2009 International Symposium on Computing, Communication, and Control (ISCCC 2009)
Proc .of CSIT vol.1 (2011) © (2011) IACSIT Press, Singapore
Analysis of IP Network for different Quality of Service
Ajith Kumar V. 1 and Sheela Ganesh Thorenoor 2+
1
Associate Consultant, Talent Transformation, Wipro Technologies
2
Consultant, Talent Transformation, Wipro Technologies,
Abstract. Quality of Service defines a set of criteria used to classify the level of service allotted to a
consumer or application. These criteria include, but are not limited to, data rate, round trip delay, jitter and
packet loss. Quality of Service is the ability to provide different priorities to different applications, users, or
data flows, or to guarantee a certain level of performance to a data flow. For example, a required bit rate,
delay, jitter, packet dropping probability and/or bit error rate may be guaranteed. QoS guarantees are
important if the network capacity is insufficient, especially for real-time streaming multimedia applications
such as voice over IP and IPTV, since these often require fixed bit rate and are delay sensitive and in
networks where the capacity is a limited resource, for example in cellular data communication.
Keywords: Quality of Service, Differentiated Service, Queuing discipline, Integrated Service, Traffic
Shaping, Traffic Policing.
1. Introduction
The ultimate goal of QoS is to provide adequate service levels [1] for certain heterogeneous applications
without reducing the service experienced by other applications. Early work on QoS for the Internet used the
"IntServ" [2] philosophy of reserving network resources. In this model, applications used the Resource
reservation protocol (RSVP) to request and reserve resources through a network. While IntServ [3]
mechanisms do work, it was realized that in a broadband network typical of a larger service provider, core
routers would be required to accept, maintain, and tear down thousands or possibly tens of thousands of
reservations. It was believed that this approach would not scale with the growth of the Internet.
The second and currently accepted approach is "DiffServ" or differentiated services. In the DiffServ
model, packets are marked according to the type of service they need. In response to these markings, routers
and switches use various queuing strategies to tailor performance to requirements. (At the IP layer,
differentiated services code point (DSCP) markings use the 6 bits in the IP packet header. At the MAC layer,
VLAN IEEE 802.1Q and IEEE 802.1D can be used to carry essentially the same information)
Routers supporting DiffServ use multiple queues for packets awaiting transmission from bandwidth
constrained (e.g., wide area) interfaces. Router vendors provide different capabilities for configuring this
behavior, to include the number of queues supported, the relative priorities of queues, and bandwidth
reserved for each queue.
In practice, when a packet must be forwarded from an interface with queuing, packets requiring low jitter
(e.g., VoIP or VTC) are given priority over packets in other queues. Typically, some bandwidth is allocated
by default to network control packets (e.g., ICMP and routing protocols), while best effort traffic might
simply be given whatever bandwidth is left over.
+
Corresponding author.
E-mail address: (ajith.vyasarao@wipro.com,sheela.ganesh@wipro.com).
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In this paper we use Opnet (the leading network R&D) tool to examine both IntServ (RSVP) and
DiffServ (PQ, CQ, FIFO, RED, and WRED) mechanisms and their impact on the network.
QOS refers to traffic control mechanisms that seek to differentiate performance based on application or
network operator requirements and also provide predictable or guaranteed performance to applications’
sessions.
QoS is an issue because the default service in many packet switched networks is to give all applications
the same service and does not consider any service requirements to the network. This is also referred to as
best-effort service.
IP service is best effort service and it is different from probabilistic model. In case of probabilistic
service there is a chance factor for success or failure. IP packets sometimes never reach the destination, the
reason is that they take the best path from source to destination. IP packets are routed and routing is
connectionless. Sometimes IP packets are discarded by the routers, hence they will not be able to reach the
destination. IP packets are dropped by the router for some reason. Router cannot unscrupulously discard the
packet. Router should state the valid reason for dropping the packet that is why it is known as best effort.
It is very difficult to support QoS in a pure IP network; there is no single definition for the term QoS.
QoS requirements are different for Audio and video application, QoS requirements are different for the
interfaces and the network elements. Even at system level, QoS requirements are different and also vary
from user to user.
