When users complain of that ticker information is slow, ops staff must quickly learn why. But how can staff isolate the cause of the delay? Are the distribution T1 frame circuits oversubscribed? Have application information flows changed in a way that was not anticipated, ore have new flows been introduced without advance notice and planning?

Providing an immediate, initial response to these questions is an application for the Troubleshooting toolset. Visual UpTime™ graphically depicts access channel usage. The ops staff use this tool to investigate incidences where access channel utilization deviates from the norm. The ops staff can also identify the most active of the PVCs on this access channel. Short-term views of traffic per access channel are used to isolate unanticipated increases in traffic over the Frame Relay network.

For some problems, the ops staff turn to the PVC summary statistics view in the Troubleshooting toolset to identify hosts that are "Top Talkers". This information is used to take measures to suppress the use of the unanticipated application, and may be passed to network planning staff, who use it to determine whether the CIR for a particular PVC must be increased.

Visual UpTime™ plots PVC throughput according to network protocol. This is extremely valuable for networks where delay-sensitive traffic such as SNA and best-effort IP traffic are forwarded over common PVCs. Per protocol histograms of utilization help network planners make informed decisions regarding the bandwidth required to minimize latency. Traffic shaping can be applied in router software to assure that SNA traffic is processed at a higher priority than IP traffic.

How important is this? Absent a clear understanding of how multiple network protocols coexist and compete for bandwidth share on a PVC and access channel, network planning is guesswork. A common reaction to loss and latency is to throw bandwidth at the problem: increase CIR on a PVC, or create separate PVCs for select protocols. Such actions add to the WAN service cost, when all that is necessary in many situations is better tuning of network equipment to utilize existing bandwidth cost-effectively. With Visual UpTime™, you manage bandwidth and maximize your return from WAN services.

Understanding and Managing FR Congestion

While the ops staff have access to individual enterprise network elements and to CPE components of a Frame Relay access line, some of the Frame Relay network—the switching fabric, for example—remains a blind spot. When the ops staff suspect that the Frame Relay network may be the source of unexpected delay, they rely on Visual UpTime™ to illustrate the percentage of seconds where frames received from the network had Congestion Notifications (CN) set. If the congested seconds percentage is high, Frame Relay switches may be having difficulty meeting service levels.Congestion notifications typically mean that FR switches are receiving frames from subscriber access lines faster than they can process and deliver them, causing frames to be held in buffers longer or even discarded.

Frame Relay subscribers can put such information to good use. In practice, both FR user and network provider benefit from a cooperative effort to avoid congestion on the FR network. Properly instrumented routers and FRADs support packet scheduling and traffic shaping mechanisms and react to CN’s by dynamically adjusting operating rates over FR down when congestion is present, and up when congestion abates. Routers and FRADs require tuning of these parameters, but absent the kind of concrete data derived from a tool like the Congestion A ctivity monitor, insufficient data is available to support such fine tuning.

Managing Bursty Data over Frame Relay

A unique feature of the Visual UpTime toolset is the Visual Burst Advisor. This feature displays upstream and downstream Access Channel or FR PVC utilization. Ops staff observe Utilization graphs, which display throughput as percentage of either Access Channel speed or CIR, to quickly identify brief traffic bursts. Pie charts provide a breakdown of utilization by percentage, allowing ops staff to summarize Access Channel or PVC utilization during 15-minute intervals. This is especially useful as an aggregation tool when traffic flow is highly variable. For trending over a longer period, the Burst Advisor provides bandwidth summarizes and CIR utilization during the past two weeks, and performs a three-tier analysis to produce recommended capacity planning actions for the affected Access Line or PVC: increase, decrease, no change. The Burst Advisor’s ability to identify under-utilized access lines helps enterprises reduce overall WAN services expenditures.

WAN Delay Analysis

The subject company’s operations staff currently uses the Event Processor and Troubleshooting toolsets is best described as reactive management — when services fail and when end users report poor performance, the staff tries to determine the cause. Reactive management is a necessarily evil, but can be complemented by other activities to run any network more cost-effectively.

The Visual UpTime™ Troubleshooting toolset provides the subject company with a Round Trip Time (RTT) Measurement tool that does not require any investment in custom software. WAN delay analysis can be performed by correlating frame transmission and reception from ASEs on both ends of a PVC, resulting in a protocol independent, non-intrusive analysis which measures only that portion of the application delay that is attributable to Frame Relay.

We believe the appropriate application for the RTT measurement feature of is a two-fold practice of asserting a baseline by measuring current response times which appear satisfactory to customers, and periodically monitoring Frame Relay to confirm that this baseline continues to be met. This information will prove useful if the Frame Relay service degrades over time, or when the subject company finds it necessary to reevaluate and make changes to network connectivity .

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