December 1998

MPLS: Labeling IP For Speed

BY FRED SAMMARTINO

Demands for increased bandwidth are a fact of life for Internet service providers (ISPs). As the Internet moves into the new millennium, ISPs will face an additional challenge in ensuring the quality transfer of delay-sensitive data. Today's Internet backbone networks are overloaded with data, and packet loss rates as high as 30 percent make the Internet of questionable utility for applications such as high-quality voice or video conferencing. An increasingly sophisticated market is demanding Quality of Service (QoS), Virtual Private Networks (VPNs), voice and video over IP, and IP Multicast. The industry should look to the convergence of routing and switching led by the Multiprotocol Label Switching (MPLS) standard as one way to further the Internet's evolution.

THE ATM SWITCH
The MPLS standard enables this approach by integrating the efficiency of Layer 2 ATM switching with the intelligence of Layer 3 IP routing. A unified effort from ISPs to update equipment will set up the framework to implement MPLS on a broad scale. Routing will always be an essential part of the equation to define reachability, but ATM switching technology will provide the enhanced backbone required for further growth. ATM addresses the three main issues service providers face: meeting increasing backbone traffic demands, providing QoS for that traffic, and enabling logical partitioning of data for traffic engineering. And ATM can serve as a multiservice infrastructure: it has QoS characteristics that enable effective Service Level Agreements (SLAs), and as a Layer 2, connection-oriented technology, it provides effective control over scarce and expensive wide-area facilities.

ROUTING THE IP PACKET
IP has become the standard interface for data transmission and destination routing. Enter MPLS, which reduces transmission delays by using the underlying ATM infrastructure to create predefined circuits from every switch to every other switch within the network. When IP packets enter the edge of the network, the first switch does a route lookup to determine which circuit to use in sending the packet to the destination switch. The IP packet is then labeled to identify the appropriate circuit. This saves time, since the switches between the source and destination only look at the Layer 2 label to determine the next hop, rather than performing a full Layer 3 IP route lookup at every hop along the path. This mechanism allows relatively simple, inexpensive, and fast ATM switches to move IP packets efficiently through the network. Today, commercially available ATM switches can carry approximately 50 million IP packets per second, compared to the one million packets per second performance of commonly used IP routers.

This kind of capacity is essential for providing toll-quality transmission for such services as Internet telephony. With analysts predicting that as much as 30 percent of all voice calls will be carried over IP networks by the year 2003, IP backbones must be able to provide predictable performance approaching the consistent quality of today's public telephone networks. Existing approaches, such as overbuilding IP networks, are still, and may always be, prohibitively expensive. MPLS efficiently provides the necessary quality while filling the remaining bandwidth with low-priority traffic.

A CALL TO ALL ISPs
MPLS-driven QoS from end to end across the Internet is estimated to be about a year away. But because most Internet traffic crosses multiple ISPs, widespread QoS capability requires coordination on several fronts. These include upgrading existing ISP routing equipment to switching/routing implements that can perform billing, bandwidth reservation, policing, priority queuing, and fast packet processing. There also must be a method of performing bandwidth reservation across separate ISPs. In addition, there must be a method for identifying ISPs that do not have QoS-capable equipment for choosing source and destination routes.

The MPLS standard is well underway, and some vendors have had pre-standard implementations available for about a year. But most data transfer on the Internet still uses "best-effort" mechanisms that provide no guarantees regarding packet delays or delivery. This was sufficient when the Internet was primarily used for e-mail and file transfer applications, which are not delay sensitive, but this is no longer the case. As more and more service providers begin implementing the MPLS standard, the Internet will begin to move beyond "best-effort."

Continued Internet growth will constantly challenge the ability of service providers to meet traffic demands and desire for QoS features. By incorporating the many benefits of ATM technology with the proven intelligence of IP, MPLS offers the best way for service providers to keep pace with competition and consumer demands as the Internet moves into the next generation.

Fred Sammartino is the director of IP product marketing, Core Switching Division, of Ascend Communications, Inc. Ascend Communications, Inc., is one of the leading providers of technology and equipment solutions for telecommunications carriers, ISPs, and corporate customers worldwide. Ascend delivers a comprehensive set of best-of-breed solutions in the key areas required to build a high-performance, cost-effective public and private network infrastructure from end to end. For more information, contact the company at 800-ASCEND4, or visit their Web site at www.ascend.com.