A method of enabling extension of a network service of a first domain to a remote customer site hosted by an Access Gateway (AG) in a Provider Ethernet domain. In the first domain, the remote customer site is represented as being hosted by a border gateway (BG) connected to the Provider Ethernet domain, such that subscriber packets associated with the network service are forwarded to or from the remote customer site via the BG. In the Provider Ethernet domain, a trunk connection is instantiated through the Provider Ethernet domain between the host AG and the BG. A trunk cross-connection function is installed in the host AG, for transferring subscriber packets associated with the network service between a respective attachment virtual circuit (AVC) through which the remote customer site is connected to the host AG and an extended AVC tunnelled through the trunk connection. A common service instance identifier (I-SID) is used to identify both the AVC between the host AG and the remote customer site and the extended AVC between the host AG and the BG.