Two ISDN BRI interfaces

[tomd10]

Hello,

I got two routers with ISDN WICs (2620 and 1941, both with WIC-1B-S/T-V3 I think). Is it possible to somehow use them (set up a connection between these two routers via telephone wires)? I am young so I missed the ISDN era, so I know almost nothing about it :)

Thanks for you answer.

[mlund]

Hi

From top of my head (it's fifteen years, or twenty, since i worked with isdn), no, you can't connect the isdn back-to-back, or direct to telephone line. Unless the lines are actually isdn lines.

Isdn to work needs a magic box in the middle that handles the isdn call setup and numbercoding, and I'm not aware of any cisco equipment that can simulate that. Maybe some other old man on the forum has a better memory than mine.

/Mikael

[Giuseppe Larosa · Accepted solution]

Hello Tomd10,

unfortunately you cannot connect them in back to back because ISDN has its own protocol stack.

An ISDN switch would be needed in the middle. There are some ISDN switch emulator for testing purposes.

I remember we had one in the lab 15 years ago able to support a single call setup.

a BRI is made of two B channels 64 kbps each and one D channel 16 kbps for signaling (Q.921 roughly L2 Q.931 roughly L3 and so on).

Try to look for ISDN switch emulator on the web I have no idea how much it costs.

The only kind of interfaces you can connect back to back over a telephone pair is SDSL a form of symmetric DSL where you could connect one side to act as central office = DCE and the other as remote = DTE. Also SHDSL may be able to do it.

Hope to help

Giuseppe