scope:

The present document specifically describes the framework of IP emulation services for PSTN modem call types. The present document provides, inter alia, a description of:

• the problem statement;

• summary of IP bearer services;

• overview of media-type configurations; and

• a collection of example network use cases;

for PSTN modem calls.

Conventions

SDP Offer/Answer protocol variants

The present document provides example signalling syntax. There are two models for the Session Description Protocol (SDP) concerning the indication and negotiation of media and transport capabilities:

• the name "legacy SDP Offer/Answer" indicates SDP Offer/Answer according RFC 3264 [i.1];

• the name "revised SDP Offer/Answer" indicates SDP Offer/Answer according RFC 5939 [i.4] and RFC MediaCapNeg [i.5].

The two SDP Offer/Answer protocol variants differ in terms of supported SDP syntax, but also in terms of negotiation logic on semantical level (see also Annex D).

Configuration (Codec) list

The term media configuration (briefly configuration) is more comprehensive than the term codec. A media configuration covers typically media type, media format, all media format attributes, media transport stack, media transport capacity and all associated parameter values.

The term configuration list represents consequently a list of configurations within the SDP media description block.