Mazharul Islam Khan (063457056)


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Mazharul Islam Khan (063457056)

  1. 1. 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
  2. 2. 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
  3. 3. 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.
  4. 4. 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).
  5. 5. 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).
  6. 6. 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
  7. 7. 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.
  8. 8. 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
  9. 9. 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
  10. 10. 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.