MPLS emerges to soothe network headaches

Multiprotocol Label Switching (MPLS) offers top-of-the-line speeds and many other benefits for both enterprises and carriers.

By Paul Korzeniowski | Posted Jun 12, 2000
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At the end of 1999, UUNet, an MCI WorldCom company in Ashburn, Va., examined how to upgrade its U.S. core network from OC-48 connections operating at speeds of 2.4Gbps, all the way up to OC-192 links that work at 10Gbps. "ATM and Frame Relay were not options because they aren't fast enough, so we turned to an IP network with MPLS [Multiprotocol Label Switching]," said Kevin Boyne, senior vice president of global network services for the carrier. By March, the company had installed M160 routers from equipment supplier Juniper Networks Inc., of Mt. View, Calif., to support high-speed links between sites in Chicago, New York, and Washington, D.C. UUNet expects to have a dozen more routers with similar configurations operating by the end of the year.

MPLS's appealing features

"The MPLS approach delivers ATM-like benefits without its significant complexity and enables carriers to add bandwidth to their networks without sacrificing their staffs' familiarity with IP. "

In addition to support for top-of-the-line speeds, MPLS is gaining attention because it can solve common networking problems for carriers as well as enterprises. Currently, companies construct networks with various link-level protocols: Asynchronous Transfer Mode (ATM), Frame Relay, and Internet protocol (IP). Doing so forces them to operate autonomous networks controlled by multiple management systems. MPLS is able to ride above these layers and provide a common network infrastructure. This feature appealed to AT&T Corp., of Basking Ridge, N.J., as it examined how to provide users with emerging IP services, such as virtual private networks (VPNs), without scrapping its significant investments in Frame Relay and ATM equipment.

Currently, the carrier uses MPLS to IP-enable its Frame Relay lines, and it may follow the same course with its ATM links. MPLS offers another plus: It adds traffic management features (typically associated with ATM networks) to switched connection networks like the Internet, regardless of the underlying protocol. In an MPLS network, edge routers assign a label to packets as data enters the network; each label specifies a transmission's route and priority. From there, MPLS-compliant devices simply look at the label information to move a packet along to its destination. This approach delivers ATM-like benefits without its significant complexity and enables carriers to add bandwidth to their networks without sacrificing their staffs' familiarity with IP. The protocol also delivers the bandwidth control and throughput guarantee mechanisms needed to support emerging voice and video services. Within an MPLS-enabled network, packet-based services gain latency reductions and can rely on congestion-control features to ensure that bandwidth is available for usage-intensive applications.

This feature enables carriers to differentiate themselves by delivering value-added services:

  • Classes of service--Represents a best attempt to ensure bandwidth for specific applications


  • Quality of service (QoS)--Does not begin a transmission unless bandwidth is guaranteed


  • VPNs--Includes end-to-end security features for sensitive transmissions "Carriers of all sizes--not just the major ones--are using MPSL to support their VPN service rollouts," said John Stewart, a marketing engineer at Juniper. Another MPLS plus is that the technology simplifies large router network topologies. Carriers can transform hierarchical and multi-hop routed infrastructures--which have a pyramid design--to single-hop, flat infrastructures. That change makes their networks easier to deploy, operate, and manage. "By moving from Frame Relay links to MPLS connections, we can decrease the number of PVCs (Permanent Virtual Circuits) that need to be established on a 25-node network from 300 to 25," stated Keith Falter, executive technical manager for AT&T Data and Internet Services.

Signaling: CR-LDP vs. RSVP

Although the protocol has great potential, a couple of issues need to be ironed out before it is widely adopted. Its signaling component, which is responsible for distributing labels from node to node in a network and provides the foundation for the valued-added traffic engineering features, has to be solidified. Two techniques--Constraint-based Routing Label Distribution Protocol (CR-LDP) and Resource Reservation Protocol (RSVP)--have emerged as possibilities. The two establish connections from point A to point B in different ways:

  • RSVP examines how much bandwidth is being used in the network, deduces whether there is enough bandwidth for a transmission, and then moves data from device to device in a piecemeal rather than end-to-end fashion. This approach does not offer as much network assurance, but it uses network resources more efficiently.


  • CR-LDP starts at A, determines whether there is a clear path to B, and then moves information along a predefined path. This approach offers a high degree of certainty that bandwidth will be available at each point along a connection.

