposing EID information on an untrusted network. A non-zero-length EID Data SHALL contain the UTF-8 encoded EID of some singleton endpoint in which the sending node is a member, in the canonical format of <scheme name>:<scheme-specific part>. This EID encoding is consistent with [I-D.ietf-dtn-bpbis].
Together these fields represent protocol extension data not defined by this specification. The Header Extension Length is the total number of octets to follow which are used to encode the Header Extension Item list. The encoding of each Header Extension Item is identical form as described in Section 4.1.1.
CAN_TLS 0x01 If bit is set, indicates that the sending peer is capable of TLS security.
A one-octet field containing generic bit flags about the item, which are listed in Table 2. If a TCPCL node receives an extension item with an unknown Item Type and the CRITICAL flag set, the node SHALL close the TCPCL session with SHUTDOWN reason code of "Contact Failure". If the CRITICAL flag is not set, an node SHALL skip over and ignore any item with an unknown Item Type.
A 16-bit unsigned integer field containing the type of the extension item. This specification does not define any extension types directly, but does allocate an IANA registry for such codes (see Section 8.3).
A 32-bit unsigned integer field containing the number of Item Value octets to follow.
A variable-length data field which is interpreted according to the associated Item Type. This specification places no restrictions on an extensions use of available Item Value data. Extension specification SHOULD avoid the use of large data exchanges within the TCPCLv4 contact header as no bundle transfers can begin until the a full contact exchange and negotiation has been completed.
CRITICAL 0x01 If bit is set, indicates that the receiving peer must handle the extension item.
Upon reception of the contact header, each node follows the following procedures to ensure the validity of the TCPCL session and to negotiate values for the session parameters.
If the magic string is not present or is not valid, the connection MUST be terminated. The intent of the magic string is to provide some protection against an inadvertent TCP connection by a different protocol than the one described in this document. To prevent a flood of repeated connections from a misconfigured application, a node MAY elect to hold an invalid connection open and idle for some time before closing it.
A connecting TCPCL node SHALL send the highest TCPCL protocol version on a first session attempt for a TCPCL peer. If a connecting node receives a SHUTDOWN message with reason of "Version Mismatch", that node MAY attempt further TCPCL sessions with the peer using earlier protocol version numbers in decreasing order. Managing multi-TCPCL-session state such as this is an implementation matter.
If a node receives a contact header containing a version that is greater than the current version of the protocol that the node implements, then the node SHALL shutdown the session with a reason code of "Version mismatch". If a node receives a contact header with a version that is lower than the version of the protocol that the node implements, the node MAY either terminate the session (with a reason code of "Version mismatch"). Otherwise, the node MAY adapt its operation to conform to the older version of the protocol. The decision of version fall-back is an implementation matter.
A node calculates the parameters for a TCPCL session by negotiating the values from its own preferences (conveyed by the contact header it sent to the peer) with the preferences of the peer node (expressed in the contact header that it received from the peer). The negotiated parameters defined by this specification are described in the following paragraphs.
Negotiation of the Session Keepalive parameter is performed by taking the minimum of this two contact headers' Keepalive Interval. If the negotiated Session Keepalive is zero (i.e. one or both contact headers contains a zero Keepalive Interval), then the keepalive feature (described in Section 5.2.1) is disabled. There is no logical minimum value for the keepalive interval, but when used for many sessions on an open, shared network a short interval could lead to excessive traffic. For shared network use, nodes SHOULD choose a keepalive interval no shorter than 30 seconds. There is no logical maximum value for the keepalive interval, but an idle TCP connection is liable for closure by the host operating system if the keepalive time is longer than tens-of-minutes. Nodes SHOULD choose a keepalive interval no longer than 10 minutes (600 seconds).
Negotiation of the Enable TLS parameter is performed by taking the logical AND of the two contact headers' CAN_TLS flags. If the negotiated Enable TLS value is true then TLS negotiation feature (described in Section 4.3) begins immediately following the contact header exchange. The security policy on either node MAY forbid the establishment of a TCPCL session for any Enable TLS result (or for any combination of local or peer CAN_TLS flag), in which case the node SHALL shutdown the session with a reason code of "Contact Failure". For example, one node may disallow TCPCL sessions without TLS, while a second node may disallow sessions with TLS. Also note that this Contact Failure (of the header negotiation) is different than a TLS Failure (after an agreed-upon Enable TLS state).
Once this process of parameter negotiation is completed (which includes a possible completed TLS handshake of the connection to use TLS), this protocol defines no additional mechanism to change the parameters of an established session; to effect such a change, the TCPCL session MUST be terminated and a new session established.
This version of the TCPCL supports establishing a Transport Layer Security (TLS) session within an existing TCP connection. Negotiation of whether or not to initiate TLS within a TCPCL session is part of the contact header as described in Section 4.2. The TLS handshake, if it occurs, is considered to be part of the contact negotiation before the TCPCL session itself is established. Specifics about sensitive data exposure are discussed in Section 7.
When TLS is used within the TCPCL it affects the entire session. By convention, this protocol uses the node which initiated the underlying TCP connection as the "client" role of the TLS handshake request. Once a TLS session is established within TCPCL, there is no mechanism provided to end the TLS session and downgrade the session. If a non-TLS session is desired after a TLS session is started then the entire TCPCL session MUST be shutdown first.
After negotiating an Enable TLS parameter of true, and before any other TCPCL messages are sent within the session, the session nodes SHALL begin a TLS handshake in accordance with [RFC5246]. The parameters within each TLS nqion are implementation dependent but any TCPCL node SHOULD follow all recommended best practices of [RFC7525].
If a TLS handshake cannot negotiate a TLS session, both nodes of the TCPCL session SHALL cause a TCPCL shutdown with reason "TLS Failure".
After a TLS session is successfully established, both TCPCL nodes SHALL re-exchange TCPCL Contact Header messages. Any information cached from the prior Contact Header exchange SHALL be discarded. This re-exchange avoids man-in-the-middle attack in identical fashion to [RFC2595]. Each re-exchange header CAN_TLS flag SHALL be identical to the original header CAN_TLS flag from the same node. The CAN_TLS logic (TLS negotiation) SHALL NOT apply during header re-exchange. This reinforces the fact that there is no TLS downgrade mechanism.
A summary of a typical CAN_TLS usage is shown in the sequence in Figure 5 below.
This section describes the protocol operation for the duration of an established session, including the mechanism for transmitting bundles over the session.
Indicates the type of the message as per Table 3 below. Encoded values are listed in Section 8.4.
XFER_INIT Contains the length (in octets) of the next transfer, as described in Section 5.3.2.
XFER_SEGMENT Indicates the transmission of a segment of bundle data, as described in Section 5.3.3.
XFER_ACK Acknowledges reception of a data segment, as described in Section 5.3.4.
XFER_REFUSE Indicates that the transmission of the current bundle SHALL be stopped, as described in Section 5.3.5.
KEEPALIVE Used to keep TCPCL session active, as described in Section 5.2.1.
SHUTDOWN Indicates that one of the nodes participating in the session wishes to cleanly terminate the session, as described in Section 6.
MSG_REJECT Contains a TCPCL message rejection, as described in Section 5.2.2.
The protocol includes a provision for transmission of KEEPALIVE messages over the TCPCL session to help determine if the underlying TCP connection has been disrupted.
As described in Section 4.1, one of the parameters in the contact header is the Keepalive Interval. Both sides populate this field with their requested intervals (in seconds) between KEEPALIVE messages.
The format of a KEEPALIVE message is a one-octet message type code of KEEPALIVE (as described in Table 3) with no additional data. Both sides SHOULD send a KEEPALIVE message whenever the negotiated interval has elapsed with no transmission of any message (KEEPALIVE or other).
If no message (KEEPALIVE or other) has been received for at least twice the Keepalive Interval, then either party MAY terminate the session by transmitting a one-octet SHUTDOWN message (as described in Section 6.1) with reason code "Idle Timeout", and by closing the session.
Note: The Keepalive Interval SHOULD not be chosen too short as TCP retransmissions MAY occur in case of packet loss. Those will have to be triggered by a timeout (TCP retransmission timeout (RTO)), which is dependent on the measured RTT for the TCP connection so that KEEPALIVE messages MAY experience noticeable latency.
If a TCPCL node receives a message which is unknown to it (possibly due to an unhandled protocol mismatch) or is inappropriate for the current session state (e.g. a KEEPALIVE message received after contact header negotiation has disabled that feature), there is a protocol-level message to signal this condition in the form of a MSG_REJECT reply.
A one-octet refusal reason code interpreted according to the descriptions in Table 4.
