1 TCP for Seamless Vertical Handoff in Hybrid Mobile Data Networks Speaker : Tse-Hsien Lin Date...
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Transcript of 1 TCP for Seamless Vertical Handoff in Hybrid Mobile Data Networks Speaker : Tse-Hsien Lin Date...
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TCP for Seamless Vertical Handoff in Hybrid Mobile Data Networks
Speaker : Tse-Hsien Lin
Date : 93.12.30
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Outline
Introduction Challenges on Vertical Handoff Overview of TCP for wireless networks TCP for Seamless Vertical Handoff Performance Conclusions
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Introduction
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Introduction
Vertical Handoff
Share authentication, mobility management and resource management
Minimum functionality for interworking, such as mobile IP
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Challenges on Vertical Handoff
The Handoff triggering time Received Signal Strength (RSS) and
Velocity of a MH A seamless mobility management
Mobile IP Authentication procedure
Security and Billing TCP scheme
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Radio Resource Control Module
Gather measurement data such as RSS and velocity from both of the physical layers
Select a physical interface based on the measurement data from the physical layer
Trigger a vertical handoff or a horizontal handoff
Notify an impending handoff to the TCP layer so that the TCP receiver module sets its HO optional field
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Overview of TCP for wireless networks
TCP assumes the packet losses are caused only by congestion and adjusts its data rate according to the packet losses
In the wireless mobile network, losses are more caused by high bit error rate and fading effect and temporary disconnection
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TCP categorization
Link layer solution Snoop protocol
Split connection approach I-TCP and M-TCP
End-to-End protocol Freeze-TCP
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Snoop Protocol
The snoop protocol introduces a module, called the snoop agent, at the base station
The agent monitors every packet that passes through the TCP connection in both directions, and maintains a cache of TCP segments sent across the link that have not yet been acknowledged by the receiver
Packet loss is detected by the arrival of small number of Dup_ACKs from the receiver or by a local timeout
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Indirect-TCP and Mobile-TCP
They are split the TCP connection as Fixed Host (FH) to BS and BS to MH
I-TCP The link between BS-MH might not be
TCP M-TCP
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Freeze-TCP
A receiver sends a Zero Window Advertisement (ZWA) to the sender when handoff is impending
The Sender freezes all timeout timers and halts the data transmission when it receives ZWA
After the handoff is finished, the receiver sends 3 Dup_ACKs with available receive window size
Then the sender resumes data transmission with its old congestion window size.
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Drawbacks
For link layer solution and split connection approach the BS has a function to cache the packet
s and retransmit the lost packets For end-to-end protocol
Their TCP scheme is suitable for the horizontal handoff not the vertical handoff
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TCP FOR SEAMLESS VERTICAL HANDOFF
Motivation Considering these facts, a TCP sender
needs to temporarily halt its data transmission during handoff to avoid a timeout and packet losses
Different from Freeze-TCP by starting in the slow start state when the handoff is completed, and using the option field in a TCP header for indicating an impending HO
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Design a TCP receiver for vertical handoff
Optional field
No HO 00
Horizontal HO 10
Vertical HO 11
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PERFORMANCE
We evaluate the performance of the proposed TCP scheme using ns-2
The data rate of 3G cellular network is 144kbps and end-to-end RTT over a 3G cellular network is 300msec
The data rate within WLAN is 2Mbps and end-to-end RTT over a WLAN network is 100msec
We assume the handoff occurs at 70 sec and is completes at 73 sec
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Conclusion
After a vertical handoff, the sender tries to re-adjust its data rate, since the new network has a drastically different characteristic
In contrast with a horizontal handoff in which keeping the same data rate produces better performance
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Reference
Sung-Eun Kim; Copeland, J.A.; “TCP for Seamless Vertical Handoff in Hybrid Mobile Data Networks ”, GLOBECOM '03. IEEE , Volume: 2 Dec.2003
Goff, T.; Moronski, J.; Phatak, D.S.; Gupta, V.; “Freeze-TCP: a true end-to-end TCP enhancement mechanism for mobile environments ”, INFOCOM 2000. March 2000