Performance Comparison of Video Multicasting over Asynchronous Transfer Mode (ATM) &

Multiprotocol Label Switching (MPLS) Networks

Zakaria Bin Ali Mustaffa Samad Habibah Hashim

Universiti Teknologi MARA (UiTM)

Shah Alam, Selangor

Abstract –Multicast is a well-known protocol that has been tested to be a highly effective method to deliver real time applications over the network. In this paper, two Virtual Private Network (VPN) based technologies are considered in delivering real-time based applications namely Multiprotocol Label Switching (MPLS) and Asynchronous Transfer Mode (ATM). The performance comparison of video multicast of the two technologies is described. Both platforms were modeled and simulations executed with multicast protocol enabled. For real time traffic, selected parameters were carefully defined and configured such as delay, throughput and packet loss. The objective of this study is to compare performance of MPLS and ATM based on these selected parameters, particularly in the case of delivering video traffic in the presence of congestion. The study showed that with VPN enabled on both technologies, MPLS had performed better than ATM in terms of throughput and packet drop. Keywords – Multicast, Virtual Private Network (VPN), Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM), OPNET, video traffic, congestion .

I. INTRODUCTION

Video streaming has become one of the most utilised applications over the internet worldwide. Various types of protocols and networks have been designed in order to provide the most efficient technique, while at the same time catering to other applications, such as web browsing (http), e-mail (smtp), file transfer (ftp) etc. Bandwidth limitation on the network is the main constraint when

delivering video streaming on the network via unicast. Multicast would be able to provide a better solution in overcoming this bandwidth limitation.

Performance comparison of IP, ATM and MPLS, with regards to their ability to deliver all types of data including video using unicast protocol were discussed in a study conducted using OPNET [1]. The results showed that MPLS and ATM performed well with regards to three parameters namely delay, throughput and utilization. However, for video streaming, unicast routing is not suitable to be used for delivering the streaming because it will consume a lot of bandwidth on the core network. To best deal with video streaming, multicast technique would be the better solution to overcome bandwidth constraint issues.

There are numerous researches focused on multicast

performance over MPLS and ATM. ATM has proven to be a good switching technology in terms of scalability and switching speed, but some problems arise when attempting to offer multicast forwarding of cells through an ATM network [2]. However, the introduction of LANE [3] to deliver multicast data over ATM was shown to improve the performance. Performance of multicasting over MPLS [4] had been shown to be very impressive. However the above research did not focus much on video multicast performance in particular over MPLS and ATM.

In the coming sections, multicast protocol will be

briefly discussed, followed by brief description of multicast on MPLS and multicast on ATM. The multicast will be enabled and simulated on both MPLS and ATM and their performance will be discussed in the last section.

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II. MULTICAST OVERVIEW

Multicast is a bandwidth-conserving technology specifically designed to reduce traffic by simultaneously delivering a single stream of information to potentially thousands of corporate recipients or homes. By replacing copies for all recipients with the delivery of a single stream of information, multicast is able to minimize the burden on both sending and receiving hosts and reduce overall network traffic. In the case of video delivery, a multicast video stream is only forwarded on the links that lead to the multicast group members.

Figure 1: Multicast concept

In Figure 1, the source will send a copy of data and it then will be replicated in the network to be sent to multiple recipients.

Multicast routing protocols enable a collection of multicast routers to build (join) distribution trees when a host on a directly attached subnet wants to receive traffic from a certain multicast group. In this research study, PIM-SM will be used as the multicast protocol for MPLS platform. In PIM-SM, in order to receive multicast data, routers must explicitly tell their upstream neighbours about their interest in particular groups and sources. Routers use PIM Join and Prune messages to join and leave multicast distribution trees. PIM-SM by default uses shared trees, which are multicast distribution trees rooted at some selected node (called the Rendezvous Point, or RP) and used by all sources sending to the multicast group

By its nature [5], IP Multicast forwarding is different from IP Unicast and has additional addressing requirements to consider. IP multicast addresses have been assigned to the old Class “D” address space by the Internet Assigned Number Authority (IANA). Addresses in this space are denoted with a binary “1110” prefix in the first four bits

of the first octet. This result in IP multicast addresses spanning a range from 224.0.0.0 through 239.255.255.255.