The Rejected Message Header is a copy of the Message Header to which the MSG_REJECT message is sent as a response.
Message Type Unknown 0x01 A message was received with a Message Type code unknown to the TCPCL node.
Message Unsupported 0x02 A message was received but the TCPCL node cannot comply with the message contents.
Message Unexpected 0x03 A message was received while the session is in a state in which the message is not expected.
All of the message in this section are directly associated with transferring a bundle between TCPCL nodes.
A single TCPCL transfer results in a bundle (handled by the convergence layer as opaque data) being exchanged from one node to the other. In TCPCL a transfer is accomplished by dividing a single bundle up into "segments" based on the receiving-side Segment MRU (see Section 4.1).
A single transfer (and by extension a single segment) SHALL NOT contain data of more than a single bundle. This requirement is imposed on the agent using the TCPCL rather than TCPCL itself.
Each of the bundle transfer messages contains a Transfer ID number which is used to correlate messages originating from sender and receiver of a bundle. A Transfer ID does not attempt to address uniqueness of the bundle data itself and has no relation to concepts such as bundle fragmentation. Each invocation of TCPCL by the bundle protocol agent, requesting transmission of a bundle (fragmentary or otherwise), results in the initiation of a single TCPCL transfer. Each transfer entails the sending of a XFER_INIT message and some number of XFER_SEGMENT and XFER_ACK messages; all are correlated by the same Transfer ID.
Transfer IDs from each node SHALL be unique within a single TCPCL session. The initial Transfer ID from each node SHALL have value zero. Subsequent Transfer ID values SHALL be incremented from the prior Transfer ID value by one. Upon exhaustion of the entire 64-bit Transfer ID space, the sending node SHALL terminate the session with SHUTDOWN reason code "Resource Exhaustion".
For bidirectional bundle transfers, a TCPCL node SHOULD NOT rely on any relation between Transfer IDs originating from each side of the TCPCL session.
The XFER_INIT message contains the total length, in octets, of the bundle data in the associated transfer. The total length is formatted as a 64-bit unsigned integer.
The purpose of the XFER_INIT message is to allow nodes to preemptively refuse bundles that would exceed their resources or to prepare storage on the receiving node for the upcoming bundle data. See Section 5.3.5 for details on when refusal based on XFER_INIT content is acceptable.
The Total Bundle Length field within a XFER_INIT message SHALL be treated as authoritative by the receiver. If, for whatever reason, the actual total length of bundle data received differs from the value indicated by the XFER_INIT message, the receiver SHOULD treat the transmitted data as invalid.
A 64-bit unsigned integer identifying the transfer about to begin.
A 64-bit unsigned integer indicating the size of the data-to-be-transferred.
An XFER_INIT message SHALL be sent immediately before transmission of any XFER_SEGMENT messages for each Transfer ID. XFER_INIT messages MUST NOT be sent unless the next XFER_SEGMENT message has the 'START' bit set to "1" (i.e., just before the start of a new transfer).
A receiver MAY send a BUNDLE_REFUSE message as soon as it receives a XFER_INIT message without waiting for the next XFER_SEGMENT message. The sender MUST be prepared for this and MUST associate the refusal with the correct bundle via the Transfer ID fields.
Each bundle is transmitted in one or more data segments. The format of a XFER_SEGMENT message follows in Figure 9.
A one-octet field of single-bit flags, interpreted according to the descriptions in Table 5.
A 64-bit unsigned integer identifying the transfer being made.
A 64-bit unsigned integer indicating the number of octets in the Data contents to follow.
The variable-length data payload of the message.
END 0x01 If bit is set, indicates that this is the last segment of the transfer.
START 0x02 If bit is set, indicates that this is the first segment of the transfer.
The flags portion of the message contains two optional values in the two low-order bits, denoted 'START' and 'END' in Table 5. The 'START' bit MUST be set to one if it precedes the transmission of the first segment of a transfer. The 'END' bit MUST be set to one when transmitting the last segment of a transfer. In the case where an entire transfer is accomplished in a single segment, both the 'START' and 'END' bits MUST be set to one.
Once a transfer of a bundle has commenced, the node MUST only send segments containing sequential portions of that bundle until it sends a segment with the 'END' bit set. No interleaving of multiple transfers from the same node is possible within a single TCPCL session. Simultaneous transfers between two nodes MAY be achieved using multiple TCPCL sessions.
Although the TCP transport provides reliable transfer of data between transport peers, the typical BSD sockets interface provides no means to inform a sending application of when the receiving application has processed some amount of transmitted data. Thus, after transmitting some data, a Bundle Protocol agent needs an additional mechanism to determine whether the receiving agent has successfully received the segment. To this end, the TCPCL protocol provides feedback messaging whereby a receiving node transmits acknowledgments of reception of data segments.
The format of an XFER_ACK message follows in Figure 10.
A 64-bit unsigned integer identifying the transfer being acknowledged.
A 64-bit unsigned integer indicating the total number of octets in the transfer which are being acknowledged.
A receiving TCPCL endpoing SHALL send an XFER_ACK message in response to each received XFER_SEGMENT message. The flags portion of the XFER_ACK header SHALL be set to match the corresponding DATA_SEGMENT message being acknowledged. The acknowledged length of each XFER_ACK contains the sum of the data length fields of all XFER_SEGMENT messages received so far in the course of the indicated transfer.
For example, suppose the sending node transmits four segments of bundle data with lengths 100, 200, 500, and 1000, respectively. After receiving the first segment, the node sends an acknowledgment of length 100. After the second segment is received, the node sends an acknowledgment of length 300. The third and fourth acknowledgments are of length 800 and 1800, respectively.
The TCPCL supports an mechanism by which a receiving node can indicate to the sender that it does not want to receive the corresponding bundle. To do so, upon receiving a XFER_INIT or XFER_SEGMENT message, the node MAY transmit a XFER_REFUSE message. As data segments and acknowledgments MAY cross on the wire, the bundle that is being refused SHALL be identified by the Transfer ID of the refusal.
There is no required relation between the Transfer MRU of a TCPCL node (which is supposed to represent a firm limitation of what the node will accept) and sending of a XFER_REFUSE message. A XFER_REFUSE can be used in cases where the agent's bundle storage is temporarily depleted or somehow constrained. A XFER_REFUSE can also be used after the bundle header or any bundle data is inspected by an agent and determined to be unacceptable.
A one-octet refusal reason code interpreted according to the descriptions in Table 6.
A 64-bit unsigned integer identifying the transfer being refused.
Unknown Reason for refusal is unknown or not specified.
Completed The receiver already has the complete bundle. The sender MAY consider the bundle as completely received.
No Resources The receiver's resources are exhausted. The sender SHOULD apply reactive bundle fragmentation before retrying.
Retransmit The receiver has encountered a problem that requires the bundle to be retransmitted in its entirety.
The receiver MUST, for each transfer preceding the one to be refused, have either acknowledged all XFER_SEGMENTs or refused the bundle transfer.
The bundle transfer refusal MAY be sent before an entire data segment is received. If a sender receives a XFER_REFUSE message, the sender MUST complete the transmission of any partially sent XFER_SEGMENT message. There is no way to interrupt an individual TCPCL message partway through sending it. The sender MUST NOT commence transmission of any further segments of the refused bundle subsequently. Note, however, that this requirement does not ensure that a node will not receive another XFER_SEGMENT for the same bundle after transmitting a XFER_REFUSE message since messages MAY cross on the wire; if this happens, subsequent segments of the bundle SHOULD also be refused with a XFER_REFUSE message.
Note: If a bundle transmission is aborted in this way, the receiver MAY not receive a segment with the 'END' flag set to '1' for the aborted bundle. The beginning of the next bundle is identified by the 'START' bit set to '1', indicating the start of a new transfer, and with a distinct Transfer ID value.
This section describes the procedures for ending a TCPCL session.
To cleanly shut down a session, a SHUTDOWN message MUST be transmitted by either node at any point following complete transmission of any other message. After sending a SHUTDOWN message, the sender of the message MAY send further acknowledgments (XFER_ACK or XFER_REFUSE) but no further data messages (XFER_INIT or XFER_SEGMENT). A receiving node SHOULD acknowledge all received data segments before sending a SHUTDOWN message to end the session. A transmitting node SHALL treat a SHUTDOWN message received mid-transfer (i.e. before the final acknowledgment) as a failure of the transfer.
After transmitting a SHUTDOWN message, an node MAY immediately close the associated TCP connection. Once the SHUTDOWN message is sent, any further received data on the TCP connection SHOULD be ignored. Any delay between request to terminate the TCP connection and actual closing of the connection (a "half-closed" state) MAY be ignored by the TCPCL node.
A one-octet field of single-bit flags, interpreted according to the descriptions in Table 7.
A one-octet refusal reason code interpreted according to the descriptions in Table 8. The Reason Code is present or absent as indicated by one of the flags.
