Page 43 - Mobile Computing

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Transaction-oriented TCP

 TCP phases
o setup, data transmission, connection release
o using 3-way-handshake needs 3 packets for setup and release, respectively
o thus, even short messages need a minimum of 7 packets!

Transaction oriented TCP
o RFC1644, T-TCP, describes a TCP version to avoid this overhead
o connection setup, data transfer and connection release can be combined
o thus, only 2 or 3 packets are needed

Advantage: efficiency
Disadvantage
o Requires changed TCP
o Mobility no longer transparent

Approach Mechanism Advantages Disadvantages
Splits TCP connection Isolation of Loss of TCP
Indirect TCP into two connections wireless link, semantics, higher
simple latency at handover,
security problems
Snoops data and Transparent for end- Insufficient isolation
Snooping TCP acknowledgements, local to- end connection, of wireless link,
retransmission MAC security problems
integration
possible

Splits TCP Maintains end- to-end Bad isolation of
M-TCP connection, chokes semantics, andles long wireless link,
sender via window term and frequent processing overhead
size disconnections due to bandwidth
management, security
problems
Fast retransmit/ Avoids slow-start Simple and Mixed layers, not
fast recovery after roaming efficient transparent

Transmission / time- Freezes TCP state at Independent of Changes in TCP
out freezing disconnection, resumes content, works for required, MAC
after reconnection longer interruptions dependent

Selective Retransmits only lost Slightly more
retransmission data Very efficient complex receiver
software, more
buffer space needed
Transaction- Combines connection Efficient for Changes in TCP
oriented TCP setup/release and data certain applications required, not
transmission transparent,
security problems