Mobile computing : Indirect TCP

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1
Mobile Transport Layer
Lesson 05
Indirect TCP, selective repeat and
mobile-end transport protocols

2
Indirect TCP suggests splitting of the
TCP layer into two TCP sub-layers
1. TCPM connection─ between the mobile
node (MN) and the base transceiver
(BTS) and between the BTS and a fixed
node (FN)
2. TCP connection─ Fixed nodes (FN)
• The BTS has an access point at an
agent TCPM for TCP connection
• TCPM sends and receives the packets to
and from the MN through the BTS

3
Indirect TCP sub-layer between BTS and fixed
node and conventional TCP between fixed nodes

4
Indirect TCP functions
1. TCPM sends and receives the packets to
and from the TCPF layer at the fixed
node
• The transfer mechanism simple as there
only one hop
• Retransmission delay between TCPM to
TCPF very small, unlike that between the
fixed nodes

5
TCPM functioning
• The data streams received from the
service access point (application) at the
MN and buffered at TCPM

6
Indirect TCP functions
2. TCPF layer at the fixed node sends and
receives the packets to and from another
fixed node TCP'F
• TCPF to TCP'F transfer mechanism using
multiple hops through the routers

7
Handover mechanism in case of
indirect TCP

8
Handover mechanism when the MN
visits a foreign network
• Packets for transmission buffered at TCPM
are transferred to TCP'M
• On handover, the socket (port and IP
address) and its present state migrate
from TCPM to TCP'M
• The transfer from TCPM to TCP'M latency
period

9
Advantage of indirect TCP
• Mobile part of the network isolated from
the conventional
• No change required in the existing TCP
network

10
Disadvantages of indirect TCP
• High latency period during handover of
packets
• Possible loss of data at the base
• Deviation from the end-to-end connection
feature of conventional TCP, which
guarantees reliable packet delivery
• Deviation─ an acknowledgement to a
sender may be lost during handover
latency

11
Selective Repeat Protocol
• Modification of the indirect TCP
• Between TCPM at the BTS and MN
selective repetition of the data using UDP
• Between TCPM at one end and TCP'F and
TCP'M at the other end, the data stream
transferred, as in case of conventional
fixed-end TCP

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Use of UDP in Selective Repeat Protocol
• UDP─ a connectionless protocol
• Selective repeat protocol does not
guarantee the in-order delivery between
the BTS and the MN, unlike TCP

13
Modification in indirect TCP in selective repeat
protocol using the UDP between BTS and MN

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Mobile-end transport protocol─
Modification of indirect TCP
• Guarantees the in-order delivery between
the BTS and the MN, like TCP
• Data transferred between TCPM at the
BTS and the MN by using the mobile-end
transport protocol
• Data stream transferred between TCPM at
one end and TCPF and TCPM at the other
end, the, as in case of conventional fixed
end TCP

15
Modification in indirect TCP by
using mobile-end transport protocol

16
Summary
• Split TCP protocol
• TCPM sends and receives the packets
to and from the TCPF layer at the fixed
node and between fixed points on
conventional network by TCP
• Selective repeat Protocol use (i) UDP
between MN and BTS, (ii) TCPM
between BTS and fixed node and (iii)
TCP between fixed node …

17
… Summary
• A TCP agent in Mobile-end transport
protocol in place of TCPM or UDP
between MN and BTS

18
End of Lesson 05
Indirect TCP, selective repeat and
mobile-end transport protocols

Mobile computing : Indirect TCP

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Mobile computing : Indirect TCP