 the CN for the mobile node originally through the HA can therefore now be sent to the mobile node at the foreign network (subnet B). To do this tunneling used. From this point on, the mobile node can start to communicate with the CN directly through the foreign agent (Figure 22.1). 22.2.2.2.2 Mobility management using SIP The initial design of SIP did not consider mobility management of the end nodes as an issue and hence mobility management using SIP is an after thought. However, to support real- time applications, it is essential to address mobility of nodes to ensure there is no disruption of communication due to lost attachment and poor link quality. When mobile nodes move, they make, break and re-establish connections with their correspondent nodes. This mobility affects the performance of SIP. Using IPv6 SIP can support terminal mobility without increasing the SIP payload but incurs delay penalties resulting from the desire to handoff. terminal mobility, the terminal changes access between two nodes or subnets to maintain communication. This change could be as a result of better received signals from the new node or better link conditions to the new node. Which ever one of this is involved, there are delays to be considered during handoff. In the mobility management scheme described in Figure 22.2, during an active communication session the mobile node obtains a new address through a DHCP server and sends a new session invitation (SIP re-INVITE) to the correspondent node (1). This invitation message contains details of the iden- tity of the mobile node, its new IP address and the new subnet it is attached to. Usually this is done through updating the session description. The corre- spondent node therefore knows where to send data to the mobile node first by issuing a SIP OK message (2) and sending data (3). A re-registrar message is sent to SIP server to complete the signaling. There are two crucial problems with SIP mobility management scheme. Firstly, SIP does not offer a solution for the mobility manage