It explain the need for congestion control and quality of service.Congestion control refers to the mechanisms and techniques to control the congestion and keep the load below the capacity.

1. CONGESTION CONTROL AND QUALITY
OF SERVICES
By
Jawad Ahmad

2. WHAT IS CONGESTION?
Congestion in a network may occur if the load on the
network-the number of packets sent to the network-is
greater than the capacity of the network.

3. CONGESTION CONTROL
Congestion control refers to the mechanisms and
techniques to control the congestion and keep the load
below the capacity.

4. NETWORK PERFORMANCE
Network performance refers to measures of service
quality of a telecommunications product as seen by
the customer.
Congestion control involves two factors that measure the
performance of a network
Delay
Throughput

5. DELAY VERSUS LOAD
when the load is much less than the capacity of the
network, the delay is at a minimum. This minimum
delay is composed of propagation delay and processing
delay, both of which are negligible. However, when the
load reaches the network capacity, the delay increases
sharply because we now need to add the waiting time in
the queues to the total delay.

6. THROUGHPUT VERSUS LOAD
Throughput in a network as the number of packets
passing through the network in a unit of time. when the
load is below the capacity of the network, the throughput
increases proportionally with the load.

7. CONGESTION CONTROL CATEGORIES

8. CONGESTION CONTROL CATEGORIES
 Open-Loop Congestion Control:
In open-loop congestion control, policies are applied to
prevent congestion before it happens. In these
mechanisms, congestion control is handled by either the
source.
 Closed-Loop Congestion Control:
Closed-loop congestion control mechanisms try to
alleviate congestion after it happens.

9. OPEN-LOOP CONGESTION CONTROL
CATEGORIES
 Retransmission policy
 Window policy
 Acknowledgement policy
 Discard policy
 Admission policy

10. CLOSE-LOOP CONGESTION CONTROL
CATEGORIES
 Back pressure
 Choke point
 Implicit signaling
 Explicit signaling

11. TWO EXAMPLES
To better understand the concept of congestion
control, let us give two examples: one in TCP and
the other in Frame Relay.
Congestion Control in TCP
Congestion Control in Frame Relay

12. CONGESTION CONTROL IN TCP
Slow start, exponential increase:

13. CONGESTION CONTROL IN TCP
Congestion avoidance, additive increase:

14. CONGESTION CONTROL IN TCP
TCP congestion policy summary:

15. CONGESTION CONTROL IN FRAME RELAY
BECN:

16. CONGESTION CONTROL IN FRAME RELAY
 FECN:

17. CONGESTION CONTROL IN FRAME RELAY
Four cases of congestion:

18. QUALITY OF SERVICE
On the Internet and in other networks, QoS (Quality of
Service) is the idea that transmission rates, error rates,
and other characteristics can be measured, improved,
and, to some extent, guaranteed in advance. QoS is of
particular concern for the continuous transmission of
high-bandwidth video and multimedia information.

19. FLOW CHARACTERISTICS
Four types of characteristics are attributed to a flow:
Reliability
Delay
Jitter
Bandwidth

20. RELIABILITY
Reliability is a characteristic that a flow needs. Lack of
reliability means losing a packet or acknowledgment,
which entails retransmission. However, the sensitivity o
application programs to reliability is not the same.

21. DELAY
Source-to-destination delay is another flow
characteristic. Again applications can tolerate delay in
different degrees.

22. JITTER
Jitter is the variation in delay for packets belonging to the
same flow. For example, if four packets depart at times 0,
1, 2, 3 and arrive at 20, 21, 22, 23, all have the same
delay, 20 units of time.

23. BANDWIDTH
Different applications need different bandwidths. In
video conferencing we need to send millions of bits per
second to refresh a color screen while the total number of
bits in an e-mail may not reach even a million.

24. FLOW CLASSES
Based on the flow characteristics, we can classify flows
into groups, with each group having similar levels of
characteristics. This categorization is not formal or
universal; some protocols such as ATM have defined
classes.

25. IMPROVE THE QUALITY OF SERVICE
Scheduling
Traffic shaping
Admission control
Resource reservation

26. FIFO QUEUE

27. PRIORITY QUEUING

28. WEIGHTED FAIR QUEUING

29. LEAKY BUCKET

30. TOKEN BUCKET

31. APPLICATION OF QOS
 Operating System Support for Quality of Service
• QoS Support in Microsoft Windows
• QoS Support in Linux
• Operational/Practical Issues for QoS on End Hosts