A 16-bit unsigned integer indicating the desired delay until further TCPCL sessions to the sending node. The Reconnection Delay is present or absent as indicated by one of the flags.
D 0x01 If bit is set, indicates that a Reconnection Delay field is present.
R 0x02 If bit is set, indicates that a Reason Code field is present.
Idle timeout The session is being closed due to idleness.
Version mismatch The node cannot conform to the specified TCPCL protocol version.
Busy The node is too busy to handle the current session.
Contact Failure The node cannot interpret or negotiate contact header option.
TLS Failure The node failed to negotiate TLS session and cannot continue the session.
Resource Exhaustion The node has run into some resource limit and cannot continue the session.
It is also possible to convey a requested reconnection delay to indicate how long the other node MUST wait before attempting session re-establishment. To do so, the node sets the 'D' bit in the message flags and then transmits an 16-bit unsigned integer specifying the requested delay, in seconds, following the message header (and optionally, the SHUTDOWN reason code). The value 0 SHALL be interpreted as an infinite delay, i.e., that the connecting node MUST NOT re-establish the session. In contrast, if the node does not wish to request a delay, it SHOULD omit the reconnection delay field (and set the 'D' bit to zero).
A session shutdown MAY occur immediately after TCP connection establishment or reception of a contact header (and prior to any further data exchange). This MAY, for example, be used to notify that the node is currently not able or willing to communicate. However, a node MUST always send the contact header to its peer before sending a SHUTDOWN message.
If either node terminates a session prematurely in this manner, it SHOULD send a SHUTDOWN message and MUST indicate a reason code unless the incoming connection did not include the magic string. If the magic string was not present, a node SHOULD close the TCP connection without sending a SHUTDOWN message. If a node does not want its peer to reopen a connection immediately, it SHOULD set the 'D' bit in the flags and include a reconnection delay to indicate when the peer is allowed to attempt another session setup.
If a session is to be terminated before a protocol message has completed being sent, then the node MUST NOT transmit the SHUTDOWN message but still SHOULD close the TCP connection. Each TCPCL message is contiguous in the octet stream and has no ability to be cut short and/or preempted by an other message. This is particularly important when large segment sizes are being transmitted; either entire XFER_SEGMENT is sent before a SHUTDOWN message or the connection is simply terminated mid-XFER_SEGMENT.
The protocol includes a provision for clean shutdown of idle sessions. Determining the length of time to wait before closing idle sessions, if they are to be closed at all, is an implementation and configuration matter.
If there is a configured time to close idle links and if no TCPCL messages (other than KEEPALIVE messages) has been received for at least that amount of time, then either node MAY terminate the session by transmitting a SHUTDOWN message indicating the reason code of 'Idle timeout' (as described in Table 8).
One security consideration for this protocol relates to the fact that nodes present their endpoint identifier as part of the contact header exchange. It would be possible for a node to fake this value and present the identity of a singleton endpoint in which the node is not a member, essentially masquerading as another DTN node. If this identifier is used outside of a TLS-secured session or without further verification as a means to determine which bundles are transmitted over the session, then the node that has falsified its identity would be able to obtain bundles that it otherwise would not have. Therefore, a node SHALL NOT use the EID value of an unsecured contact header to derive a peer node's identity unless it can corroborate it via other means. When TCPCL session security mandated by a TCPCL peer, that peer SHALL transmit initial unsecured contact header values indicated in Table 9 in order. These values avoid unnecessarily leaking endpoing parameters and will be ignored when secure contact header re-exchange occurs.
Flags The USE_TLS flag is set.
Keepalive Interval Zero, indicating no keepalive.
Segment MRU Zero, indicating all segments are refused.
Transfer MRU Zero, indicating all transfers are refused.
EID Empty, indicating lack of EID.
TCPCL can be used to provide point-to-point transport security, but does not provide security of data-at-rest and does not guarantee end-to-end bundle security. The mechanisms defined in [RFC6257] and [I-D.ietf-dtn-bpsec] are to be used instead.
Even when using TLS to secure the TCPCL session, the actual ciphersuite negotiated between the TLS peers MAY be insecure. TLS can be used to perform authentication without data confidentiality, for example. It is up to security policies within each TCPCL node to ensure that the negotiated TLS ciphersuite meets transport security requirements. This is identical behavior to STARTTLS use in [RFC2595].
Another consideration for this protocol relates to denial-of-service attacks. A node MAY send a large amount of data over a TCPCL session, requiring the receiving node to handle the data, attempt to stop the flood of data by sending a XFER_REFUSE message, or forcibly terminate the session. This burden could cause denial of service on other, well-behaving sessions. There is also nothing to prevent a malicious node from continually establishing sessions and repeatedly trying to send copious amounts of bundle data. A listening node MAY take countermeasures such as ignoring TCP SYN messages, closing TCP connections as soon as they are established, waiting before sending the contact header, sending a SHUTDOWN message quickly or with a delay, etc.
In this section, registration procedures are as defined in [RFC5226].
Some of the registries below are created new for TCPCLv4 but share code values with TCPCLv3. This was done to disambiguate the use of these values between TCPCLv3 and TCPCLv4 while preserving the semantics of some values.
Port number 4556 has been previously assigned as the default port for the TCP convergence layer in [RFC7242]. This assignment is unchanged by protocol version 4. Each TCPCL node identifies its TCPCL protocol version in its initial contact (see Section 8.2), so there is no ambiguity about what protocol is being used.
IANA has created, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version Numbers" and initialized it with the following table. The registration procedure is RFC Required.
EDITOR NOTE: sub-registry to-be-created upon publication of this specification.
IANA will create, under the "Bundle Protocol" registry, a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version 4 Header Extension Types" and initialized it with the contents of Table 10. The registration procedure is RFC Required within the lower range 0x0001--0x3fff. Values in the range 0x8000--0xffff are reserved for use on private networks for functions not published to the IANA.
IANA will create, under the "Bundle Protocol" registry, a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version 4 Message Types" and initialized it with the contents of Table 11. The registration procedure is RFC Required.
IANA will create, under the "Bundle Protocol" registry, a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version 4 XFER_REFUSE Reason Codes" and initialized it with the contents of Table 12. The registration procedure is RFC Required.
IANA will create, under the "Bundle Protocol" registry, a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version 4 SHUTDOWN Reason Codes" and initialized it with the contents of Table 13. The registration procedure is RFC Required.
IANA will create, under the "Bundle Protocol" registry, a sub-registry titled "Bundle Protocol TCP Convergence-Layer Version 4 MSG_REJECT Reason Codes" and initialized it with the contents of Table 14. The registration procedure is RFC Required.
This memo is based on comments on implementation of [RFC7242] provided from Scott Burleigh.
[I-D.ietf-dtn-bpbis] Burleigh, S., Fall, K. and E. Birrane, "Bundle Protocol Version 7", Internet-Draft draft-ietf-dtn-bpbis-10, November 2017.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989.
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol Specification", RFC 5050, DOI 10.17487/RFC5050, November 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008.
[RFC7525] Sheffer, Y., Holz, R. and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015.
[I-D.ietf-dtn-bpsec] Birrane, E. and K. McKeever, "Bundle Protocol Security Specification", Internet-Draft draft-ietf-dtn-bpsec-06, October 2017.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, DOI 10.17487/RFC2595, June 1999.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R., Scott, K., Fall, K. and H. Weiss, "Delay-Tolerant Networking Architecture", RFC 4838, DOI 10.17487/RFC4838, April 2007.
[RFC6257] Symington, S., Farrell, S., Weiss, H. and P. Lovell, "Bundle Security Protocol Specification", RFC 6257, DOI 10.17487/RFC6257, May 2011.
[RFC7242] Demmer, M., Ott, J. and S. Perreault, "Delay-Tolerant Networking TCP Convergence-Layer Protocol", RFC 7242, DOI 10.17487/RFC7242, June 2014.
Changed contact header content to limit number of negotiated options.
Added contact option to negotiate maximum segment size (per each direction).
Added contact header extension capability.
Defined new IANA registries for message / type / reason codes to allow renaming some codes for clarity.
Expanded Message Header to octet-aligned fields instead of bit-packing.
Added a bundle transfer identification number to all bundle-related messages (XFER_INIT, XFER_SEGMENT, XFER_ACK, XFER_REFUSE).
Use flags in XFER_ACK to mirror flags from XFER_SEGMENT.
Removed all uses of SDNV fields and replaced with fixed-bit-length fields.
Added contact negotiation failure SHUTDOWN reason code.
Added MSG_REJECT message to indicate an unknown or unhandled message was received.
Added TLS session security mechanism.
Added TLS failure SHUTDOWN reason code.


