Subject: General Media Descriptor - SDP

From: Ruppelt Christian <[email-masked]>
Date: Fri, 17 Sep 1999 14:04:31 +0200

stressing my point again in V10.

Local and Remote Descriptors (7.1.9.) are encoded as SDP strings OR
tag-value pairs (see Annex D).
If one decide to choose SDP my assumption was, forget about the
General Media Attributes in Annex D!
(ANNEX D supports that thinking beginning with: "As an alternative to
SDP...")

But, a mapping is NOT possible (e.g. gain, echo canceller,...)!
And in the current protocol ANNEX D is therefore obviously mandatory?
see Example in Annex G
Here the tag-value pairs are used to describe the properties of a
termination
within LocalControl.
So, if you want to use SDP for Local/Remote you better not forget parts of
Annex D for Local Control.

                                    LocalControl {
                         Mode = SendReceive,
                         Package1/GainControl=2,  ; in dB,
                         Package1/Encryption=xxx,
                         Package1/EchoCancellation=G165,
                         Package1/VoiceActDet=yes
                     },
                     Local = SDP {c=LOCAL
                                  m=audio 0 LOCAL 0
                                  a=sendrecv
                                  a=ptime:10
The next alternative is described in 7.1.8
Here it is written that the properties of a termination are defined in
Packages.
So, if you want to use SDP for Local/Remote you have to define
(e.g. gain/echo canceller) in the packages?

Is this variety intended?
I prefer a clear description and distinction for the two ways.

regards
Christian Ruppelt

---

From: Christian Huitema <[email-masked]>
Date: Fri, 17 Sep 1999 09:01:33 -0400

>                         Package1/EchoCancellation=G165,

Christian,

I think that you are misunderstanding the scope of SDP or annex D
Descriptors. In fact, "LocalControl" maps very closely to the
LocalConnectionOptions parameter of MGCP's connection handling commands.
The main difference is the use of package-defined parameters, instead of
global space parameters in MGCP.  A reasonable assumption is that we the
current MGCP parameters will be defined in the combination of at least two
packages, one generic (Usage of echo cancellation, Usage of silence
suppression or voice activity detection, Usage of signal level adaptation
and noise level reduction, or "gain control") and one specific to RTP
(Encoding Method, Packetization period, Bandwidth, Type of Service, Usage
of reservation service, Usage of RTP security).

There is however one subparameter of MGCP's LocalConnectionOptions that
does not fit squarely into the "package" approach.  The "Type of network"
is used to specify whether the new connection should be built over IP,
Frame relay, ATM, etc. This is quite useful in multi-protocol gateways,
specially if we decide that termination names have no structure and no
implied meaning. If a gateway receives a command such as: Transaction=x{
ctx=$ { add=${...}}}, how can it decide whether to create an RTP
connection, rather than using AAL2?

I suggest that a "type of network" attribute be added as a generic
subparameter in the LocalControl definition.

-- Christian Huitema