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Security in Wireless Ad Hoc and Sensor Networks by Chunming Rong, Erdal Cayirci

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6

Reliability, Flow and Congestion Control

In OSI, reliability and flow control are tasks for both the data link and transport layers. Error correction and/or detection schemes, explained in Chapter 4, are used to ensure reliability during transmission on a link basis by the data link layer. The transport layer provides reliability as well as flow and congestion control on an end-to-end basis. We elaborate on the challenges and solutions related to transport layer issues for wireless ad hoc networks in this chapter.

6.1 Reliability

The reliability schemes in the transport layer are generally based on retransmission. A data segment is resent by the source node, or sometimes by an intermediate node that has the segment, when it was not delivered successfully on the previous attempt. There are two challenges to achieving this:

  • detecting that a data segment has not been delivered successfully, i.e. has been lost or garbled during transmission;
  • initiating the retransmission of the segment.

Detection of an unsuccessful delivery can be made either by the source or the destination. If a node that receives the data always acknowledges a successful delivery, this is called positive acknowledgement. When the positive acknowledgement scheme is used, if the source node does not receive an acknowledgement for a transmitted segment, it indicates that either the segment has not been delivered successfully or the acknowledgement has been lost. In this scheme the responsibility for detection is ...

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