The Cisco Network Analysis Module (NAM) is one of the non-AMD devices from which the CAS can report monitoring information. NAM statistics appear on the CAS Network, Network
View, Software Services View, Link View, and Reporting Groups View.
For consistency, the CAS reports NAM measurements with the DCRUM equivalents of NAM metrics where possible. However, not all NAM measurements have DCRUM equivalents, so some NAM data does not appear on CAS reports.
Most AMD and NAM metrics are calculated differently, which may result in different metric values provided by the devices. Depending on the data source (NAM or AMD), you may have a metric calculated based on two different algorithms on one CAS report. On Network View,
Software Services View, and Reporting Groups View reports, if both devices monitor the
same traffic, CAS reports show information coming from AMD only, and not from NAM. On
Link View reports, however, statistics from both devices will appear.
For traffic that is monitored only by NAM, CAS shows traffic statistics coming directly from NAM, only using DCRUM metric equivalents.
Table 3. NAM Metrics and DCRUM Equivalents
AMD NAM
Slow operations Number of late responses
DCRUM equivalent of the NAM metric. Total number of responses with maximum response
time exceeding the predefined threshold.
Operation time Total transaction time
DCRUM equivalent of the NAM metric. Time (ms) elapsed from the start of a client request
to the completion of the server response.
TCP connection attempts Number of connections
DCRUM equivalent of the NAM metric. Number of TCP connections (new sessions) made
during the monitoring interval.
Operations
Table 3. NAM Metrics and DCRUM Equivalents (continued)
AMD NAM
DCRUM equivalent of the NAM metric. Number of transactions completed during the
measurement interval.
Client bytes
Client bytes
The number of bytes sent by the clients. Note that this includes headers.
Number of TCP bytes sent from a client during the monitoring interval. This metric does not include header bytes.
Server bytes
Server bytes
The number of bytes sent by servers. The number includes headers.
Number of TCP bytes sent from a server during the monitoring interval. This metric does not include header bytes.
Server time
Application delay (average)
The time it took the server to produce a response for the given request.
The average time it takes a server application (for example, a Web server application) to respond to a request. It is the time between the client request arriving at the server application and the first response being returned by the application. This metric does not include measurements from slow responses.
End-to-end RTT
Network delay (average)
The time it takes for a SYN packet to travel from the client to a monitored server and back again. The network round trip (flight time) between a client
and a server through the NAM switch or router. It is equal to the sum of client network delay and server network delay. NAM measures the network delay using TCP 3-way handshakes. If there are no new TCP connections made during the monitoring interval, this metric is not reported.
This metric does not include measurements from slow responses.
Server RTT
Server network delay (average)
The time it takes for a SYN packet (sent by a user) to travel from the AMD to a monitored server and The network round-trip time between a server and
the NAM switch or router. In WAAS monitoring,
back again. Also provided are minimum, maximum and standard deviation values.
Server Network Delay from a Server data source represents the network RTT between the server and its core WAE.
Client AMD Server
Server RTT SYN ACK SYN ACK T1 T6 T7 T2 T5 T8 T3 T4
This metric does not include measurements from slow responses.
Table 3. NAM Metrics and DCRUM Equivalents (continued)
AMD NAM
Client RTT
Client network delay (average)
Client RTT is the time it takes for a SYN packet (sent by a server) to travel from the AMD to the The network round trip time (or flight time) between
a client and the NAM switch or router. In WAAS
client and back again, as shown in the following picture.
monitoring, Client Network Delay from a WAE client data source represents the network RTT between the client and its edge WAE, while Client
Client AMD Server
Client RTT SYN ACK SYN ACK T1 T6 T7 T2 T5 T8 T3 T4 T9
Network Delay from the WAE server data source represents the WAN RTT (between the edge and core WAEs).
This metric does not include measurements from slow responses.
A client RTT measurement begins when the SYN ACK packet from the server to the client passes by the AMD (T5). The packet reaches the client machine (T6) and is processed, while an acknowledgment is sent back to the server (T7). Client processing time impact (T7-T6) is again very low. Client RTT measurement ends when the ACK packet reaches the AMD (T8). Therefore, the Client Round Trip Time is calculated as T8-T5. Depending on the actual setup, Client RTT measurements may vary dramatically. In corporate environments, it may be a few milliseconds for LAN-connected clients or a couple dozens milliseconds for WAN-connected clients. In this case, where the client is coming from the Internet, the end-to-end Client RTT measurement is a compound of transit time through the Internet backbone as well as through the "last mile" access network. The impact of the last mile can be easily calculated, based on the connection speed and the packet size (56B in case of TCP SYN packet). For a 28 kbps dial-up connection, this amounts to 16 milliseconds one way, or 32 milliseconds for a complete round-trip measurement. For a 1.6 Mbps DSL line, this makes 56 microseconds towards complete client RTT measurement.
N/A
Number of responses
- Total number of responses observed during the
monitoring interval.
N/A
Response time (average)
Table 3. NAM Metrics and DCRUM Equivalents (continued)
AMD NAM
- Amount of time it takes a server to send the initial
response to a client request as seen by the NAM. This is the initial server think time.
N/A
Number of responses by response time
- Seven-bucket histogram.
N/A
Total delay (average)
- Total amount of time from the first packet of a client
request until the client receives the first response packet from the application server. Total delay is the sum of the network delay and the application delay.
Total loss rate Number of retries
Although AMD does not supply such information directly, the CAS shows similar data as total loss
Number of packets retransmitted.
rate metric on the Link View report. The metric value is calculated based on data provided by NAM. For a given monitoring interval this is the percentage of retransmitted packets relative to the total number of packets (in this monitoring interval).
Note also that a number of DCRUM compound metrics (such as client bandwidth usage, server bandwidth usage, or network time) will also be influenced by the measurement differences.