[Asterisk-Dev] E1/PRA connection to existing PBX with Asterisk - SETUP ACK with Suggested Channel ID missing ?

Pertti Pikkarainen ppik at lanwan.fi
Tue Dec 2 13:50:56 MST 2003

I have seen this just recently with a setup that is quite close to the 
one you are using.
The problem happened when I tried to upgrade all: Zaptel, Libpri and 

PSTN -----Asterisk ---[existingPBX]

PSTN <-> SIP   Worked ok both ways.

PSTN <- * <- PBX  The same problem ( Missing mandatory IE ... )

At that time I downgraded back to  CVS-09-29
and got it working again. Probably Libpri would have been enough.

Then again I have exactly the same setup elsewhere where
the PBX is running the latest software. There I'm able to
use the latest CVS.


Nicolas Dramais wrote:

> Dear Asterisk experts,
> I would like to draw your valuable attention on the following 
> situation to see whether some of you have encountered it before and 
> have found solutions / workarounds.
> We want to place Asterisk behind an existing PBX (connected to the 
> PSTN) using an E1/PRA line.
> PSTN -- Telco E1 -- [existing PBX] -- E1/PRA -- [Asterisk+Digium 
> E100P] -- SIP phones
> We observe the following behaviour:
>     * in the call direction "Asterisk" to "existing PBX" (SIP phone
>       calling out to PSTN), it works great
>     * in the call direction "existing PBX" to "Asterisk" (PSTN user
>       calling in to SIP phone), we get the following error on the
>       Asterisk console:
>WARNING[11276]: File chan_zap.c, Line 5719 (zt_pri_error): PRI: XXX
>> >>>>Missing mandatory IE 24/Channel Identification XXX
>     * in the call direction "existing PBX" to "Asterisk", we observe
>       that the Q.931 SETUP message sent by the "existing PBX" doesn't
>       contain a channel identification IE
> We double-checked the Q.931 SETUP format on DSS1 specification and we 
> found that the Channel Identification is: "Mandatory in the 
> network-to-user direction. Included in the user-to-network direction 
> when a user wants to indicate a channel. If not included, its absence 
> is interpreted as 'any channel acceptable'." (section 3.1.14, note 4).
> We assume that the call direction "existing PBX" -> "Asterisk PBX" is 
> "user-to-network", which means that the channel identification IE is 
> optional in SETUP messages sent by the "existing PBX", meaning 'any 
> channel acceptable'.
> (Asterisk is configured to play the NETWORK side with 
> "signalling=pri_net" in zapata.conf)
> However, Asterisk doesn't seem to want to select a channel and return 
> it to the "existing PBX" in the SETUP ACK (as does a Cisco gateway in 
> the exact same configuration).
> In conclusion, it seems that the functionality to answer a call 
> without a given channel is not there in Asterisk and we think missing 
> this functionality is critical as we believe the above scenario is an 
> important and likely usage scenario for many people.
> Can someone please confirm the above observation ?
> If yes, does anyone (Mark ?) have plans to add that functionality into 
> Asterisk in the near future ?
> We'd be happy to help beta test it .
> Thank you all in advance for your answers and thank you all anyhow for 
> the great work you've done with Asterisk.
> Best regards,
> Nicolas Dramais - Belgium

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