PERFORMANCE ANALYSIS OF VOIP OVER MPLS

Performance Analysis of VoIP over MPLS

Performance Analysis of VoIP over MPLS

Introduction

An overlay network is a logical application-layer topology established by overlay nodes. The logical connections between the overlay nodes are provided by overlay links, each of which may be a long path traversing multiple routers and physical links in the Internet. VoIP (Voice over IP) service is one of the peer-to-peer applications of overlay network, and constructs a VoIP service overlay network by VoIP service components and VoIP user agents. The VoIP service overlay network can effectively use the Internet as a lower level transport network to provide VoIP services to end users.

Nowadays, VoIP applications (Huang,2004)are ubiquitous in the Internet due to its low cost compared to conventional voice service via Public Switched Telephone Network (PSTN). The VoIP service overlay networks have emerged as a means to enhance end-to-end availability and quality of service (QoS). The services require not only adequate bandwidth to support voice transmission but also end-to-end transmission quality between end users. Inherited from its interactive and real-time nature, it is very sensitive to network congestions and it requires more stringent QoS than data traffic. Some QoS requirements shall be maintained to make them attractive to users (Huang,2004), for example, good voice quality and short call waiting time.

The DiffServ-based MPLS technology is scalable and practical; therefore, this technology has been deployed in most advanced routers. With QoS provisioning, this technology can realize the QoS guarantee of VoIP service overlay network very well.(Goode,2002)

A VoIP service provider purchases bandwidth with certain QoS guarantees from individual network domains via Service Level Agreement (SLA) to build a logical VoIP service overlay network on top of existing data transport networks. Via a service contract, the VoIP service provider directly receives the revenue from VoIP users. First, besides service discovery and service interworking, the VoIP service provider faces the issues of QoS guarantee and service profit. One way to accommodate users' resource demanding, thus to guarantee their demand volume and QoS, is to employ new infrastructure to increase extra many bandwidth to avoid congestions; however, such business strategy is not cost-effective. An alternative prominent strategy to meet the QoS requirements is to raise the system utilization of a network by doing the bandwidth provisioning. In addition, network provisioning can give users better QoS, avoid network congestions and maximize the network efficiency.(Goode,2002)

Second, in DiffServ/ MPLS networks, the VoIP service provider also faces the QoS-mapping issue between overlay network and transport network. The conventional VoIP service providers support only either one of the three service classes in a single VoIP trunk to a group of VoIP subscribers, i.e., Expedited Forwarding (EF)-class, Assured Forwarding (AF)-class, and Best Effort (BF)-class. EF-class traffic receives the highest forwarding priority while BF-class traffic receives the lowest forwarding priority among the three. Transport core networks intend to provide EF-class users with low delay, low jitter and low loss services by serving them at a configured rate . In contract, an AF-class may be configurable to receive more bandwidth ...