01-09-2008 07:22 AM
Friends,
I am currently working on voip setup. With the existing tdm network, dialup
users from different sites dial Remote Access Server in central site. When i
will put routers into that network, can users be able to connect again via
voip setup. Topology includes cisco 3800 routers that connect with Ericson
MD110 pbx through E1 (Pri Qsig). Routers are connected point to point
through E1. RAS is non-cisco.
Existing Topology:
IP Network ---------RAS------------PBX--------------------------------------------PBX--------------Dialup
User (Modem)
Topology after voip setup:
IP Network
---------RAS------------PBX---------Router-----------------------------Router--------PBX--------------Dialup
User (Modem)
With some study i come to know that there is concept of modem passthrough
that can be used but someone please explain it briefly. And if someone
currently using it, please write down a sample configuration according to my
voip topology.
Best Regards
01-09-2008 10:55 AM
01-14-2008 12:44 AM
Friends,
I configured routers with for modem passthrough. When my modem dial RAS number, It starts negotiation with RAS but keep negotiate and not connected. Means repeat negotiation again and again till timeout. Once it surprisingly connected but within 30 sec it disconnected. Network Topology below:
RAS--------PBX-----Rt-A--------------------Rt-B----PBX-----------DialupUser
And Configuration below:
hostname Rt-B
isdn switch-type primary-qsig
voice service voip
modem passthrough nse codec g711alaw
controller E1 0/0/0
channel-group 0 timeslots 1-31
controller E1 0/1/0
pri-group timeslots 1-31
interface Serial0/0/0:0
ip address 10.0.0.2 255.255.255.252
interface Serial0/1/0:15
no ip address
encapsulation hdlc
isdn switch-type primary-qsig
isdn overlap-receiving
isdn incoming-voice voice
isdn bchan-number-order ascending
no cdp enable
router ospf 100
network 0.0.0.0 255.255.255.255 area 0
dial-peer voice 786 voip
destination-pattern 786$
modem passthrough nse codec g711alaw
session target ipv4:10.0.0.1
no vad
!
dial-peer voice 785 pots
incoming called-number 786$
direct-inward-dial
port 0/1/0:15
-------- Router A ---------
hostname Rt-A
isdn switch-type primary-qsig
voice service voip
modem passthrough nse codec g711alaw
!
controller E1 0/0/0
channel-group 0 timeslots 1-31
controller E1 0/1/0
pri-group timeslots 1-31
interface Serial0/0/0:0
ip address 10.0.0.1 255.255.255.252
router ospf 100
network 0.0.0.0 255.255.255.255 area 0
dial-peer voice 786 pots
destination-pattern 786$
direct-inward-dial
port 0/1/0:15
forward-digits 3
!
dial-peer voice 785 voip
modem passthrough nse codec g711alaw
incoming called-number 786$
no vad
Note: i omit all unnecessary configuration.
Waiting for your immediate response.......
Best Regards
01-14-2008 07:26 AM
OK from what you are saying it sounds like there may be some issue with the RTP stream itself. Modem and fax calls are vary vary sensitive to jitter, concealment , and packet loss - things you would not even notice in a voice call.
I would suggest using modem relay instead of passthorugh:http://cisco.com/en/US/products/sw/iosswrel/ps5207/products_configuration_guide_chapter09186a008053b58c.html
If you still have issues, use show call act vo or sh call hist and see what the RTP stats are for the call.
01-15-2008 09:13 PM
Sir,
I studied about modem relay and come to know that it can support maximum 33 kbps speed that is not acceptable for our us due to some limitations. If you can assist me for modem passthrough, i will be thankful.
Best Regards
01-16-2008 07:01 AM
I Understand....
You will need to look at the RTP stream itself then either by capturing statistics for the call with sh call act or after the call is complete with sh call hist. A sniffer capture of RTP in both directions would tell you the same thing. For modem to passthrough to work as well as you are expecting, that RTP stream needs to be as close to flawless as you can make it.
Hope this helps.....
01-16-2008 07:01 AM
I Understand....
You will need to look at the RTP stream itself then either by capturing statistics for the call with sh call act or after the call is complete with sh call hist. A sniffer capture of RTP in both directions would tell you the same thing. For modem to passthrough to work as well as you are expecting, that RTP stream needs to be as close to flawless as you can make it.
Hope this helps.....
01-16-2008 07:03 AM
I Understand....
You will need to look at the RTP stream itself then either by capturing statistics for the call with sh call act or after the call is complete with sh call hist. A sniffer capture of RTP in both directions would tell you the same thing. For modem to passthrough to work as well as you are expecting, that RTP stream needs to be as close to flawless as you can make it.
Hope this helps.....
01-17-2008 08:34 PM
Thanks again for responding. I will analyze rtp stream but i forget to tell you that all routers and BPXs in a same lab so no delay, congestion and media at all. Tell me, are there any other commands beside these for modem passthrough or commands to tweak it???
Thanks Again for your assistance.
Regards
01-18-2008 05:33 AM
Can you do a 'sh controller e1' and post the result in here please. Also post the complete SH RUN of both routers as well.
If you see any clock slips on the E1 interfaces of either controller, then this will be what is making the modem passthrough fail.
Why ?
http://www.cisco.com/en/US/products/hw/routers/ps259/products_tech_note09186a008031a072.shtml
If this is due to slips, it should be easy to clear them once we see the configs.
01-18-2008 09:26 PM
Dear pcameron/crieman,
Thank again for reply. I am on leave for few days thats why i cann't perform steps you mention above. I will get you back very soon..
Thanks & Regards
01-30-2008 06:47 AM
01-30-2008 07:00 AM
Hi - yes you have some clock slips here, you will need to use the network-clock-select commands (and show network-clocks) to eliminate them.
http://cisco.com/en/US/products/hw/routers/ps259/products_tech_note09186a008031a072.shtml
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