efined by ITU-T is 400 ms. Greater delays than this are unacceptable as the voice quality becomes highly distorted. Delay due to transmission is very low compared to delay introduced by packetisation/buffering and codec delays. These are introduced in the user equipments, radio access network and MGW elements. It is therefore important to keep the number of MGWs taking part in the call establishment to a minimum. As a partial solution to the problem, in the MGW and following, the AAL2 nodal function is extended to the Nb interface. The AAL 2 nodal function makes it possible for originating and destination MGWs to 3GPP Release 4 Circuit Core Network establish a user plane channel through transit MGWs without involving the controlling MSS. Moreover, the internal handling of the traffic in the transit MGWs would be significantly different and that would reduce some delay. MGW Termination of the A interface Implementation of the MGW for a 3GPP release 4 network offers the possibility of terminating an A interface of the GSM. This allows a common backbone network to be used for both GSM and UMTS networks. When an A interface is terminated in the MGWs, the BSSAP signalling is terminated in the controlling MSS. MGW becomes a signalling gateway and terminates the SS7 MTP transport layer while relaying application part messages on top of Sigtran to the MSS. The MGW performs the needed adaptations of the user plane traffic from the G.711 codec received on the A interface to the codec used in the Nb or MGW-MGW interface. The bandwidth needs for the GSM user plane traffic (voice) in the Nb interface depends on the codec supported in the MGW and on the capabilities of the transcoder (TC) element used between the Ater and A interfaces. There are several methods used to enhance voice quality for GSM traffic in the release 4 network. Tandem Free Operation (TFO) TFO is achieved by the TCs using in-band signalling. The transcoders are physically present along the communication path but the transcoding is partially or fully disable