Transport Layer

Transport Control Protocol (TCP)

  • Operation of TCP
    • When a sender transmits a segment, it also starts a timer.
    • When the segment arrives at the destination, the receiving TCP entity sends back a segment (with data if any) bearing an acknowledgement number equal to the next sequence number it expects to receive.
    • If the sender’s timer goes off before the acknowledgement is received, the sender transmits the segment again.
  • 3-way handshaking
    • 3-way handshaking
    • To release a connection, either party can send a TCP segment with the FIN bit set.

TCP Segments

TCP-Segments

Data Traffic

The main focus of congestion control and quality of service is data traffic.

  • In congestion control we try to avoid traffic congestion.
  • In quality of service, we try to create an appropriate environment for the traffic.
  • So, before talking about congestion control and quality of service, we discuss the data traffic itself.

Traffic Profile

Congestion Control

In general, we can divide congestion control mechanisms into two broad categories: open-loop congestion control (prevention) and closed-loop congestion control (removal).

  • Open-loop
    • Retransmission Policy
    • Window Policy
    • Acknowledgement Policy
    • Discard Policy
    • Admission Policy
  • Closed-loop
    • Back Pressure
    • Choke Packet
    • Implicit signaling
    • Explicit signaling

Metrics Used to Monitor a Subnet for Congestion

  • Percentage of all packets discarded for lack of buffer space;
  • Average of queue lengths;
  • Number of packets that time out and are retransmitted;
  • Average packet delay;
  • Standard deviation of packet delay, etc.
Table Of Contents
Transport Layer
Transport Control Protocol (TCP)
TCP Segments
Data Traffic
Congestion Control