SIP latency

Discussion in 'UK VOIP' started by Theo Markettos, Jul 29, 2013.

  1. Been doing some traceroutes of SIP providers and thought folks might be

    Hops Host Loss% Snt Last Avg Best Wrst StDev

    15. (voxbeam)0.0% 36 117.1 119.5 115.9 129.5 3.5

    13. 0.0% 49 29.5 32.2 28.6 53.7 4.7
    17. (Betamax) 0.0% 34 33.1 35.2 31.9 43.8 2.8

    15. 0.0% 35 40.8 36.5 31.5 66.5 6.3

    11. 0.0% 36 14.8 14.4 11.0 26.8 3.3
    (12th hop doesn't reply to traceroute, this could be incomplete)
    12. 0.0% 31 24.5 26.2 22.3 33.3 3.3
    11. 0.0% 40 16.1 20.6 15.4 34.0 4.6

    Anycast, geolocate says Mountain View:
    14. 0.0% 35 28.3 26.4 23.2 38.2 2.8
    (Google Voice)

    Setup is Virgin Media cable connection in Cambridge, takes ~14ms and 7 hops
    from my machine to exiting * About 1ms of that is local.

    It's an interesting thought... if you pick the wrong SIP provider you end up
    with 200ms more latency. Though you never know what the routes do beyond
    the provider.

    Theo Markettos, Jul 29, 2013
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  2. These are statistics for ICMP echo, not for SIP, or what you probably
    meant, RTP. ICMP echo is likely to be given low priority for
    transmission, and high priority for being discarded, compared with even
    non-QoSed RTP. (It is unlikely that a mass market ISP would honour QoS
    on SIP or RTP, as it would be too open to abuse for non-VoIP traffic,
    but they are still likely to give ICMP echo lower QoS.)

    If you want to provide statistics for RTP, use the QoS monitoring tools
    in your SIP user agents. This will give information for both directions.
    David Woolley, Jul 30, 2013
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  3. Fair point, though I don't have accounts in those places to be able to set
    up SIP calls. Does anyone post such stats from active calls?

    Theo Markettos, Jul 30, 2013
  4. Indeed, there's a fairly good relationship. My point is it's not entirely
    obvious for some... eg Betamax (Swiss company trading via Luxembourg routes
    from Netherlands), or is actually in Germany (but
    is in the US). Not that Europe really matters, but a transatlantic
    roundtrips starts getting annoying. Particularly if it's on top of the VOIP
    routing - caller/UK-US-callee/UK-US-caller/UK where there are 4x
    transatlantic transits for every echo.

    Theo Markettos, Jul 30, 2013
  5. Theo Markettos

    Nick Guest

    The point is obvious but for RTP not SIP. I just checked (with
    wireshark) and is indeed running RTP apparently out of
    Dussledorf (from a uk pots call) .

    If the distance/delay relationship were dominated by the speed of light
    I would expect this to introduce a delay of ~4ms. However I actually
    expect this distance/delay relationship is dominated by electronic stuff
    (maybe boosters/routers/switches).

    Personally I can live with the extra 20ms I see on ping
    Nick, Jul 31, 2013
  6. If a packet network isn't somewhat congested, it isn't being used
    David Woolley, Aug 15, 2013
  7. Theo Markettos

    Stephen Guest

    In practice speed of light approximation we use at work for fibre is ~
    2/3rds of vacuum

    The useful rule of thumb is 1 mSec per 100 Km round trip
    The paths use for IP bear some relationship with distance - but what
    matters is the path used for the fibre and those tend to meander
    Not usually over continent sized WANs
    - a lot of the traffic rides over lambdas on the fibre, with
    amplification as colours, and only store and forward delays at a
    - since the high end routes will be carried in 10 Gbps+ pipes those
    get fairly small.
    - forwarding latency through a high end router is usually small
    numbers of uSec as well, so the route distance dominates.
    some of which is probably down to dejitter buffers and software delays
    in the end points......
    Stephen, Aug 18, 2013
  8. Theo Markettos

    Nick Guest

    Um, yes I had forgotten the refractive index of glass.
    Fair enough. So I guess it applies to 6000km to Orlando but not so much
    to the 450km to Düsseldorf.

    Wouldn't they be present in all connections. So if my connection is 20
    ms to a local connection and 40ms to Düsseldorf that would already be
    accounted for? Actually I hadn't realised any thing apart from my voip
    software implemented a jitter buffer.
    Nick, Aug 18, 2013
  9. That depends on where the PSTN breakout is. For example:

    (and the same again for the receive channel)

    won't be able to optimise the path. Occasionally VOIP calls terminating on
    the PSTN get 'international' CLID - I have no idea where they originate
    from, but US might be a possibility.

    Theo Markettos, Aug 19, 2013
  10. Theo Markettos

    Stephen Guest

    Even there.

    remember there is the North Sea in the way - they will be using a
    subsea cable, or fibre thru the Tunnel etc

    A lot of routes go between the "national carrier hotels" once they get
    past the landing stations - some of the subsea bits:

    so maybe London -> France via Tunnel, -> Paris / Amsterdam ->
    Frankfurt (everything to Germany seems to go via Frankfurt) 1st.....
    ordinary applications dont.

    Lots of the audio / video stuff at work does since IP and variable
    latency is a new complication for a codec :)
    Stephen, Aug 21, 2013
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