Performance Comparison of IP_MPLS and ATM

8/13/2019 Performance Comparison of IP_MPLS and ATM

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Performance Comparison of IP, MPLS and ATM

Based Network Cores using OPNET

Hafiz M. Asif1and Md. Golam Kaosar

2

Department of Computer Engineering, King Fahd University of Petroleum and Minerals Dhahran 31261, [email protected], [email protected]

Abstract - The core components of a network play vital role in

its enhancement. For launching and providing Internet

applications and services, vendors have come up with a

variety of different technology based network cores and other

components of Internet backbone. Among all the challenges

for an efficient network core, traffic-routing is the most

important. Both the routing algorithms and the router-

technology are supposed to perform efficiently. We find that

there are a number of technologies that offer packet routing

service of which IP, ATM and MPLS are prominent. Some

of the routers are designed to provide delivery of specific kind

of traffic. The percentage of real time traffic (voice and

video) over Internet is rapidly increasing due to growing

trend of using real-time traffic oriented applications. People

want to talk, watch TV, do video conferencing etc over

Internet. This kind of real time traffic requires extra care

because of more delay sensitivity, minimum QoS

requirements and limited bandwidth. ATM and MPLS have

some especial features to support real time traffic. On the

other hand, it is almost impossible to replace already existing

IP based network and Internet. Therefore numerous new

features have been introduced in IP technology to support

real time traffic. Thus, we find enough motivation to

compare these three technologies in terms of their routing

capability based on different performance metrics using

OPNET simulator. We find that ATM and MPLS

outperform pure IP (without modification) in terms of delay

and response time to the exposed data.

I INTRODUCTION

The core components of a network play key role as far

as overall network performance is concerned and it has

nothing to do with end systems. The technology used for

routing can also make significant difference. Currently,

we have three main technologies for routing used in

network cores: IP, ATM and MPLS based routing. IP is

the oldest and highly used in network cores and a lot has

been done and still research is going on it for further

improvement. In order to enhance IP performance,

various modifications to the routing techniques were

proposed [1]. Similarly ATM and MPLS implementations

were also carried out [2-4]. Moreover, the hybrid

approach has also been studied in [5-7]. IP is still leading

among them due to its pre-diverse usage and has grown

relative features with which ATM and MPLS tried to

dominate. Along with network core optimization problem

in general, researchers are facing another challenge due to

rapid increase in the usage of multimedia traffic

(voice/video) over the Internet. The goal of this paper is

to analyze the performance comparison of IP, ATM and

MPLS based network cores when exposed to multimedia

traffic. Our simulation study shows that MPLS and ATM

outperform IP with respect to most of the selected

performance metrics.

The remainder of the paper is organized as follows. In

the next section, we briefly review three routers / switches

based on certain key characteristics. In Section III, we

describe the simulation model and traffic scenarios. We

then present the simulation results and evaluate the

performance of different queuing disciplines in Section IV.

Finally, we conclude our paper in Section V.

II NETWORK CORE

A network core is backbone of the entire network into

which other personal or enterprise networks inject data.

Design and capacity of the network core must be robust to

serve all the connected subnets or independent nodesefficiently. Therefore, the core usually consists of high

capacity links and efficient routing devices. We consider

IP, ATM and MPLS based network cores in our work to

see their effect on the network performance. IP based

network core is designed to give efficient service based on

certain features like best effort delivery, dynamic path

establishment etc. Such a core shows poor performance at

the time of congestion. On the other hand, ATM and

MPLS tackle this problem in an efficient manner by

making use of virtual path establishment and layered

architecture approach. Owing to more careful strategies

about delay and efficient use of available bandwidth, these

cores are well suited for multimedia traffic. The key ideaof enhanced performance of ATM is its well-defined

structure with exact degree of description about payload

and other packet format. It is a cell based network

protocol which encodes data traffic into fixed size cells.

The frame size is 53 bytes where 48 bytes are data and the

rest are for header information. It is, unlike IP, a

connection-oriented technology, in which a connection is

established between the two endpoints before the transfer

of actual data starts. ATM supports several classes of


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service to provide prioritization to certain type of data

such as voice, video etc. Therefore, as mentioned earlier,

it ensures QoS to real time traffic. However, this

improvement is achieved in IP by making use of very high

speed links available today (but we do not take this

improvement into consideration for the sake of

comparison). Similar to ATM, Multiprotocol Label

Switching (MPLS) has been evolved to ensure some

solutions to network problems like speed, scalability,

traffic engineering and quality of service management with

architecture different to that of ATM. More details about

these technologies can be found in [8, 9].