III. MULTICAST ON MPLS

MPLS is VPN based device with its vigorous Label Switch Path (LSP) technology. One would think that multicast and MPLS are two complementary technologies. Merging these two technologies, where multicast trees are constructed in MPLS networks will enhance performance and present an efficient solution for multicast scalability. Many multicast protocols have been proposed to best suit with MPLS and are in use today on the Internet. Amongst them, PIM-SM is the most widely implemented protocol. It is a protocol that at times builds source-rooted shortest path trees. The implementation of the PIM-SM protocol over MPLS networks is done in a very simple manner as shown in Figure 2 below.

Figure 2: Basic Concept of PIM-SM on MPLS

When a data packet arrives, instead of doing only one label switching, the data packet is replicated, and for each copy a label switching is done. These copies are transmitted then to the convenient outgoing interfaces [4].

IV. MULTICAST ON ATM

ATM’s capability to create VPN using its Virtual Path (VP) facilities has made this technology being chosen as core network amongst Service Provider. A multicast enabled ATM switch is a very important component for multicast services which copy cells or packets from a single input port to a selected number of output ports. This type of switch, which is capable of cell replications and switching is usually accomplished by a copy network (CN) and followed by a point-to-point routing network (RN). The CN of both multicast switches replicate input cells from various sources and then the RN routes all the copies to their final destination [6].

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ATM based IP hosts and routers use a Multicast Address Resolution Server (MARS) to support IP multicast over the ATM for point to multipoint connection service. MARS is an extension of the ATM ARP Server. It acts as a registry, associating layer 3 multicast group identifiers with the ATM interfaces representing the group’s members. MARS messages support the distribution of multicast group membership information between MARS and endpoints (hosts or routers). Endpoint address resolution entities query the MARS when a layer 3 address needs to be resolved to the set of ATM endpoints making up the group at any one time. Endpoints keep the MARS informed when they need to join or leave particular layer 3 groups. To provide for asynchronous notification of group membership changes, the MARS manages a point to multipoint VCC out to all endpoints.

To realize multicast on ATM, the above technique was implemented with creating LANE (LAN Emulation) model over the ATM. The MARS in this model is known as LES (LANE Emulation Server) and BUS (Broadcast/Unknown Server). The end client and server known as LEC (LANE Emulation Client).

V. SIMULATION SETUP AND SCENARIO OPNET Modeler is used to perform all simulations in this research study. STAR topology shown in Figure 3 is used for both MPLS and ATM to deliver video multicast stream.

All connecting link node-to-node and node-to-hosts are using PPP_E1 (2.048 Mbps). The reason of using the STAR topology is to see the performance of video multicast on real multicast tree platform. In multicasting, the server will feed single stream of data to the network. Whenever there are requests from clients to join the multicast group, the node inside the network will duplicate the data stream and send the duplicated data to the requested clients. This multicast technique can be effectively simulated on STAR topology because we know exactly which node at which branch is doing data duplication.

The simulation executed under two scenarios. For the first scenario, video multicast is implemented under MPLS with LSP technology environment with. The second scenario, video multicast is implemented under ATM technology environment. The results of these two scenarios

were compared based on the following parameters: throughput, link utilization, queuing delay, round trip delay and packet drop. In this simulation, the buffer size at all interfaces of both MPLS and ATM were set to 512 Kbytes.