    Faced with multiple options, certain carriers have been holding off from endorsing either. "We are monitoring how much acceptance CR-LDP and RSVP will gain in the marketplace," said AT&T's Falter.

    Not everyone see much of a debate. "The reality is all MPLS implementations to date have relied on RSVP, and I haven't seen anything special in CR-LDP that will change that," stated Stewart at Juniper. "Customers want technologies with a proven track record: RSVP has one; CR-LDP is just starting to emerge."

    In addition, improvements to RSVP have made it better able to support value-added services. "RSVP now offers carriers more granularity when allocating bandwidth," said Rob Redford, a director of marketing at Cisco Systems Inc., of San Jose, Calif. "It no longer routes data just by flow, where the network doesn't know what type of packets it is carrying; but by class, so a carrier can identify bandwidth-intensive services, such as video."

Adding features vs. building new networks

Carriers must also decide whether to add MPLS features to existing ATM networks or to build MPLS-enabled networks without ATM. Service providers with no existing infrastructure are able to take an MPLS-only approach, but other carriers have made significant investments in ATM equipment and may not be willing to dump it.

"I find talk of carriers immediately moving to all IP networks as ludicrous," stated Tom Nolle, president and founder of CIMI Corp., a Voorhees, N.J., consulting firm. "They have invested billions of dollars in their current network infrastructures and simply don't have enough money to replace them."

So, rather than broad-scale replacements, MPLS may find its way into networks slowly. "I see carriers pushing ATM out from the network core to the edge and using it to consolidate different types of traffic for transport on MPLS backbones," stated Juniper's Stewart.

Interoperability issues and the MPLS Forum

Interoperability is usually an issue with any new standard, and it applies to MPLS. "Right now, no one is really sure what MPLS compliance means," admitted David Drury, vice president of technology strategy for Marconi PLC.'s, Pittsburgh, Pa. office.

Although interest in the protocol has picked up recently, the Internet Engineering Task Force (IETF) has been working on the specification for three years. Consequently, equipment vendors--such as Cisco; Harris & Jefferies Inc., of Dedham, Mass.; Lucent Technologies Inc., of Murray Hills, N.J.; and Juniper--are now shipping products that support some MPLS features.

The devices include basic MPLS features; but support for high-end items, like traffic engineering, is spotty. Consequently, a carrier could purchase two MPLS devices and discover they have different feature sets. "We wish vendors would have moved a little quicker to address MPLS interoperability issues," stated UUNet's Boyne.

Compliance testing falls outside the bailiwick of the IETF. So, in March 2000, 16 vendors--including Nokia High-Speed Access Products Inc., of Irving, Texas; Lucent Technologies; Marconi; Qwest Communications International Inc., of Denver, Colo.; and Telcordia Technologies Inc., of San Diego, Calif.--formed the MPLS Forum. Marconi's Drury is the forum's President and Chairman.

The Fremont, Calif.-based vendor consortium plans to ensure MPSL consistency by sponsoring interoperability tests and multi-vendor connectivity demonstrations at events, such as industry trade shows. The forum also plans to:

  • Publish MPLS Implementation Agreements


  • Act as a central reference on MPLS resources


  • Educate the market on the protocol's capabilities and advantages


  • Be the liaison between MPSL advocates and standards bodies, such as the IETF, the International Telecommunications Union, the ATM Forum, and the Frame Relay Forum

Making inroads

Despite the handful of hurdles, the early users seem content. UUNet added MPLS features to its European core network, which has six 2.4Gbps core sites, in the summer of 1999. "We encountered few implementation issues," stated UUNet's Boyne.

Other companies seem interested in the protocol. "Recently, we've seen 70 percent of our new switches go out the door as MPLS-enabled devices," stated Cisco's Redford.

Although the initial focus has been mainly on carrier networks, the technology is expected to make its way into enterprise networks, as well. "We've seen some large companies bring remote locations into their enterprise networks via VPNs riding on MPLS," stated Cisco's Redford.

More service providers and enterprises are expected to make decisions like UUNet and include MPLS as a key component in their networks. "MPLS will be successful because it offers carriers and enterprises a way to bridge legacy networks with new IP services, and that is the direction everyone wants to go," concluded CIMI' s Nolle.

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