Transcript ppt

TCP for Seamless Vertical Handoff in
Hybrid Mobile Data Networks
Speaker：Tse-Hsien Lin
Date：93.12.30
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Outline
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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
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Vertical Handoff
Minimum
Share
authentication,
functionality for
mobility management
interworking,
such as and
resource
mobile
IPmanagement
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Challenges on Vertical Handoff
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The Handoff triggering time
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A seamless mobility management
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Mobile IP
Authentication procedure
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Received Signal Strength (RSS) and
Velocity of a MH
Security and Billing
TCP scheme
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Challenges on Vertical Handoff
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Design of a dual-mode Mobile Host for interworking
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Radio Resource Control Module
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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
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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
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Link layer solution
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Split connection approach
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Snoop protocol
I-TCP and M-TCP
End-to-End protocol
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Freeze-TCP
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Snoop Protocol
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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
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They are split the TCP connection as
Fixed Host (FH) to BS and BS to MH
I-TCP
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The link between BS-MH might not be
TCP
M-TCP
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Freeze-TCP
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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
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For link layer solution and split
connection approach
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the BS has a function to cache the
packets and retransmit the lost packets
For end-to-end protocol
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Their TCP scheme is suitable for the
horizontal handoff not the vertical handoff
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TCP FOR SEAMLESS VERTICAL
HANDOFF
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Motivation
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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
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Horizontal HO
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Vertical HO
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Design a TCP sender for vertical
handoff
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PERFORMANCE
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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
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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
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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
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