Subject: Re: [Ieprep] access and enterprise networks

From: [email-masked]
Date: Wed, 2 Apr 2003 23:04:55 EST

In a message dated 4/2/2003 10:46:50 AM Eastern Standard Time, 
[email-masked] writes:

>   - qos.  In the emergency services situations I dealt with in a former
> life, I was generally happy when I had comms.  Whether it was 'high
> quality' comms was never an issue.  Personally, I find the arguments
> about QoS a bit tiresome and I can't shake the opinion that we're
> chasing after a non-problem to the neglect of the real problems.
> 

I couldn't agree more. This QoS issue and bickering has been sidetracking the 
real issue, especially since QoS is generally equated with the few parameters 
associated with transfer of speech packets (loss, delay, delay variation) and 
not with the broader call setup "QOS" parameters such as call setup time, 
probability of call failure, probability of premature disconnect, etc.

There has recently been some suggestions that what ETS or Assured Service 
wants is better QOS than the normal traffic gets during normal times. This is 
not true. As Rex indicated, emergency users would be satisfied with worse QOS 
(regarding transmission of speech) as long as the connection is set up. That 
is, in an emergency situation when normal users have something close to 0% 
chance of getting a call through, the emergency working must have a 
significantly higher probability.

Mike

---

From: Sean Donelan <[email-masked]>
Date: Thu, 3 Apr 2003 05:04:23 -0500 (EST)

On Wed, 2 Apr 2003 [email-masked] wrote:
> not true.

This is not a recent development, many times it has been stated that there
needs to be a "better than best effort" level of service for emergency
traffic.

Since during normal times, providers may offer "best effort" service,
during an emergency the definition may be "best available" service.  But
in neither case will it be better than the best service the provider
offers.

> As Rex indicated, emergency users would be satisfied with worse QOS

The connection is set up?  What does that mean in a packet switched
network?  The probability of a packet getting through to "set up"
the connection will be similar to the packets getting through during
the "call" (instaneously changing depending on network conditions).

If there is close to 0% chance of setting up the call on a packet
switched network, then even if you do magic to set up the call, there
will be probably close to 0% chance of receiving any speech packets on
the same packet switched network (modulo the issue with gateways, proxies,
and directories using different transmission paths) so emergency works
will hear dead air.

What I've found interesting using IP telephony is its easier to
set up a call than it is to transmit and receive the speech packets.
One of the most common trouble shooting problems I have is the
phones ring, say connected, but get dead air or unintelligible
audio.  Because the call set up messages are relatively small and
are re-transmitted, even in extremely congested networks the SIP
messages seem to get through with little user visible delay.

Most of the reports I've seen on whether VOIP is ready for prime time
concern the problems with the quality of the speech path, not with getting
the call set up packets through the network.

So if I was looking at the real problems I'm seeing in the network, call
set up doesn't seem to be the problem needing to be solved.

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