My
specialty is not voice, but I do know QoS and the company I
work for is one of the top technically as far as VoIP capabilities.
However, I
am not a spokesperson for my company and anything I contribute to
NNSquad is my
personal opinion and does not reflect the opinion of my company.
With
respect to what you say about QoS, it is true only if you
assume certain things about the network. First and foremost is the
bandwidth (link
speed) available end-to-end. Often the largest component of the delay
between
two points is the serialization delay on a particular link. For the
typical
enterprise network, this has historically been WAN links. Now even
this is changing,
with the availability of affordable high-speed links such as NLMI and
Metro-E.
However, at a certain point, slow link speed can cause major problems
when the
speed falls below a certain level and there is data traffic that is
composed of
large sized packets. The serialization delay at low-speed links can
cause a
significant delay if the voice packet is not queued first (low latency
queuing)
and technologies such as link fragmentation and interleaving (LFI) is
not
deployed. The speed of broadband Internet connectivity does not have
this
problem, so what are we left with?
What
we are left with is packet loss and jitter. Jitter should
not be a problem if you don’t have a queuing or link speed problem. If
there
is a link speed problem then there could be significant jitter, as
packets take
different amounts of time to traverse the network and can cause
problems if the
jitter buffer of the end-stations are exceeded (causing end-station
packet
drops, as the packet is no longer useful from a voice perspective as
far as
using the data contained in the packet to recreate the voice stream).
So, we
are down to packet loss.
Packet
loss is the primary concern. And it is only a concern if
any links between end-stations are so congested that packets are
dropped. The
major problem we are discussing here is network neutrality and the
behavior of
ISP’s in attempting to reduce the upstream traffic (primarily) due to
its
relative scarcity. This may or may not be true depending on the
last-mile
connectivity, as wireless is different from FiOS which is different
than
cable. However, let’s go with cable as an example. Cable has much
greater
downstream bandwidth as compared to upstream bandwidth. P2P
technologies
actually use upstream bandwidth in a much more “even” manner than
tradition
protocols used on the Internet. Traditionally, Internet communications
has
been heavy on the download side and slim on the upload side.
So,
we are left with certain circumstances, or possible
scenarios, in which the upstream bandwidth is congested, and packets
will
necessarily be dropped. That may not actually be accurate at this
point, yet.
However, it is certainly a concern of ISP’s, and I believe a major
reason why they
exhibit such behavior. I do not believe it is some altruistic desire
to be the
police of the Internet. If there were no bandwidth problems I don’t
believe
the ISP’s would be particularly concerned about interfering in P2P
traffic.
They may not believe it is ethical or legal, but I doubt they would
take it
upon themselves to police their customers if it was not affecting their
bottom
line. However, it is an issue in certain locations / communities, and
ISP’s
are probably attempting to avoid issues in the majority of locations.
So this
is evidence that there is a bandwidth problem >somewhere< on
their
networks, and upstream seems to be the culprit.
Brett says himself that “I do have control over my local network and over my interface to my backbone provider. And when I prioritize VoIP on those, it helps tremendously.” I think this is an indication that there is, in fact, an issue.
So, what traffic do you drop? Drop more than two or three VoIP packet, depending on the encoding and other configuration issues, and you will notice voice effects. So QoS, while it may NOT have been required in Internet communications in the past, is becoming MORE important than it has ever been in the past. In the past, when low-speed connections (dial-up) were only possible, VoIP communications itself was not possible. Then there was a time of high-speed communications, with no contention. Now we are entering a time of high speed communications (no delay issue), but with contention (packet loss issues). To overlook this, or to allow the ISP’s to come up with their own solutions without input from others, is not in the best interest of anyone but the ISP’s.
Fred,
I have to take exception to your suggestion that QoS is "definitely
required" for proper VoIP operation. Most VoIP today operates without
any
specific QoS support -- even ISPs that offer this 'thinly veiled VoIP
tax' have
carried VoIP successfully without traffic management for years. I have
worked
as a VoIP software architect and can state unequivocally that QoS is
not
required for VoIP operation -- in fact, its not even close to the top
reliability concern -- which is actually 'traffic management' of
inbound ports.