Figure 3 : STAR topology network

There are three types of application streams injected into the network topology namely video, ftp and email application stream. Video stream is the main subject in this study as we will analyze the multicast behavior, fed into the network using multicast routing protocol; make use of UDP as transport protocol with transmitting rate of 1.2 Mbps. While ftp and email data stream used to create congestion on the channel. They are fed into the network using unicast routing protocol; make use TCP as their transport protocol with transmitting rate of 600 kbps and 400 kbps respectively. There are four streams created for each ftp and email applications designated to four clients each. Video traffic definition is being setup according to predefined low video conference parameters in OPNET Modeler that use frame rate of 10 frames/sec and frame size of 128 x 120 pixels.

VI. SIMULATION RESULTS AND ANALYSIS

In this simulation it was observed that the backhaul links were fully utilized as the total traffic fed to the network are exceeded the E1 bandwidth of 2.048 Mbps. This condition was simulated specifically to enable the whole network to experience congestion. The simulations had demonstrated both MPLS and ATM produced highest throughput for video compared to ftp and email application. In ATM, there were packets drop detected as the buffer had overflowed and the network could not cope with the traffic

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demands. The overall performance of MATM with regards to video multicast tr

A. Video Throughput

With reference to the graph inwas a significant difference in throbetween MPLS and ATM platformtransmitted video stream of 1,200 kbpsfor MPLS and to 600 kbps for ATM.

Figure 4: Video throughput over M

The throughput performanceover both ATM and MPLS was degradsource of video,. There are two throughput degradation. The first is dthat exists along the barrier. In this simboth the video multicast is shared background traffic namely ftp and emcreated traffic congestion on the barrierthis simulation also, there is no Qualenabled. So the video multicast trafbandwidth on best effort basis.

The second possible factor ththis throughput degradation is the packfrom source to destination. We will sedrop in the next analysis result. From above, the throughput performance ofATM.

B. Utilization

In this simulation, both MPconfigured with bi-directional E1 for client) to the edge router. The utilizathis analysis were made against the b

MPLS was better than raffic application.

n Figure 4 below, there oughput performance m. On average, the s dropped to 700 kbps

MPLS & ATM

e of video streaming ed, as compared to the possible reasons for due to the congestion mulation, the path for with the other two

mail traffic. This has r of both platforms. In lity of Service (QoS) ffic had to share the

hat might contribute to ket drop along the way ee the effect of packet the graph in Figure 4

f MPLS is better than

PLS and ATM were all hosts (server and

ation measurements in bandwidth link of E1

speed (2.048 Mbps). From theutilization of MPLS is 41% and

Figure 5: Bandw

It can be seen that banmore efficient as compared to had been used on both platfovideo multicast. Knowing Uprotocol, there is no packet repacket drop during transmisstransmission will contribute toSo the only factor that may exthan ATM as shown in Figthroughput of video multicast as discussed in previous section

C. Queuing Delay

Queuing delay isinstantaneous measurement otransmission channel’s queue. below, it is observed that thMPLS is longer than ATM. Tlonger in MPLS because thenode is faster than in ATM. Ththe router to the channel are fahandle the incoming packetschannel.

D. Network Latency

Latency is round triptravel from source to destinalower latency, the better wouldThe graph in Figure 7 belowbefore multicast session start, u

e graph, the average bandwidth d ATM is 28%.

width utilization

ndwidth utilization in MPLS is ATM. In this simulation, UDP

orms as transport protocol for UPD as the connection-less e-transmission even if there is ion. Normally, the packet re-o higher bandwidth utilization. xplain why the MPLS is better gure 5 above is because the on MPLS is greater than ATM n analysis.

s the statistic represents f packet waiting times in the Based on the graph in Figure 6

he average queuing delay for The queuing delay observed is e packet processing in MPLS hus, packets sending rate out of aster. When the receiver cannot , then delay will increase in

delay taken for the packet to ation and back to surce. The d be the network performance.

w illustrated the latency result up to the 15th minute for both

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Figure 6: Average Queuing

MPLS and ATM. From the graph, the observed for both platform.

Normally the round trip delaynetwork congestion and link condition error or not). From the simulation, noconnecting link in MPLS and ATMgenerally we can see that the latencyrespect to time on both platforms. increasing of traffic on the path whenstarted.

