ISDN Circuit Simulator

With a bit of ingenuity & an T1/E1 crossover cable it's possible to build your own ISDN PRI circuit simulator using spare parts. For this you'll need:

1. T1/E1 crossover cable (pinouts here)
2. 2x ISDN VIC/VWIC cards
3. Enough PVDMs to handle the ISDN card
4. Cisco routers with appropriate feature set

Using the isdn protocol-emulate command, one ISDN card is set to act as the network side & the other the user side. They're then cabled together using the crossover cable & suitable dial-peers configured to allow calls.
My test rig was a 3845 equipped with a PVDM2-64 & 2x VWIC-1MFT-E1, using my nifty Universal Network Cable for crossover. Config snippets below:

isdn switch-type primary-net5
!       
controller E1 0/0/0
 clock source internal
 pri-group timeslots 1-31
 description Network E1
!
controller E1 0/1/0
 pri-group timeslots 1-31
 description User E1
!
interface Serial0/0/0:15
 no ip address
 encapsulation hdlc
 isdn switch-type primary-net5
 isdn protocol-emulate network
 isdn incoming-voice voice
 no cdp enable
!
interface Serial0/1/0:15
 no ip address
 encapsulation hdlc
 isdn switch-type primary-net5
 isdn incoming-voice voice
 isdn negotiate-bchan
 no cdp enable
!
voice-port 0/0/0:15
 cptone GB
 bearer-cap Speech
!
voice-port 0/1/0:15
 cptone GB
 bearer-cap Speech
!
dial-peer voice 1 pots
 incoming called-number .%
 direct-inward-dial
 port 0/0/0:15
!
dial-peer voice 2 pots
 destination-pattern .T
 incoming called-number .%
 direct-inward-dial
 port 0/1/0:15


Using some test IP phones to place calls, you can see from the debug isdn q931 output that the call exits Se0/1/0 & enters Se0/0/0:

*Oct  3 14:37:22.591: ISDN Se0/1/0:15 Q931: Applying typeplan for sw-type 0x12 is 0x0 0x1, Calling num 200
*Oct  3 14:37:22.591: ISDN Se0/1/0:15 Q931: Applying typeplan for sw-type 0x12 is 0x0 0x1, Called num 123
*Oct  3 14:37:22.591: ISDN Se0/1/0:15 Q931: TX -> SETUP pd = 8  callref = 0x0136
        Bearer Capability i = 0x8090A3
                Standard = CCITT
                Transfer Capability = Speech 
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0xA1839F
                Preferred, Channel 31
        Progress Ind i = 0x8183 - Origination address is non-ISDN 
        Calling Party Number i = 0x0180, '200'
                Plan:ISDN, Type:Unknown
        Called Party Number i = 0x81, '123'
                Plan:ISDN, Type:Unknown
*Oct  3 14:37:22.599: ISDN Se0/0/0:15 Q931: RX <- SETUP pd = 8  callref = 0x0136
        Bearer Capability i = 0x8090A3
                Standard = CCITT
                Transfer Capability = Speech 
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0xA1839F
                Preferred, Channel 31
        Progress Ind i = 0x8183 - Origination address is non-ISDN 
        Calling Party Number i = 0x0180, '200'
                Plan:ISDN, Type:Unknown
        Called Party Number i = 0x81, '123'
                Plan:ISDN, Type:Unknown
*Oct  3 14:37:22.603: ISDN Se0/0/0:15 Q931: TX -> CALL_PROC pd = 8  callref = 0x8136
        Channel ID i = 0xA9839F
                Exclusive, Channel 31
*Oct  3 14:37:22.607: ISDN Se0/0/0:15 Q931: TX -> ALERTING pd = 8  callref = 0x8136
        Progress Ind i = 0x8188 - In-band info or appropriate now available
*Oct  3 14:37:22.607: ISDN Se0/1/0:15 Q931: RX <- CALL_PROC pd = 8  callref = 0x8136
        Channel ID i = 0xA9839F
                Exclusive, Channel 31
*Oct  3 14:37:22.611: ISDN Se0/1/0:15 Q931: RX <- ALERTING pd = 8  callref = 0x8136
        Progress Ind i = 0x8188 - In-band info or appropriate now available
*Oct  3 14:37:27.759: %ISDN-6-CONNECT: Interface Serial0/0/0:30 is now connected to 200 N/A
*Oct  3 14:37:27.759: ISDN Se0/0/0:15 Q931: TX -> CONNECT pd = 8  callref = 0x8136
*Oct  3 14:37:27.763: ISDN Se0/1/0:15 Q931: RX <- CONNECT pd = 8  callref = 0x8136
*Oct  3 14:37:27.763: %ISDN-6-CONNECT: Interface Serial0/1/0:30 is now connected to 123 N/A
*Oct  3 14:37:27.763: ISDN Se0/1/0:15 Q931: TX -> CONNECT_ACK pd = 8  callref = 0x0136
*Oct  3 14:37:27.767: ISDN Se0/0/0:15 Q931: RX <- CONNECT_ACK pd = 8  callref = 0x0136
*Oct  3 14:37:33.759: %ISDN-6-CONNECT: Interface Serial0/0/0:30 is now connected to 200 N/A
*Oct  3 14:37:33.763: %ISDN-6-CONNECT: Interface Serial0/1/0:30 is now connected to 123 N/A
*Oct  3 14:37:34.567: %ISDN-6-DISCONNECT: Interface Serial0/0/0:30  disconnected from 200 , call lasted 6 seconds
*Oct  3 14:37:34.567: ISDN Se0/0/0:15 Q931: TX -> DISCONNECT pd = 8  callref = 0x8136
        Cause i = 0x8290 - Normal call clearing
*Oct  3 14:37:34.571: ISDN Se0/1/0:15 Q931: RX <- DISCONNECT pd = 8  callref = 0x8136
        Cause i = 0x8290 - Normal call clearing
*Oct  3 14:37:34.571: %ISDN-6-DISCONNECT: Interface Serial0/1/0:30  disconnected from 123 , call lasted 6 seconds
*Oct  3 14:37:34.571: ISDN Se0/1/0:15 Q931: TX -> RELEASE pd = 8  callref = 0x0136
*Oct  3 14:37:34.575: ISDN Se0/0/0:15 Q931: RX <- RELEASE pd = 8  callref = 0x0136
*Oct  3 14:37:34.579: ISDN Se0/0/0:15 Q931: TX -> RELEASE_COMP pd = 8  callref = 0x8136
*Oct  3 14:37:34.583: ISDN Se0/1/0:15 Q931: RX <- RELEASE_COMP pd = 8  callref = 0x8136

For a proper ISDN PRI simulator you'd want to implement a complete inbound dial plan with call routing to some IP phones or analogue phones connected to FXS ports to handle test calls. Then it'll be possible to have a proper Unified Communications lab with simulated PSTN connections.