VoiP Faxing, QoS, and MGCP Debugging

QOS always helps but may not be your problem. First, you always need to use G.711 as the codec for faxing and modem use, the reason is that that the voice signal (fax in this case) is  uncompressed. Using any other codec causes compression (removes parts of the signal), which causes problems with faxing.

Here is a link that is specific to some of your equipment:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t11/ft_ghost.htm

below is taken from the above link:

Modem and Fax Passthrough Switchover
When the gateways detect a data modem, both the originating gateway and the terminating gateway switch to modem passthrough mode. This switchover includes the following:

•Switching to the G.711 codec

•Disabling the high pass filter

•Disabling Voice Activity Detection (VAD)

•Using special jitter buffer management algorithms

•On detection of modem phase reversal tone, disabling the echo canceler

At the end of the modem or fax call, the voice ports revert to the previous configuration and the DSPs switch back to the original voice codec.

I have the codecs enabled and have been using them for quite some time.  I have g711ULAW enabled across the network.  No other codecs are enabled, with a few exceptions...

The pass through statements are part of my default config on all of the gateways.

Any configuration examples or troubleshhoting tips would be appreciated.

OK, without seeing actual configs, l will assume that all is well on the Western Front. So letys turn to some troubleshooting:

The Cisco 2420 is using a T1 for the WAN, what about the connection to the fax machines? Are you using another T1 or FXS ports? Can you hang a Cisco 2420 locally to the Softswitch, 6509 and Voice Gateway? What the goal is to do is to cut out the WAN portion out of the equation. If you can cut out the WAN and duplicate the problem then you know its something that is local, if not, then something about the WAN side (its a starting point).

Also, are you using G.726  at all? The 2420's have been know to fail during faxing when the codec is part of the configuration, even if it is not being used. You mentioned that you are using G.711 all except...remove the exceptions and see if problems clear up.

Also, if you are using FXS ports, try using a DTMF analyzer to see if DTMF digits are being distorted.

Keep me posted

I haven't had any problems with other T1 customers faxing.  Only very early on when we first implemented the platform, but since we ironed out those bugs, its been pretty reliable.  The WAN is T1, and this is a 16 Port FXS IAD.  

I looked at the Show MGCP, and there are 2 statements in there for G726...but it says dynamic, and it won't let me remove them...They are listed below:
MGCP Dynamic payload type for G.726-16K codec
MGCP Dynamic payload type for G.726-24K codec

Also, here is a copy of the config on the IAD at this customers site:

