1 TCP for Seamless Vertical Handoff in Hybrid Mobile Data Networks Speaker ： Tse-Hsien Lin Date ：

2 Outline Introduction Challenges on Vertical Handoff Overview of TCP for wireless networks TCP for Seamless Vertical Handoff Performance Conclusions

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4 Introduction Vertical Handoff Share authentication, mobility management and resource management Minimum functionality for interworking, such as mobile IP

5 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

6 Challenges on Vertical Handoff Design of a dual-mode Mobile Host for interworking

7 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

8 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

9 TCP categorization Link layer solution  Snoop protocol Split connection approach  I-TCP and M-TCP End-to-End protocol  Freeze-TCP

10 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

11 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

12 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.

13 Additive Increase Multiplicative Decrease (AIMD)

14 Drawbacks For link layer solution and split connection approach  the BS has a function to cache the packets and retransmit the lost packets For end-to-end protocol  Their TCP scheme is suitable for the horizontal handoff not the vertical handoff

15 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 HOslow start state

16 Design a TCP receiver for vertical handoff Optional field No HO00 Horizontal HO10 Vertical HO11

17 Design a TCP sender for vertical handoff

18 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

19 Downward vertical handoff Congestion window size vs. time

20 Downward vertical handoff Sequence No. vs. time

21 Upward vertical handoff Congestion window size vs. time

22 Upward vertical handoff Sequence No. vs. time

23 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

24 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 March 2000