[Asterisk-Users] Optimum online-upload throttling confirmed.

[Jeff Heath]

On Thu, 2005-08-18 at 21:08, gw at adcomcorp.com wrote:
> Hello All,
> I was recently fighting with an optimum online connection in NY.
> 
> I finally got in touch with someone that confirmed they are throttling
> my upload connection.

I know they watch for people doing peer to peer file sharing and
throttle those connections quite severely, but I wasn't aware that they
do general throttling.
> 
> I just wanted to make everyone aware of it, so if you have problems if
> your ping times jump erratically, this could be the cause.
> 
> Their suggestions were, although you can upload a lot, do not do it
> constantly.  They do not want any constant outgoing connections.
> 
> Even on business class, they do throttle.  All business class primarily
> does is allow port 25 to pass.
> 
> Now I am going to look and see if I can get a decent upload speed dsl or
> something to correct this problem.

I have a friend who uses Vonage (on a ComCast cable modem, not
Cablevision) and many times when I talk to him, the voice quality is
bad.  The reason is the way that _all_ cable companies deploy their data
services (it's a CableLabs DOCSIS standard that they all use).

Remember that cable modem networks are shared media.  The downstream to
the cable modem is a broadcast and each cable modem listens for traffic
to it.  No latency problems here. However, on the upstream, each cable
modem requests permission to send and then the cable modem termination
system (CMTS) grants it a token to send.  Very significant latency and
jitter problems here for VoIP.

For their own service offerings, the cable companies solve the problem
by identifying the VoIP call flows during the call setup and scheduling
the media packet stream (RTP packets) grants in advance.  Therefore,
when I use my Cablevision optimum voice line, my RTP packets are given
special priority and the latency and jitter problem is solved.  But if
you are using Vonage or your own Asterisk box, your RTP packets are
treated the same as any other data packet.  Not good for VoIP quality. 
And the problem becomes very bad when the network gets busy.

The bottom line is that I wouldn't try to use any cable modem service
(ComCast, Cox, Time Warner, Cablevision, doesn't matter) for a VoIP
service where voice quality really matters a lot.

> 
> Regards,
> Greg
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