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Reliability and Recovery
276 Avaya Application Solutions IP Telephony Deployment Guide
A C-LAN provides two basic reliability functions:
●
A C-LAN hides server interchanges from the IP endpoints. The signaling channels of the
endpoints remain intact during server interchanges, and do not have to be reestablished
with the new active server.
endpoints remain intact during server interchanges, and do not have to be reestablished
with the new active server.
●
A C-LAN terminates TCP keepalive messages from the endpoints, and thus frees the
server from handling frequent keepalive messages.
server from handling frequent keepalive messages.
Recovery algorithm
The recovery algorithm is designed to minimize service disruption to an IP endpoint in the case
of a signaling channel failure. When connectivity to a gatekeeper is lost, the IP endpoint
progresses through three phases:
of a signaling channel failure. When connectivity to a gatekeeper is lost, the IP endpoint
progresses through three phases:
●
Recognition of the loss of the gatekeeper
●
Search for (discovery of) a new gatekeeper
●
Re-registration
When the IP endpoint first registers with the C-LAN, the endpoint receives a list of alternate
gatekeeper addresses from the DHCP server. The telephone uses the list of addresses to
recover from a signaling link failure to the C-LAN/gatekeeper.
When the IP phone detects a failure with the signaling channel (H.225/Q.931), its recovery
algorithm depends on the call state of the endpoint:
gatekeeper addresses from the DHCP server. The telephone uses the list of addresses to
recover from a signaling link failure to the C-LAN/gatekeeper.
When the IP phone detects a failure with the signaling channel (H.225/Q.931), its recovery
algorithm depends on the call state of the endpoint:
●
If the user of the phone is on a call and the phone loses its call signaling channel, the new
IP Robustness algorithm will allow the phone to reestablish the link with its gatekeeper
without dropping the call. As a result, the call is preserved. Call features are not available
during the time the phone is trying to reestablish the connection.
IP Robustness algorithm will allow the phone to reestablish the link with its gatekeeper
without dropping the call. As a result, the call is preserved. Call features are not available
during the time the phone is trying to reestablish the connection.
●
If the user of the phone is not on a call, the phone closes its signaling channels and
searches for a gatekeeper using the algorithm defined below.
searches for a gatekeeper using the algorithm defined below.
To reestablish the link, the phone tries to register with a C-LAN on its gatekeeper list. The new
C-LAN Load Balancing algorithm looks for the C-LAN on the list with the least number of
phones registered to it. As a result, the recovery time will be short, and there will be no
congestion due to too many phones trying to register to a single C-LAN board.
In the S8300/G700 or G350 configuration, the IP endpoint connects directly to the S8300 Server
(there is no C-LAN.) The connectivity path between the endpoint and the server is:
C-LAN Load Balancing algorithm looks for the C-LAN on the list with the least number of
phones registered to it. As a result, the recovery time will be short, and there will be no
congestion due to too many phones trying to register to a single C-LAN board.
In the S8300/G700 or G350 configuration, the IP endpoint connects directly to the S8300 Server
(there is no C-LAN.) The connectivity path between the endpoint and the server is:
Endpoint
⇔
IP network
⇔
S8300
To discover connectivity failure, keepalive messages are exchanged between the IP end point
and the server. When the endpoint discovers that it no longer has communication with its
primary gatekeeper, it looks at the next address on its list. If the next address is for an LSP, the
LSP accepts the registration and begins call processing.
and the server. When the endpoint discovers that it no longer has communication with its
primary gatekeeper, it looks at the next address on its list. If the next address is for an LSP, the
LSP accepts the registration and begins call processing.