version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Router
!
enable secret 5 $1$UedP$0Dg7yOJ8pslL1iei3v6LV/
!
clock timezone Central -5
network-clock base-rate 64k
ip subnet-zero
ip cef
!
!
ip domain name domain.net
ip name-server xxx.xxx.xxx.xxx
ip name-server xxx.xxx.xxx.xxx
ip name-server xxx.xxx.xxx.xx!
ip audit notify log
ip audit po max-events 100
!
class-map match-all MGCP
  match ip precedence 4
class-map match-all RTP
  match ip precedence 5
!
!
policy-map T1_QOS
  class RTP
    priority percent 90
  class MGCP
   bandwidth percent 4
!        
!
!
voice call carrier capacity active
!
voice service voatm
 !
 session protocol aal2
 no voice detect
  vbd-playout-delay mode passthrough
!
voice service voip
 fax protocol t38 ls-redundancy 0 hs-redundancy 0
!
!
!
!
!
!
!
no voice confirmation-tone
!
!
voice-card 0
!
!
controller T1 0
 framing esf
 linecode b8zs
 channel-group 0 timeslots 1-24 speed 64
!
!
!
!
interface Ethernet0
 ip address xxx.xxx.xxx.xxx 255.255.255.252
 no ip mroute-cache
 no cdp enable
!
interface Serial0
 no ip address
 no ip mroute-cache
 shutdown
!
interface Serial0:0
 ip address xxx.xxx.xxx.xxx 255.255.255.252
 max-reserved-bandwidth 99
 service-policy output T1_QOS
 no cdp enable
!
ip nat inside source list 1 interface Serial0:0 overload
ip classless
ip route 0.0.0.0 0.0.0.0 Serial0:0
no ip http server
!
!
snmp-server community
snmp-server community
snmp-server enable traps tty
call rsvp-sync
!
voice-port 1/1
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/2
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/3
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/4
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/5
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/6
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/7
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/8
 description FAX 246-3330
!
voice-port 1/9
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/10
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/11
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/12
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/13
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!        
voice-port 1/14
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/15
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
voice-port 1/16
 echo-cancel coverage 32
 timing hookflash-in 750
 idle-voltage high
!
mgcp
mgcp call-agent  service-type mgcp version 1.0
mgcp modem passthrough voip mode nse
mgcp ip qos dscp cs4 signaling
mgcp playout fixed 60
mgcp package-capability rtp-package
mgcp default-package dtmf-package
no mgcp timer receive-rtcp
mgcp fax t38 inhibit
!
mgcp profile default
 timeout tsmax 40
 max1 retries 3
 max2 retries 5
!
dial-peer cor custom
!
!
!
dial-peer voice 1 pots
 application mgcpapp
 port 1/1
!
dial-peer voice 2 pots
 application mgcpapp
 port 1/2
!
dial-peer voice 3 pots
 application mgcpapp
 port 1/3
!
dial-peer voice 4 pots
 application mgcpapp
 port 1/4
!
dial-peer voice 5 pots
 application mgcpapp
 port 1/5
!
dial-peer voice 6 pots
 application mgcpapp
 port 1/6
!
dial-peer voice 7 pots
 application mgcpapp
 port 1/7
!
dial-peer voice 8 pots
 application mgcpapp
 information-type fax
 port 1/8
!
dial-peer voice 9 pots
 application mgcpapp
 port 1/9
!
dial-peer voice 10 pots
 application mgcpapp
 port 1/10
!
dial-peer voice 11 pots
 application mgcpapp
 port 1/11
!
dial-peer voice 12 pots
 application mgcpapp
 port 1/12
!
dial-peer voice 13 pots
 application mgcpapp
 port 1/13
!
dial-peer voice 14 pots
 application mgcpapp
 port 1/14
!
dial-peer voice 15 pots
 application mgcpapp
 port 1/15
!
dial-peer voice 16 pots
 application mgcpapp
 port 1/16
!
rtr 1
 type jitter dest-ipaddr xxx.xxx.xxx.xxx dest-port 32726 interval 1
!
line con 0
 exec-timeout 0 0
 password
 login
line aux 0
line 2 3
line vty 0 4
 exec-timeout 0 0
 password
 login
!
ntp clock-period 17207587
ntp server xxx.xxx.xxx.xxx prefer
end

Thanks,

Parry

Just toook a quick look at the config: since we are looking for the needle inthe haystack, I want to summarize:

Clients faxes randomly fail, more so when they are over one page long?

The clients fax machines are connected directly to the Cisco IAD FXS port?

Voice quality is good for VoIP based calls?

T1 network between you and clients (by the way how many clients) point-to-point?

Are all the T1's terminated on the same carrier? How large is the geographical region?


There are a few things that jump out at me that I would change. I am going to wait for your response prior to adding thoughts. This way my answer will be more specific to your enviroment.

One more question, do you happen to know what type of fax machines your clients are using?

Your summary is correct......All clients are Point-to-Point T1's....Using Multiple Carriers, but of course 90% still traverse the SBC Network....Geographic Area is Indianapolis and some of the outlying areas....

This particular fax machine is a Canon 4000....There are 2 letters before the 4000, but cannot remember what they are.