Perceptual parameters are translated to System QoS, for example picture detail is a perceptual parameter
defined in terms of pixel resolution, picture color accuracy maps to color information per pixel, video rate
maps to frame rate, video smoothness maps to frame rate jitter and audio quality depends up on sampling
rate and quantization.
2. Components of QoS Framework
QoS has to be implemented at various places in the network. IP network comprises of Nodes, Switches,
Routers and Gateways. One has to implement packet classification and scheduling at the Router level, traffic
conditioning at the network entrance, admission control at routers or somewhere in the network and there is a
need for signaling between host and the routers.
Admission control is the first line of defense against attacks on QoS. Network should not commit any
guarantee if available resources are not sufficient to support the request. Admission control functions must
examine both traffic and QoS parameters carefully before accepting or rejecting a new request for QoS.
2.1. Traffic Policing
Users violating the traffic policies can jeopardize the QoS of other connections, the network must protect
well behaving users against such traffic violations. We can make sure that all entering traffic is subjected to
policing. Policing functions are deployed at the edge of the network. If arriving traffic conforms to the
traffic norms then it will be allowed inside the network and non-conforming traffic is dropped by the traffic
policing entity.
2.2. Traffic Shaping
Traffic shaping entity will not drop the non-conforming traffic instead it will be more interested in
smoothening the traffic. Arriving traffic might be having undesirable characteristics but Traffic shaping
entity will buffer the input traffic to smoothen it so that out going traffic will be having desirable
characteristics.
2.3. QoS Management
Goals of the QoS management are sharing the bandwidth requirements, fairness to competing flows,
meeting bandwidth, packet loss, delay guarantees and reducing the delay variations.
3. QoS Architecture for the Internet
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Two QoS architectures have been defined for Internet. Integrated Services (IntServ) and Differentiated
Services (DiffServ)
3.1. Integrated Services
This architecture was proposed in 1994, and support Per-flow Quality of Service. In this scheme
Resource reservation/admission control is implemented and can support delay guarantees. IntServ specifies
two types of services, Guaranteed Service and Controlled Load Service.
3.2. Guaranteed Service
This service is characterized by having guaranteed bandwidth, End-to-end delay bounds and no loss due
to buffer overflows.
3.3. Controlled Load Service
Controlled Load Service provides a service that is equivalent to a best effort service in a lightly loaded
network and is characterized by low loss, low delay and no absolute guarantees
Integrated Service is having the advantage of having strong guarantees (bounded delays) but suffers from
the following disadvantages that it requires all routers to be implemented with IntServ. Scalability concerns
since routers must maintain state information, charging and authentication of reservations must be solved
and Inter domain issues are difficult to resolve.
3.4. Differentiated Services (DiffServ)
This architecture was proposed in 1998 and supports Class-based QoS.
reservation is not always needed
In this scheme Resource
DiffServ specifies two types of services, Assured Forwarding and Expedited Forwarding. In Assured
Forwarding service, customers sign service agreements with ISPs and edge routers mark packets as being
“in” or “out” of profile, core routers run RIO, RED with in/out. This service distinguishes different classes.
Expedited Forwarding has hard guarantee on the delay and delay variants.
DiffServ has the following advantages. There is no per-flow processing in network core and per-flow
processing only at the network edge. This service is simpler to implement than IntServ, because there is no
requirement of a signaling protocol. DiffServ has the following disadvantages; Assured Forwarding has
weaker service guarantees and Expedited Forwarding service raises same issues with charging and
authentication as IntServ services.
4. Packet Scheduling
To support QoS we need a facility for packet classification and marking. We have CoS bits (Class of
Service) at layer 2 for classifying the traffic and TOS (Type of Service) bits at Network Layer.
4.1. First in, first out (FIFO)
FIFO queuing is the most basic queue scheduling discipline. In FIFO queuing, all packets are treated
equally by placing them into a single queue, and then servicing them in the same order that they were placed
into the queue. FIFO queuing is also referred to as First come, first served (FCFS) queuing.
4.2. Priority Queuing
Priority Queuing used in QoS, Priority queuing supports some number of queues, usually from high to
low. Queues are serviced in strict order of queue priority, so that high queue always is serviced first, than the
next-lower priority and so on.
