[Asterisk-Users] MTU and Voice Delay (latency??)

[pdhales at optusnet.com.au]

We had phones in Perth hooked up to an Asterisk box in Melbourne, and the call was fine - so I know it can be done.

PaulH
  ----- Original Message ----- 
  From: Rusty Dekema 
  To: Asterisk Users Mailing List - Non-Commercial Discussion 
  Sent: Tuesday, January 10, 2006 11:02 AM
  Subject: Re: [Asterisk-Users] MTU and Voice Delay (latency??)


  How far (physically) is the Asterisk server location from the location of the phones? Have you tried pinging the Asterisk server from the network to which the phones are connected? 

  As a rule of thumb, If the two sites are within 2500 miles of each other and the network connection between them is working properly, the round trip time for a 64 byte ping should be less than 100 ms, the round trip time should not vary from one ping to another by more than 2-5 ms (typical), and there should be virtually no dropped packets (well under 0.1%). 

  If your network does not meet these standards, then it may well be the cause of your problems. In that case, if you e-mail me a traceroute from the phone location to the Asterisk location as well as the output of a ping from the phone location to the Asterisk location (preferably including at least 100 repetitions), I will take a look at it and let you know what I think. 

  If your network seems fine by the above standards, then you/we will have to pursue other Asterisk/SIP/RTP-related avenues of troubleshooting. 

  Regards,
  Rusty




  On 1/9/06, Geoff Manning <gmanning at zoom.com> wrote:
    Our users are experiencing some unacceptable delay when trying to have a
    conversation. The delay is so noticeable that they keep stepping on each
    others words and resort to calling the customers via cell phone.

    Here is the setup

    SDSL Connection (PPPoA)
    Speedtouch 610 SDSL Modem
    3Com 2224PWR Plus Switch (phones on separate VLAN)
    8 Cisco 796 Phones

    All connecting to a remote Asterisk Server.

    We found that the MTU for the SDSL modem was set to 1500 and I have since 
    changed it to 1458 which is the ISP's recommended setting.

    Can this MTU difference cause the delay my users are experiencing? All the
    voice packets would become fragmented so it sounds logical.

    And simply changing the MTU on the modem, will that fix it, I can't find a 
    way to change it at the Cisco phone level.

    Thanks,
    Geoff Manning

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