How to emulate the PSTN with an E1 interface

Here’s how to configure the network end of an E1-E1 back-to-back setup:

network-clock-participate wic 2 
isdn switch-type primary-net5
!
controller E1 0/2/0 
 clock source internal pri-group timeslots 1-3,16 
!
interface Serial0/2/0:15 
 no ip address 
 encapsulation hdlc 
 isdn switch-type primary-net5 
 isdn protocol-emulate network 
 isdn incoming-voice voice 
 no cdp enable 
!

Ofcourse, the 2 statements that differ from a normal setup are (the first under the controller configuration, the last under the serial interface configuration):

clock source internal 
isdn protocol-emulate network

If all is well, the command show isdn status gives:

Global ISDN Switchtype = primary-net5
ISDN Serial0/2/0:15 interface
        ******* Network side configuration *******
        dsl 2, interface ISDN Switchtype = primary-net5
    Layer 1 Status:
        ACTIVE
    Layer 2 Status:
        TEI = 0, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED
    Layer 3 Status:
        0 Active Layer 3 Call(s)
    Active dsl 2 CCBs = 0
    The Free Channel Mask:  0x80000007
    Number of L2 Discards = 0, L2 Session ID = 107
    Total Allocated ISDN CCBs = 0

E1-E1 RJ45 cross-over cable

Here’s how to connect 2 E1 RJ45 interfaces back-to-back:

First End

PIN 1 ORANGE 
PIN 2 WHITE/ORANGE 
PIN 4 BLUE
PIN 5 WHITE/BLUE

Second End

PIN 1 BLUE 
PIN 2 WHITE/BLUE 
PIN 4 ORANGE 
PIN 5 WHITE/ORANGE

Forwarding incoming calls to external destinations on CME

The other day I was working on a setup that would forward an incoming call to an external destination using an ISDN BRI interface. This would come in handy if nobody’s at the office, but you don’t want to miss calls placed to the main number. Time and again my attempts were failing with:

Cause i = 0×82E46C – Invalid information element contents

Searching the Internets for this cause code didn’t yield many results, but I did find some documentation on the Cisco website: Call Forward from CallManager Express to an External Number Fails. CME might also use the original calling number for the inbound call as the calling number for the outbound call leg. To prevent this from happening, you can use outgoing translation rules. A likely indication that this might work for you would be:

Cause i = 0×829C – Invalid number format(incomplete number) 

This didn’t solve my problem. In the end it turned out to be the numbering plan type as somebody pointed out. I configured the following, which made it work:

interface bri 0/0
 isdn map address . plan unknown type unknown
!