III METHODOLOGY AND APPROACH

A Simulation Model

We used OPNET Simulator to compare the three

network cores. OPNET is a real time simulator

specifically designed for network design and analysis. For

our experiment, we consider a hypothetical network

model. The core of the network consists of a number ofrouters in each of the three cases (ATM, IP, and MPLS).

There are three types of traffic: FTP, VOICE and VIDEO

on client sides with three corresponding servers on the

receiving end. Table 1 shows the typical values and

parameters of our traffic model. Note that the given data

rates are just a typical value for one run which are varied

to observe the performance metrics.

In order to demonstrate the performance of the core

consisting of a particular kind of routers in each of three

scenarios, we considered a hypothetical network topology

as illustrated in Fig. 1. The core of the network consists

of routers of ATM, IP, and MPLS for each single scenario.

All clients (FTP, VOICE and VIDEO) were connected tothe leftmost edge router whereas the single server was

connected to the right edge router.

Fig. 1 Network Topology for Simulation

TABLE 1Link Speed 10Mbps

Average FTP file size 5000 Bytes

FTP data rate 100kbps

Packet Size 2KByte

Video frame rate 10 fps

Video frame size 128x144 pixels

Video data rate 56kbps

Voice data rate 8kbps

Voice codec G.729

Video codec H.263

For FTP traffic, we used exponential distribution for

packet arrival, constant packet size and best-effort type of

service. We use low resolution video starting at 10 fps

(frames per sec) arrival rate and 128x120 pixels and keep

increasing this rate and size. The ToS is Streaming

Multimedia. For voice traffic, the voice encoder scheme is

G.729, the silence and talk spurt lengths are exponentially

distributed and ToS is Interactive Voice. All these settings

were made using OPNET Application Attributes Profile.

There are basically five types of delay that contribute to

the overall end-to-end delay i.e. forwarding, propagation,

queuing, packetization, and serialization. Forwarding

delay is technology dependent and is measured in tens or

hundreds of seconds (0.000001 sec). Propagation delay is

trivial to calculate provided link speed and packet size are

given. Serialization delay is the time it takes to place the

bits of a packet onto the link when a router transmits apacket. It depends on packet size and link speed and

typical value is around 1 msec [10]. Queuing delay is the

time a packet has to wait in a queue and it can vary over

time between zero seconds for a noncongested link, to the

sum of the times that it takes to transmit each of the other

packets that are queued ahead of it [10]. For Cisco

routers, its typical value is around 8 msec for real time

traffic.

B Performance Metrics

We use the following metrics for comparison and

analysis purpose:

Delay (sec) represents end-to-end delay. It is thesummation of all delays discussed in previous

section.

Throughput (pps) represents the total number ofpackets forwarded to higher layers per second.

Utilization represents percentage of theconsumption of an available channel bandwidth

where a value of 100.0 would indicate full usage.


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FTP Download Response Time (sec) is the timebetween the request for channel is made and

when the system starts download file.

Normalized Delivered TrafficIt is the number ofcorrectly received packets normalized by sent

packets from all clients. It indirectly shows the

percentage of the dropped traffic over the

network during simulation.

For analysis purpose, we set the maximum queue size to

be 500 packets.

IV SIMULATION RESULTS AND ANALYSIS

A Throughput

Throughput depends on link speed and nature of the

technology being used to transmit the data. We can see

from the Fig. 2 that the throughput increases linearly with

load until the channel gets saturated. Afterwards, it almost

remains almost constant in cases of ATM and MPLS but

there is an observable decrease in the case of IP due toboth its connectionless nature and heavy packet drop that

may be because of congestion. Moreover, IP does produce

relatively less throughput on account of its connectionless

and best effort service characteristics. On the other hand,

there is a virtual path defined for each packet in ATM and

MPLS based network cores (each router / switch) which is

responsible for the reduction of unreliability factor and

thus improvement in overall network performance.

0

10

20

30

40

50

60

10 20 30 40 50 100 200

Load (kpps)

Throughput(kpps)

IPMPLSATM

Fig. 2 Throughput of the Network

B Delay

The absence of virtual connection is the key reason of

relatively larger delay in IP based cores especially when

compared with ATM, which has been clearly depicted in

Fig. 3. MPLS falls between these two although its

behavior is similar to that of ATM. This, in turn, verifies

our earlier conclusion that ATM is supposed to be fit for

real time traffic due to its prior path establishment feature.