text:
Tag Archives: BDN
Nolan Smith upgraded to probable
March 12, 2009 Mark Watson
BDN Photo - Nolan Smith
Here is the official word from Duke Sports Information -
"Sophomore guard Nolan Smith is probable for Duke's opening round game of the ACC Tournament on Friday. Smith has missed the Blue Devils last three games after suffering a mild concussion on Feb. 25 at Maryland. He is averaging 8.5 points and 2.3 rebounds per game in 28 contests this season."
We fully expect him to play in that he has been practicing close to full speed.
BDNBDN PhotosDuke BasketballDuke Basketball Injury ReportNolan Smith
Duke Women's Basketball
Duke Women run over Georgia Tech for 15th straight win
January 25, 2009 Duke Sports Information
DURHAM, N.C. – The fourth-ranked Duke women's basketball team used a stellar defensive effort on Sunday afternoon to down Georgia Tech, 60-34, to win its 15th straight game this season and 29th straight contest against the Yellow Jackets. The Blue Devils held Georgia Tech to its second-worst single-game output in school history, while holding the Yellow Jackets to only 25.5 percent shooting.
Abby Waner scored 14 points, while Chante Black and Jasmine Thomas each added 10 points for the Blue Devils.
For a full recap, click on www.GoDuke.com
Abby WanerBDNCoach PDuke
BDN Premium Articles, Duke Basketball, Duke Basketball Recruiting News
Getting to know Duke commitment Tyler Thornton (Free Premium Interview)
January 22, 2009 Andrew Slater
In early September, junior guard Tyler Thornton verbally committed to Duke University along with his AAU teammate, Josh Hairston. This past weekend the Gonzaga playmaker headed to the birthplace of basketball, Springfield, Massachusetts, where he led his team to a victory over repeat
Tyler Thornton (front) and future Duke teammate (Josh Hairston)
New England Prep School champions, St. Mark's, which features a pair of elite level big men in 6'10" Erik Murphy (Florida) and 6'8" Nate Lubick (Georgetown). After the hard-fought victory, Tyler spoke with Blue Devil Nation about topics ranging from what the Duke coaches have asked him to work on and a scouting report on Josh Hairston to Kendall Marshall and his mother, the future loudest Cameron Crazy. Enjoy the interview -
Blue Devil Nation: One of the things that your coach Steve Turner has talked about is your leadership. He's mentioned since you walked through the door as a freshman, you've been Gonzaga's leader. Was that a conscious effort on your part to establish that early on or more of a natural aspect of your personality?
Tyler Thornton: It was more of a natural thing. Coming in, before high school, I was always the biggest guy and most likely the best player on my team.
BDN: Setting the tone early?
TT: Yeah, and then after a while, they just understand that's how you play. When I came here my freshman year, it was a natural thing. I would say my first couple of games I was just nervous, but then the guys, you know, the guys they was just picking me up.
BDN: People like Max Kenyii?
TT: Yeah, Max Kenyii who's going to Harvard. They were looking for me to be the vocal leader on the team and run the team. The biggest thing that they trusted me.
BDN: Did you start as a freshman at point guard or off guard?
TT: Freshman year, I started midway through the season as the point guard.
BDN: Do you consider yourself to be a vocal leader, one who leads through actions, or both?
TT: More of a vocal leader You know I always talk on offense and defense making sure everybody's where they're supposed to be at. You know that just makes it a lot easier for us as a team and for the coaches on the sidelines so that they don't have to yell every single thing from the sidelines.
BDN: One of the other attributes that comes up a lot with you is winner. The Assault team won seven large tournaments in a row until Akron then you won the Bob Gibbons, and then you ultimately won the MVP at the big tournament in Vegas at the end of the summer. Gonzaga has been now 49-3 over the past two years with you running the show in the WCAC, arguably one of the toughest conferences in the nation. What do you attribute that to?
TT: You know that's something I can't do on my own. You've got to trust your teammates and they trust you. Guys are building chemistry and you're just loving playing with each other.
BDN: Both teams.
TT: Yeah, that's for both teams. We enjoy playing with each other. You know everybody loves to win so, you know, they're gonna sacrifice and that's what its all about.
BDN: There's nothing more important. At the end of the day, these guys (St. Marks) are walking past us with their heads down.
TT: Exactly, exactly
BDN: What do you consider to be your greatest strength right now?
Tyler Thornton: Right now, defensively, Id like to get in my mans face.
BDN: You're very intense defensively.
TT: Yeah, and I like to play help side defense too. On this team, they look to me for offense, but, as you can see, other guys step up and, if they're on fire, I'm gonna definitely get them the ball. You know, I can score on offense, but, if someone else is on fire, I'm gonna get it to them.
BDN: What would you like to work on before you arrive at Duke?
TT: You know especially now, when I'm working towards college, its my three point shot. That's what Coach K told me he'd like me to be able to knock them down.
BDN: I didn't think I saw you shoot one today.
TT: I didn't.
BDN: But you're working on it.
TT: Yes, yes.
BDN: What, if anything else, has the Duke coaching staff asked you to work on? Either in terms of on the court or with your body.
TT: Besides the three point shot, you know, Coach Collins was telling me you know how there were those lanky guys that were real big and I couldn't really finish around them
BDN: (laughs) I saw you covering (Erik) Murphy on that one possession.
TT:(laughs) Yeah, yeah. You saw around the basket how I tried to use my floater. I didn't hit today, but that was one thing he told me to work on, especially in college cause everyone's big and everybody's getting on the glass so, you know, work on the floater.
BDN: Whats your favorite move right now?
TT: Move? As in offense, I cant tell you. (laughs)
BDN: Alright, alright. Thats' fair. What players do you try to emulate your game after?
TT: You know I just try to take a little bit from everybody. Chris Paul, Jason Kidd, Nolan Smith. I play a similar position as Now.
BDN: You're both D.C. Assault guys.
TT: (laughs) Yeah, Yeah. Just take a little bit from everybody because, you know, everybody has good attributes.
BDN: In the past, you weren't asked to score as much as this year. How did you feel about the added responsibility?
TT: It's not really added, you know, because it was already part of my game. Its just the teams we had before at Gonzaga I wasn't expected to score or I didn't have to. Its different with D.C. Assault, you know, when Coach tells me to score, I score. The offense that were in here we swing the ball around, you know, kick it out. If somebody has an open shot, they're gonna take it, you know, they're not going to swing it.
BDN: You guys have a lot of players with good court vision, even the big guys. Talk about the competition you face in the WCAC, arguably one of the top 5 leagues in the country
TT: I think its number one.
BDN: And how that might prepare you for the ACC better than the average public school kid in America.
TT: Exactly, you know, that's why everybody in our area just wants to play in schools in WCAC because they know that its going to prepare them for the next level, you know, the coaches the players everybody you know, so I'd say its like a mini-ACC. Everybodys trying to win and everybody can knock everybody out.
BDN: Especially in your class There's one match up of yours that Duke fans will be looking to for the next few years. You and Kendall Marshall. Lets talk about it.
TT: Kendall. That's like my best friend . We went to middle school together and played on the same team.
BDN: He's with Boo Williams.
TT: Yeah, I'm D.C. Assault
BDN: You beat him three out of four times last year and outscored him 25-17 in front of Coach K in December.
TT: Yeah, but they won that night.
BDN: Alright, well, I didn't want to bring that up. (laughs)
TT: That's okay.(laughs). Its alright. He's my man. I'm looking forward to playing against him for the next, what, six years.
BDN: Maybe beyond
TT: (laughs) Yeah, hopefully
Blue Devil Nation: How do you match up against him? What do you better and what does he do better at this point?
Tyler Thornton: Kendall, you know, he's a great point guard with great court vision and a nice touch. Hes got an all-around game. Kendall's a great player.
BDN: Talk about the differences in what you're asked to do at Gonzaga as compared to D.C. Assault.
TT: In AAU, there are teams that are stacked and teams that are not as good. In high school, we have more of a set type offense. We run like a Princeton style offense and in AAU we just, like, run and gun.
BDN: You, Eric Atkins, Hairston
TT: Yeah, you know, maybe, a secondary break-drive it to the middle, kick it out, pick-and-roll. Its a different style of offense, but the intensity is still there. Were still trying to win.
BDN: Could you give a scouting report on Josh Hairston and tell the audience about him as a person?
TT: I'd say basically a mix between KG and Tim Duncan.
BDN: Wow, that's something to look forward to for the fans.
TT: (laughs) Of course, you know, he finishes great around the basket.
BDN: He's developing a nice little hook.
TT: Yeah, he can step out, face up, take his man off of the dribble or shoot the jumper. Hes great on defense, you know, blocking shots -- rebounding. He's got an all around game.
BDN :He talked about what a major step up his game took when he joined the Assault. He felt it really helped his game a lot.
TT: Yeah, you know, when he came, I think he was a little nervous at first, but he seen that we trusted him. The first time he came he really wasn't looking to score or doing what we know he could do.
BDN: He was just trying to fit in.
TT: Yeah, so we was like, man, just play. You're gonna miss shots, but everybody here gonna misses shots. So if you shoot the ball, that's better for us, its a better chance for us to get buckets.
BDN: Sure, you're simply closer.
TT: Yeah, so me and Eric the other guards we don't have problems with keep dumping it down. It helps everything out for us because we keep scoring.
