What vexes VoIP users?
frnkblk at iname.com
Tue Mar 1 23:55:16 CST 2011
Are you saying that the large MSOs don't use CM configuration files that create separate downstream and upstream service flows for Internet, voice signaling, and voice bearer traffic?
From: Scott Helms [mailto:khelms at ispalliance.net]
Sent: Tuesday, March 01, 2011 8:35 AM
To: nanog at nanog.org
Subject: Re: What vexes VoIP users?
offered through the various broadband providers I have had.
> Let us be clear: if you're getting "digital telephone" service from a
> cable television provider, it is *not* "VoIP", in the usage in which
> most speakers mean that term -- "Voice Over Internet" is what they should
> be saying, and cable-phone isn't that; the voice traffic rides over a
> separate DOCSiS channel, protected from both the Internet and CATV
> traffic on the link.
No, this incorrect. Packet Cable most certainly _is_ VOIP (a MGCP
variant to be precise until 2.0 after which it is SIP). While a few
providers, usually for non-technical reasons, did deploy an entirely
separate set of downstream and upstream interfaces that is far from the
norm. AFAIK the only top 20 MSO to do so in scale was Charter and I
don't know if they continue that today. Comcast, the largest cable
telephone provider certainly does not nor do providers need to since any
Packetcable CMTS and EMTA combo offers reliable prioritization in the
same channel(s) as the normal data path.
> So of course Vonage and other VoN products will be less rugged.
> As I recall, this questionably fair competitive advantage has been
> looked into by ... someone. (Cablecos won't permit competing VoIP
> services to utilize this protected channel, somewhere between "generally"
> and "ever".)
As I said, this second channel doesn't exist in almost all cases (its
not cost effective nor needed in almost all cases). Having said that
over the top VOIP providers do suffer in comparison because they don't
get the benefit of prioritization in the local cable plant.
> -- jra
Vice President of Technology
ISP Alliance, Inc. DBA ZCorum
More information about the NANOG