Alternate latency is measured

Document ID : KB000023998
Last Modified Date : 14/02/2018
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Question:
How alternate latency is measured

Answer:
For alternate latency, the default number of pings sent during a polling interval is 5. The first is dropped (only used to find a path) and the remaining 4 are averaged. This number is then collected by the Network Health poller. The packet size, number of ping packets and ping timeout are set by the Environment variables defined below.

Network Health creates and removes the ping process on each poll using the
following default parameters:

* Ping packet sizes of 100 bytes
* Five ping packets
* Ping timeout of 2,000 milliseconds

These parameters can be changed using Network Health environment
variables:

1. To change the default ping packet size, define the
NH_CISCO_PING_PKTSIZE variable and specify the size of the packet in
bytes. If you do not define this variable, Network Health uses the value of
NH_POLL_PING_PKTSIZE, which is 100 bytes by default.

2. To change the number of ping packets that Network Health sends, define
the NH_CISCO_PING_PKT_COUNT variable and specify the number of
packets to send.

3. To change the timeout value for the ping request, define the
NH_CISCO_PING_TIMEOUT variable and specify the maximum
number of milliseconds that the latency source should wait for a response
to the ping request.

Subsequent PINGs (ICMP echo requests) are sent after the previous request
has been responded to OR upon the PING timeout.
There is no deferring of the PING request, its one after another throttled by the response time or configured timeout.

For more information on the collection of alternate latency, refer to the solution How does eHealth collect alternate latency data.