Brian Cruickshank (cruicb@nortelnetworks.com)
Wed, 13 Dec 2000 11:43:55 -0600
To me, there are the following pros/cons to G.711 and MS-GSM:
Advantages to MS-GSM:
- Less Storage Space
- Faster to download to client
- Faster to send between servers
Advantages to G.711:
- Better Voice Quality
- "Universal" Client Support
- Fewer MIPs / lower complexity / easy to implement
Storage Space:
With 72Gig drives available and storage capacity following Moore's Law, I
think it is fair to say that the 'Less Storage Space' argument will become
less and less of a factor over time. I understand that there are size
limits on mailboxes which come into play but if this is of paramount concern
then perhaps the Unified Messaging vendor would want to transcode into a
lower bitrate format than MS-GSM (e.g G.729A, G.723.1, etc.). If the VPIM
codec was G.711 then this would be more easily accommodated than if it was
MS-GSM, and with better voice quality.
Download to Client:
Because G.711 is such a light-weight codec in terms of the CPU required to
convert 16b linear to / from G.711, vendors can easily transcode VPIM
messages into whatever codec they prefer for downloading messages to
low-bandwidth clients. If the preferred client codec is MS-GSM, then the
'Fewer MIPS' advantage for G.711 is nullified but if the preferred client
codec is NOT MS-GSM (e.g. it could be G.723.1 for a Voice over IP
connection) then the 'Fewer MIPs' and 'Voice Quality' advantages for G.711
become even more important.
Faster to Send Between Servers:
To me, the strongest argument for MS-GSM is that it takes ~ 1/4 of the
bandwidth to send an MS-GSM encoded voice message between 2 universal
messaging servers than it takes to send a G.711 encoded message. This
translates into a lower operational cost to the service provider. With the
'cost per managed bit' dropping in half every 9 months, however, this may
not be a significant factor for very long.
I think that the main advantages of G.711 - ease of implementation,
universal client support and better voice quality - will make it simpler for
vendors to adopt and will keep the intelligibility of voice messages high.
Brian Cruickshank
Nortel Networks
-----Original Message-----
From: Charles Eliot [mailto:charle@Exchange.Microsoft.com]
Sent: Tuesday, December 12, 2000 8:12 PM
To: Anthony Baxter
Cc: IETF VPIM List
Subject: RE: [VPIM] RE: 3GPP-T-WG3 codecs
The ability to take voicemail offline, ie to download onto your laptop
and read/reply without an active connection, has been one of the most
compelling scenarios for unified messaging adoption by corporate road
warriers. I'll try to dig up reference studies.
-----Original Message-----
From: Anthony Baxter [mailto:anthony@interlink.com.au]
Sent: Wednesday, December 13, 2000 3:21 AM
To: Charles Eliot
Cc: IETF VPIM List
Subject: Re: [VPIM] RE: 3GPP-T-WG3 codecs
>>> "Charles Eliot" wrote
> Turns out - after much sighing and gnashing of teeth - that there is
no
> patent issue. MS-GSM implements the GSM codec, and the proposed RFC
> describes how to format a GSM bitstream in such a way that the MS-GSM
> codec can read it.
>
> The balance between file size and desktop ubiquity is always going to
be
> tricky. I'm leaning these days towards G.711, but as Eric Burger
pointed
> out there is still a lot of slow-link dialup going on out there.
As I mentioned in my last mail, though - surely this is more of an
issue for real time voice, like a phone call, rather than
store-and-forward
as for voicemail?
If you are working with low bandwidth clients, I see no reason why
you couldn't offer a voicemail listen page (say, in a webmail type
situation) that sends the data in a more compressed format - has
there been any studies done on how many of those low-bandwidth users
will actually be pulling their email down to their local PCs, versus
leaving it on a webmail service (hotmail, or whatever)?
Anthony
This archive was generated by hypermail 2.0b3 on Wed Dec 13 2000 - 19:47:10 IST