To increase the number of subscriber network ports which may be accessed on a Broadband Integrated Services Digital (B-ISDN) access network using Asynchronous Transfer Mode (ATM) technology where a Concentration Function is provided by statistical multiplexers, a Grooming Function by ATM switches and own-access-network connections is provided by combining "upstream" ports into the core network(s) and the "downstream" ports to subscribers into a common address group and each subscriber port and each core network(s) access port is allocated a unique OSI Layer 2 address the access network destination address being carried in the Virtual Path Identifier (VPI) field of each ATM cell formatted according to relevant CCITT recommendations for the User Network Interface (UNI) or the Network to Network Interface (NNI) and the Virtual Channel Identifier (VCI) field of the CCITT recommendations is divided into two sub-fields which carry the OSI Layer 2 source address and a Terminal Equipment Identifier (TEI) field respectively, the TEI field being used to identify a virtual channel at the source and destination ends of a path.