If a lower-priority queue is being serviced and a packet enters a higher queue, that queue is serviced
immediately. This mechanism is good for important traffic, but can lead to queue starvation
4.3. Custom Queuing
Custom Queuing (CQ) assigns a certain percentage of the bandwidth (denoted as byte count) to each
queue to assure predictable throughput for other queues. It is designed for environments that need to
guarantee a minimal level of service to all traffic.
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4.4. Weighted Fair Queuing:
Weighted Fair Queuing (WFQ) allocates a percentage of the output bandwidth equal to the relative
weight of each traffic class during periods of congestion
5. Analysis of QOS for IP Networks using OPNET
In this simulation model, we have used OPNET IT Guru to build a small IP network and apply QoS
policies, to analyze the performance of the network in terms of packet loss and delay for different kinds of
video streaming applications.
.
Figure 1. Basic IP Network
Here we are connecting two different LAN networks, one consisting of different video streaming clients
and the other consisting of the corresponding video servers. Here there are four clients connected to Router
A through the switch. There are four servers connected to Router B again through another switch and clients
are accessing the servers through IP network. The bottleneck has been created in the link between router A
and router B.
Figure 2. IP Router interface with no QoS configuration
In this scenario IP Router interfaces not configured for any QoS as shown in the figure. In the Opnet
simulation model, profile confiigurator describes the activity patterns of a user or group of users in terms of
the combination of applications defined through application confiigurator, used over a period of time.
5.1. Application configuration
Application Config is used to specify applications that will be used to configure user profiles. Even
though there are different possible applications which can be configured, like database access, email, file
transfer, file print, telnet session, video conferencing, we have chosen different types of video conferencing
applications for individual clients
Figure 3. Application configuration.
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We have then customized the application requirements by setting the parameters for the selected
application.
Like this a baseline model has been built in which case all the profile, application and other interface
parameters have been set as mentioned above, but without configuring any of the router interfaces for QoS.
Figure 4. QoS configuration on the Router’s interface
For Discrete Event Simulation (DES), those parameters which need to be verified are to be selected, like
IP, IP interface Video called party, video calling party, video conferencing., end to end packet loss, delay,
jitter etc. These settings are done by choosing the respective parameters under global and node statistics of
DES parameter settings. Now the simulation engine is run and the different parameters under observation
are noted
5.2. Priority Queuing configuration
As a second scenario, router interfaces are configured for QoS parameters and are set to priority queuing
as ToS
Figure 5. QoS configuration set to Priority Queuing.
Figure depicts the QoS configuration parameters of priority queuing that s set to the priority of ToS.
Then the network is simulated for these conditions are the results are noted.
Similarly for the same network QoS configurations are set to custom queuing and Weighted Fair
Queuing as another two different scenarios and the corresponding results are noted after running the
simulation engine.
Then we compared the effect of different QoS configuration settings in terms of queuing delay at the
router, end to end delay, packet loss., jitter etc on all different types of video conferencing signals already
defined.
You can also verify the QoS configuration, in this scenario we have configure Custom Queuing as the
QoS settings on the router’s interface.
6. Results
After successfully running the simulation, we can compare the results as plotted in the following two
graphs
It can be noticed that in all the four types of video application, the number of packets sent were the same,
but the number of packets received has varied based on the type of configuration, as this would affect the
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buffer size and thereby the packets that are going to be lost at router B and in turn the packets received at the
receiving node. Also end to end delay variation is different for different applications and is also
corresponding to the different QoS settings.
Figure 6. Packets sent
Figure 7. Packets received under four different QoS Settings
Figure 8. End to end delays being different for different video conferencing applications
We can measure the QOS parameters fro various settings, such as end to end delay and packet loss, these
parameters give an indication regarding the performance of the network for a given Quality of Service.
7. Conclusion
In conclusion, it can be mentioned that for a given condition of a QoS, among the four different video
streaming applications like background, standard, excellent effort and streaming multimedia, the delay is
highest for background and the lowest for streaming multimedia, thus proving the different queue delays and
sizes will in turn decide upon the packet loss and also end to end delay.
8. References
[1]
Cormac Long. IP Network Design, Tata McGraw- Hill Publishing Company, New Delhi. 200
[2] Behrouz and A. Forouzan, Data Communications and Networking, Ed. New York: McGraw-Hill, 2003.
[3] Alberto Leon-Garcia and Indra Widjaja, Communication Networks, Ed. New York: McGraw- Hill, 2004.
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