TCP IN WIRELESS DOMAIN - IUPUI Indiana University …TCP在无线领域联合分校印第安那大学….ppt

TCP IN WIRELESS DOMAIN - IUPUI Indiana University …TCP在无线领域联合分校印第安那大学…
Contents
Introduction
Traditional TCP
TCP Oll errors. - FEC (Forward Error Correction): redundancy is encoded into  the message. - Redundancy is introduced only if error possibility is found. - Retransmission at link layer
TCP- Unaware Link Layer
Main aim is to simulate the behavior of the snoop TCP without requiring the link layer at the BS to be TCP aware.
At the BS ,link layer retransmission is used to perform local error recovery.
In this, retransmissions are triggered by link level ACKs.
Mobile TCP
Connection between MN and BS is lost for small intervals of time.
This leads to time out by sender or data buffered by AP may be too large or results in slow start.
MTCP handles this situation using a supervisory host.
MTCP maintains end-end TCP semantics even though TCP connection is split at the supervisory host.
Advantages:
Avoids Retransmission
Avoids closing of contention window
Avoids slow start at the sender
Explicit Loss Notification (ELN)
WTCP - Reliable Transmission Control Protocol for Wide Area Wireless Networks (WTCP)
Wireless TCP unique characteristic is separate mechanisms for congestion control and reliability.
TCP Selective ACK (TCP SACK)
Transaction-Oriented TCP (T-TCP)
TCP connection setup and tear-down is huge overhead for a small amount of data, uses 3-way handshake
3 packets for a single transaction, 2 transactions per connection cycle
3 packets for setup + 1 for data + 3 packets for release = 7 packets minimum
To improve performance use T-TCP for small amount of data.
Integrate connection setup, tear-down, and data transfer combined into single transaction
Usually only 2 or 3 packets are needed
Advantage
Larger efficiency (low overhead)
Disadvantage
Changed TCP
Mobility not transparent, can’t affect existing framework
Impact of Mobility
Fast retransm