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

2. 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

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

4. 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

5. 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!!

6. 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.

7. 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

8. 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.

9. 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.

10. 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