In a PMIPv6 domain, it inevitably experiences the packet loss or handover latency until it attaches to the new MAG when an MN moves to a new access network. In recent years, several fast handover mechanisms have been proposed to reduce the handover latency and packet loss with PMIPv6. Xia [12] et al. proposed a method to improve the performance of the network-layer handover using FMIPv6 signal. The MN will provide the target base station information, e.g. target-BS (MAG) ID before it moves from the serving base station to the target base sta-tion. Based on this information, the MN gets the IP address of the target MAG and performs the network-layer handover process before the actual handover starts. However, this scheme has some limitations including that each MAG needs to know all MAGs’ IP address and BS-IDs beforehand, a packet ordering problem may occurs between the packets buffered at previous
MAG (pMAG) and the packets form the LMA after registration after a handover, and the MN needs to provide the information about target base station to pMAG through link-layer signal-ing. Yokota [5] et al. used FMIPv6 signaling to improve the performance of the network-layer handover, called FPMIPv6. Before an MN moves from the current serving MAG to the tar-get MAG, it needs to report the tartar-get AR’s information to previous AR using the link-layer handover signaling process. The PAR then performs network-layer handover and establishes the bidirectional tunnel with NAR using the information from MN’s handover indication. The detailed signaling flow is shown in Figure 2.6.
MN PAR LMA
Figure 2.6 Predictive Fast handover with PMIPv6.
Figure 2.6 shows the signaling flow of the predictive fast handover procedures for PMIPv6.
We do not show the reactive fast handover here because it is similar to FMIPv6. Suppose that an MN first connected to the PAR which has a bidirectional tunnel with a LMA for user data
of the MN. To complete the handover while the bidirectional tunnel is switched to the NAR, a data-forwarding tunnel is established between the PAR and the NAR, according to the following procedures:
1. before executing handover, the MN detects that a handover is imminent and reports its network identifier (MN-ID) and the target access point identifier (New AP ID) to which the MN is most likely to move;
2. the PAR begins preparations for the MN’s handover and sends the HI message to the NAR.
The HI message must includes the MN-ID and include the MN’s home network prefix, the MN’s interface identifier (MN-IID) and the address of the LMA which is currently serving the MN;
3. on receiving HI message from PAR, the NAR replies the HAck message;
4. after the PAR receives HAck message from NAR, a bidirectional tunnel is established between PAR and NAR and all packet heading for the MN are forwarded from the PAR to the NAR via this tunnel;
5. the packet delivered by CN will be de-capsulated and buffered at NAR;
6. if the connection between the NAR and N-AN has already been established, those packets may be forwarded to the N-AN;
7. when the MN moves to the NAR domain, it establishes a connection with the N-AN. The connection will be established between the N-AN and NAR if it has not been established already;
8. after the MN is attached to the NAR, the NAR begins forwarding packets heading for the MN via the N-AN; and
9. the NAR sends the PBU message to the LMA, and then the LMA updates its BCE and replies PBA message to the NAR. Afterward the uplink and downlink packets can com-municate directly with the MN.
In FPMIPv6, the NAR may buffer the user data in its buffer resource before the MN is attached to the NAR. The user data buffered in NAR’s buffer resource are released when the NAR recognizes that the MN is attached. However, this scheme has some limitations:
• Each AR needs to have a tuple that contains the AP-IDs and IP address for all the ARs in PMIPv6 domain.
• After a handover, the packet out-of order problem may occur between the packets buffered at the PAR and the packets from the LMA after registration.
• The MN should provide information about the target access point identifier to PAR through link-layer signaling.
2.7 Summary
In Chapter 2, we briefly describe the handover procedure of MIPv6, PMIPv6 HMIPv6, FHMIPv6, and FPMIPv6. In Table 2.1, we present a summary of the main characteristics of host-based mobility protocol compared with network-based mobility protocol [4, 5], which we mentioned in previous sections. The detailed description for these mobility support protocols is provided in [1]-[6].
Table 2.1 Mobility Management Protocols Comparison.
Protocol Characterize MIPv6 HMIPv6 FMIPv6 FHMIPv6 PMIPv6 FPMIPv6
Mobility scope Global Local Global/Local Local Local Local
Required infrastructure HA HA, MAP HA, AR HA, MAP, AR LMA, MAG HA, AR
MN modification Required Not Required
MN address HoA/CoA LCoA CoA LCoA HoA(always) HoA(always)
Handover latency Bad Moderate Good Good Good Good
Seamless handover Not supported Not supported Supported Supported Not supported Supported
Mobility Management Host-based Network-based
Duplicate
address Performed at every subnet movement Performed only one time
detection (DAD)
Basically, FMIPv6 and its enhancement protocols such as FHMIPv6 and FPMIPv6 support seamless handover. On the other hand, MIPv6 and PMIPv6 do not support seamless handover.
Furthermore, realizing successful deployment of MIPv6 and their enhancement protocols such as FMIPv6, HMIPv6, and FHMIPv6 basically requires the addition or modification of some functionality in both the network and MN sides. In contrast, PMIPv6 and FPMIPv6 do not require any modification on MN’s protocol stack.