Look-Ahead Interflow
8-10 Issue 4 September 1995
Figure 8-4. LAI Using a Tandem Switch
Sending Switch Operation
The sending switch is unaware that its Look-Ahead Interflow call is b eing
tandemed to an alternate switc h . The op erati on of the sending switch in the
tandem switch configuration is the same as that in the two switch configuration.
Tandem Switch Operation
If the receiving switch executes a
route-to
command that routes the call over an
ISDN facility b efore call a cceptance, the
route-to
command is performed on a
“look ahead” basis in the same manner as a sending switch. If the call is
accepted at the far end switch, acc eptance is pass ed to the sending switch, and
call control is passed to the far end switch, along with tandeming of the original
calling party information and the original DNIS name. If the call is d enied, the
next step of the tandem switc h vector is executed.
Here’s an example of a tandem switch vector:
Figure 8-5. Tandem Switch Vector
SENDING
SWITCH TANDEM
SWITCH FAR END
SWITCH
ISDN - PRI
INCOMING
CALLS
ALTERNATE
BACKUP
SPLIT
ISDN - PRI
BACKUP
SPLIT
MAIN
SPLIT
1. goto step 6 if calls-queued in split 30 pri h > 5
2. queue-to main split 30 pri h
3. announcement 200
4. wait-time 2 seconds hearing silence
5. stop
6. route-to number 4000 with cov n if unconditionally
7. busy