As service providers look to the future, they face a challenging dilemma. To remain profitable, they must balance today's highly successful Frame Relay services with the future promise of new, differentiated IP-based services. Doing so, however, is not an easy proposition. Existing networks are capital constrained, and enabling new services or service bundling can be difficult, if not impossible. What's more, today's capital-constrained climate prevents carriers from building out new networks or abandoning existing ones.

These factors have led carriers to realize that the only way to achieve greater profitability and operational efficiencies is by evolving from static, single-service networks to a revolutionary multi-service infrastructure that supports both switched and routed data services.

The ECI ST-series Service Edge Routers were designed specifically for this purpose. By bringing together the best of switching and routing technology in a single device, the ST-series provides the QoS and connection management required for switched data services, as well as the scalable routing necessary for IP-based services and IP-enabled switched services. The ST is the only edge router in the industry that can precisely match the high levels of QoS previously only associated with Frame Relay and ATM switches. The unmatched service agility of the ST allows carriers to deliver any type of switched or routed data service, from low to high speeds, over a range of access networks. The result is a more flexible, scalable and simpler architecture with minimal capital investment.

The ST-series is ideally suited for a range of service provider and carrier applications:

· Incumbent carriers can leverage existing Frame Relay equipment while adding high-speed Frame Relay services or bundled services such as IP-enabled Frame Relay.
· Next-generation/greenfield carriers can deploy a flexible, simplified architecture, offering both switched and routed data services over a common IP/MPLS backbone.

Frame Relay Service Delivery on the ST-series

The ST-series delivers the key functionality required for Frame Relay service delivery, including:

Comprehensive Interface Support
Sophisticated Quality of Service
Frame-based Policing
Per Virtual Circuit Queuing
Frame Relay Switching
Port Mode
Local Management Interface Support
Service Interworking

Comprehensive Interface Support

The ST provides Frame Relay service capabilities on a wide range of SONET/SDH interfaces, from speeds of NxDS-0 to OC-48, including:

· 16-port OC-3/STM-1 PHY, channelized to DS-3/AU-3, STS-1/STM-0 and STS-3c/STM-1

· 2-port OC-12/STM-4, channelized to NxDS-0, T1/E1 and DS-3/AU-3

· 8-port OC-12/STM-4 PHY, channelized to DS-3/AU-3, STS-1/STM-0, STS-3c/STM-1 and STS-12c/STM-4

· 8-port OC-12c/STM-4 PHY

· 2-port OC-48/STM-16 PHY, channelized to DS-3/AU-3, STS-1/STM-0, STS-3c/STM-1, STS-12c/STM-4 and STS-48c/STM-16

· 2-port OC-48c/STM-16 PHY

Sophisticated Quality of Service

To ensure that existing service levels agreements (SLAs) are met, the ST-series provides robust QoS and traffic management capabilities for Frame Relay traffic, enabling each customer's traffic to be managed independently with dedicated software-configurable traffic policers, queues and schedulers.

Key features include:

· Wire-speed packet classification and filtering provide differentiated services based on destination or application.

· Standard and custom policing schemes enable the creation of burstable services with guaranteed bandwidth.

· Flexible queuing strategies meet SLAs while providing multiple distinct service classes for each customer.

· Traffic shapers ensure that customers receive only their purchased bandwidth - nothing more, nothing less.

Frame-based Policing

The ST-series's frame-based policing function is based on the ANSI specification T1.606a-1992 (ANSI Frame), ITU-T I.370 and RFC 2698 two rate three color marker (trTCM) policing schemes, which measure the following traffic parameters:

· Committed information rate (CIR), in bits per second
· Committed burst (Bc), in bits
· Extended information rate (EIR), in bits per second
· Excess burst (Be), in bits

Any frames that do not conform to these parameters are either dropped or tagged according to the value of their discard eligible (DE) bit. Frames that have a DE value of 0 are unlikely to be dropped, while those with a DE value of 1 have a higher probability of being dropped under congested conditions.

For proper traffic queuing and shaping, the ST-series supports standard Frame Relay service categories, including: real-time variable frame rate (rt-VFR), non-real-time variable frame rate (nrt-VFR) and unspecified frame rate (UFR). The categories are strictly prioritized, meaning that rt-VFR is always serviced first to ensure low latency, jitter and loss.

Per Virtual Circuit Queuing

The ST-series supports a single queue per virtual circuit or permanent virtual circuit (PVC). Each queue can be configured with a weighted random early detection (WRED) profile that drops DE=1 traffic during periods of congestion.

The ST-series also supports per virtual circuit scheduling and shaping. For example, real-time VFR connections are scheduled according to their configured rate to ensure very low latency and jitter. Non-real-time VFR connections are scheduled to allow some latency and jitter, but low cell loss. UFR connections are scheduled without rate guarantees.

Frame Relay Switching

The ST-series supports point-to-point data link connection identifier (DLCI) transport across an IP/MPLS network using the encapsulation and signaling methods defined in ANSI T1.617-1991 Annex D and ITU Q.933a Annex A. For this service, the ST200 performs segmentation and reassembly (SAR) for DLCI connections on DS-3, OC-3c, OC-12c and OC-48c interfaces and transports the Frame Relay frames over MPLS. This provides an efficient packet-switching service using Frame Relay access links.

Port Mode

The ST-series also supports a Frame Relay port-switching mode. This mode can be used to transparently interconnect Frame Relay switches across an MPLS network.

Local Management Interface Support

The ST200 supports the local management interfaces (LMIs) defined in ANSI T1.617-1991 Annex D and ITU Q.933a Annex A.

Service Interworking

The ST-series provides carriers the ability to conduct service interworking via the Frame Relay Forum Frame Relay/ATM PVC Service Interworking Implementation Agreement (FRF.8.1). The ST200 supports interworking with any speed Frame Relay and ATM interfaces, including high-speed OC-3, OC-12 and OC-48 interfaces.

In addition to interworking between Frame Relay and ATM, the ST-series also provides interworking to Ethernet from both Frame Relay and ATM. Ethernet interworking allows new Ethernet customer sites to be connected to existing Frame Relay or ATM customer sites. The following interworking capabilities are offered on the ST200 today:

. FRF.8.1 ATM to Frame Relay
. Any-to-Any ATM, Frame Relay, and Ethernet interworking (IPL2T)
. Any-to-Any ATM, Frame Relay, and Ethernet interworking (Ethernet L2T)

Conclusion

To remain profitable, today's service providers must increase the capacity of their existing Frame Relay services while deriving additional service revenues from new, differentiated IP-based services. And they must do so without sacrificing current revenue or service quality. The ECI ST-series Service Edge Routers combine switching and routing technology in a single device, providing the flexibility to turn on new services while dramatically reducing costs and complexity.