North South University

ETE 605(2): IP Telephony

Project Report on

“VOIP on MPLS Network- Technology”

Submitted By

Md. Mazharul Islam Khan

ID# 063457056

Section: ETE-605(2)

Submitted To

Dr. Moshiour Rahman

Department of computer science and Engineering

North South University

Submission Date

15/04/2008

Contents

Page No.

Over View 3

Multiprotocol Level Switching (MPLS) 4

Why does MPLS matter for VOIP 6

How MPLS- Enables VOIP analysis 7

MPLS-QOS 7

What will MPLS do for VOIP Network 8

Voice Over MPLS / Diffserv Architechere 8

Challenges with VOIP 10

Conclution 10

Over view

Multi-protocol Label Switching (MPLS) has often been presented as a technology that

will help service providers deliver better performance and availability, including specific

benefits for demanding applications such as voice and video. In recent years, many

service providers have implemented MPLS technology in their core networks. Now, with

MPLS backbones in place, these carriers are offering MPLS-based services to enterprise

customers in support of voice over IP (VoIP) and video applications. The carriers are also

aggressively advertising the benefits of MPLS, claiming large improvements in

performance and availability when compared with using the public Internet.

Figure1: Basic Terminology of VOIP over MPLS Network

As shown in Figure 1: CNA was deployed at three of the customer’s branch offices.

These three offices are linked to parallel network fabrics by MPLS and Internet links at

T1 speeds. Through its monitoring and assessing mechanisms, CNA evaluated the quality

of voice communication between Branch Site 1 and Branch Site 2 and between Branch

Site 1 and Branch Site 3, 2004. The assessment was done using CNA configured to use

its Voice Application Model.

CNA Application Models follow a five-stage methodology, shown in Figure 2. From the

bottom, the five steps include:

1. The measurement of low-level network quantities such as latency, loss, and jitter for

each available path between locations.

2. The computation of transport delays from the raw scores or the impact on applications

in general, not taking specific application sensitivities into consideration.

3. The computation of application delay, specifically the mouth-to-ear delay that affects

VoIP. Note that high jitter would result in high application delay; similarly, sustained loss

results in lost speech and unintelligibility, leading to increased application delay

.4. The determination of an application quality metric, using a ranking from zero to five

stars, similar to movie ratings. For VoIP, this step effectively equates to a Mean Opinion

Score (MOS) calculation for the network: the larger the jitter or the greater the sustained

loss, the lower the MOS rating.

5. Finally, the time periods where the voice quality is determined to be unacceptable are

logged as “bad minutes” for that path.

Using this methodology, kept a cumulative count of all “bad minutes” observed on the

various MPLS and Internet path choices between the sites in question

Multi-protocol Label Switching (MPLS)

MPLS is a standards-approved technology for speeding up network traffic flow and

making it easier to manage. In addition to moving traffic faster overall, MPLS is flexible,

fast, cost efficient and allows for network segmentation. While MPLS technology has

been around for several years, businesses are now taking advantage of service provider

offerings and beginning their own corporate implementations. It's a good idea for

network architects and engineers to get a head start on the technology.

Multiprotocol Label Switching (MPLS) is a standards-approved technology for speeding

up network traffic flow and making it easier to manage. MPLS involves setting up a

specific path for a given sequence of packets, identified by a label put in each packet,

thus saving the time needed for a router to look up the address to the next node to forward

the packet to. MPLS is called multi protocol because it works with the Internet Protocol

(IP).

With reference to the standard model for a network (the Open Systems Interconnection,

or OSI model), MPLS allows most packets to be forwarded at the layer 2 (switching)

level rather than at the layer 3 (routing) level. In addition to moving traffic faster overall,

MPLS makes it easy to manage a network for quality of service (QoS). For these reasons,

the technique is expected to be readily adopted as networks begin to carry more and

different mixtures of traffic.

Figure 4: Multi protocol Level Switching Architecture

Like any significant business decision, a number of qualifying factors usually drive a

potential migration to MPLS. Several common reasons are:

• Converged services capabilities (voice, video, data).

• Any-to-any connectivity without the high cost of individual circuits.

• Advanced features for ingress and egress routing policies (load sharing, policy

routing).

