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Cisco Call Manager Attenuation

illfusion82 asked
Medium Priority
Last Modified: 2012-08-13
We have Cisco Call Manager and Cisco IP Phone 7940 series. We have been experiencing issues with static calls intermittenly through out the day. Would modifying the input gain and output attenuation make a difference on the static calls? What is the recommended settings for the input gain and output attenuation.
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input gain and output attenuation are used in analog solutions, if the issue is on an ip based call there really isn't a way to adjust that.
To assist with your issue we will probably need a better idea of what the nature of the problem is. are the users experienceing static between ip phones at one site, ip phones at different sites or ip phones out to the PSTN?
Is this occuring on all phones or a few? On the phones that it is occuring on, does the issue persist when the call goes to the speaker?
If none of those questions have gotten you closer to isolating and resolving the issue, then we will need more info about the specific calls themselves.
when a user is on a call you can get real time call detail reporting from the phone that can assist you in troubleshooting the issue. To get access to the call session details on a call that is presenting issues, hit the "?" button twice in rapid succession. It will give you a bunch of stats, what is of interest would be the jitter and the lost packets. can you let us know what you are getting for these on a bad call? also what is the average ping time from the ip address of one phone to another during a time where there are issues?
more often than not static is an artifact of an analogue connection, this could be the result of issues outside of your network that would show up as errored or slipped seconds on a PRI/BRI interface. There could be contention on an oversubscribed circuit going inbetween sites and QoS needs to be implemented. There could be the cable on a handset that is getting ready to give up the ghost.

hope this helps,



Thanks for the information. The issue is with IP phones to the PSTN. We run a call center and customers call in to us; we experience static calls intermittently, maybe five to ten calls a day out of a couple hundred. The issue happens on random phones.

what kind of PSTN connection(s) do you have and are the calls coming in on the same circuits or different ones? look at the call details and for a bad call and see what it shows. you can also add QRT to the template for your phones so if a call has issues then they can select the QRT soft button and identify the issues on the call with a simple menu. the call manager will flag the call for further investigations.

hope this helps,



I'm not sure how to check what type of PSTN connection we have. All the calls do come in on the same circuit. I have informed people in the office to check the call details when they experience static calls. I will let you know the results.

for the type of PSTN connection is it terminated on a cisco router or something else? if it is a serial interface on a cisco router, what doe the show interface serial ?/? show you? are there any errors?



Yes it is terminated at the Cisco router. Below is what came up when I did sh int serial 0/2/0:23

Serial0/2/0:23 is up, line protocol is up (spoofing)
  Hardware is DSX1
  MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, loopback not set
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops)
     Conversations  0/1/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 48 kilobits/sec
  5 minute input rate 0 bits/sec, 1 packets/sec
  5 minute output rate 0 bits/sec, 1 packets/sec
     4199572 packets input, 48077393 bytes, 0 no buffer
     Received 0 broadcasts, 1 runts, 0 giants, 0 throttles
     51 input errors, 51 CRC, 0 frame, 0 overrun, 0 ignored, 21 abort
     4197859 packets output, 28839663 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions
  Timeslot(s) Used:24, SCC: 0, Transmitter delay is 0 flags
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