CSE 4340/5349 Mobile Systems Engineering M. Kumar Spring 2010 Week 4

Mobile IP Triangle routing, indirect routing Direct Routing Home agents Foreign agents Registrations HA FA Anchor FA Care of address Encapsulation Agent discovery Registration TCP – Transmission Control Protocol IP – Internet protocol BS – Base Station MH – Mobile host CH – Correspondent host HA – Home agent FA- Foreign agent

TCP Transport layer protocol Reliable, uses ACKs Congestion control Adjusts to network conditions Error control Packets buffered until ACKs received Buffered packets resent

Desired (in Mobile systems) No disruption of services as the user moves Changes point of attachment How to ensure? Autonomous transfer Minimal delays and losses

Effects of Mobility IP and Mobile IP Packets are routed to their destinations according to IP addresses. IP addresses are associated with a fixed network location. Mobile IP Packets may be destined to mobile nodes Seamless roaming to applications and users. Shield mobility effects from applications higher level protocols TCP/IP was designed for wired networks; But it has survived in the wireless world; well, till now at least!!

Effects of Mobility TCP congestion control mechanism Acks not received Slow start or other control mechanisms Window size is reduced Slow start TCP congestion control mechanism in mobile environments When a MH hands-off from one network , it does not receive packets until it registers at another network. In the meanwhile TCP mechanism at the sender assumes the packets have been lost and goes into congestion recovery mode. Congestion window size is reduced and/or packets are retransmitted. Overall effect –performance deterioration.

Encapsulation/Tunneling Messages originating at the CH have The home or original address of the MH The HA encapsulates the message with the address of the FA in the foreign network and forwards the packet to the foreign network The FA peels off the ‘new address’ and forwards the original packet to the MH in the foreign network. This process of appending and peeling off care off addresses is called tunneling or encapsulation. Original Address New Address

Split Connections Split at BS Selective ACK of out of sequence packets Mobile TCP Core network CH MH BS BS The TCP/IP connection is split at the BS. The BS ACKs packets, buffers them and forwards to the MH.

Supervising host One host as a controller in the core network Keep track of CHs and MHs Supervising Host MH MH MH MH The supervising host (SH)resides in the wired network and keeps track of all the MHs. The supervising host is contacted for all correspondence related to MHs. The SH maintains a directory of MH locations. One can envision a set of distributed SHs catering to groups of MHs.

Snoop protocol Lower layer solution Processing between TCP and IP at the BS Packets are snooped (processed) Snoop module reads packet addresses to determine which packets have not been ACKed. Facilitates retransmission at the BS Requires packets to be buffered at the BS Multicast solution MH uses a multicast address as the care-of-address All BSs the MH has been (And will be in) contact with are invited to be members of the multicast group The BS where he MH is residing currently will forward the packets. Remaining BSs discard the packet TCP IP Snoop CH BS BS BS MH