664 Chapter 9: Management Tools and QoS Design

Service Assurance Agent

The Cisco Service Assurance Agent (SAA) allows a router IOS to measure network performance and availability by sending probes into the network. Based on configuration commands, a router generates and sends packets, called probes. The router sends the probes to specified remote destinations, which in some cases are other routers, and in other cases, other hosts. The router or host receiving the probes sends a response packet. Based on the replies, the router that sent the probe can calculate statistics, such as one-way and two-way delay, jitter, and simple availability.

SAA can create simple probes using Internet Control Message Protocol (ICMP) echo, but it’s true value shines through with the more advanced probes. For instance, voice delay and jitter can be measured with SAA probes that generate Real Time Protocol (RTP) traffic. SAA supports probes for data-link switching (DLSw) traffic, because SAA was originally created to replace some legacy System Network Architecture (SNA) features. SAA can even generate HTTP traffic when downloading objects from live web servers. In many cases, you can create probes to match each traffic class specified in your QoS policies.

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SAA is not a separate product, but rather an IOS feature that was first supported in the mid1990s. (It was called the Response Time Reporter [RTR] tool then.) You can configure rtr commands inside IOS, creating probes and responders (which respond to probes). Then you can use show commands to look at the statistics. Because the rtr command has many options, it takes some experimentation to learn how to configure the commands effectively.

An easier way to configure SAA is to use IPM or SMS, which both rely on SAA. In other words, configure SAA indirectly. Suppose you want to see a real-time graph of delay and jitter for voice traffic between two routers. You can specify the endpoints as targets in IPM by assigning a target type of Cisco SAA Responder for the routers. IPM can then map an operation type, such as ICMP echo, to each SAA endpoint and test the QoS values between the endpoints. You can also see the same information, but trended over time (to compare today’s performance with other days, for instance). Use SMS to do this, which also programs the routers with rtr commands, based on your input.

Table 9-4 lists some of the types of SAA probes supported in Cisco IOS Software Release 12.2.

Table 9-4 Types of SAA Probes

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To meet the requirement to gather larger amounts of network performance information, SMS includes several components. Figure 9-2 shows the components.

Figure 9-2 Service Management Solution Components

SAA Agents

Network Devices

SMS includes two main components. First, the Service Level Manager (SLM) is software that runs on the same host as CiscoWorks2000. SLM provides information to the end user of SMS, and generates the configuration of the probes based on end-user input. SMS Collection Managers (CMs) are software agents that run on computers spread around the network for scaling purposes, or a CM can reside on the SLM server for small installations. The CMs actually collect the information that is created by the SAA probes running on the devices in the network. The CMs collectively offload the intensive collection requirement from the SLM host, creating a more scalable and available architecture. If the SLM host goes down, for instance, the CMs can still collect the data. The SLM will asynchronously collect the data from the CMs, most typically during off-hours when the network is much less busy.

NOTE Cisco formerly sold a product called the Cisco Management Engine 1100, which was a piece of hardware on which to run CM. Although it isn’t not sold anymore, the course upon which the exam is based still mentions the product, so you should at least be aware of it.