APM MIB and ART MIB
Several extensions to the original RMON specification have been described. However, all of them focused on the inspection of packets per interface or VLAN. None of them considered an end-to-end approach. This is the value-add that the Application Performance Measurement (APM) MIB offers, because it measures the delay between request-response sequences in application flows for protocols such as HTTP and FTP. The original proposal was defined by Netscout as the Application Response Time (ART) MIB; it was proposed to the IETF RMON working groups and standardized as RFC 3729. Cisco currently implements the ART MIB at the NAM. The ART MIB can be customized to support any application that uses well-known TCP ports. If multiple agents are placed in the network, ART can distinguish between the response time of the network component (packet flight time) and the client or server response time (processing time). The results are aggregated into six different response time buckets, which the user can configure via an NMS application. Because ART takes a passive approach to collecting user traffic in the network, concerns exists about the scalability of resources at the probe as well as the number of required probes in the network. ART provides the most useful results when a probe is deployed close to a connection's source and destination. Figure 5-6 illustrates the placement of the Cisco NAM to collect application response time and distinguish between network response time and client and server response time.
Figure 5-6. NAM Placements for Collecting Application Response Time Details
The ART MIB principles are as follows:
It collects application response times in the network.
It supports only well-known TCP ports.
It aggregates collection details in six different buckets.
It contains 32-bit and 64-bit SNMP counters.
Supported Devices and IOS Versions
Cisco routers and switches do not support the ART MIB. However, it is fully supported by the Cisco NAM for the Catalyst 6500 series as well as the Branch Router Series NAM.
CLI Operations
Cisco routers and switches do not support ART. For configuration details on the Cisco NAM, refer to the online documentation at http://www.cisco.com/go/nam.
SNMP Operations
The ART MIB augments the RMON 2 protocol directory by adding a column to the protocolDirTable. The protocolDir2ArtConfig object describes the probe's capabilities and configures the artControlTable. This table consists of six response time objects (artControlRspTime {1...6} in milliseconds), with collection and report details for each corresponding data source.
Suggested default values for the response time ranges are as follows:
artControlRspTime1: 25 milliseconds
artControlRspTime2: 50 milliseconds
artControlRspTime3: 100 milliseconds
artControlRspTime4: 200 milliseconds
artControlRspTime5: 400 milliseconds
artControlRspTime6: 800 milliseconds
Additional MIB details include the collection start time, the sampling period, the maximum number of collection entries for the associated data source, and the number of dropped frames. The ART report table contains details for each client/server connection. The ART summary report table reports the arithmetic mean of the individual response times observed during the collection interval.
Examples
Cisco routers and switches do not support ART. For configuration details on the Cisco NAM, refer to the online documentation at http://www.cisco.com.
Collection Monitoring
Figure 5-7 shows a summary report of the ART MIB, collected by the Cisco NAM module. The chart on the left is a graphical representation of the response time distribution. The right side provides the server details in the upper part and the table for response time distribution in the lower part.
Figure 5-7. ART MIB Measurement Example of a Catalyst 6500 NAM Details