Blue Devil Nation: What kind of advantage do you think you'll have by knowing where he likes the ball and his tendencies by the time you arrive at Duke?
Tyler Thornton: I think it'll tremendously help our chemistry on the court if we end up being on the court at the same time or even in practice going against the older guys. I think it'll help us a lot. I know where he likes the ball and know where he likes to put the ball. Its always good to have somebody that you know that you enjoy playing with going through the system with you together.
BDN: Have you visited the Hall of Fame yet on this trip? Is this your first trip? If so, what were your impressions?
TT: Yeah, we went yesterday. It was my first time going. There was a lot of good stuff in there. Last night there was a dunk contest, two ball, three point shooting
BDN: Was everybody there?
TT: Yeah, all the teams.
BDN: Whats your current height and weight?
TT: I'd say 6-1 and three quarters and ...
BDN: (laughs) Alright, alright ...
TT: (laughs) and maybe 185...190
Blue Devil Nation: Okay, what would you like to be by the time you get to Duke?
Tyler Thornton: You know Coach. Coach K has told me that my body weight is fine. He actually wants me to lose a couple pounds so that, you know, Id still be strong, but Id be even a little quicker.
BDN: Do you have a weight room at school?
TT: Yes, and actually our trainer was here today. He works us out in the off seasons. He comes in and tells us what to do during the season too.
Blue Devil Nation: Have you had a chance to watch Duke much this year on TV? What is your take on this years team?
Tyler Thornton: Yeah, after practice, I try to catch all their games.
BDN: So you caught the Georgetown game?
TT: Yeah, that was a big game for me.
BDN: (laughs) I know it was a big game for you. I wasn't sure about bringing it up, but.. (Georgetown recruited Tyler)
TT: (laughs) Yeah, definitely, definitely. Yeah, but hopefully I get a chance to go down there and watch them play.
Blue Devil Nation: What would you like fans to know about Tyler Thornton, both as a person and as a player?
Tyler Thornton: You know I don't consider myself to be a big star or nothing so
BDN: Oh, come on! You're the reason I'm here at this thing (laughs)
TT:(laughs) I'm just a laid back kid. I like to have fun and just chill. I just like to laugh and have fun, you know, so.
BDN: What about on the court? What do you want people to remember you as?
TT: Someone who played hard and left it all out on the court. He fought until the last minute.
BDN: A winner too.
TT: Yeah, you know I just hate to lose. If were down five with five seconds left, Im still thinking in my mind that were gonna win this game.
Blue Devil Nation: You won the title last year and now your team has a couple of early losses to O'Connell and that team in Ohio, but you seem to be hitting your stride now.
Tyler Thornton: This year everybody around our area sees all of the players that we sent to college last year and they think the new guys won't fill the void for them. But it's not about those guys trying to do what they did. It's about guys playing a role and, if they play their roles right, we can win. You see today the height advantage they had was tremendous.
BDN: Yeah, I know, I thought My God, this is the one game I'm gonna have to interview you after.
TT:( laughs) Yeah, the height advantage was a tremendous difference, but our coach told us to box out. He told the guards we have to rebound and get out and run the floor.
BDN: Yeah, you pushed it, spread the floor, and wound up getting their guys in foul trouble.
Blue Devil Nation: Are you going to the inauguration?
Tyler Thornton: Unfortunately not, we've got practice. We've got school the next day. I'll go to practice, stay off of my feet a little bit, and just watch it on TV.
BDN: Who's the toughest guard you ever faced?
TT: Oh, about two years ago we faced Joe Jackson down at Bob Gibbons. He just killed us (laughs) He gave us about thirty. You know Kendall and Josh Selby and Markel. They're always great competitors.
BDN: Well, I mean it's help you to face them each once or twice a season ...
TT: Yeah, it helps everybody on my team, not just me. It helps everyone in our area. Our area is so great. The competition is so hard.
Blue Devil Nation: Lastly, your mother! I know that's gotta be your mother.
Tyler Thornton: (laughs) Yeah, yeah, yeah.
BDN: I said that has got to be your mother. I've seen her at the D.C. Assault games with the other mothers, but they're much louder there. They've got the cheers and everything. I never mention mothers, but they're so impressively loud and into the games. Shes got to be coming down to Duke when you start up. (laughs)
TT: (Laughs) Oh, of course. She's gonna be one of the Cameron Crazies.
Blue Devil Nation: Oh, when you and Josh signed, I thought to myself, I hope that woman is one of your mothers cause she is the one woman who is louder than the Cameron Crazies.
Tyler Thornton:(laughs) I know. I know. With the D.C. Assault, that's a great boost to have.
BDN: It is. It definitely is.
TT: Not only my mother, but everybody elses mother too.
BDN: Yeah, I love it when she goes (imitating Tyler Thornton's mother) Deeeefense, boyyyyyys, defense( laughs)
TT: (laughs, clapping his hands together ) Yeah, that's it! Yeah. Especially, if we're down, they start and it up and it gives us a boost. Its great to have a mother that's into the game like that.
BDN: Sure, absolutely. I also noticed that shes got the same look around the eyes too.
TT: Yeah, yeah, that's my mother.
BDN: Well, Tyler, it was very nice to meet you.
TT: It was a pleasure to meet you too.
The Blue Devil Nation welcomes aboard, Andrew Slater. Andrew is one of the more knowledgeble folks I know when it comes to AAU ball, prospects and recruiting. He brings with him a uniques and detailed style which is sure to please our members.
BDNBlue Devil Nation interviewsDuke Basketball RecruitinterviewTyler Thornton
Cutcliffe's weekly teleconference
October 20, 2008 Mark Watson
[private] Opening statement -
I apologize for being a little late, but recruiting comes first and we've been recruiting. It's amazing to look at the tape and see how many good things we did but we are not pleased with the plays made against us. There were some good lessons learned, but give Miami the credit. We had some opportunities in the game, but we didn't step up at critical times and the game got away from us.
On his feelings after the Miami game-
I'm still angry. I just told out team that I just did not sense any energy in our team. I watched the tape and we played hard, but we did not have the energy or the look in your eye that we were going to win the game in the fourth quarter when we were down 11. That's unacceptable. There's a difference in playing hard and competing to win and I didn't think we competing to win.
On Vanderbilt -
I've seen Vanderbilt on TV, but very little of them on tape thus far. We will do a little work against Vanderbilt this evening. I know a little bit about their team playing them the last two years. I know the staff ... they're an exceptional football team and they do a tremendous job and it will challenge us to go over there and stay in the game.
More on Miami and his displeasure -
I just think you've got the believe you can win and I don't think we thought we could win. You can only accomplish what you think you can accomplish. You have to fight through the adversity. My confidence has wavered at times in my career, but you earn it back. I just sensed we were not going to win. I sensed it and you could have gone in and turned the light off. I looked around, the stadium was empty with fifteen minutes to go. It's a situation we have to break. I believed we could, that was until I walked around looked and it was not just guys playing in the game. All of our back up guys ... there was no hunger in their eyes, no attack in their eyes. I saw the hunger in earlier games, but you've got to do it when it's hard. I know that Rome wasn't built in a day, I'm not mad at them but you have to earn it. None of these guys - what I thought about last night was that I didn't have any of these guys that have done it before. They haven't done it, they haven't lived it.
On the 77 yard punt with a 5 yard penalty which switched field position -
That was a howitzer. I don't think anyone could have caught that ball. I've never seen one get caught in the wind like that one did. It flipped the field position on us. We then had a bad series, which is easy to do when you get backed up deep in your territory.
More on Miami and their freshman quarterback -
They were bigger than us and faster than us. You can't back off of them and just let them make the plays. They just made the plays. Every time the QB ran he made the play. I was surprised he ran the ball as well as he did. Once he got out of the pocket guys didn't know whether to leave go to the ball or stay on their man.
Riley struggled on Saturday. How do you as a coach get other kids to step up and make plays?
Well, you just keep going at it and practiced. Again, I hate to keep using that word, but they have to "earn" their confidence level and then they have to learn our (staffs) confidence. Eron is not going to drop balls like that all the time - he hadn't been doing so in practice. You are going to ride your horses pretty good ... I had actually talked to our seniors about them making big plays until our young guys can get into that mode. We haven't had a chance to talk (since Miami game) on both sides of the ball on how we are going to have to make some big plays.
On the rushing attack having more success and game calls -
Well, I've told y'all on many occasions that we were going to work on that in the off week and challenge our kids. It's still a work in progress. At the end you could see how explosive their athletes were. I let the time run off the clock late in the first half was to consider keeping the ball. I know we needed the points with a field goal, but we thought about trying to run the ball off the clock. Had we gone for it and been successful, we would have gone in up 14-7, 17-7 or 21-7. I really wanted that clock to run down, but they just ripped down the field in less than two minutes to score. (making it 17-14 at the half)
Alright folks, thank you very much and I apologize for being late, but obviously, we've got a lot of recruiting to do.[/private]
BDNCoach CutCoach CutcliffeDuke Football

