When to use this
TDM / ISDN PSTN Trunk
Use caseTDM/ISDN circuits (PRI) as the PSTN connection instead of SIP
ChallengeTDM-IP call flows require a two-leg routing model to enable media path optimization on the Webex call leg
Loopback peersDial-peers 10, 11, 12 create an internal IP hop between the Webex and PSTN legs
Routing tagsOver-decadic digits (A) added/removed via translation rules to guide calls and prevent loops
Translation rule logic
Webex direction (A1A tag)
voice translation-rule 200
rule 1 /^/ /A1A/
voice translation-rule 11
rule 1 /^A1A/ //
Adds A1A tag on PSTN inbound, strips it before delivering to Webex
PSTN direction (A2A tag)
voice translation-rule 100
rule 1 /^\+/ /A2A/
voice translation-rule 12
rule 1 /^A2A44/ /0/
Strips E.164 + and adds A2A tag on Webex inbound, strips it before delivering to PSTN
PRI interface example
card type e1 0 2
isdn switch-type primary-net5
controller E1 0/2/0
pri-group timeslots 1-31