Wireless Ad Hoc and Sensor Networks Out Outline e (Transport Layer) • Introduction and challenges (self learning) • Which transport layer protocols? (self learning) Application – Traditional TCP (self learning) – A Brief Revisit to Traditional TCP (self learning) A B i f R i it t T diti l TCP Transport Protocol • Design goals and Classification of a Transport layer protocols for wireless ad hoc networks. protocols for wireless ad hoc networks Network Protocol N k P l • Enhancements to TCP for wireless ad hoc networks WS 2010/2011 – TCP-based TCP based Media Access Protocol Media Access Protocol – Others Prof. Dr. Dieter Hogrefe • Summary y Physical Channel (Radio) Physical Channel (Radio) Dr. Omar Alfandi Dr. Omar Alfandi 2 Introduction : Transport layer objectives Introduction : Transport layer objectives Introduction : Challenge Introduction : Challenge • Setting up : – end-to-end connection • The traditional wired transport layer protocols are not – end-to-end delivery of data packets suitable for wireless ad hoc networks due to the – flow control and congestion control flow control and congestion control inherent problems associated with ad hoc networks. inherent problems associated with ad hoc networks • There are: • There are: • TCP protocol does not work well in ad hoc networks TCP protocol does not ork ell in ad hoc net orks – Connection-less transport layer protocols such as UDP – What are the major reasons behind that ? – Connection-oriented transport layer protocols such as TCP p y p 3 4
Introduction : Major reasons (1/4) Introduction : Major reasons (1/4) Introduction : Major reasons (2/4) Introduction : Major reasons (2/4) • Misinterpretation of packet loss: • Effects of contention (dependency on path length) – Wired connection : packets loss are mainly due to – Within the increase in the number of hops in the path congestions; throughput decreases exponentially – Wireless ad hoc networks : high packet loss due to : Wireless ad hoc networks : high packet loss due to : • Misinterpretation of congestion window (CW) • Misinterpretation of congestion window (CW) • High BER (wired link < 10 E-9, wireless link 10 E-5 ~ 10 E-4 – CW is the rate that is acceptable for the network and the and even higher) receiver • Collision due to hidden terminal problem • Collision due to hidden terminal problem • Asymmetric link behaviour • Interference: wired link are well isolated, wireless links interfere; – Sometimes wireless link are directional in ad hoc networks • Frequent path breaks: wired due to failures, wireless: mobility; leading to l di t • Large-scale and small-scale propagation phenomenon. • Delivery of a packet to a node and failure in the delivery of ACK • Frequent path breaks • Some routing protocols require the forward and backward paths g p q p – Topology changes, route reconfigurations, etc .. T l h t fi ti t to be the same 5 6 Introduction : Major reasons (3/4) Introduction : Major reasons (3/4) Introduction : Major reasons (4/4) Introduction : Major reasons (4/4) • Resources contention • Network partitioning and merging – Both DATA and ACK require RTS-CTS-DATA-ACK at the B th DATA d ACK i RTS CTS DATA ACK t th TCP receiver TCP receiver TCP receiver data-link layer for session A for session A for session A TCP receiver TCP receiver TCP receiver – Contention for resources in the same link at forward and for session B for session B for session B for session B for session B for session B backward paths • Multipath routing – Some routing protocols use multiple paths between the source and destination leading to: TCP sender TCP sender for session A for session A • High number of out-of-order packets leading to DUPACKs g p g TCP sender TCP sender TCP sender for session A • Different RTO values leading to unnecessary retransmission for session B TCP sender TCP sender for session B for session B RTO: Retransmit TimeOut DUPACKs: Duplicate Acknowledgments 7 8
Which transport layer protocols? Which transport layer protocols? Outline Out e • Introduction and challenges (self learning) • TCP is reliable, incorporates congestion control, incorporates end-to-end and flow control mechanisms i t d t d d fl t l h i • Which transport layer protocols? (self learning) • Observations concerning ad hoc networks – Traditional TCP (self learning) – A Brief Revisit to Traditional TCP (self learning) A B i f R i it t T diti l TCP – It is preferable to seamlessly integrate TCP in ad hoc It i f bl t l l i t t TCP i d h networks: • Design goals and Classification of a Transport layer • To enable seamless operation of higher layer protocols such as protocols for wireless ad hoc networks protocols for wireless ad hoc networks. FTP,HTTP • Enhancements to TCP for wireless ad hoc networks – If not, to make as less modifications to TCP as possible: – TCP-based TCP based • To make wireless and wired TCPs understands each other To make wireless and wired TCPs understands each other seamlessly – Others – If not, to split the TCP into wireless and wired part: • Summary y • To concentrate internetworking functions in gateways T t t i t t ki f ti i t 9 10 Traditional TCP Traditional TCP Outline Out e • Introduction and challenges (self learning) The major responsibilities of TCP in an active session are to: t • Which transport layer protocols? (self learning) • provide reliable in-order transport of data: – Traditional TCP (self learning) – A Brief Revisit to Traditional TCP (self learning) A B i f R i it t T diti l TCP – to not allow losses of data. t t ll l f d t • Design goals and Classification of a Transport layer • control congestions in the networks: protocols for wireless ad hoc networks. protocols for wireless ad hoc networks – to not allow degradation of the network performance. to not allow degradation of the network performance • Enhancements to TCP for wireless ad hoc networks • control a packet flow between the transmitter and the receiver: receiver: – TCP-based TCP based – Others – to not exceed the receiver's capacity. • Summary y 11 12
In general In general TCP segment structure TCP segment structure we distinguish between the following operational phases in TCP: h i TCP – slow-start phase (also known as exponential start); – congestion avoidance phase; congestion avoidance phase; – congestion control phase; – fast retransmit phase; p – fast recovery. 13 14 TCP connection establishment and termination C co ect o estab s e t a d te at o Outline Out e • Introduction and challenges • Which transport layer protocols? – Traditional TCP – A Brief Revisit to Traditional TCP A B i f R i it t T diti l TCP • Design goals and Classification of a Transport layer protocols for wireless ad hoc networks protocols for wireless ad hoc networks. • Enhancements to TCP for wireless ad hoc networks – TCP-based TCP based – Others • Summary y 15 16
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