128 Kbps ISDN Leased Line problem

[vijay-agrawal]

I am facing a problem with 128 Kbps ISDN leased lines, the telco switch is Siemens EWSD. I am using Cisco2611 router with 4 port ISDN modules connected to 4 other locations using 1720/1 port ISDN card. There is no sureity when a link will be up after getting down, it is just hit and trial to get the link up, shut/no-shut i/f, CONF the port from telco switch, reload router, etc. There are absolutely no i/f error counters when the link is working so media is also not a problem.

Any suggestions?

Thanks in anticipation.

Vijay

[tepatel]

Need to verify the status for layer 2 when the line went down..So lets have

sh isdn status

Also have

debug isdn q931

debug dialer

debug ppp negotiation

when you try to bring it up using shut/no shut etc..to see router is even trying to bring the layer 3 up or not..

Here is the link which discuss the "trouleshooting" part along with the config too.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t4/ftlswbri.htm#xtocid925510

Thanks...Tejal

[vijay-agrawal]

Dear Tejal,

Thanks for your suggestions but I have one concern, mine is a Leased line while the debugging options you have suggested are for dial-up one, also I am using default (HDLC) encapsulation.

Please suggest what to do now?

Thanks

Vijay

[vanwijk]

Are you sure you configured them as LL. If they are not configured as LL the line goes up and down whenever packets needs to be transmitted, like in normal ISDN-operation

Edwin van Wijk

[vijay-agrawal]

Yes Edwin, I am sure I have configured them as 128 Kbps LL. The command used was isdn leased-line BRI1/0 128. Now what next?

Vijay

[jinhong-im]

When I was implementing ISDN network 5years ago with 2503 as back-up network; primary was frame-relay, I experienced such a problem so many times. But only the causes to run abnormal was switch problem such TDX1b or TDX10. At that times TDX network was so instable. The TDX symptoms were;

- not release a call without TDX's card reset.

- not call estabilish randomly.

- not route a call setup message to destination at certain TDX on the routing way.

It was found out software problem of TDX, but it couldn't solved easily.

Finally I gave up ISDN network as a back-up.

Please check TDX switch with network provider, if your configuration is accurate.

If you have any questions feel free contect at jinhong.im@cylink.co.kr

Cheers

[andreas.richter]

Hi Vijay,

I would recommend to configure ppp multilink with authentication chap. The ISDN leased line configuration always causes problems, because the two b-channels might not have delay.

Andreas

[vijay-agrawal]

Dear Andreas,

Thanks for your concern but I am unable to relate "delay", can you please explain what type of delay your are refering to? Is it some sort of delay from Telco switch or some other.

Also, I am using default HDLC encapsulation with single 128 Kbps config instead of two subinterfaces of 64K each.

I also noticed CPUHOG messages in case of link down.

Please help.

[dong-lee]

Have you try to set the "isdn switch-type"? It isn't really necessity for a leased line, but sometimes it just works.

If that doesn't help, try an upgrade to a more recent IOS, there have been

a number of bugs concerning isdn leased lines.

Good Luck

Dong

[vijay-agrawal]

Yes Dong, isdn switch-type is already set to basic-net3. Presently I am running 12.2(7)b, enterprise version.

The same behavious is happening with 12.0 & 12.1 images.

[vijayagrawal]

I had tried changing the router and ISDN module, it didn't helped.