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1. QoS
(Quality of Service)

2. Content
• Introduction
• IP QoS: Mechanisms
• IP QoS Frameworks
• QoS in Wireless Networks

3. Introduction
Page 3
Point 2 is
Imposiblle
1. Computer networking relies on sharing of limited network resources for
communications.
2. If communications resources were unlimited, a direct point-to-point link of
unlimited bandwidth would be possible between any two end-points that
wished to communicate.
Agree..!!

4. Page 4
In the real world, two end-points that wish to communicate, unless they are
connected to the same LAN, need to communicate through a network of links
that have the following characteristics:
1. The links are shared between
traffic from multiple sources to
multiple destinations
2. The links have limited bandwidth
3. The links have propagation
latency (i.e., time taken for data to
traverse the links)
4. The nodes directly connected to
each link have limited processing
power and memory capacity
Introduction

5. Page 5
How should these
limited resource
be shared?
FIFO (first in first out)
Introduction

6. Page 6
However, this simple treatment of packets is not sufficient for today’s
multiservice networks.
The different applications have different requirement on the communications
services provided by the network.
Voice
Video
1. Voice and Video have very stringent delay and latency
requirements, as already discussed in chapter 4.
2. File transfer, on the other hand, does
not have the same delay and latency
requirments.
Introduction

7. Page 7
Introduction
These kind of requirements, plus others such as “guaranteed” bandwidth
requirements, are know as QoS requirements, and the whole field that is
about these requirement and the ways they are met in networks, is known
as:
QoS
(Quality of Service)

8. Page 8
Introduction
Table 1. shows some different categories of traffic and their QoS
requirements

9. Page 9
IP QoS Mechanisms
1.Introduction to IP QoS
2.Resource Reservation
3.Admission Control
4.Packet Classification and Marking
5.Queuing Disciplines
6.Traffic Shaping
7.Policing
8.Routing Control and Traffic Engineering

10. Page 10
Introduction to IP QoS
The existing internet is largely a best-effort network.
Internet
No guarantees are
provided that
packet will not loss

11. Page 11
Introduction to IP QoS
The IP QoS solution is predicated on three fundamental requirements:
1.To Provide mechanisms to offer different levels
of services to different users, even though some
users might get better service than others.
Thus, IP QoS is inherently “unfair”
2.The Service should not usually be completely
denied to lower-priority traffic.
3.The mechanisms are efficient, not wasteful of
valuable network resources.

12. Page 12
IP QoS Mechanism
Resource Reservation
Perhaps a natural first step in moving away from a purely best-effort-service
Internet is to Provide away to reserve resources for selected users while still
using traditional IP Routing. Resource reservation refers to dynamic
arrangements for QoS provisioning that can be made end-to-end over one or
more intermediate networks. Usually, a reservation is specified by a traffic
profile, a description of the rate, burst size, and other feature of the reserved
traffic.

13. Page 13
IP QoS Mechanism
Resource Reservation Protocol (RSVP)
RSVP is a signaling protocol that allows
resource reservation to be coordinated in a
network. RSVP signaling generally results in
resources being reserved in rsvp capable routers
in the transit path of a traffic flow. Each of these
routers maintains a soft state that needs to be
periodically refresh. RSVP is unidirectional-
resources are reserved in one direction from
source to destination only.

14. Page 14
IP QoS Mechanism
Resource Reservation Protocol (RSVP)
Resources are reserved using the following procedures. See figure 1

15. Page 15
IP QoS Mechanism
Admission
Admission control refers to the decision whether
to admit a certain flow or aggregation of flows into
a network, in response to a request for resource
reservation. It makes sense for admission control
decsions to be made by an entity with an overall
view of network resources.

16. Page 16
IP QoS Mechanism
Bandwidth Brokers
There are two basic choices for dynamic allocation of bandwidth
resources in the routers in a given network.
1. Each router makes its own decisions, perhaps as configured
manually or by policy.
2. A single entity makes the decisions for the network, taking into
account the dynamic conditions in the network. This entity is often
called a bandwidth broker
By the nature of its functions, it is typical that each domain would have
its own
bandwidth broker to control its bandwidth resources. It would be
involved in negotiations
(perhaps with another domain’s bandwidth broker) for resource
allocation
for interdomain traffic, making decisions on

17. Page 17
IP QoS Mechanism
Figure 2.shows an example of a bandwidth broker providing
admission control services to administrative domain
Bandwidth Brokers

18. Page 18
IP QoS Mechanism
Packet Classification and Marking
Packet classification is the separation of packets into
different classes based on some criteria
Example:
1. Classifacation may be port-based (the input and/or output port of the
packet)
2. Transport protocol-based (TCP or UDP),
3. Application-Based (such as HTTP-based)
4. Address –Based (Based on the source or destination address of the
packet).
It is also possible that out-of-profile packet are
reclassified, typically into a lower priority class.

19. Page 19
IP QoS Mechanism
Packet Classification and Marking
Marking is the setting of bits in the packet header
corresponding to the packet class. The bits marked could
be the three bits in the type of service (ToS) field and the
three bits in the precedence field of the IP header
Packet classification and marking allows differential
treatment of different, packet classes using
other, complementary QoS. Packet classification and
marking may be handled by external sources like a
customer or other network. When the packets enter a new
network, that network can accept the classification or
reclassify.
The decision depends on the QoS architecture and
policies used..

