Generally the distinction is made between the service interworking and the network interworking.
6.1 Service interworking
Service interworking is required when the Teleservices at the calling and called terminals are different (e.g. Teletex interworking with facsimile). These aspects are not dealt with in the present document.
6.2 Network interworking
Network interworking is required whenever a GSM PLMN and a non‑GSM PLMN together are involved to provide an end to end connection and may be required in instances of GSM PLMN to GSM PLMN connections. The first case applies to the subject matter of the present document and thus dealt with herein after.