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| Multi-Protocol Label Switching (MPLS) Conformance and Performance Testing |
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| Multi-Protocol Label Switching (MPLS) Conformance and Performance Testing |
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AbstractToday抯 communication networks and services are migrating to a converged paradigm centered on IP (Internet Protocol). MPLS (Multi-Protocol Label Switching) has emerged as a key enabling technology for this migration. MPLS technology has proven its value for delivering new services while at the same time allowing migration from old to new networks. The rollout of MPLS brings the challenges associated with any new networking technology ?validating proper conformance with industry standards prior to production deployment and verifying acceptable performance. This white paper provides an overview of MPLS, and Ixia抯 approach to testing and validating that technology.IntroductionSeveral forces shape the current worldwide communications landscape. One is the general economic slowdown since early 2000, in particular, the pop of the telecommunications industry bubble. Another is the much-ballyhooed convergence of digital communications networks (voice, video, data) and the emergence of IP as the protocol of choice. Finally, globalization and deregulation have combined to level the playing field and increase competitive pressures. The economic slowdown of recent years and resulting over-capacity in core networks has forced service providers and carriers to look seriously at their return on investment from network assets. With pure bandwidth becoming, in essence, a commodity, industry focus has shifted to supplying the value-add services customers need. As new technologies are adopted, the provider抯 ability to consolidate disparate existing networks is a key to deploying all services, old and new, profitably. The enterprise market has shown a similar response to the slowdown ?increasing efficiencies by pragmatically applying the new technologies that make such improvements possible. Consequently, MPLS has great appeal for telecommunications providers. It can handle a variety of services, both legacy and new, over a single network. It enables higher-value applications and services to be delivered from the service provider抯 network, thereby reducing requirements on customer-premises equipment. Integration and consolidation speak loudly in today抯 business environment. It抯 clear that the migration to MPLS is well under way. Every major carrier in the US, and many internationally, have deployed or announced plans for MPLS backbones. A 2003 study by Infonetics Research shows 62 percent of service providers are now engaged in some form of data network convergence over IP or IP/MPLS, with 86 percent doing so in 2004. Since legacy services, such as Frame Relay and ATM, can be carried over the MPLS network, this network convergence is often transparent to the end user enterprise. Moving forward, newer low cost services such as Ethernet will drive further adoption. Beyond large carrier networks, MPLS is also finding its way into the larger enterprise networks of organizations such as retailers, investment companies, government agencies and the military, health care organizations, and technology enterprises. What is MPLS? Historical perspective MPLS is based on the concept of label switching: an independent and unique 搇abel?is added to each data packet and this label is used to switch and route the packet through the network. The label is simple ?essentially a short hand version of the packet抯 header information ?so network equipment can be optimized around processing the label and forwarding traffic. This concept has been around the data communications industry for years. X.25, Frame Relay, and ATM are examples of label switching technologies. Several label switching initiatives emerged in the mid-1990抯 to improve the performance of software-based IP routers and provide Quality of Service (QoS). Among these were IP Switching (Ipsilon/ Nokia), Tag Switching (Cisco), and ARIS (IBM). In early 1997, an Internet Engineering Task Force (IETF) Working Group was chartered to standardize a label switching technology. MPLS emerged from this effort as another labeling scheme, but one with this distinct advantage: it uses the same routing and host addressing schemes as IP ?the protocol of choice in today抯 networks. Today MPLS is defined by a set of IETF Request for Comments (RFCs) and draft specifications (under development). MPLS and IP It is important to understand the differences in the way MPLS and IP routing forward data across a network. Traditional IP packet forwarding uses the IP destination address in the packet抯 header to make an independent forwarding decision at each router in the network. These hop-by-hop decisions are based on network layer routing protocols, such as Open Shortest Path First (OPSF) or Border Gateway Protocol (BGP). These routing protocols are designed to find the shortest path through the network, and do not consider other factors, such as latency or traffic congestion. MPLS creates a connection-based model overlaid onto the traditionally