Figure 7: Round-trip delay in M

The other factor that might contribcaused by path congestion of the two othe same path i.e ftp and email trafficase can be further classified due processing and queuing delay on easecond view, the graph shows that Mthan ATM. The possible factors thatbecause of slow processing of the indatagram in ATM switch.

Delay

incremental trend was

y is used to check the n (whether the link has o error detected on all M. From the graph, y keep increased with

This is due to the n the multicast session

MPLS and ATM

butes to the delay was other traffic that utilize ic. Congestion in this to buffer size, slow ach platform. In the

MPLS performs better t may explain this is

ncoming and outgoing

E. Packet Drop

To best deliver any dbe no packet drop during transthere is no packet drop detecttraffics sent including multicasare packet drop detected at tfrom video server) as indicatgraph, higher packet drop detedefaulted to carry ftp and emadrop detected for CBR streamvideo multicast packet.

The packet dropped buffer memory for that partic(see Figure 9). The packets htime waiting in queue due to it

Figure 8 : Traff

Figure 9: Buffe

data in the network, there must smission. From the simulation, ted on MPLS platform for all st packets. While in ATM there the first node (receiving node ed in Figure 8 below. In this ected for UBR stream that was ail data. There is lesser packet m that was defaulted to carry

in ATM occurred because the cular interface was fully used have been dropped after some s TTL threshold exceeded.

fic drop in ATM

r usage in ATM

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VII. CONCLUSION

In this study, five parameters have been discussed with respect to the performance of MPLS and ATM in delivering video using multicast protocol. From the above analysis, it can be seen that the performance of MPLS is better than ATM in multicasting video traffic. There are two conclusions that can be made based on the analysis on five statistics above.

First, the ATM switch itself is unable to perform multicasting. In order to enable multicast on ATM network, the platform must be equipped with LES/BUS server. This server’s function is to create and handle the VCC for multicast traffic between video server and hosts. The processing time taken by the server to process and handle the VCC had downgraded the overall performance of multicast in ATM. While in MPLS, there is no extra server required to process the multicast. The MPLS router itself is capable to handle the multicasting process including duplicating the packet and handling multicast request by the hosts.

Secondly, with reference to the seven layer of OSI model, ATM switch operates at the second layer (Data Link Layer). While MPLS operates at the third layer (Network Layer) and dealt with packets. Multicast protocol itself is the third layer protocol with regards to OSI model. This is one of the factors that enables MPLS to handle multicast better compared to ATM.

For the purpose of thorough comparison of MPLS and ATM in carrying multicast, there is still a need to study on the multicast performance on the bigger scale of both networks. Furthermore, multicast with QoS enabled is yet to be explored in detail as both platforms are capable of providing such service.

REFERENCES

[1] Hafiz M. Asif and Md. Golam Kaosar, "Performance Comparison of IP, MPLS and ATM Based Network Cores using OPNET," 2006.

[2] Josef Mangues-Bafalluy and Jordi Domingo-Pascal, " Multicast Forwarding Over ATM: Native Approaches," in The Electronic Magazine of Original Peer-Reviewed Survey Articles, 2000.

[3] Hong-Yi Li and Hung-Keng Pung Lek-Heng Ngoh, "A Direct ATM Multicast Service with Quality-of-Service Guarantees," in Proceedings of MULTIMEDIA ’96, 1996.

[4] Bernard Cousin Ali Boudani, Chadi Jawhar, Mahmoud Doughan, "Multicast Routing Simulator over MPLS Networks."

[5] Cisco White Paper, "Guidelines For Enterprise IP Multicast Address Allocation," 2004.

[6] H. Hamirul’Aini And K. R Ashwani, "A Performance Study of ATM Multicast Switch With Different Traffics," Malaysian Journal of Computer Science, Vol. 15 No. 2, December 2002, pp. 34-42, Dec 2002.

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