• Secure flexibility of adding future businesses and partners (multiple VPN

support).

• Circuit consolidation (frame, T-X, ATM).

Why does MPLS matter for VOIP? Multi-protocol label switching (MPLS) enables a common IP-based network to be used

for all network services and for multiple customers of a network operator. It allows IP

networks to carry voice, data and video traffic with differentiated service-level

performance parameters. MPLS also enables Voice over Internet protocol (VOIP)

services over IP networks, so that a network operator can offer private networking

services to multiple customers on a shared infrastructure. Although MPLS may be used

with non-IP networks, it is IP networking; and more specifically data, voice, video

services over IP networks; that makes MPLS an attractive and growing technology.

MPLS is used to ensure that all packets in a particular flow take the same route over a

backbone. Deployed by many telcos and service providers, MPLS can enable traffic

engineering to deliver the quality of service (QoS) required to support real-time voice and

video as well as service level agreements (SLAs) that guarantee bandwidth. An MPLS

network ingress element attaches labels to IP packets. This label instructs the routers and

switches in the network where to forward the packets based on reestablished IP routing

information. Label switched paths (LSP) are defined in routing tables, and are used to

send tagged packets on specific paths through the network. LSPs represent a new type of

virtual paths for segregating traffic in an IP network. MPLS has been applied to

implementing Virtual Private Networks, which is a key revenue generator for service

providers offering enterprise services.

engineering, and other techniques.

Figure 6: Call routing through MPLS

How MPLS-enabled VOIP analysis

The application of MPLS to IP networks adds a new challenge, but also a new

opportunity, for VoIP analysis and testing. The challenge is that VoIP traffic from

multiple different virtual networks and service class tiers are mixed on common physical

links. The opportunity is that MPLS provides a means to separate this traffic for targeted

analysis. It simply requires theright tools to do this.

The Network Analyzer comprises many MPLS capabilities that not only enable targeted

VoIP analysis over MPLS in specific domains (VPNs, LSPs, service tiers, etc), but also

enable analysis of underlying network layers including MPLS networks. When MPLS is

used in DiffServ architectures to provide prioritization for different services, diagnosing

performance problems can be significantly expedited by focusing the analysis domain on

specific LSPs. Using the Network Analyzer, one can see VoIP performance for all traffic

on a link, and for traffic in specific domains. These domains can be based on MPLS To

analyze in a specific domain, one first applies a capture filter for a specific LSP. A filter

can be applied for up to 6 values of labels in a label stack. One can further filter on

specific values for Class of Service (CoS). This enables one to then analyze VoIP for that

LSP, for targeted analysis\

of performance for that service tier. One can view traffic performance, for both VoIP and

non-VoIP traffic, per LSP and CoS.

MPLS Quality of Service

QoS on an MPLS backbone is used to provide predictable, guaranteed performance

metrics required to transport real time and mission critical traffic. The providers have an

overall QoS architecture that is used to deliver a subset of QoS services to each customer.

Since MPLS also supports reservation of Layer 2 resources, MPLS can deliver finely

grained quality of service, much in the same manner as ATM and Frame Relay. DiffServ

can support up to 64 classes while the MPLS shim label supports up to 8 classes. --

MPLS Resource Center QoS for IP/MPLS Networks by Santiago Alvarez is a practical

guide that will help you facilitate the design, deployment, and operation of QoS using

Cisco IOS Software and Cisco IOS XR Software. The book provides a thorough

explanation of the technology behind MPLS QoS and related technologies, including the

different design options you can use to build an MPLS network with strict performance

requirements.

Figure 7: QoS Over MPLS Solutions

What will MPLS do for VOIP network?

MPLS based VOIP ( which offers exclusive and interconnectivity using Internet protocol

to computers or Local Area Networks across the PSTN) reduce customer-networking

complexity, costs and do away with the requirement of in-house WAN specialists.

Rather than setting up and managing individual point-to-point circuits between each

office using pair of Leased Lines, MPLS VOIP customers will need only one connection

from each office router to a Edge Router. MPLS VOIP is a technology that allows a

Service Provider to have complete control over parameters that are critical to offering its

customers service guarantees with regard to a high level of QOS e.g. bandwidth,

throughputs, latencies, jitters and availability. Many Company has tied up with various

Networking solution providers to provide end-to-end solution to its valued customers,

including Customer End (CE) routers and other networking components.