connectionless framework of IP routed networks. This connection-oriented architecture opens the door to a wealth of new possibilities for managing traffic on an IP network. MPLS builds on IP, combining the intelligence of routing, which is fundamental to the operation of the Internet and today抯 IP networks, with the high performance of switching. Beyond its applicability to IP networking, MPLS is being expanded for more general applications in the form of Generalized MPLS (GMPLS), with applications in optical and Time-Division Multiplexing (TDM) networks. Advantages of MPLS MPLS enables a single converged network to support both new and legacy services, creating an efficient migration path to an IP-based infrastructure. MPLS operates over both legacy (DS3, SONET) and new infrastructure (10/100/1000/10G Ethernet) and networks (IP, ATM, Frame Relay, Ethernet, and TDM). MPLS enables traffic engineering. Explicit traffic routing and engineering help squeeze more data into available bandwidth. MPLS supports the delivery of services with Quality of Service (QoS) guarantees. Packets can be marked for high quality, enabling providers to maintain a specified low end-to-end latency for voice and video. MPLS reduces router processing requirements, since routers simply forward packets based on fixed labels. MPLS provides the appropriate level of security to make IP as secure as Frame Relay in the WAN, while reducing the need for encryption on public IP networks. MPLS VPNs scale better than customer-based VPNs since they are provider-network-based, reducing the configuration and management requirements for the customer. How Does MPLS Work? MPLS is a technology used for optimizing traffic forwarding through a network. Though MPLS can be applied in many different network environments, this discussion will focus primarily on MPLS in IP packet networks ?by far the most common application of MPLS today. MPLS assigns labels to packets for transport across a network. The labels are contained in an MPLS header inserted into the data packet (Figure 1). These short, fixed-length labels carry the information that tells each switching node (router) how to process and forward the packets, from source to destination. They have significance only on a local node-to-node connection. As each node forwards the packet, it swaps the current label for the appropriate label to route the packet to the next node. This mechanism enables very-high-speed switching of the packets through the core MPLS network. MPLS combines the best of both Layer 3 IP routing and Layer 2 switching. In fact, it is sometimes called a 揕ayer 2綌 protocol. While routers require network-level intelligence to determine where to send traffic, switches only send data to the next hop, and so are inherently simpler, faster, and less costly. MPLS relies on traditional IP routing protocols to advertise and establish the network topology. MPLS is then overlaid on top of this topology. MPLS predetermines the path data takes across a network and encodes that information into a label that the network抯 routers understand. This is the connection-oriented approach previously discussed. Since route planning occurs ahead of time and at the edge of the network (where the customer and service provider network meet), MPLS-labeled data requires less router horsepower to traverse the core of the service providers network. MPLS routing MPLS networks establish Label-Switched Paths (LSPs) for data crossing the network. An LSP is defined by a sequence of labels assigned to nodes on the packet抯 path from source to destination. LSPs direct packets in one of two ways: hop-by-hop routing or explicit routing.Hop-by-hop routing. In hop-by-hop routing, each MPLS router independently selects the next hop for a given Forwarding Equivalency Class (FEC). A FEC describes a group of packets of the same type; all packets assigned to a FEC receive the same routing treatment. FECs can be based on an IP address route or the service requirements for a packet, such as low latency. Figure 1. MPLS header format on an MPLS packet. In the case of hop-by-hop routing, MPLS uses the network topology information distributed by traditional Interior Gateway Protocols (IGPs) ?routing protocols such as OSPF or IS-IS. This process is similar to traditional routing in IP networks, and the LSPs follow the routes the IGPs dictate. Explicit routing. In explicit routing, the entire list of nodes traversed by the LSP is specified in advance. The path specified could be optimal or not, but is based on the overall view of the network topology and, potentially, on additional constraints. This is called Constraint-Based Routing. Along the path, resources may be reserved to ensure QoS. This permits traffic engineering to be deployed in the network to optimize use of bandwidth. Label Information Base. As the network is established and signaled, each MPLS router builds a Label Information Base (LIB)梐 table that specifies how to forward a packet. This table associates each label with its corresponding FE [1] [2] [3] [4] [5] [6] 下一页
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| 原始作者:佚名 |
录入时间:2006-12-26 2:25:10 |
| 信息来源:不详 |
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