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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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Challenges on Vertical Handoff

Design of a dual-mode Mobile Host for interworking

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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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Design a TCP sender for vertical handoff

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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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Downward vertical handoff Congestion window size vs. time

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Downward vertical handoff Sequence No. vs. time

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Upward vertical handoff Congestion window size vs. time

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Upward vertical handoff Sequence No. vs. time

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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