I just got back from this customers site, and I found some interesting cabling on the T1 extension from the demark.  At the smartjack, the jack was wired as follows:  
Smart Jack Side:  Pin 1:  White-Orange,  Pin 2:  Orange,  Pin 4:  White-Green,  Pin 5:  Blue
Extension Side:  Pin 1:  White-Orange,  Pin 2:  Orange,  Pin 4:  White-Blue,  Pin 5:  Blue

I don't know how this T1 was working at all...After seeing that only 3 wires were actually connected...and the T1 was not taking errors.....

I reconnected it with 1, 2, 4, & 5 straight through as it is supposed to be, and I was able to send the following faxes to multiple places:  2, 5, 7, 10, 15 Pages.... All went through....

The customer is going to let me know tomorrow what their sucess rate was for the day, and tomorrow morning.

Please let me know what your additional thoughts are.  Also if you happen to know how to interpret MGCP Debugs, a little lesson on that would be appreciated...

I appreciate all of your help..

Parry Sands

The fax is on Port 8, if you look at the config, I have it at its defaults.  Idle voltage-Low, and I don't remember what the default HookFlash is.

I really appreciate all of the help and the info...I will definately try to get a copy of the Telcom book you mentioned.

Also, I tried to duplicate the problem after I fixed, but it would never come back up....Had to be just a fluke with the original wiring.  I re-used the cable, just cut off the ends and re-wired it....so I don't have the original cable anymore...

I look forward to seeing the MGCP info....Just curious...Do you work for Cisco ?

No on working for Cisco, but my last name throws most people off. I have done alot of Telecom engineering across the country the past 13 years, worked on just about everything (Cisco, AT&T, Nortel, AVAYA, etc). In regards to debugging I found a good link from Cisco with sample debugs, but prior to viewing that, you need to understand the MGCP protocol. Also, if you are not familar with the basic telecom skills of call setup and teardown, Cisco also has a good link for that information also. Once you go thru this all of this I can answer any questions you may have to help clarify.

The Netwon Telecom book is great, he is on the 20th edition I think, I strarted with the 10th edition, it has changed over the years as the technology evolved.

Here is a list of links to keep you busy this weekend:

http://www.protocols.com/pbook/VoIPFamily.htm    basic overview of VoIP

http://www.cisco.com/warp/public/788/signalling/net_signal_control.html      basic telecom link

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a0080174804.shtml    debug sample

http://www.cisco.com/application/pdf/en/us/guest/products/ps5037/c2001/ccmigration_09186a008011bd39.pdf   all of IOS voice commands

MGCP rfc's below

http://www.faqs.org/rfcs/rfc2705.html
http://www.faqs.org/rfcs/rfc3525.html
http://www.faqs.org/rfcs/rfc3660.html
http://www.faqs.org/rfcs/rfc3661.html 

http://www.protocols.com/pbook/VoIP.htm

Thanks....I'll go ahead and close out this topic, and award you the points...It might take a while to get through all of the docs listed here....

Should I post specific questions about MGCP here, or should I contact you a different way ?

Thanks Again for all of the help..

Parry

I am not sure about direct contact (postingpersonal emails) or if you can send emails to my account here at the EE. But I do monitor the entire site for VoIP based questions. Contact the EE admin to see what the exact policy is. But I do believe that you can post addtional comments for this thread even after you award/close it out.

With all the docs, go thru the Cisco link on basic telecom in a detailed manner. The rest you can skim thru and focuss on what is most important for your application. Remeber that H.323, SIP, MGCP are the all encompassing protocol suites, and that there are many protocols that make up the suite. This is why I am stateing not to go crazy on those at first, the basic telecom link will have the most impact since all of the above protocols were develeoped from the foundation of basic telecom communications which is covered in the basic link (my opinion).



Kindest regards,

Joel

Thanks Again...

Parry

Just remebered one of my older books that actually has been updated, great book on T1's then and sure its even better now.


Guide to T-1 Networking: How to Buy, Install & Use T-1 From Desktop to Ds-3
by William A. Flangan


Joel