How frequently does the letter "d" appear in:
Network Working Group A. Malis Request for Comments: 4816 Verizon Category: Standards Track L. Martini Cisco Systems J. Brayley ECI Telecom T. Walsh Juniper Networks February 2007 Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM) Transparent Cell Transport document describes a transparent cell transport service that makes use of the "N-to-one" cell relay mode for Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer-Mode (ATM) cell encapsulation. 1. Introduction This transparent cell transport service allows migration of ATM services to a PSN without having to provision the ATM subscriber or customer edge (CE) devices. The ATM CEs will view the ATM transparent cell transport service as if they were directly connected via a Time Division Multiplexer (TDM) leased line. This service is most likely to be used as an internal function in an ATM service provider's network as a way to connect existing ATM switches via a higher-speed PSN, or to provide ATM "backhaul" services for remote access to existing ATM networks. Malis, et al. Standards Track [Page 1]
RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007 1.1. Specification of Requirements 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 RFC 2119 [1]. 2. Transparent Cell Transport Definition The transparent port service is a natural application of the "N-to- one" Virtual Circuit Connection (VCC) cell transport mode for PWE3 ATM encapsulation described in [2], and MUST be used with pseudowires of type 0x0003, "ATM transparent cell transport" [4]. The ATM transparent port service emulates connectivity between two remote ATM ports. This service is useful when one desires to connect two CEs without processing or switching at the Virtual Path Connection (VPC) or VCC layer. The ingress PE discards any idle/unassigned cells received from the ingress ATM port, and maps all other received cells to a single pseudowire. The egress PE does not change the Virtual Path Identifier (VPI), Virtual Circuit Identifier (VCI), Payload Type Identifier (PTI), or Cell Loss Priority (CLP) bits when it sends these cells on the egress ATM port. Therefore, the transparent port service appears to emulate an ATM transmission convergence layer connection between two ports. However, since the ingress PE discards idle/unassigned cells, this service benefits from statistical multiplexing bandwidth savings. In accordance with [2], cell concatenation MAY be used for transparent cell-relay transport in order to save the PSN bandwidth. If used, it MUST be agreed between the ingress and egress PEs. In particular, if the Pseudo Wire has been set up using the PWE3 control protocol [3], the ingress PE MUST NOT exceed the value of the "Maximum Number of concatenated ATM cells" Pseudowire Interface Parameter Sub-TLV (Interface Parameter ID = 0x02 [4]) received in the Label Mapping message for the Pseudo Wire, and MUST NOT use cell concatenation if this parameter has been omitted by the egress PE. ATM Operations and Management (OAM) cells MUST be transported transparently, and the PEs do not act on them. If the PEs detect a PSN or pseudowire failure between them, they do not generate any OAM cells, but rather bring down the ATM interfaces to the CEs (e.g., generating LOS on the ATM port), just as if it were a transmission layer failure. Malis, et al. Standards Track [Page 2] 5]
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I counted ninety-three "d"s in that text.
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