Voice over MPLS /Diffserv Architecture:

It is observed that the premium service (EF) of Diffserv is not enough alone to ensure the

quality of service. Some research results have shown the failure of EF PHB in meeting

the delay and jitter targets if an EF packet arrives on an output link on which a large BE

packet is already in the middle of being transmitted. Therefore it is important that some

type of prior reservation be made for transmission of real-time voice across a domain.

MPLS provides the mechanism that can be used to separate the BE traffic path from EF

and AF traffic path and to install explicitly routed LSP's (Label Switched Paths). We

have set up voice over MPLS/Diffserv using NS-2 simulator and its associated modules.

We are in the process of designing rules and specifications for an architecture to support

voice in an MPLS and Diffserv domain. These rules will dictate the formation of LSP's

carrying voice calls and aggregation of LSP's into virtual trunks across the domain. The

specifications are supposed to standardize the treatment of voice calls in the IP networks

and to make it easy to perform traffic engineering in a domain that deals with voice calls.

additional ports to the VOIP gateway and the voice data (in data form) is processed easily

by the PC. A Gateway interconnects the Voice source to the network through the local

exchange, forwards the voice to the destined subscriber across the Internet, and sends the

incoming calls to the corresponding extension via the PXB. VOIP delivers real-time and

two way synchronous voice traffic over the Internet or Intranet[2].

The IP telephony provides a number of benefits as compared to the Public Switched

Telephone Network (PSTN) such as: integration of voice, data and fax, sound grading,

video telephony, unified messaging, low-cost voice calls, real-time billing, remote

teleworking, enhanced teleconferencing, etc. It may face many technical challenges such

as: loss, delay, and jitter[3]. Internet telephony has caught the world's attention despite

the inferior quality for many of these connections. Many companies have introduced

products that improve and commercialize the technology. New protocols such as Diffserv

and MPLS are being introduced with additional features like QoS, reliability and traffic

engineering that improve the performance of voice transmission over the IP network.

Unlike data, VOIP is more sensitive to delay than loss, thus sufficient bandwidth must be

guaranteed to the voice application. Some protocols that decrease voice transmission

delay by giving high priority to the voice than data traffic have been introduced.

Resource reSerVation Protocol (RSVP) provides for the routers to reserve the required

bandwidth for the voice connections, and Real-time Transport Protocol (RTP) uses

synchronization.

Figure 8: The Voice architecture over MPLS / Diffserv domain

Challenges with VOIP

Voice is a real-time service. It must be delivered with minimal delay (150 milliseconds

end-to-end is a common recommendation) and it must be reproduced with a constant bit

stream on the egress network or endpoint. Due to the delay requirements, IP

retransmissions are not allowed. Therefore, packets that are dropped on the network, or

late packets dropped by a jitter buffer, are not saved or reproduced. IP’s best effort

delivery and non-deterministic routing introduce delay and more importantly variance in

delay, also known as packet jitter, in the voice transmission. VOIP packets may be lost

due to packets dropped in router queues or by the jitter buffer.

Conclusion

MPLS enables service providers to deliver new services governed by specific SLAs and

COS. These services comprise the triple play: offering real-time voice and video along

with data on a common network. It is the real-time services like voice that will generate

the most revenue. The ability to keep these services running at quality levels that meet

customer expectations is crucial to retaining customers and realizing revenues. While

MPLS introduces new challenges to diagnosing and troubleshooting service-level

problems, advanced tools like the Agilest Network Analyzer makes this job simple and

fast for next generation network engineers and technicians.

These results suggest that an MPLS service is not the panacea for VoIP. MPLS service is

in fact essentially comparable to Internet service. Both provide good base connectivity,

but by themselves neither can deliver the quality and availability required for business-

quality voice communication.

To discover how can reduce the impact of bad minutes on VOIP communication over

both MPLS and Internet links, please refer to Performance of Virtualized MPLS Internet

Infrastructure in Delivering VOIP Service.