redpajama_set_name: RedPajamaCommonCrawl


We originally thought that the work world through 2020 would provide much opportunity for knowledge workers who keep their skills current. The future looked bright in 2006 & 2007. However, as we move into the 21st century, there is continuing change, chaos and increasing complexity, both in our professional and personal lives. Traditional rules managing our careers and selecting career options are passé.
As we move through 2014 there will be many opportunities for the talented technology/ information worker, but it will demand much more careful career planning. Deciding what will bring you satisfaction in your work and which option has the most promise can be a real challenge, especially since many of us have not spent quality, focused time in assessing what is really important to us. What are our the "glass balls" as opposed to the "rubber balls" in our lives? The glass balls are so critical for us to feel successful that we cannot drop them. If a mirror is broken, it can never be repaired to restore the original image; it will always be distorted. Rubber balls can be let loose and picked up later without a great loss. Making a decision on your glass balls is critical!
Many families, for example, decide that close attention to rearing their children is a major glass ball – we don't get a second chance at this. Keeping our health is certainly a critical glass ball. As clients go through the CDA Career Enhancement Process, they bring to the surface the factors that they know are deeply important and they list them. These "glass balls" become their "Success Criteria" – what they must have to feel good about themselves in their work lives.
Some clients, especially males, will tell me that making a six-figure income is their first and only Success Criteria. Frequently this is because our society has geared them to think of success in terms of money and status only. As they work through some sound self-assessment this may move off their list entirely or certainly drop down on the list.
As you accumulate your Success Criteria, write out specific examples of how you will know when you are achieving a particular criteria. These are some samples of the criteria I hear most from professionals.
I tell all my clients that I want "meaning and money – purpose and profit".
It is very important in the coming work world that we become the entrepreneurs of our own careers. We must be in charge. Developing the list of Success Criteria is basic to that goal. If we can't name or put words to these, we can get them only by hit and miss – a risky way to live your work life.
So sit down and list your Success Criteria, your glass balls, and define how you will know when you get them. This criteria will become your written prescription for your present and future jobs.
Download the Success Criteria form!
Excerpted from Capitalizing on Career Chaos: Bringing Creativity and Purpose to Your Work and Life. Order your copy today.


Located on the second floor of Venerable Hong Choon Memorial Hall is the dining hall where Sangha members and devotees have their mindful meals.
The dining hall can accommodate a total of 116 round tables.
Around 928 people can eat together at one time.
On the eve of Vesak, the dining hall operates overnight. Food and drinks are prepared for devotees participating in the Vesak activities.
Temple encourages mindful eating in the dining hall. Mindfulness in queuing, collecting food and consumption.
On occasion where there are chanting by sangha members during mealtime, one can practice observation of silence or meal contemplation together.
Vegetarian Steamboat and Yusheng available at lunch time.
Qing Ming, Dumplings Festival and Ulambana.
Traditional dumplings handmade by monastery and its volunteers.
Vegetarian Moon Cake of various popular favours available.


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Q: if else error message always shows else statement message I think this is a simple problem. But, I don't know how to solve this problem. I have posted my codes below. Here, In this below code if else statement always shows No Sarees. I got the result from mysql table but it always shows with No Sarees text. I have checked this using var_dump($categories) it returns array(0){} . How can I solve this problem?
<?php if ($categories) { ?>

        <?php if (count($categories) <= 5) { ?>

            <?php foreach ($categories as $category) { ?>

<a href="<?php echo $category['href']; ?>"><?php echo $category['name']; ?>

            <?php } ?>

        <?php } else { ?>
            <?php for ($i = 0; $i < count($categories);) { ?>
                <?php $j = $i + ceil(count($categories) / 4); ?>
                <?php for (; $i < $j; $i++) { ?>
                    <?php if (isset($categories[$i])) { ?>

<a href="<?php echo $categories[$i]['href']; ?>"><?php echo $categories[$i]['name']; ?>

                    <?php } ?>
                <?php } ?>
            <?php } ?>
        <?php } ?>

<?php } else {
    ?>

No Sarees

<?php } ?>

A: If your $categories is empty array then in if($categories) your array is converted to boolean value. If it's empty array (and you say it is) then it's get converted to false.
Check this:
$categories = array();  //empty array

var_dump((boolean)$categories); //this will show what variable will look like after converting to boolean value

if ($categories){
  echo '$categories IS NOT empty';
}else{
  echo '$categories IS empty';
}

redpajama_set_name: RedPajamaStackExchange


Cylinder Rebore, Replating and Repair.
The Extreme Hayabusa Starter Clutch is designed to protect the starter motor and gear train from damage caused by low battery power and involuntary reverses caused by spinning a car.
By introducing a slipping element into the sprag gear in the upper starter train a measure of protection is introduced.
The arrangement is available as a sprag gear with outer cover which will work with the standard inner cover, or with a new billet machined hard anodised inner cover to complete the look.
Replacement gear for the standard Hayabusa crankshaft starter.


