Contents: Data Traffic Congestion Congestion Control Quality of Service Techniques to improve QOS How QOS is implemented within the Internet References..

1. BY: ARYA
Quality of service
in
Internetworking….

2. CONTENTS:
• Data Traffic
• Congestion
• Congestion Control
• Quality of Service
• Techniques to improve QOS
• How QOS is implemented within the Internet
• References

3. 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.

4. 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 (the number of packets a network
can handle).
• Congestion control refers to the mechanisms
and techniques to control the congestion and
keep the load below the capacity.

5. CONGESTION CONTROL
• Congestion control refers to techniques and
mechanisms that can either prevent
congestion, before it happens, or remove
congestion, after it has happened. In general,
we can divide congestion control mechanisms
into two broad categories: open-loop
congestion control (prevention) and closed-
loop congestion control (removal).

6. The rapid growth of the Internet, and increasing
levels of traffic, make it difficult for Internet users
to enjoy consistent and predictable end to end
levels of service quality.
What causes poor service quality within the
Internet?
what are the components of service quality
and how can they
be measured?

7. QUALITY OF SERVICE
• Quality of service is the overall performance of a
telephony or computer network, particularly the
performance seen by the users of the network.
• The ability to provide different priority to different
applications, users, or data flows
• Guarrante a certain level of performance to a data
flow. For example, a required bit rate, delay, jitter.
• Something a flow seeks to attain.

8. Flow characteristics

9. Delay:
Delay is the elapsed time for a packet to be passed from the sender,
through the network, to the receiver.
It is made of four components : propagation time, transmission time,
queuing time and processing time.
The higher the delay, the greater the stress that is placed on the
transport protocol to operate efficiently.
For example : Telephony, audio conferencing and video conferencing
needs minimum delay.
Jitter:
Packets from the source will reach the destination with different
delays. This variation in delay is known as jitter .
Jitter causes the signal to be distorted and are unacceptable in
situations where the application is real-time based, such as an
audio or video signal.
It can seriously affect the quality of streaming audio and/or video.

10. Bandwidth:
Bandwidth is the maximal data transfer rate that can be sustained
between two end points.
Bit rate directly proportional to bandwidth.
This is limited by the physical infrastructure of the traffic path
within the transit networks .
Different application needs different bandwidth.
For example: In video conferencing we need to send millions of bits
per sec while in e-mail we may not reach even a million.
Reliability:
Network reliability is measured by frequency of failure means how
long it takes a link to recover from a failure.
Lack of reliability means loss of packets or ACK. So, retransmission
required.
For example: e-mail, file transfer must have reliable transmission.

11. TECHNIQUES TO IMPROVE QUALITY OF
SERVICE
We briefly discuss four common methods:
I. Scheduling.
II. Traffic shaping.
III. Admission control.
IV. Resource reservation.

12. SCHEDULING
Three techniques designed to improve quality of
service:
• FIFO Queuing.
• Priority Queuing.
• Weighted Fair Queuing.

13. 24.13
1.FIFO queue

14. 24.14
2.Priority queuing

15. 24.15
3. Weighted fair queuing

16. TRAFFIC SHAPING
There are two techniques that can control the
rate of traffic.
• Leaky Bucket
• Token Bucket.

17. 24.17
1. Leaky Bucket

18. 24.18
Leaky bucket implementation:

19. 24.19
A leaky bucket algorithm shapes bursty traffic
into fixed-rate traffic by averaging the data rate.
It may drop the packets if the bucket is full.
Note

20. 24.20
2. Token bucket

21. 24.21
The token bucket allows bursty traffic at a regulated
maximum rate.
Note

22. How is Quality of service implemented within
the Internet?
The Internet is composed of a collection of routers and transmission
links.
Routers receive an incoming packet, determine the next hop
interface, and place the packet on the output queue for the selected
interface.
Poor service quality is typically encountered when the level of traffic
selecting a particular hop exceeds the transmission bandwidth of the
hop for an extended period of time.

23. In such cases, the router's output queues associated
with the saturated transmission hop begin to fill, causing
additional transit delay (increased jitter and
delay), until the point is reached where the queue is filled, and
the router is then forced to discard packets
(reduced reliability).
This in turn forces adaptive flows to reduce their sending rate to
minimize congestion loss, reducing the available bandwidth for
the application.
Poor service quality can be generated in other ways, as well.
Instability in the routing protocols may cause the routers to
rapidly alter their selection of the best next hop interface, causing
traffic within an end to end flow to take divergent paths, which in
turn will induce significant levels of jitter, and an increased
probability of out of order packet delivery (reduced reliability).

24. References:
• Data Communications & Networking by Behrouz A.
Forouzan.
• https://www.wikipedia.org

25. Thank You
Any Queries………