Nortel Networks 9150 - Manual (Page 64)

34 Remote Gateway 9150 Installation and Administration Guide
Remote Gateway 9150 description Standard 3.1
QoS Transitioning Technology
Communications between the Remote Gateway 9150 unit in your office and the
host PBX take place across the IP network using a 10BaseT Ethernet interface.
You can configure the Remote Gateway 9150 unit to switch automatically from
the IP network to the PSTN when the voice QoS falls below a predetermined
threshold. Within the QoS settings, you can also enable Differentiated Services
(DiffServ) and 802.1Q Mapping to give priority to voice over IP traffic on your
network.
Both the RLC and the Remote Gateway 9150 unit monitor the IP network’s QoS
constantly. If the IP network QoS degrades, causing poor voice quality, the
Remote Gateway 9150 unit moves, or transitions, the call to the PSTN. When
the QoS returns to normal, the Remote Gateway 9150 unit transitions the call
back to the IP network.
QoS transition recovery
Due to the requirement for on-demand router support, the IP network is not
continually tested during QoS transition situations. It is tested only when there
are active voice calls over the PSTN. As a result, to switch back to the IP
network, QoS Transitioning Technology needs active calls for the user-
configured recovery period.
If you test QoS transition by disconnecting the Ethernet cable from the Remote
Gateway 9100 Series unit, or RLC, expect up to a 20-second delay before the
Remote Gateway 9100 Series unit can place or receive a call. You do not
encounter this delay when the network degrades and calls switch to BRI as
designed.
For detailed instructions on configuring the thresholds, refer to the Reach Line
Card Installation and Administration Guide (NTP 555-8421-210). For
guidelines on evaluating and adjusting the QoS on your IP network, refer to the
Remote Gateway 9100 Series Network Engineering Guidelines
(NTP 555-8421-103).
Voicemail messages and Quality of Service transitions
It can take several seconds of sustained errors to cause a Quality of Service
(QoS) transition to the PSTN. During this time, voice quality may suffer due to
errors. If a message to a voice mailbox is being recorded during these errors,
portions of the message can be unintelligible.