ISDN data calls unable to pass PPP

[tom.storey]

Hi everyone.

Im testing out some configuration in my lab where I am attempting to use a Cisco 3825 for PSTN simulation and dialup termination.

In this 3825 I have a VIC2-2BRI-NT/TE configured to emulate network, and connected to this is a WIC-1B-S/T-V3 in an 1841.

Also in the 3825 is a VWIC-2MFT-E1-DI configured to emulate network, and connected to that is an NM-CE1T1-PRI. Furter to that is an NM-30DM.

The topology looks like this:

[1841 (bri0/0/0)] <-> [3825 (bri0/0/0)]
                     [3825 (se0/1/0:15)] <-+
                      [3825 (se1/0:15)] <--+

When attempting an analogue from an old school modem connected to the aux port of the 1841 via an FXS port in the 3825, I am able to successfully establish a dialup connection to the NM-30DM.

Now Im attempting to get ISDN data calls working, but I seem to be hitting a snag where, although the ISDN call appears to complete succesfully, and I then subsequently see both ends TXing PPP packets, neither end is receiving PPP from the other side.

Attached is the output of debug isdn q931 on the 3825 showing what I believe is the successful setup of a 64k ISDN data call.

Also attached is the output of show isdn status showing all of the individual ISDN interfaces and what they are doing.

And finally attached is the config from both of the boxes.

Can anyone point me in the direction of what Im missing, either config or knowledge wise? I did a little research over the last couple of weeks and discovered that the 2800 and 3800 platforms are supposed to be capable of TDM switching. In my admittedly limited knowledge I would have thought this to mean that I should be able to switch calls natively between ISDN interfaces, but I am wondering if there is some kind of incompatability with the VIC2-2BRI-NT/TE where it just wont pass the payload of an ISDN data call?

Im not trying to terminate ISDN calls on the VIC, but using a dialpeer Im switching them out of the VWIC which lands them on the NM where they should be terminated.

Any pointers appreciated. Im at a loss trying to work out why PPP cant seem to make it across the circuit.

Thanks!

[brett.harding]

Could you include a ppp negotiation and chap debug?

Some thoughts .... on the 3825 have you tried;

interface BRI0/0/0
 encapsulation ppp
 isdn incoming-voice data
!
interface Serial0/1/0:15
 encapsulation ppp
 isdn incoming-voice data

[tom.storey]

Hi Brett,

I played around with a few different combinations of encap ppp on all of the interfaces, but I didnt try isdn incoming-voice data on both at the same time. Didnt think that would apply to calls going out of an interface? Will try that later today though.

Will also get ppp debugs.

Thanks!

[tom.storey]

interface BRI0/0/0
 encapsulation ppp

This isnt supported because its a VIC, and now I remember I did try that.

I tried all other commands and same result.

Attached is debug ppp nego/authen results, though its not getting past the nego stage, so theres nothing related to authen.

Something I do see is a lot of input/crc/frame errors on the Se1/0:0 and Di0 interfaces, which would be the two extremeties of the circuit I guess. No errors anywhere in between on any other interfaces though...

The uncommon portion of the circuit was the BRI connection, so I tried swapping out the VIC2-2BRI in the 3825 which made no difference. Unfortunately I dont have a spare WIC-1B to swap out with at the moment.

[brett.harding]

Hi Tom,

Yes, I think it might be worth checking to see if your VIC module can actually support data calls. Based on the debug output we can see that the PPP state never transitions from ESTABLISHING to AUTHENTICATING. We see outbound PPP configuration request (CONFREQ) packets, but we never see any inbound PPP packets (CONFACK or CONFREJ) and finally LCP times out.

[tom.storey]

After a bit more playing I have managed to successfully establish data calls through the VIC-2BRI, but what I had to do was to use a VoIP dial peer to another router where I have an E1 VWIC which is then in turn connected to the 3825.

In this configuration, it works 100%, though not necessarily ideal as a lab solution if I need two routers just to accomplish this.

So it seems possible, if only I could get it all to work in one box with TDM!