To fulfill increasing mobile requirements of network equipment, Internet Engineering Task Force (IETF) proposed a Mobile IPv6 (MIPv6) protocol. IETF then proposed improved MIPv6 protocols, such as Hierarchical Mobile IPv6 (HMIPv6), Fast Mobile IPv6 (FMIPv6), and the like. The MIPv6, HMIPv6 and FMIPv6 protocols can improve the handover and communication performance of a mobile IPv6 terminal.
In Internet route mode, a route is selected according to a destination address in the Network Layer; data packets are transmitted to the network where the destination address is located; and then the data packets are transmitted to a node represented by the destination address. In order to make a mobile terminal maintain a continuous ongoing communication during the procedure of Layer 3 network handover, it is necessary to ensure that the mobility of the mobile terminal is transparent to the communication application, that is, to ensure that the IP address of the mobile terminal which is identified by the Network Layer of the communication application remains unchanged. This problem is solved by the scheme of Mobile IPv6.
Next, a general description of Mobile IPv6 will be given.
When a mobile node (MN) is in its home network, it communicates with a correspondent node (CN) in accordance with a conventional route technology using its home address, in which there needs no intervention of mobile IPv6.
When the MN moves to a foreign link, its home address remains the same; meanwhile, the MN acquires a temporary IP address (i.e. care-of address). The MN informs the home agent (HA) of the mapping between the home address and the care-of address. In this case, the communication procedure between the CN and the MN is as follows: data packets sent from the CN to the MN are still transmitted to the home network of the MN according to its home address; HA of the MN intercepts these data packets and forwards them to the care-of address of the MN via tunneling, according to the acquired mapping relationship between the home address and the care-of address. The above communication procedure is also referred to as triangular routing, where the MN communicates with the CN via its HA.
The MN can also inform the CN of the mapping relationship between the home address and care-of address, and therefore the CN acquires the care-of address of the MN and can forward data packets directly to the foreign network where the care-of address of the MN is located. In this way, the CN and the MN can communicate directly with each other. The above communication procedure is referred to as a route optimized communication procedure between the CN and the MN.
The disadvantage of the above scheme of Mobile IPv6 lies in that, when the MN hands over between access routers (ARs), the handover latency is long and the packet loss rate is high. In an actual application environment, the MN needs to hand over between neighboring ARs frequently. In this case, the MN has to register with its HA the mapping relationship between the home address and care-of address frequently, which significantly increases the burden of the HA and is very costly. Meanwhile, duplicate address detection operation is performed on the registered care-of address to verify its validity, which is quite time consuming.
Next, a brief introduction to the Hierarchical Mobile IPv6 will be given.
Based on the scheme of Mobile IPv6, Hierarchical Mobile IPv6 scheme introduces Mobility Anchor Point (MAP) to improve handover performance of the MN in the MAP domain.
When a MN enters a MAP domain, it will receive a Router Advertisement (RA) which contains MAP information. The MN needs to configure two care-of addresses, namely Regional Care-of Address (RCoA) and On-link Care-of Address (LCoA). The MN performs Duplicate Address Detection operation on the LCoA and sends a local binding update message to the MAP when the detection is successful. Upon receiving the local binding update message, the MAP performs Duplicate Address Detection operation on the RCoA as well and returns a local binding update acknowledgment message to the MN when the detection is successful. Upon receiving the local binding update acknowledgment message, the MN registers a new RCoA with its HA and the CN.
If the MN performs a handover within the MAP domain, for example, an AR is changed, then RCoA of the MN is kept the same and only LCoA of the MN is reconfigured. Duplicate Address Detection operation is performed on the reconfigured LCoA which is registered with the MAP when the detection is successful. The MAP does not need to perform Duplicate Address Detection and registration operations on the RCoA.
The disadvantage of the above scheme of HMIPv6 lies in that, though it solves, to a certain extent, the problem of long handover latency for handover within the MAP domain of the MIPv6 scheme, the handover latency is still too long, compared with the requirement of network real time application. Specifically, in the HMIPv6 scheme, the latency of performing Duplicate Address Detection operation on the LCoA and RCoA during handover makes up most of the total handover latency.
Next, a brief introduction to Fast Handover for Mobile IPv6 is given.
Fast Handovers for Mobile IPv6 is a scheme for improving the capability that a Mobile IPv6 node fast switches access points on the network. This scheme reduces or eliminates the latency of the MN establishing a new communication path and reduces the handover latency and the packet loss rate when the MN hands over across regions. In this scheme, before the MN is switched to a new link, it first initiates a handover procedure to acquire the care-of address of the new link beforehand. The handover procedure is realized by exchanging newly-added messages between the new and previous ARs as well as between the AR and the MN. This scheme requires that the MN is previously aware of the new link to which it will be moved, and therefore it requires support from Layer 2.