20. Page 20
IP QoS Mechanism
Queuing Disciplines
Queuing is fundamental to IP QoS schemes
because each router has one or more input
queues and one or more output queues that may
be where the bulk of “processing time” is spent.
The use of various queuing disciplines can be
used to change such functions as processing
times and flow rates. Most of the queuing
disciplines discussed here operate on router
output queues, although priority queuing could be
implemented to operate jointly on input/output
queues.

21. Page 21
IP QoS Mechanism
Queuing Disciplines
1. FIFO Queuing
2. Priority Queuing
3. Fair Queuing (FQ), Weighted Fair Queuing
(WFQ), and Class-Based Queuing (CBQ)

22. Page 22
IP QoS Mechanism
FIFO Queuing
FIFO queuing is the standard, basic queuing discipline. All packets
are treated equally without preference except that earlier arriving
packets leave before later arriving packets.
Advantages :
1. Highly optimized forwarding performance resulting from years of
experience by router manufacturers.
2. For lightly loaded networks with sufficient transmission and switching
capacity, queuing is necessary only for smoothing intermittent traffic
bursts. FIFO does this very efficiently.
Disadvantages :
1. For networks that are not lightly loaded, FIFO queuing may result in loss
of packets through discarding when the queues are full.
2. FIFO does not allow certain packets to receive priority/preference over
other packets.

23. Page 23
IP QoS Mechanism
Priority Queuing (PQ)
PQ (see Figure 3) is a non-FIFO queuing discipline. The router
examines the input queue, takes high-priority packets and places
them in the output queue ahead of normal packets. This effectively
reorders packets according to priority.

24. Page 24
IP QoS Mechanism
Fair Queuing (FQ), Weighted Fair Queuing (WFQ), and Class-Based
Queuing (CBQ)
Therefore, FQ results in preferential treatment to low-volume traffic
flows.
WFQ is a variation and generalization of FQ that weights the outputs
of the per-flow queues (according to the IP ToS field, for example) as
well.
Advantages of WFQ include:
1. It prevents a misbehaving TCP session from consuming a large
fraction of
resources at the expense of other flows.
2. The fairness aspect of this type of scheme prevents buffer
starvation.
Disadvantages of WFQ include:
1. WFQ is a way to approximate generalized processor sharing
(GPS), where
the link sharing between queues is accomplished by scheduling
alone.

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IP QoS Mechanism
Comparison of Queuing Disciplines

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IP QoS Mechanism
7.2.8 Traffic Shaping
Traffic shaping refers to controlling the rate of traffic passing through a
given
router. It is often used at the ingress points of a network as a form of
soft admission control.
1. Leaky bucket traffic shaping constrains the rate to be less than a
maximum
value, while
2. token bucket traffic shaping constrains the average rate to be less
than a
maximum value.

27. Page 27
IP QoS Mechanism
7.2.9 Policing
There are multiple definitions of policing in the literature, which all
have to do with treatment of packets that are nonconforming (with a
profile). According to one definition, policing refers to the process of
dropping packets from a flow that are nonconforming

28. Page 28
IP QoS Mechanism
7.2.10 Routing Control and Traffic Engineering
The basic functional requirements for traffic engineering are :
• Distribution of topology information, to allow nodes to build correct
topology maps and to assist in path selection;
• Path selection, to select a path based on some criteria, such as
bandwidth,
delay, shortest path;
• Directing traffic along computed paths, using forwarding tables
(computed
independently at each node using traditional IP routing protocols or
signaled
protocols such as MPLS).

29. IP QoS Framework
Page 29
The mechanisms discussed in Section 7.2 are often used in
combination in networks, in order to provide end-to-end QoS, or to
enforce some QoS policies in a network domain. Routers typically
combine some of these mechanisms, for example as shown in
Figures 7.6 and 7.7.

30. IP QoS Framework
Page 30
There should be ways to more systematically coordinate the various
QoS
mechanisms used in a network according to some kind of framework
to allow endto-end provision of QoS for a variety of network traffic,
consistent with some idea of network QoS policy.
IntServ and DiffServ are two such frameworks.

31. QoS in Wireless Networks
Page 31
In wireless networks, there are a number of issues related to providing
QoS. 1. there are the issues associated with all wireless networks
regardless of host mobility, because of the characteristics of the
wireless link, including relatively lower bandwidth, higher latency, and
higher errors than comparable wired links.
2. there are the additional complications that come with mobility.

32. QoS in Wireless Networks
Page 32
7.4.1 WLAN QoS Support
The 802.11 MAC consists of a distributed coordination function (DCF)
and a point coordination function (PCF). The DCF is implemented in
all stations and can be used in both ad hoc and infrastructure modes.

33. 7.5 Summary
Page 33
As introduced in this chapter, techniques are needed for providing
differentiated QoS because limited resources in networks are
shared, and because the network needs to be able to treat different
classes of traffic differently based on issues including different
application requirements and different subscriptions. We overview a
number of different mechanisms for IP QoS, including resource
reservation (using RSVP), admission control (e.g., using bandwidth
brokers), packet classification and marking (e.g., using bits in the ToS
field of the IP header), queuing (FIFO, priority queuing, WFQ, and
CBQ), traffic shaping (leaky bucket and token bucket), policing
(e.g., policing token bucket), and traffic engineering or QoS routing.
We touch upon the two QoS frameworks for IP networks, the IntServ
and DiffServ frameworks that provide ways to systematically apply
QoS mechanisms. Then we explore QoS in wireless networks, looking
at some length at QoS in 802.11, and the interactions of mobility
protocols with QoS mechanisms.

34. References
Page 34
Dn, T. Y., & Yyepg, T. (2005). TeAm YYePG Wireless Internet.