Soft Handover Procedure in mSCTP

In this section, we describe how to use mSCTP for soft handover in the transport layer. For an example, we consider a mobile node (MN) that initiates an SCTP association with a correspondent node (CN) in IPv6 networks. The case in IPv4 has similar procedures as those in IPv6 networks. After initiation of an SCTP association, the MN moves from access router A to access router B, as shown in Fig. 1.

Figure 1

It is assumed that an MN initiates an association with a CN. The resulting SCTP association consists of IP address 2 for MN and IP address 1 for CN. Then the procedural steps described
below, from Step 1 through 4, will be repeated whenever the MN moves to a new location, until the SCTP association will be released.

Step 1) Obtaining an IP address for a new location: Let us assume that the MN moves from AR A to AR B and thus it is now in the overlapping region. In this phase, we also need to assume that the MN can obtain a new IP address 3 from the AR B by using IPv6 stateless
address configuration.

Step 2) Adding the new IP address to the SCTP association: After obtaining a new IP address, the MN’s SCTP informs the CN’s SCTP that it will use a new IP address. This is done by sending an SCTP ASCONF chunk to the CN. The MN receives the responding ASCONF-ACK Chunk from the CN.

Step 3) Changing the primary IP address: While the MN further continues to move toward AR B, it needs to change the new IP address into its primary IP address according at an appropriate rule. Actually, the configuration of a specific rule to trigger this “primary address change” is a challenging issue of the mSCTP.

Step 4) Deleting the old IP address from the SCTP association: As the MN progresses to move toward AR B, if the old IP address gets inactive, the MN must delete it from the address list. The rule for determining if the IP address is inactive may also be implemented by using information from the underlying network
or physical layer.

Source : mSCTP for Soft Handover in Transport Layer, Seok Joo Koh, Moon Jeong Chang, and Meejeong Lee, Member, IEEE