Problem with Drop and Insert

Unanswered Question
Aug 2nd, 2007

Hi all

I am configuring "Drop and Insert" in VWIC2-2MFT-T1/E1 on router 3845.My topo follos: PBX--R3845---Wan(voice and data)---R3845---PBX.

After configuring, Voice and data is OK. I can make a phone call and ping successfully. But Fax and Modem analog do not work. I don't know why?

Please help me.


I have this problem too.
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Paolo Bevilacqua Thu, 08/02/2007 - 23:58


Hi, check out, there is special configuration to make fax/modem work reliably over VoIP, namely fax and modem relay. Just search CCO and begin reading.

Note: this is not really Drop & Insert application.

Thucnk_FPT_FIS_6 Fri, 08/03/2007 - 17:22

Hi p.bevilacqua.

I think you don't understand my idea. The 3845 Routers are connected to Switchs. I used 15 channels for Voice and 15 channel for Data in WAN link.

Detail about my topo:




I configured Drop and insert in VWIC2 on 3845Routers. One VWIC connects to PBX, the other connects WAN.

Sample configure file in a R3845:

controller E1 0/0/0

framing NO-CRC4

ds0-group 0 timeslots 9-15,25-31 type e&m-wink-start dtmf dnis

tdm-group 1 timeslots 1-8,17-24 type e&m

description Tuyen E1 tra ve Tong dai


controller E1 0/0/1

framing NO-CRC4

clock source internal

channel-group 0 timeslots 9-15,25-31

tdm-group 1 timeslots 1-8,17-24 type e&m

description Tuyen E1 di DN


connect TDM_to_Data_DN E1 0/0/0 1 E1 0/0/1 1

interface Serial0/0/1:0

description Ket noi den trung tam vung Da Nang

ip address


Paolo Bevilacqua Sat, 08/04/2007 - 03:50


Could be a clocking problem, please send "show controllers e1" and check inf PBX and SW wants internal or external clock.

you wiol need "network-clocks-participate" and network-clocks-select" to define how you are using clock in this design. Likely, source from the E1 circuit and give to PBX and switches.

Thucnk_FPT_FIS_6 Sun, 08/05/2007 - 18:00

Hi p.bevilacqua.

In R3845, The E1 port ,Which connects PBX , is set Clock source internal. The other(to WAN) is set clock source line. I also used "network-clock-participate wic 0" .

I think If clock encounter problem , I can't ping Successfully and make a phone call.

Please,Give me more your ideas about this.


Paolo Bevilacqua Mon, 08/06/2007 - 01:46

well, if the problem with modem and fax happens to on the PBX that are using VoIP, as I said initially you must do special configuration, T.38 for tax, and modem realy for modem. In any case, check "show controller e1" for slips.


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