VoIP doesn't need QoS, and this is just another mechanism ISPs are
using to
leverage their own 'digital phone' offerings at the expense of the free
market.
For more details refer to Vonage Canada's filing about Shaw Cable to
the CRTC
that was made about Shaw's $10/mo VoIP QoS "service". Maybe we should
let the VoIP companies, not the incumbent competitors tell us what type
of
traffic management is required. From my perspective, they already have,
and are
against these types of anti competitive services.
>From my perspective, QoS is totally unnecessary on public links, and
ample
alternative business models exist to the carriers plans of radical
over-subscription.
$0.02
Kevin McArthur
Fred Reimer wrote:
Hmm. I have to agree with Brett on most of his comments. QoS is definitely
part of the IETF RFC's. And QoS is definitely required for VoIP, in any
network, for it to work properly. The problem is that there is no common
global, or for that matter national, agreement as to how classifications and
markings are done. Without that there would be little reason for the
various network owners to trust each other. There may be one-off agreements
between two ISP's or an ISP and a backbone carrier. However, unless there
is a national/global standard then we would never get to the point where
end-users can mark their own traffic as they see fit, and have those
markings honored throughout the Internet as long as they complied with their
agreement with their ISP.
I disagree when it comes to the intelligence of the network, and whether
network owners should be able to make policy as to what types of content is
appropriate just because the routers and other network infrastructure
devices have "intelligence." The Internet is an end-to-end network, not a
client-server network.
Fred Reimer
-----Original Message-----
From: nnsquad-bounces+freimer=ctiusa.com@nnsquad.org
[mailto:nnsquad-bounces+freimer=ctiusa.com@nnsquad.org] On Behalf Of Brett
Glass
Sent: Friday, February 29, 2008 3:04 PM
To: Bob Frankston; nnsquad@nnsquad.org
Subject: [ NNSquad ] Re: INTELLIGENT network management? (far from IP)
At 12:28 PM 2/29/2008, Bob Frankston wrote:
If you require QoS for VoIP then you have the PSTN not the Internet.
Period.
QoS was (and is) part of the original design of the Internet. Note the
"Type of Service" fields in both IPv4 and IPv6, as well as the "push"
bit. (Interestingly, there's no "shove" bit. Don't know why. ;-) )
VoIP cannot rely on QoS because you don't have enough control over the
network.
I do have control over my local network and over my interface to my
backbone provider. And when I prioritize VoIP on those, it helps
tremendously.
And VoIP does not rely on QoS -- I verified this with Tom Evslin
who supplied much of the backbone for VoIP.
VoIP becomes nearly unusable in times of heavy loads without QoS. In
fact, it becomes unusable when someone on the same node runs
unthrottled BitTorrent. That's why we prioritize and do P2P mitigation.
Let's not base policies on misconceptions.
I agree. Hopefully the above will clear up some of those misconceptions.
Yes you can build your own
intelligent network but let's not confuse it with the Internet.
The Internet was never meant to be unintelligent. By design, it relies upon
routers which have tremendous computing power and very large amounts of
memory. (And it must. It can't scale or have redundancy without these
things.)
What's more, every end node is ITSELF a router and devotes intelligence to
that. It is unreasonable to attempt to exile technology, innovation, or
intelligence from any part of the Internet.
If VoIP fails it fails.
You may be able to say that, but we can't. We lose the customer if he or
she can't do VoIP.
And if you require real time HD streaming that may fail to. So what?
I believe that it was you who, in a previous message, were voicing
discontent with the performance of HD streaming on your FiOS connection.
We can't support HD streaming on the typical residential connection, but
we DO want to support it if the customer is buying sufficient bandwidth.
If we don't, again, we're out of business. Or someone goes to the FCC
and complains that we're not supporting that medium and must be
regulated....
--Brett Glass