Avaya Definity SI, Руководство по обслуживанию, Страница: 158 / 2968

Routine Maintenance Procedures
555-233-123 5-54 Issue 4 May 2002
Calls Terminate Correctly but Are Unstable
Description
A number of conditions will lead to some or all endpoints having stability problems
during the course of a conference. A lack of stability from an endpoint is
noticeable by a lack of a video switching while the party is the only talker or
excessive disconnects from that endpoint.
Synchronization
Generally, the most common problem is a mismatch in synchronization sources
between the endpoint and the DEFINITY MMCH. This typically causes low-level
(Px64) handshake problems that can trigger the endpoint/MMCH to disconnect
the call. The MCCH’s timers are set to sufficiently high values so that, normally,
the endpoint will timeout and disconnect first. If installed in a customer network, it
is a good idea to perform an audit of the path synchronization is being supplied. If
there are different clock sources between endpoints and the DEFINITY MMCH,
some problems are sure to occur. The severity of these problems can range from
a handshake failure every few seconds to one per day. Depending on the type of
endpoint, this can cause the endpoint to disconnect or just freeze video until the
main problem is resolved.
Specifically, PictureTel System 4000 endpoints seem to be the most sensitive to
instability. The Avaya Vistium also disconnects fairly infrequently. Last, the CLI
Rembrandt II VP freezes video and waits for framing to be recovered.
Network Configuration Concerns with
Synchronization
When auditing a network for synchronization, avoid unnecessary hops. Thus, a
switch providing star-configuration synchronization is preferred over a daisy-chain
configuration. Additionally, if there are DEFINITY PBXs that have EPNs,
synchronization should be provided to sub nodes from the same port network
through which the PBX receives its synchronization. Passing synchronization
through the PBX Expansion Interface adds an unnecessary hop to the path and
creates another potential point of failure.
Expansion Interface Duplication
If a customer’s network uses PBX EPNs with duplicated Expansion Interfaces,
scheduled switching of the Expansion Interface links should be disabled on the
PBX via change system-parameters maintenance. When scheduled
maintenance runs and switches the links, there is a brief corruption of the data
path. If endpoints have active calls when the switch occurs, this corruption of the
data path causes Px64 handshake problems, which lead to the endpoints losing
video source status, and sometimes disconnecting as described above. Disabling
the EI switching is in the customer’s best interest to prevent the disruption of the
Px64 data stream. The customer will get the same level of alarm indications and
maintenance on the EI links, regardless of the status of scheduled switching.