Re: H.248-controlled T.38 configurations: SDP- vs Property-based H.248 signalling

Hello Albrecht,

Yes I would agree that signalling elements from H.248.2 relate to the =

T.38 termination on a MG, i.e. the endpoint on a local MG. H.245 Annex B =

also indicates that T.38 parameters such as fillBiTRemoval and =

TranscodingJBIG indicate the gateway is in scope.

Regards, Christian

On 2/08/2012 12:16 AM, Schwarz, Albrecht (Albrecht) wrote:
> [Cc=92d megaco list due to H.248.2]
> The *T.38 parameters* as defined by ITU-T T.38 are related to a *T.38 =

> endpoint implementation*, such as the *T.38 user plane interworking =

> function* as e.g. located in an H.248 IP-to-TDM media gateway (e.g. =

> 3GPP IM-MGW).
> There are fundamentally two signaling options for such T.38 =

> configurations:
>
>  1. *SDP-based*: using *T.38 Annex D* defined SDP elements embedded in
>     H.248 descriptors
>  2. *Property-based*: using *H.248.2, IP Fax package* defined
>     properties, such as specified by clauses 10.1.3 to 10.1.7
>
> Both H.248 signalling options are basically equivalent, - independent =

> of SDP- or Property-based signaling elements. The signaling elements =

> relate to the T.38 endpoint, but NOT to any remote G3FE.
> [Note: the H.248 IP fax package version 1 (from 2005/2007) does not =

> yet contain the latest T.38V4 (2010) parameter. But this aspect is =

> irrelevant in this discussion due to the proposal in 3GPP for the =

> SDP-based method.]
> Thus,
> all =93T.38 SDP attributes=94 (in C3-121327) are related to gateway =

> capabilities (such as supported T.38 configurations by an IM-MGW =

> implementation) (NOTE: attached is T.38 Table B.1 for H.323 gateways, =

> which again underlines the relation to gateway capabilities).
> The MGC / MGCF may be either
>
>  1. aware of the supported T.38 configuration(s) by his associated MGs or
>  2. unaware.
>
> Awareness may be achieved via auditing or configuration management.
> Unawareness is basically possible, but may lead to inefficient or even =

> ineffective H.248 scenarios for T.38.
> Dependent on the amount of =93supported T.38 configuration(s)=94 knowledg=
e =

> at MGC level would be the content of the SIP-level SDP O/A procedures.
> Conclusions for *C3-121327* =

> (_http://www.3gpp.org/ftp/tsg_ct/WG3_interworking_ex-CN3/TSGC3_70_Chicago=
/Docs/C3-121327.zip_):
> NOTEs 1 and 2 in Table X.3.1 are incorrect in my opinion.
> The *text* related to =93remote CS FAX equipment=94 (term should be anywa=
y =

> replaced by term G3FE) should be just *deleted*. And there would be =

> correspondent changes at other tables.
> -Albrecht
>
>
> _______________________________________________
> Megaco mailing list
> [email protected]
> https://www.ietf.org/mailman/listinfo/megaco