Current data service networks supporting ATM and Frame Relay services generate billions of dollars in revenue and provide sophisticated Quality of Service (QoS) and traffic management, yet they are limited in service delivery and ill equipped to support the future promise and continuing growth of IP-driven applications. These multiple, disparate networks also make service bundling and new service offerings a difficult proposition.

Savvy carriers recognize that future profitability can only be ensured through a multi-service infrastructure that supports both switched and routed data services, providing the flexibility to enable new services while reducing network complexity and operating costs.

Enter the ECI ST-series Service Edge Routers. Designed from the ground up specifically for the multi-service edge, the ST-series routers include 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-series can precisely match the high levels of QoS previously only associated with ATM and Frame Relay switches. The ST adds another important feature - unprecedented service agility - that enables carriers to offer any type of data service at any speed over any type of customer access network. This level of flexibility is key to evolving services as requirements change, today and in the future.

The ST50 features precisely the same technology as the award winning ST200 all in a smaller footprint ideal for deployment in small to medium-sized service provider points of presence (POPs).

ATM Service Delivery on the ST-series

The revolutionary ST-series offers the key functionality required for ATM service delivery, including:

Comprehensive Interface Support
Sophisticated Quality of Service
Policing Schemes
Per Virtual Circuit Queuing
VCC and VPC Cell Relay
VCC AAL5
Port Mode
PVC Cell Concatenation
Service Interworking

Comprehensive Interface Support

The ST-series provides ATM service capabilities on a wide range of SONET/SDH interfaces, from speeds of DS-3 to OC-48:

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

· 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 Layer 2 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.

Policing Schemes

The ST-series supports both cell-based and frame-based policing and follows established standards including the ATM Forum Traffic Management Specification Version 4.1, ANSI specification T1.606a-1992, ITU-T I.370 and RFC 2698.

Cell-based Policing

The ST-series's cell-based policing function is based on the dual leaky bucket algorithm and supports the following ATM Forum TM 4.1 policing schemes: CBR.1, VBR.1, VBR.2, VBR.3, UBR.1 and UBR.2. A custom policer type is also available, enabling user-configurable policing schemes.

The dual leaky bucket algorithm determines whether cells entering the network conform to the following ATM traffic parameters:

· Peak cell rate (PCR), in cells per second or bits per second
· Cell delay variation tolerance (CDVT), in microseconds
· Sustainable cell rate (SCR), in cells per second or bits per second
· Maximum burst size (MBS), in cells or bytes

Any cells that do not conform to these parameters are either dropped or tagged as follows:

For proper traffic queuing and shaping, the ST supports standard ATM service categories, including: constant bit rate (CBR), variable bit rate (VBR) and unspecified bit rate (UBR). The categories are strictly prioritized, meaning that CBR traffic is always serviced first to ensure low latency, jitter and loss.

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 Frame Relay 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 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 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 CLP=1 traffic during periods of congestion.

The ST also supports per virtual circuit scheduling and shaping. For example, CBR connections are scheduled according to their configured rate to ensure very low latency and jitter. VBR connections are scheduled to allow some latency and jitter, but low cell loss. UBR connections are scheduled without rate guarantees.

VCC and VPC Cell Relay

The ST provides point-to-point ATM virtual channel connection (VCC) and virtual path connection (VPC) cell relay connections across an IP/MPLS network using the encapsulation and signaling methods defined in IETF draft-martini-l2circuit-encap-mpls-04.txt and draft-martini-l2circuit-trans-mpls-08.txt. This functionality enables incumbent carriers to offer existing PVC cell relay services across an MPLS-enabled IP backbone while enabling next-generation carriers to deploy new value-added services.

VCC AAL5

The ST supports point-to-point ATM adaptation layer 5 (AAL5) transport using the encapsulation and signaling methods defined in IETF draft-martini-l2circuit-encap-mpls-04.txt and draft-martini-l2circuit-trans-mpls-08.txt. For this service, the ST-series performs segmentation and reassembly (SAR) for AAL5 mode on DS-3, OC-3c, OC-12c and OC-48c interfaces and transports the AAL5 frames over MPLS. This provides an efficient packet-switching service using ATM access links.

Port Mode

The ST also supports an ATM port-switching mode as defined in IETF draft-martini-l2circuit-encap-mpls-04.txt and draft-martini-l2circuit-trans-mpls-08.txt. This mode can be used to transparently interconnect ATM switches across an MPLS network.

PVC Cell Concatenation

The ST supports PVC cell concatenation, enabling carriers to bundle multiple cells into a single MPLS protocol data unit (PDU) for improved encapsulation efficiency. Without cell concatenation, several bytes of overhead are incurred due to the MPLS labels and Layer 2 headers, resulting in inefficiencies.

The concatenation feature can also be used to avoid packet reordering in certain MPLS core networks.

Service Interworking

The ST 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 ST-series supports interworking with any speed ATM and Frame Relay interfaces, including high-speed OC-3, OC-12 and OC-48 interfaces.

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

As service providers transition from the single-service networks of today to the dynamic multi-service infrastructure of the future, they must take special care to ensure that current service guarantees and revenue streams are not sacrificed. Only ECI's service edge routing solution combines 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 - providing flexible service delivery today and in the future.

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