Mobile computing : Indirect TCP
- 1. © Oxford University Press 2007. All rights reserved. 1 Mobile Transport Layer Lesson 05 Indirect TCP, selective repeat and mobile-end transport protocols
- 2. © Oxford University Press 2007. All rights reserved. 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. © Oxford University Press 2007. All rights reserved. 3 Indirect TCP sub-layer between BTS and fixed node and conventional TCP between fixed nodes
- 4. © Oxford University Press 2007. All rights reserved. 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. © Oxford University Press 2007. All rights reserved. 5 TCPM functioning • The data streams received from the service access point (application) at the MN and buffered at TCPM
- 6. © Oxford University Press 2007. All rights reserved. 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. © Oxford University Press 2007. All rights reserved. 7 Handover mechanism in case of indirect TCP
- 8. © Oxford University Press 2007. All rights reserved. 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. © Oxford University Press 2007. All rights reserved. 9 Advantage of indirect TCP • Mobile part of the network isolated from the conventional • No change required in the existing TCP network
- 10. © Oxford University Press 2007. All rights reserved. 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. © Oxford University Press 2007. All rights reserved. 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
- 12. © Oxford University Press 2007. All rights reserved. 12 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. © Oxford University Press 2007. All rights reserved. 13 Modification in indirect TCP in selective repeat protocol using the UDP between BTS and MN
- 14. © Oxford University Press 2007. All rights reserved. 14 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. © Oxford University Press 2007. All rights reserved. 15 Modification in indirect TCP by using mobile-end transport protocol
- 16. © Oxford University Press 2007. All rights reserved. 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. © Oxford University Press 2007. All rights reserved. 17 … Summary • A TCP agent in Mobile-end transport protocol in place of TCPM or UDP between MN and BTS
- 18. © Oxford University Press 2007. All rights reserved. 18 End of Lesson 05 Indirect TCP, selective repeat and mobile-end transport protocols