Finally, the quality of the real time traffic, especially for

voice data, is deteriorated on such a high value of the

delay.

0

150

300

450

600

750

20 30 40 50 100 200

Load

Delay(msec)

IP

M PLSATM

Fig. 3 Average End-to-End Delay of the Network

C Utilization

This is one of the key metrics to check the efficiency of

the technology. This weighs how efficiently the

technology makes use of the available resources such as

bandwidth etc.

The general trend of the utilization is to linearly

increase with load till the point of saturation is reached(Fig. 4). Note that IP relatively makes good use of the

0

0.2

0.4

0.6

0.8

1

1.2

20 30 40 50 100 200

Load

Utilization

IPMPLSATM

Fig. 4 Utilization of the Network versus Load


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available bandwidth although it produces lower

throughput. This is because number of packets is large in

case of IP compared to other two technologies because of

no prior path establishment time. Moreover, IP router

needs extra bandwidth in order to run routing algorithm

several times to predict the best available path. Relatively

less utilization of ATM and MPLS does not mean

inefficiency. Instead it will benefit at the time of

congestion and overloading situations.

D FTP Download Response Time

As mentioned earlier in section 2, ATM gives best

response to all kinds of traffic. It means that there is little

delay required to initiate the conversation and to let the

client start sending its data. As shown in Fig. 5, FTP

response time of ATM is considerably less compared to

other two technologies. IP based core shows the worst

behavior because of its random path detection (there is no

virtual circuit in IP). This feature is very useful and can be

exploited well for real time traffic such as voice and video.

This directly takes us to the conclusion that ATM givesbetter performance for real time traffic as far any type of

delay is concerned.

0

5

10

15

20

25

30

35

20 30 40 50 100 200

Load

Responsetime(msec)

IPMPLSATM

Fig. 5 FTP Download Response Time for IP, ATM and MPLS

E Normalized Traffic ReceivedWe can see the effect of connectionless and connection-

oriented features of IP and other two technologies

respectively by examining Fig. 6. Connectionless behavior

of IP is responsible for more drop at the time of congestion

(e.g. at 50kpps). However, it is not always the case i.e. IP

device tries to avoid congestion by running congestion

avoidance mechanism which most of the time works

efficiently. Therefore, we can see from Fig. 6 that there is

only one short interval of time where the received traffic

normalized by traffic sent is significantly low. On the

other hand, we make full use of connection-oriented nature

of other two technologies thereby reducing dropped traffic

to almost nil. Moreover, it is important to note that there

is a gradual decrease in the received traffic common to all

network cores with the increase in offered load due to

capacity limit, network environment and some other

reasons e.g. poor performance at physical layer etc. It is

also important to mention that the current IP based

network cores do not depict such a poor performance on

account of improved IPv6 architecture and some other

technology advancement which we did not include in our

simulation. As mentioned earlier, we compare IPv4 versus

ATM and MPLS because we also do not consider the

recent improvements made in ATM and MPLS.

0.5

0.6

0.7

0.8

0.9

1

1.1

20 30 40 50 100 200

Load

ReceivedTraffic

IP

MPLS

ATM

Fig. 6 Normalized Received Traffic Comparison of IP, MPLS andATM technologies

V CONCLUSIONS

The structure of ATM and IP is entirely different (we

used IPv4 in our simulation). ATM virtually establishes

route before the transmission starts whereas IP randomly

(or on demand) establishes routes for the packets to be

transmitted by running routing algorithm (Dijkstra, DV

etc.). This feature makes a subtle difference in the

performance depicted by these two protocols. Dominanceand outclass performance of ATM over IP with respect to

end to end delay, throughput and download response time

clearly shows that prior establishment has a lot of

advantages. One of the reasons of seldom use of ATM for

Internet cores is because of the difficulty to replace the

existing IP infrastructure which is widely spread all over

the Internet. Moreover, the enhancement of IPv6 has also

made possible to overcome the demerits that we showed in

our simulation due to IPv4 structure.


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ACKNOWLEDGEMENTS

The authors would like to thank KFUPM (King Fahd

University of Petroleum & Minerals) for its support.

Special thanks must go to Dr. Abdul Waheed for his

valuable pieces of advice during the course of simulation.

Finally, we would also like to thank Muzibur Rehman

working at KFUPM for his contribution in early survey

work of this paper.

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Documents

Performance Comparison of IP_MPLS and ATM