Flow Control TCP also provides mechanisms for flow control. Flow control assists the reliability of TCP transmission by adjusting the effective rate of data flow between the two services in the session. When the source is informed that the specified amount of data in the segments is received, it can continue sending more data for this session. This Window Size field in the TCP header specifies the amount of data that can be transmitted before an acknowledgement must be received. The initial window size is determined during the session startup via the three-way handshake. TCP feedback mechanism adjusts the effective rate of data transmission to the maximum flow that the network and destination device can support without loss. TCP attempts to manage the rate of transmission so that all data will be received and retransmissions will be minimized. See the figure for a simplified representation of window size and acknowledgements. In this example, the initial window size for a TCP session represented is set to 3000 bytes. When the sender has transmitted 3000 bytes, it waits for an acknowledgement of these bytes before transmitting more segments in this session. Once the sender has received this acknowledgement from the receiver, the sender can transmit an additional 3000 bytes. During the delay in receiving the acknowledgement, the sender will not be sending any additional segments for this session. In periods when the network is congested or the resources of the receiving host are strained, the delay may increase. As this delay grows longer, the effective transmission rate of the data for this session decreases. The slowdown in data rate helps reduce the resource contention. 3.3.4
Posted on: Tue, 25 Jun 2013 11:44:25 +0000
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