t layer is the lowest end-to-end layer in the IP stack, it is a natural candidate for vertical handoff support. Moreover, in the transport layer solutions, no third party other than the endpoints participates in vertical handoff and no modification or addition of network components is required. Authors in [17] proposed a new set of options for migration of TCP con- nections from one IP address to another to support mobility. In this pro- tocol, the MN and CN determine a unique token number to identify the TCP connection when the connection is set up, calculated according to the addresses/ports numbers of the peer nodes. The MN will notify the CN of its new IP address/port number along with the token number SO that the CN can update the information in the corresponding connection. Similarly, authors of [18] and [19] propose to add a mapping layer between the IP layer and the TCP layer. All address update messages will be intercepted by the mapping layer and the data packets will be replaced with the initial connec- tion information before they are submitted to the upper layer. It also considers the situation that two peer nodes execute handoffs at the same time. During such dual roaming situations, the MN at either end cannot deliver the address update messages to its counterpart since the destination node has also changed its IP address. To overcome this problem, it is proposed in [18,19] to set up a third party subscription/notification server. When the MN roams into a new network, it will send the new address to both the peer node and the notifica- tion server. If two MNs cannot find each other after a handoff, they can find the peer node's new address from the notification server SO that the connec- tion can be maintained. The main drawback of these approaches is that TCP has been globally deployed SO that it is practically infeasible to change it in every end system. In recent years, SCTP [8] has emerged as a standard transport protocol for the Internet that can be used in place of both TCP and UDP, and is po