XLMBP 16 Series — The Shop Industrial inc.
The XLMBP trail groomer with all of the features of the full size Mogul Master in a lighter seven blade model offers unsurpassed trail grooming with smaller mid-range horsepower track vehicles. The lightweight Mogul Master XLMBP is specifically designed to allow the less aggressive track vehicles to achieve full size grooming results with Mogul Master quality trails. AC option available.
Late model mid-range horsepower track vehicles such as the Tucker 1000 and the Prinoth Trooper use Tier III engines that are producing far more power and as a result are able to effectively pull a more substantial Mogul Master. The XLMBP HD series fits the bill by incorporating many of the MBP 18 series components, increasing the height and weight, allowing more snow to be processed and moved through the drag to produce a better quality trail. The 10 foot HD can also be the right choice for many higher HP cats, i.e. Tucker 2000 or Prinoth Husky. AC option available.


The boss of a Turkish shipyard has said an accident during a lifeboat test that killed three workers had saved 19 lives.
Mehmet Oyar, founder and chief executive of the Gisan shipyard, told Turkish media the fatal accident, caused by a cable snapping, had prevented it happening during an emergency at sea, with 19 the lifeboat"s capacity.
Oyar also dismissed suggestions sandbags could have been used instead of people, saying it was normal to use workers.
Twelve other workers were injured when the Chinese-made lifeboat crashed into the water in the incident on 11 August.
The lifeboat had been installed on the 21,500-dwt Turquise T belonging to Galata Shipping, Turkish sources say.
The Gisan shipyard, sited in Istanbul"s Tuzla industrial complex, was closed after the accident but re-opened two days later.
The incident lead to fresh protests this week in Istanbul at Tuzla"s safety record and came two weeks after a shipyard worker was fatally injured in an explosion at the Gemsan shipyard.
The Turkish government has reacted to the recent spate of accidents in which dozens have died by ordering some yards to close temporarily and investigating working practices, with the heavy use of subcontractors the focus of attention.
The Gisan incident also revives concerns about the reliability of lifeboat-launch systems.
Fatal accidents during lifeboat tests worldwide are thought to number in the hundreds over the last 20 years, with fierce controversy over who should bear the responsibility.
Several lawsuits have been taken out against both shipowners and lifeboat manufacturers, but last month BP Shipping dropped its legal action against davit-maker Hatecke of Germany, brought over a 2004 accident on the Isle of Man-flagged, 37,333-dwt product tanker Baltic Champion.


I recently returned from a trip with three of my sisters and two of my brothers-in-law to Rome. I'd been before, but it had been a few years, and I was eager to return and show my family some of my favorite spots. Of course, I love the vibrancy and energy of the city–and the fabulous food!–but one of the main reasons that I travel to old cities is that my interest in history and how it continues to interject itself into the present is always nurtured by seeing and experiencing how human creation and culture grows organically, and old cities are the best places to do that.
You almost cannot walk a block in Rome without encountering some fantastic site, whether it's the curious Elephantino wearing his odd Egyptian obelisk near the Pantheon or the sunken area thought widely to be the place where Julius Caesar was murdered. My sister Taryn and I spent a long time simply looking–and we discovered that the many cats who used to roam this area have been transported elsewhere.
The present co-exists with the past, as you can see near the statue of the sixteenth-century tailor Pasquino, who began "publishing" his complaints about local politics and corruption by tacking them up where everyone could see them. Contemporary Romans and visitors keep this tradition alive by putting up their own requests and comments–though nowadays they must restrict themselves to the message board that sits next to Pasquino's statue. That doesn't stop anyone from saying what they want to!
You turn a corner, and find yourself unexpectedly in a medieval-looking courtyard–and you had better be quiet, because the residents have no patience for loud visitors, particularly nosy tourists.
I love old cities, and Rome is one of my favorites. It rings with its history, both the good and the bad, and builds upon it without forgetting or pretending. The Pantheon, the Colosseum, the Forum, the little churches that surprise with their sublime art.
For me, to write about the past, to experience the past, is to create a new present, seen through new eyes. It's a kind of double vision, to be sure. But it's the best way to understand ourselves that I know.


