[Asterisk-Users] What is acceptable network latency forvoipconnection?

Sun Jan 9 15:47:48 MST 2005

In the real world (or at least in my world) we use undersubscribed
internet connections that come with a service level agreement (SLA) that
guarantees that the jitter, delay, and packet loss with be within
defined parameters in the service agreement.

With most DSL and Cable you will not get a SLA, with the cheapest T1s
you might get one, but the only penalty to the ISP if they do not meet
is a bill credit not to exceed some low $ figure. Read the SLA and
understand it before signing, and them hold them to the deal. A good SLA
states that if they don't meet the SLA (some percentage of the time) you
don't pay.

We use pingplotter, not sure if there is a Linux version, but I think
there is. Should not matter though as long as you have at least one
windows box on the network (and who doesn't?). Tune it to emulate you
RTP stack (you will need to do some web research to learn how to do
that).

> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com [mailto:asterisk-users-
> bounces at lists.digium.com] On Behalf Of Robert Augustyn
> Sent: Saturday, January 08, 2005 1:13 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: RE: [Asterisk-Users] What is acceptable network latency
> forvoipconnection?
> 
> Damon,
> Thanks for your comments.
> This seems like serious problem, how is it done then
> in real world? I cannot see any business moving to
> voip when you cannot control quality of service.
> Can you recomend any free programs which alow you
> analyze delay,jitter and packet loss?
> Once again thank you.
> robert
> 
> 
> --- Damon Estep <damon at suburbanbroadband.net> wrote:
> 
> > That "program" will be detected by your ISP within a
> > day or so,
> > determined to be a virus, and your service will get
> > disconnected...which
> > n turn will not help your latency or jitter at all.
> >
> > VoIP can tolerate a fair amount of latency; latency
> > over about 100ms is
> > heard as a perceptible delay resulting in a
> > connection that appears to
> > be half duplex.
> >
> > Jitter, on the other had, is the real enemy. Jitter
> > is the variation in
> > packet timing, for example, packet A arrives in
> > 80ms, packet B in 120ms,
> > and packet C in 70ms. The jitter for this scenario
> > would be 120ms-70ms =
> > 50ms. Of course the jitter time is only half of the
> > story, the number of
> > packets that are "outliers" in the RTP stream will
> > also have an impact.
> > Typical jitter measurements are stated as "average
> > jitter" which helps
> > masks the problem, if you have 100,000 consistent
> > packets in a row, the
> > 10 slow packets in a row, then back to consistent,
> > the 10 packets are
> > only .1% of the total but will be heard in the voice
> > stream as a dropout
> > (the exact number of slow or dropped packets the can
> > be tolerated in a
> > row is determined by the RTP settings and the
> > devices packet buffers).
> >
> > There are only two ways to get acceptable
> > performance;
> >
> > 1. use a private or managed link between your VoIP
> > endpoints and
> > prioritize the RTP streams between the endpoints,
> > leaving the jitter,
> > delay, and packet loss for the data apps.
> > Or
> > 2. use public unmanaged links that are way
> > undersubscribed so there is
> > never any contention for bandwidth, because
> > contention for bandwidth is
> > he number one cause of jitter, delay, and packet
> > loss.
> >
> > Most consumer broadband systems do not fall into the
> > undersubscribed
> > category whereas most T1 and above commercial
> > services are much closer
> > to undersubscribed. I have seen cable systems and
> > DSL networks that are
> > oversubscribed at more than 100:1. (too much...).
> >
> > So the short answer to the question, 100ms or less
> > is desired, but
> > useless if accompanied by packet loss and jitter.
> >
> > There are programs you can use to analyze delay,
> > jitter and packet loss.
> > Search the web for a free one, tune the packet size
> > and rate to match N
> > (number of active alls) times your RTP parameters to
> > get a better
> > analysis. Run this for several minutes during a peak
> > period on your
> > network (7 to 9am and 7 to 10pm for consumer
> > broadband systems).
> >
> > The result you get is meaningful for that moment,
> > and is no indication
> > that you will continue to get the same performance.
> >
> > The real problem comes when cable operators and DSL
> > providers decide to
> > prioritize RTP for their VoIP customers over VoIP
> > traffic bound for
> > other providers when the oversubscribed links are
> > congested.
> >
> >
> >
> > > -----Original Message-----
> > > From: asterisk-users-bounces at lists.digium.com
> > [mailto:asterisk-users-
> > > bounces at lists.digium.com] On Behalf Of David Liu
> > > Sent: Saturday, January 08, 2005 8:01 AM
> > > To: Asterisk Users Mailing List - Non-Commercial
> > Discussion
> > > Subject: Re: [Asterisk-Users] What is acceptable
> > network latency for
> > > voipconnection?
> > >
> > > Well there is nothing much you can do if you don't
> > own all the routes.
> > > But in
> > > concept you can, and this is purely just
> > theoritical and a very
> > unhealthy
> > > thing for the Internet, is to write a program
> > running on your router
> > that
> > > constantly streams traffic to your end point, this
> > will maintain a
> > > constant
> > > bandwidth from your network to your far-end.
> > Then, your program
> > should
> > > detect
> > > within a few ms that you are setting a call up and
> > immediately reduce
> > your
> > > bogus traffic and make room for your "Real" voice
> > traffic.  Again this
> > is
> > > super unhealthy for the Internet, but the idea is
> > TDM on STDM -
> > constantly
> > > occupying certain trunks (bandwidth) on the
> > Internet.  So whenever you
> > > need
> > > it, you will have it.
> > >
> > > David
> > >
> > >
> > >
> > > On Sat, 8 Jan 2005 06:22:58 -0800 (PST), Robert
> > Augustyn wrote
> > > > Very good point.
> > > > So what can you do ( if anything ) to control
> > the load
> > > > on the network outside of your control?
> > > > robert
> > > >
> > > > --- David Liu <david at deltapath.com> wrote:
> > > >
> > > > > Assuming the network loading is fairly
> > constant,
> > > > > 300ms latency is actually not
> > > > > noticeable unless you put both phones next to
> > your
> > > > > ears to compare.
> > > > >
> > > > > Latency affects delay while network loading
> > affects
> > > > > voice quality (e.g. break
> > > > > ups) If the either end of your network is
> > > > > experiencing very bursty traffic
> > > > > patterns, then even a small latency won't
> > > > > necessarily guarrantee good sound
> > > > > quality.
> > > > >
> > > > > David Liu
> > > > > Hong Kong
> > > > >
> > >
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