[Cu-wireless] VoIP
Stephane Alnet
stephane at nospam.shimaore.net
Mon Feb 23 17:49:18 CST 2004
Hi,
Since I guess I was volunteered for heading this topic, here are some
thoughts. ;D
* Documentation: voice (PSTN or VoIP) is a complex subject by itself.
We need to better understand what "voice" entails; some of the topics I
think we should document are:
- VoIP signaling: architecture of H.323 and SIP(*);
- call setup & call control, features (eg: what is call transfer, how
does it work? what does a call setup look like in H.323 or SIP? what
the heck *is* a call setup? :D )
- VoIP bearers: RTP, codecs, events (DTMF, etc.);
- quality of service (end-to-end): issues with voice (impact of
delay, jitter, drop, ..), strategies (marking/queueing/etc.) -- most of
this will not be wireless-specific.
- fax, modem. Video. >:>
- existing "open" projects in the works related to VoIP
(openh323.org, gnugk.org, kphone, vovida.org, etc.).
This doesn't have to be big (we're not writing an encyclopedia),
probably just a collection of pointers to other sites with more
information for people to read, and a few people who read them and can
talk about them to the rest of the group..
(*) IMHO we should try & justify our choice of protocols-set, if only
for grant-writing purposes. For example, I don't think a call-agent
based solution is in line with the goals of the project so that makes a
case against MGCP & other call-agent based protocols. Etc. This could
be an outcome of this work.
Also let's be careful about which pieces are available in source.
(http://www.voip-info.org/wiki-Open+Source+VOIP+Software has some
starting points, I guess.)
* Voice over Wireless network: I don't think we really need to spend
too much time on "wireless phone" technology (PCS, CDMA, GSM, etc.);
however it probably would be a good idea to get a "state of art" of
issues related to (a) "voice" over 802.11b in an ad-hoc context, and
(b) "voice" in a zeroconf context.
I can think of things like:
For (a) [VoIP/802.11b/ad-hoc]:
- quality of service over a wireless shared media; IEEE 802.11e
could apply, but we don't have APs: what does that mean? ...
- path selection for voice RTP packets on a long-range wireless
network (as far as I know this topic has never been covered): most
802.11b research on QoS considers the endpoint access as the problem
(and assumes a wired backbone); but we will have wireless as our
*backbone*: what does that mean for route selection?
Are the path selection criteria for voice traffic (small packets / low
bandwidth) the same as for data? [e.g.: 802.11's 1Mb/s may not be that
good for data traffic but good for RTP voice bearer traffic if it's
reliable..]
Do we need RSVP? And what would RSVP mean in a wireless, dynamic,
ad-hoc environment?
For (b) [VoIP/zeroconf]:
- addressing / how does a device know the location of other devices?
... locating a GK (H.323) or a proxy (SIP) in a zeroconf context;
network partitioning and call routing; number assignment; directories.
- PSTN gateway location/registration (think zeroconf), selection, ..
Probably more...
* Getting it to work: also based on the first point, we should try to
get something up & running, even if it doesn't address all the problems
we can find!
Possible subtopics:
- hardware required for a PC-based endpoint;
- potential grant / donations from HW vendors for trial purposes;
- network components required for call routing (GK or SIP proxy);
- PSTN gateway(s)...
I don't think this is even close to a beginning but we can try. :) I'd
like to propose that we start by the first step (documenting/
understanding) while keeping the end goal in mind.
We'll probably need a place to store the information -- wiki or
something like that. What are the "official" resources? Then whoever
has time to start researching could work on this..
S.
--
Mayotte - http://stephane.alnet.free.fr/
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