09.043GPPInterworking between the Public Land Mobile Network (PLMN) and the Circuit Switched Public Data Network (CSPDN)TS
There are two ways to interwork with the CSPDN, directly or via the ISDN.
Interworking via ISDN:
Only synchronous interworking with the speeds 2 400, 4 800 and 9 600 shall be possible. Depending on the fact that it is impossible to flowcontrol the terminals connected to the CSPDN only transparent services in PLMN are used.
No particular functionality is needed in a VPLMN without a connected CSPDN for support of CSPDN access for roaming subscribers.