StrataCom ForeSight

Product Overview

StrataCom ForeSight is a revolutionary bandwidth management technology that improves the quality and efficiency of ATM wide-area networks. It is a rate-based, closed-loop traffic control mechanism that continuously monitors ATM trunk utilization and adjusts the rate of each ATM connection to avoid trunk congestion and make maximum use of network resources.

The benefits of closed-loop feedback mechanisms stem from the use of separate queues for each ATM connection. Connection-based queuing establishes firewalls among network users, ensuring predictable quality of service under all operating conditions, and allowing precise management of connection bandwidth. Maintaining and servicing these connection queues at broadband speeds requires powerful queue service engines on interface modules.

ForeSight is the world's first rate-based, closed-loop traffic control mechanism for ATM networks, a type of ATM traffic control that coordinates congestion management among multiple switches. Closed-loop traffic controls compliment existing ATM traffic controls such as cell-tagging and selective cell discard, improving network quality of service and efficiency. ForeSight enhances the performance of all ATM-based data services, including frame relay and other AAL5 traffic.

ForeSight continuously monitors the utilization of ATM trunks and sends information on the utilization of intermediate switches in the direction of cell transfer using congestion indicators in each cell. Destination switches use these congestion indications to track the congestion state in the forward direction of each ATM virtual circuit. This congestion state information is relayed back to the traffic source via resource management cells up to 50 times per second. The sources then adjust the sending rate of each virtual circuit based on this feedback, and buffer any additional data in per-connection queues.

The combination of per-connection queueing at ingress and rapid, cell-based feedback enables ForeSight to prevent congestion even at broadband speeds. Extensive modeling and deployment in production networks throughout the world has demonstrated the benefits of closed-loop traffic control. Cisco is working with leading vendors and the ATM Forum to extend this capability to ATM hubs, workstations and other devices.

ForeSight includes the following features:

• Reduced delay---minimizes network queuing delays which impact all connections
  

Consistently low end-to-end delay is essential for any wide-area network supporting interactive, transaction-oriented applications, particularly new client/server applications where a single transaction might involve large amounts of data. Many common LAN protocols also require low delay to provide satisfactory performance over WAN links. ForeSight guarantees consistently low delay under all network conditions.

A major source of delay in ATM WANs is the queuing delay that occurs at ATM trunks. ForeSight minimizes network queuing delays by adjusting the bandwidth of the connections to match the available capacity. When connections exceed their assigned bandwidth, the excess cells are buffered at the edge of the network, maintaining low delay for other connections.

• Fairness---allocates bandwidth fairly in proportion to connections' committed rate
  

ATM networks should ensure that the bandwidth is shared fairly among all connections. Without closed-loop feedback, switches can only ensure that each connection will get at least a committed rate by policing cells at ingress and discarding cells if congestion occurs.

ForeSight goes beyond this to ensure that network bandwidth is allocated to connections in proportion to their committed rate. Any spare capacity is shared equally, and if network failures or under-provisioning of bandwidth make it impossible to give each connection its committed rate, ForeSight ensures that each will get the same fraction of the committed rate. ForeSight guarantees users equal access to network capacity without impact by other users.

• Efficiency---carries more data traffic without performance degradation
  

Trunk bandwidth is a large component of the operating cost for any WAN, and should be used as efficiently as possible. ForeSight maximizes network efficiency and lowers operating costs by enabling more data to be sent on each trunk. By intelligently distributing buffering in per-connection queues throughout the network, ForeSight prevents momentary bursts of traffic from causing network congestion and data loss. Reliable ATM services can be delivered with trunk utilizations above 90 percent, enabling more data to be carried over a given network. Without ForeSight, ATM trunks must operate at low average utilizations of 50 percent or 60 percent to avoid performance crippling cell discards.

• Predictability---prevents bursts of data on one connection from "freezing-out" other connections
  

Although ATM WANs share bandwidth among many applications and connections, each should receive predictable service as though it were attached to a dedicated network. Connections must be isolated from each other so that one misbehaved connection cannot disrupt the performance of another.

By buffering bursts of traffic at the edge of the ATM network in separate queues for each connection, and by minimizing network queueing delays, ForeSight establishes "firewalls" and prevents bursts of traffic on some connections from affecting the performance of others.

• Reliability---reduces or eliminates discards caused by network congestion
  

Reliable delivery of user data is critical to the performance of any data application. When cells are discarded within an ATM network because of network congestion, the corresponding data frames must be retransmitted. This reduces application throughput and wastes network bandwidth.

The effects of cell loss due to network congestion include the following:

• Reduced transmission rate
  

• Protocol timeouts
  

• Unpredictable delays
  

• Wasted bandwidth
  

Most ATM switches rely on cell discard (cell loss priority) as their primary means of congestion control. Connections that transmit above their committed rate have cells tagged as discard eligible. Even momentary congestion at a switch can cause these cells to be discarded.

ForeSight continuously monitors ATM trunk queues and adjusts connection rates to avoid network congestion. Per-connection queues guarantee each connection a minimum amount of buffering. This enables application protocols to adjust their transmission rate in response to increasing delay, before cell discards becomes necessary. Connections can support sustained transmissions above their committed rate without performance degradation due to cell loss.

• Standards compliance---maintains interoperability with user equipment
  

ForeSight enhances the operation of ATM data services, including ATM and Frame Relay, while maintaining interoperability with user equipment and other switches that do not yet support this level of traffic control. Other supported standards-defined ATM traffic/congestion control mechanisms include the following:

• Usage parameter control
  

• Peak cell rate
  

• Sustained cell rate/maximum burst size
  

• Cell tagging
  

• Selective cell discard
  

• Explicit forward congestion indication
  

Product Numbers

Table 228 lists the product numbers you can use to order StrataCom ForeSight.

Table 228 : ForeSight Product Numbers

Description	Product Numbers
AXIS ForeSight license for each frame service module	AX-FS-4
BPX ForeSight license per 2-port T3 or E3 ASI card	BPX-FS-2
Frame Relay ForeSight software license per T1/E1	IGX-FS-1

Copyright 1988-1996 © Cisco Systems Inc.