LifeSize Gateway-PRI, Руководство пользователя

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Using the LifeSize Gateway 143
About Dialing In to the IP Network via the Gateway
Table 4-1 Routing Methods
Routing Method Explanation
DID The LifeSize Gateway supports two forms of DID (Direct Inward
Dialing): Multiple Subscriber Network (MSN) and
sub-addressing.
MSN—The telephone company assigns a group of
phone numbers to a particular ISDN line by the
telephone company. PRI ISDN lines are usually
assigned multiple numbers in the US and in Europe.
When MSN is used, an ISDN terminal or
phone can dial directly to an IP network
endpoint. The call is still routed through the
LifeSize Gateway but the LifeSize Gateway is
transparent to the person dialing from an
ISDN terminal.
An H.323 endpoint on the IP network
registers with the gatekeeper using one of the
MSN numbers. When an ISDN terminal dials
the MSN number, the call routes through the
LifeSize Gateway ISDN port connected to the
line with the MSN service to the endpoint that
registered using the requested number.
Sub-addressing (Gateway-PRI only)—Sub-addressing
is a one-stage DID dialing mechanism in which a phone
sends two numbers. One number is for routing on the
circuit switched network. The other number is
forwarded to the LifeSize Gateway inside a Q.931
sub-addressing information element for IP address
resolution by the gatekeeper.
Sub-addressing can also be used for
implementing ISDN fallback when not
enough bandwidth is available for routing an
IP-oriented call over IP. Implementing ISDN
fallback requires the support of the
gatekeeper.