Next, a brief description on Hierarchical-based Fast Handover for Mobile IPv6 is given.
The Hierarchical-based Fast Handover for Mobile IPv6 is a scheme in which the scheme of HMIPv6 is combined with the scheme of Fast Handover for Mobile IPv6.
When a MN enters a new MAP domain, it performs a registration of the MN to the MAP, HA as well as CN. Similarly, when the MN moves from a previous AR to a new AR in the domain, it also performs a local binding update course in the HMIPv6 protocol. At that time, if a fast handover is to be performed on the ongoing data session between the MN and the CN, the Hierarchical-based Fast Handover procedure for Mobile IPv6 is performed on the MN, the AR and the new MAP. The procedure includes the following steps:
Step 1: The MN acquires a link layer address or identifier information of a new AR that it requires, using a mechanism provided by the Link Layer.
Step 2: The MN transmits a Proxy Router Request message to the previous AR according to a handover expectation provided by the Link Layer. The Proxy Router Request message comprises the acquired link layer address or identifier information of the new AR.
Step 3: Upon receiving the Proxy Router Request message, the previous AR transmits a Proxy Router Advertisement message to the MN. The Proxy Router Advertisement message includes the information needed for the MN to configure the care-of address in the new AR domain, that is, the network prefix of the new AR needed for Stateless Address Configuration, or the care-of address of the new link in the case of a certain state. At this time, the new MAP should already know the network prefix and link layer address of the new AR.
Step 4: The MN transmits a Fast Binding Update message to the new MAP. The Fast Binding Update message includes the previous LCoA of the MN and the IP address of the new AR.
Step 5: Upon receiving the Fast Binding Update message from the MN, the new MAP transmits a Handover Initiate message to the new AR to establish a bidirectional tunnel. Upon receiving the Handover Initiate message, the new AR establishes a Host Route option for the previous LCoA of the MN and returns a Handover Response message to the new MAP. At this time, the bidirectional tunnel is established between the new MAP and the new AR.
Step 6: The new MAP transmits a Fast Binding Acknowledge message to the previous LCoA and the new LCoA at the same time. After that, the new MAP forwards to the new AR the data packets sent to the MN through tunneling.
Step 7: Upon detecting a Link Layer movement, the MN transmits a Fast Neighbor Advertisement message to the new AR. The new AR then transmits buffered data packets to the MN.
Step 8: The MN then performs a regular HMIPv6 operation and transmits the local Binding Update to the new MAP. Upon receiving the Binding Update with the Source Address being the new LCoA, the new MAP stops forwarding the packets and clears the tunnel.
Step 9: The new MAP transmits to the MN a Binding Acknowledge message, which is a response to the local Binding Update message. The Binding Acknowledge message should be sent to the link address where the MN previously is located and the current link address, simultaneously.
Step 10: If the state of the Binding Acknowledge message received by the MN Failure, the handover of the MN fails and the procedure is terminated; otherwise, if it was a handover within the MAP domain, the handover of the MN is successful and the procedure is finished. If it was a handover across the MAP domains, the MN has to send a Binding Update message to the HA and all CNs. After the HA and CNs return the Binding Acknowledge message, the handover of the MN is successful and the procedure is finished.
The drawback of the above scheme of Hierarchical-based Fast Handover for Mobile IPv6 lies in that the scheme introduces a fast handover on the basis of HMIPv6, speeds up the handover procedure, but does not reduce the latency needed for performing Duplicate Address Detection operation on the LCoA and RCoA during handover; and this latency still makes up a great part of the total handover latency. Also, the Hierarchical-based Fast Handover for Mobile IPv6 involves lots of complicated technical steps and is difficult to implement.
Next, a brief introduction on Optimistic Duplicate Address Detection protocol is given.
In a practical application, a Duplicate Address Detection operation on a stateless address auto-configured care-of address will be successful. Thus, it is not worthwhile to wait a long time for success of the Duplicate Address Detection operation in most cases. This situation is improved by the Optimistic Duplicate Address Detection protocol.
The Optimistic Duplicate Address Detection protocol is a modification of the existing IPv6 Neighbor Discovery protocol (RFC 2461) and Stateless Address Auto-configuration protocol (RFC 2462); its intention is to minimize address configuration delays in the case of successful address configuration, to reduce communication disruption as far as possible in the case of failed address configuration, and to maintain interconnection of a general host with a router.
A new type of address, i.e. Optimistic address, is introduced in Optimistic Duplicate Address Detection protocol, for indicating that an address is available but no Duplicate Address Detection operation is performed on that address.