RE: stds-80220-requirements: Latency and packet error rates
Branislav,
There's one class of traffic that doesn't appear on your matrix: if you
intend to use the networks resultant from this standard in some process
applications then you need _determinism_ or _bounded_delay_delivery.
On Fri, 2004-02-27 at 16:54, Branislav Meandzija wrote:
>
> Class Attributes of Traffic
> -----------------------------------------------------------
> Conversational | Two-way, low delay, low data loss
> | rate, sensitive to delay variations.
> -----------------------------------------------------------
> Streaming | Same as conversational, one-way,
> | less sensitive to delay. May require
> | high bandwidth.
> -----------------------------------------------------------
> Interactive | Two-way, bursty, variable
> | bandwidth requirements moderate
> | delay, moderate data loss rate
> | correctable in part.
> -----------------------------------------------------------
> Background | Highly tolerant to delay and data
> | loss rate has variable bandwidth.
> -----------------------------------------------------------
Deterministic | Application requires bounded maximum delay
| characteristics.
This requirement is omitted from the IETF diff-serv docs because it
simply isn't attainable across a multiple-segment routed network without
doing terminal violence to the connectionless nature of the network
layer. But it's practical to meet such requirements by providing some
form of ___synchronous service in the bottleneck network segments
(inevitably the radio networks) and overprovisioning the wired segments
so they never become the bottleneck.
We've been here before in wired networks; token networks had the
theoretical ability to deliver determinism and FDDI had practical
implementation. We've been here before in some radio networks too --
Link 16 (aka JTIDS, aka TADIL-J) in the military delivers synchronous
service using a TDMA structure.
Most of the requirements justification that I can produce is military in
nature -- weapons control is an obvious example. But I would guess that
SCADA applications in commercial industry would be another example.
BTW, viewing QoS requirements as purely latency ones is viewing QoS
through a keyhole. QoS is adjusting the balance across several
competing needs:
1. Bandwidth efficiency (aka throughput, but macro view)
2. Micro performance issues, incl:
a. latency
b. interactivity
c. jitter
(You've got a good handle on this in your post)
3. Determinism (aka bounded delay delivery)
Help?
> >
--
Rex Buddenberg
Naval Postgraduate School
Code IS/Bu
Monterey, Ca 93943
831/656-3576