Austrian and German Overlap mode

For us engineers that only occasionally do an install in Germany or Austria in terms of telephony this could be describe as Dante Alighieri’s trip through the 9 circles of hell. You actually miss fax troubleshooting when you are going through this. You also have variable length dial plan and ISDN Type to get correct else Telco drops the outbound call.

Cisco routers can receive an ISDN call in En bloc or Overlap modes. When configured for En bloc, the setup message should contain all necessary addressing information to route the call. In Overlap, the setup message does not contain the complete address. Additional information messages are required from the calling side to complete the called address.

So a few guidelines I picked up from different documentation I have read while trying to solve this

  • Don’t use the translations on the voice-ports. Use them on the incoming dial-peers
  • Cmd “direct inward-dial” should not be configured in the incoming dial-peer for overlap
  • Apply “isdn overlap-receiving T302 5000” on the serial interface
  • When sending complete message debug isdn q931 the wait timer T302 would stop and the next step of matching the outgoing dial-peer would proceed
  • If you see error message Recovery on timer expiry in debug isdn q931 This occurs when ISDN messages don’t arrive in specified time according to the Q.931 specification. Need to use direct-inward-dialing under that dial peer

Below I am just giving the configuration I come up with to get inbound calls to work. I am not suggestion its the best possible solution but after extensive testing we haven’t found any issues with it but I am still looking for feedback/suggestions to improve it.

Scenario

  • CUCM IP address 10.1.1.1
  • DDI range is 131558XXX
  • Digits presented by Telco 558XXX for DNIS if full number dialed eg: 131558123
  • Digits presented by Telco if main circuit number dialed for DNIS is nothing! e.g. if dialed 131558 then the DNIS is empty. In some countries the main number of a circuit is the number exuding the DDI range digits so the main number for this circuit is 131558, so if someone from the outside dials 131558 the the GW will be presented with an empty DNIS
  • All outgoing call are prefix with 0 by CUCM

OK so first let’s get the interface configured up
trunk group A1_Telekom !only one E1 put best practice to use trunk group
.carrier-id Vienna_A1_Telekom
.description Vienna_PSTN_Trunks
.hunt-scheme round-robin both
.translation-profile outgoing OUTBOUND
!only outbound, inbound is done on the dial peer

controller E1 0/0/0
.pri-group timeslots 1-31
.description A1_Telekom

interface Serial0/0/0:15
.description PSTN
.no ip address
.encapsulation hdlc
.no logging event link-status
.isdn switch-type primary-net5
.isdn overlap-receiving T302 5000
!configure the T302 timer to wait to 5 sec for next digit
.isdn incoming-voice voice
.isdn send-alerting
.isdn bchan-number-order ascending
.trunk-group A1_Telekom
.no keepalive
.no cdp enable

voice translation-rule 1
.rule 1 /\(^131558...$\)/ /+43\1/
.rule 2 /^$/ /+131558/
!Match for an empty/NULL DNIS. Not the same as blank e.g. DNIS == ” “

voice translation-rule 3
.rule 1 /^/ /00/ type national national
.rule 2 /^/ /000/ type international international

voice translation-profile INBOUND
.translate calling 3
.translate called 1

Interfaces done now dial peers
!first up incoming dial peer for POTS with full number dial e.g. 131558123
dial-peer voice 100 pots
.trunkgroup A1_Telekom
.translation-profile incoming INBOUND
.service session
.incoming called-number .T
!Match first digit “.” then wait the T302 timeout for the next digit “T”
.fax rate disable
.forward-digits all

!Next incoming dial peer for main circuit number where DNIS presented as empty
!Remember incoming called-number has a higher priority then destination-pattern
dial-peer voice 101 pots
.trunkgroup A1_Telekom
.translation-profile incoming INBOUND
.service session
.answer-address .
.direct-inward-dialing
.fax rate disable
.forward-digits all

!last out going POTS dial peer
dial-peer voice 102 pots
.trunkgroup A1_Telekom
.service session
.destination-pattern 0T
.fax rate disable
.direct-inward-dial
.forward-digits all

dial-peer voice 1001 voip
.description DID Inbound WOKUCM04
.preference 1
.service session
.destination-pattern +131558...
.progress_ind setup enable 3
.progress_ind progress enable 8
.modem passthrough nse codec g711ulaw
.session protocol sipv2
.session target ipv4:10.1.1.1
.voice-class codec 1
.dtmf-relay rtp-nte
.fax rate 14400
.ip qos dscp cs3 signaling
.no vad

dial-peer voice 1003 voip
.description reception Inbound WOKUCM04
.preference 1
.service session
.destination-pattern +131558
.progress_ind setup enable 3
.progress_ind progress enable 8
.modem passthrough nse codec g711ulaw
.session protocol sipv2
.session target ipv4:10.1.1.1
.voice-class codec 1
.dtmf-relay rtp-nte
.fax rate 14400
.ip qos dscp cs3 signaling
.no vad

Below is a list of cmd i used for troubleshooting this
debug isdn q931
debug voice dialpeer all
debug voice dialpeer inout
debug voice translation
debug voice ccapi inout

Ref:
https://supportforums.cisco.com/document/105866/overlap-receiving-issues
http://ccnp-v.blogspot.co.uk/2013/05/german-overlap-isdn-with-cme.html
http://www.cisco.com/en/US/tech/tk652/tk90/technologies_tech_note09186a008010fed1.shtml#topic5
http://www.cisco.com/en/US/docs/ios/12_3/vvf_c/dial_peer/dp_plan.html

About Alexis Katsavras

Working as Freelance Cisco Unified Communications Consultant in the UK. www.NetPacket.co.uk