Migrating legacy data technologies to Ethernet wide area transport

Raymond Smith, Global CrossingLegacy wide area network (WAN) technologies, such as SONET, Frame Relay and ATM have traditionally met the needs of enterprises for transaction-based applications, storage area networks, and general content distribution. However, today's applications, such as VoIP, Telepresence, or other bandwidth-intensive multimedia services are stretching the limits of these established data technologies.

Legacy data networks also are becoming increasingly costly to support and maintain. And today's changing business environment often requires organizations to centralize or decentralize, expand or contract, or otherwise adjust to economic fluctuations. As a result, Ethernet technologies and services offer a compelling alternative for enterprises as business applications and economics continue to dictate the need for more flexible bandwidth options and traffic sensitivity. That's why many of today's enterprises network managers are considering a more flexible architecture, such as Ethernet wide area transport.

Next Generation WAN transport services, including Layer 2 Ethernet and Layer 3 MPLS IP VPNs, are highly scalable and cost-effective WAN technologies, and offer significant improvements over legacy networks for managing the interconnection and traffic flow among regional locations to a main campus, headquarters, or data centers. Today's Ethernet Virtual Private LAN Services (VPLS) run over MPLS platforms that inherently deliver QoS, routing control, and fault tolerance, with performance comparable to Frame Relay.

A few service providers are well positioned to the meet needs of today's enterprises by leveraging their global converged IP services networks to deliver Layer 3 IP VPN and Layer 2 VPLS on a common transport platform. These hybrid wide area network solutions offer additional flexibility and cost efficiencies through the inherent features of Layer 2 and Layer 3 technologies. Next Generation service providers are now deploying highly efficient multi-service platforms in their networks, upgrading technical skills and proficiencies, and adding features like IPv6, multicast, and QoS to ensure today's enterprises efficiently move their businesses into the future.

The challenge
Enterprise networks need more bandwidth today. Frame Relay is limited in its ability to deliver on these new, expanded bandwidth requirements and it is more expensive to use Frame Relay to provide this increased bandwidth compared to Ethernet technology. Ethernet WAN transport has emerged as the technology of choice for addressing the need for higher bandwidth as a result of its lower cost, improved scalability and ability to deliver operational efficiency.

Migration to a Next Generation WAN transport solution is a significant decision because it often requires hardware or software upgrades as well as network infrastructure changes (e.g., IP addressing). Further, any new network must be scalable, easy to manage and troubleshoot, and readily adaptable to new applications that require higher bandwidth.  Key drivers that suggest the time is right to plan such a migration include:

  • upgrading from a legacy phone system to a VoIP telephony service.
  • month-to-month off-contract prices from the service provider.
  • the network has become a mission-critical component of daily operations.
  • legacy access devices (Frame Relay Access Devices--FRADs, etc.) are becoming increasingly difficult to repair and maintain.

Items to assess prior to migrating might include routing control, protocol transparency, bandwidth flexibility, QoS, number of locations, traffic flow between and among locations, security, location-specific cost of access, and overall performance. Today's Next Generation WAN transport options include Layer 3 MPLS IP VPN and Layer 2 VPLS.

The options
An MPLS IP VPN solution is similar in design to router-based Frame networks, but offers simplified implementation of clear-channel access and full-mesh connectivity in the core, with easier IP addressing. Capacity planning performed on a port or site basis also is simpler than traditional Permanent Virtual Circuit (PVC)-based planning. Local access support includes Ethernet where available and TDM (T1, DS3) everywhere else. As a managed service, MPLS IP VPN provides the benefit of an on-premises leased router to defray upfront implementation costs.

An Ethernet WAN is very similar in design to a Frame Relay Access Device (FRAD)-based network architecture, but delivers Ethernet throughout the WAN. Fortunately, similarities between the technologies facilitate the migration.  Both technologies use large Provider Edge (PE) switches; and both combine smaller interfaces and smaller committed information rate (CIR) circuits onto larger trunks for transport across the network. More specifically, Ethernet uses Ethernet Virtual Circuits (EVCs) to replace Frame Relay PVCs, the Frame Relay Data Link Connection Identifier (DLCI) is replaced with an Ethernet Virtual Local Area Network (VLAN) identifier, and the traffic is still routed from one side of the network to the other.  Hence, all the same classic topologies can be built--point-to-point, point-to-multiple end points, and full mesh of any-point-to-any-point.

The solution
The benefits of a replacing legacy data networks with an Ethernet WAN transport platform are that it:

  • supports true multipoint connectivity vs. ATM/FR PVCs from regional sites to a central hub.
  • replaces Frame Relay circuits with multiple virtual circuits over a single link.
  • possesses CIR bandwidth rules similar to Frame Relay and ATM.
  • accommodates similar virtual circuit addressing structure.
  • increases control and flexibility for QoS--like traffic shaping and bandwidth management needed by today's application-based traffic.
  • simplifies network management with fewer circuits and QoS/Class of Services (CoS) variations to manage--one interface supports all customer needs.
  • employs comparable CoS options at a lower cost.
  • avoids legacy technology upgrades, which routinely involve replacing costly fixed-rate interface hardware.
  • offers uniform standards-based operations, administration and management functions, such as Y.1731, across the wide area network, which are similar to Frame Relay.
  • provides an end-to-end Ethernet solution that delivers the most bandwidth per dollar.

Clearly, Ethernet WAN transport emerges as a sound option when compared to traditional legacy data technologies for enterprise networks. The benefits of basic Ethernet virtual private line (EVPL) service compared with Frame Relay become apparent from the perspectives of scalability, performance and cost effectiveness, although, depending upon specific requirements, IT managers could consider complementary MPLS network elements.

Raymond Smith is Senior Product Manager, Ethernet/VPLS for Global Crossing and a FierceTelecom contributor.