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text:
Home > Vol 83, No 4 (2020) >	Martyniuk
Optical properties of rat serum after intragastric administration of melanin
V. Martyniuk, T. Beregova, Yu. Tseysler, L. Stepanova, T. Kondratiuk
Taras Shevchenko National University of Kyiv, Kyiv; Taras Shevchenko National University of Kyiv, Kyiv; Taras Shevchenko National University of Kyiv, Kyiv; Taras Shevchenko National University of Kyiv, Kyiv; Taras Shevchenko National University of Kyiv, Kyiv
Previous studies of the biological activity of melanin produced by the Antarctic black yeast Pseudonadsoniela brunnea have shown its antioxidant, stress-adaptogenic, dermatotropic, wound-healing and antibacterial effects. However, the primary physicochemical mechanisms of the system influence of melanins remain insufficiently studied. Therefore, the aim of the study was to determine effects of the intragastral administration of melanin produced by the Antarctic black yeast Pseudonadsoniela brunnea on the optical properties of a protein component and an aqueous phase of rat serum. White nonbread adult male rats weighing 180–200 g were used in the experiments. The intragastric route of administration of melanin by means of soft gastric catheter at a dose of 3 mg/kg was used. Rats of the control group were administered the physiological solution in the same way. After 1 hour the animals were sacrificed by cervical dislocation and blood serum was
obtained for further studies. The absorption spectra of blood serum samples were recorded using Shimadzu Biospec-Mini spectrophotometer in the range of 190–1100 nm. Analysis of the absorption spectra of blood serum in a wide range from UV to near IR indicated that one hour after intragastral administration of melanin to rats at the dose of 3 mg/kg the optical properties of protein component were not changed, but the properties of the aqueous phase of the blood serum were changed due to statistically significant decrease of an amount of hydrogen bonds. Authors hypothesized that the appearance of substances that destruct the hydrogen bond network in the blood is one of the reasons for such changes. Changes of properties of water as the solvent and the structure-forming factor can have further systemic consequences due to changes in the hydration of biological polymers and low molecular weight metabolites, their solubility and intermolecular interactions, cell membrane permeability, molecular dynamics and functional activity of biomacromolecules, etc.
melanin, blood serum, serum proteins, water
>PDF
Solano Melanins F. Skin Pigments, Much More-Types, Structural Models, Biological Functions and Formation Routes. New Journal of Science. 2014:28.doi:http://dx.doi.org/10.1155/2014/498276
Castelvecchi D. Dark Power: Pigment seems to put radiation to good use. Science News. 2007. 171 (21): 325. doi:10.1002/scin.2007.5591712106
Falalyeyeva T.M. The influenceof melanin isolated from Antarctic yeasts on cortisolblood level of rats in conditions of stress action / Ukr. Antarctic J. – 2009. – 8. – P. 391-394.
Taburets O.V. The Effect of "Melanin-Gel" on the Wound Healing / Research Journal of Pharmaceutical, Biological and Chemical Sciences (RJPBCS). – 2016. – 7 (3). – Р. 2031-2038.
Dranitsina A.S. Tgfb1, Ptgs2 Genes Expression During Dynamics of Wound Healing and with the Treatment of Melanin / Research Journal of Pharmaceutical, Biological and Chemical Sciences (RJPBCS). – 2017 – 8 (1). – Р. 2014-2023.
Kondratiuk T. Microorganisms, perspective for biotechnology, medicine, environmenal technologies, in the collection of microscopic fungi ESC "Institute of biology and medicine", Taras Shevchenko national university of Kyiv / Bulletin of Taras Shevchenko National University of Kyiv. Series: Biology. – 2017. – 73. – P. 22-30.
Kondratyuk T., Akulenko T., Torgalo E., Beregova T., Ostapchenko L. Dependence of biomass accumulation by melanin produsor Pseudonadsoniellabrunnea (Meripilaceae, Agaricomycotina) on the cultural media content. Visnykof Taras Shevchenko National University of Kyiv: Biology. 2019.1 (77):83-86.
Kondratyuk T., Akulenko T., Torgalo E., Beregova T., Vereshaka L. Synthesis of melanin by black yeast Psedonadsoniella brunnea: dependence on the amount of L-tyrosine in the culture medium. Visnyk of Taras Shevchenko National University of Kyiv: The Problem of Regulation of Physiological Functions. 2019. 1(26): 41-46.
Kondratyuk T., Akulenko T., Torgalo E., Beregova T., Vereshaka L. Dependence of melanin synthesis by black yeast Psedonadsoniella brunnea on the amount of carbon source in the culture medium. Science Rise: Biological Science. 2019. 18(3):38-40.
Kondratiuk T., Beregova T., Ostapchenko L. Antibacterial and antifungal influence of a melanin producer Pseudonadsoniella brunnea culture fluid. Antimicrobial activity of natural substances. JB Books. Poznań, Poland. 2017:2-19.
Bertie J. E.; Lan Z. Infrared Intensities of Liquids XX: The Intensity of the OH Stretching Band of Liquid Water Revisited, and the Best Current Values of the Optical Constants of H2O(l) at 25°C between 15,000 and 1 cm–1". Applied Spectroscopy. 1996.50(8):1047–1057. doi:10.1366/0003702963905385
Warren S. G. Optical constants of ice from the ultraviolet to the microwave. Applied Optics. 1984 23 (8): 1206. doi:10.1364/AO.23.001206
Warren S. G.; Brandt R. E. Optical constants of ice from the ultraviolet to the microwave: A revised compilation. J. Geophys. Res. 2008. 113 : D14220. doi:10.1029/2007JD009744
Pope R. M.; Fry E. S. Absorption spectrum (380–700 nm) of pure water. II. Integrating cavity measurements. Applied Optics. (1997).36 (33): 8710–8723. doi:10.1364/AO.36.008710
Kalckar H. M. Differential Spectrophotometry of Purine Compounds by Means of Specific Enzymes. III. Studies of the Enzymes of Purine Metabolism, J. biol. Chem. 1947. 167:461-75.
Bulavin L.A., Malomuzh M.P., Pankratov K.M. Influence of electrolyte impurities on the nature of thermal motion of water molecules. Reports of the National Academy of Sciences of Ukraine. 2018. (8): 52-57.
Vasylkevych O.F., Slysenko В.І. Neutron studies of the processes of self-diffusion of molecules in the heavy water-glycerol system depending on temperature and concentration. Reports of the National Academy of Sciences of Ukraine. 2009. (8): 70-76. https://doi.org/10.15407/dopovidi2018.08.052
Bulavin L.A., Chekhun V.F., Vasilkevich O.A. etc. Neutron studies of self-diffusion of water molecules in plasma membranes. Journal of Physical Research. 2004. 8(4): 334-337.
Noura El-Ahmady El-Naggar, Sara M. El-Ewasy Bioproduction, characterization, anticancer and antioxidant activities of extracellular melanin pigment produced by newly isolated microbial cell factories Streptomyces glaucescens NEAE-H. Scientific Reports. 2017. 7. Article number: 42129: 1-19. doi:10.1038/srep42129
Adila Salih ElObeid, Afaf Kamal-Eldin, Mohamed Anwar K. Abdelhalim, Adil M. Haseeb Pharmacological Properties of Melanin and its Function in Health. Basic & Clinical Pharmacology & Toxicology. 2017. 120: 515–522.
Received: 1.10.2020
Revised: 2.11.2020
Singed for press: 2.11.2020
DOI: http://dx.doi.org/10.17721/1728_2748.2020.83.6-10
This journal is available according to the Creative Commons License «Attribution» («Атрибуція») 4.0 Global (CC-BY).


It wasn't just Trump that did him in.
Nothing became Scott Walker's campaign like his leaving of it. This is what he would have you believe. That he was "called" to drop out – by the Deity or by his various sugar daddies, or both – so that real conservatives could coalesce behind one candidate in opposition to the barbarian at the gates. In doing so, Mr. Big, Bold, and Unintimidated delivered his remarks and then scarpered, taking no questions about how he managed to squander money and time on a campaign that didn't last as long as the one currently promoting George Pataki. This was death by asterisk.
Walker said that because the field is so crowded, candidates have become focused on personal attacks instead of the substantial issues that matter most to voters. He said Republicans have lost the "optimistic view of America" pushed by President Ronald Reagan, Walker's political idol, and urged those still running to "get back to the basics" with a focus on creating jobs, reducing the size of government and strengthening the military.
What a guy! Also you have to love the idea of "reducing the size of government" while simultaneously "strengthening the military," which, as you know, has nothing to do with "government." That is just so Reagan.
"To refocus the debate on these types of issues will require leadership," Walker said. "I encourage other Republican presidential candidates to consider doing the same so that the voters can focus on a limited number of candidates who can offer a positive, conservative alternative to the current front-runner. This is fundamentally important to the future of the party and, more importantly, to the future of our country."
Why do I suspect that the rest of the Republican field will be reluctant to accept guidance from a guy who faded before Jim Gilmore did?
His fans back home have major sads.
Wisconsin State Assembly Speaker Robin Vos said in a statement: "Governor Walker has an amazing story to tell about turning Wisconsin around. It is unfortunate that the bluster of candidates overshadowed his substance."
What are they going to do with all those snow-white unicorns currently grazing in the fields outside Mukwonago?
Once again, I admit that I was one of the people who overrated the goggle-eyed homunculus hired by Koch Industries to manage their Midwest subsidiary formerly known as the state of Wisconsin. I thought he, or the people around him, would be smart enough to let his union-bashing, duplicitous resume do the talking up until the actual primary balloting began. As we have now seen, this was somewhat optimistic. Confronted by opponents he could neither arrest nor hide from, Walker found that facing down Donald Trump was harder than rounding up singing Grandmas. But I'm not as convinced as a lot of people are that Trump was as pivotal a figure in Walker's collapse as other people are. (I get the feeling that's going to be the easy explanation for every failed candidacy in the Republican field, of which there eventually will be 16.) To blame Walker's national collapse on the presence of the Libidinous Visitor requires that you explain why Walker was peculiarly vulnerable to that particular poltergeist phenomenon whereas putatively weaker candidates were not. (Cillizza also overrates "pizzazz" as a factor. Walker wasn't exactly standing amid a human fireworks display.) Now we have people touting Marco Rubio as the primary beneficiary of Walker's departure, as if there is genuine connective tissue within the Republican nominating scramble, and a narrative is being constructed about how Rubio revived his candidacy with a "strong" performance in last week's debate. You may have thought that Rubio spent most of his time scaring people about fictitious North Korean missile capabilities. But you are misreading how the Republicans are trying to elect a president.
The fact is that the Republican party's primary process is now an exercise in chaos theory. Things happen that are not obviously connected to one another. There is nobody controlling the process, so the process itself is running amuck. Scott Walker failed as a candidate only partly because he is Scott Walker. He also failed as a candidate because his party is failing as a party. He was one of a baker's dozen of independent entities, all orbiting independently, and all subject to unpredictable gravimetric forces of which Trump is only one. Sooner or later, there is a collision. Scott Walker is the rubble that remains after one of those, endlessly spinning around a dying sun.


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