ATCP : TCP for Mobile Ad Hoc Networks

1
ATCP TCP for Mobile Ad Hoc Networks

• By Jian Liu and Suresh Singh
• Presented By Harkirat Singh

2
Motivation

• WireLess Network is Different from
• WireLine Network
• Ad Hoc Network
• - Node Mobility
• - Network Partition

3
Mobility Example
s
s
a
a
d
d

b
b
s
s
s
T5
T20
d
d
d
4
Explicit Congestion Notification

• By S.Floyd and Team
• Active queue management with RED
• RED can drop a packet or set a bit

ECN-Echo flg 1, CWR flg 1 (SYN)
ECN-Echo flg 0, CWR flg
1 ECT 1 CE 1

ECN-Echo flg 1
5
Dynamic Source Routing
lt1,3,5,7gt
lt1,2gt
7
7
lt1gt
Dest
2
2

5
5
Dest.
lt1,3,5gt
8
8
Src
Src
lt1gt
1
3
1
3
lt1,3gt
lt1,4,6gt
6
6
lt1,4,6gt
4
4
lt1gt
lt1,4,6gt
lt1,4gt
lt1,4,6gt
Route Discover Route Record
Propagation of Route Reply
with
Route Record
6
TORA-Route Creation
(0,1)
(0,3)
(-,-)

(-,-)

7
Dst
7
2

(0,0)
Dst
2
5

5
8
(0,0)
(0,2)
(0,3)
8
.
Src
(-,-)
(-,-)
Src.
1
3
1
3
(0,3)
(-,-)
6
6
4
(0,1)
4
(-,-)
(0,2)
(-,-)
QRY packet UPD
pkt height updates
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TCP in Ad Hoc Network

• High Bit Error Rate (BER)
• Route Recomputation
• Network Partition
• Multipath Routing

8
Goal

• High BER retransmit lost pkt
• Route Recomputation Transient Partition - stop
  transmitting
• Multipath Routing No congestion control
• Maintain TCPs congestion control

9
ATCP Functioning

• States Normal, congested, loss and disconnected
• Lossy Channel ATCP loss state and TCP Persist
  state
• Disconnected ICMP destination unreachable, TCP
  in persist state and ATCP in disconnected state
• Congested ECN flag, ATCP in congested state
  and do nothing!

10
State transition diagram
Receive Destination Unreachable ICMP, CWND 1
Receive dup ACK or pkt from receiver
TCP sender put in persist state
Receive ECN
New Ack
RTO About to Expire OR 3 dup ACKs
ATCP Retransmits segments in TCPs buffer
TCP transmits a pkt
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Data flow - TCP/ATCP/IP stack
data
TCP_input()
TCP_output()
ATCP_input()
ATCP_output()
ipintr()
ip_output()
data
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Flowchart for function atcp_input()
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Flowchart for function atcp_output()
14
Performance study

• Five Pentium PCs, each with two Ethernet cards
• Emulate wireless in IP, 32 Kbps channel
• Bit error rate 10(-5)
• Random hop-by-hop delay
• Network congestion 5sec
• Partition 5 minutes and last for 1 min.
• Packet reordering 25 seconds

15
Bit Error - Performance
Sequence number
Time (seconds)
Time (seconds)
16
Bit Error, Congestion Window
Congestion Window Size
Index
Index
17
Congestion and Partition Performance
Transfer time (second)
hop by hop delay(ms) hop by hop
delay(ms)
Congestion Partition
18
Overall Performance
19
Conclusion

• End-to-End TCP semantics are maintained
• ATCP is transparent
• ATCP does not interfere with TCPs congestion
  control behavior
• ATCP improves performance by one-third
• ECN as standard - WIP

20
References

• RFC 2481
• http//www-nrg.ee.lbl.gov/floyd/ecn.html
• draft-ietf-manet-tora-spec-02.txt
  draft-ietf-manet-tora-spec-02.txt