 ITU-T G.732. Another possibility is to use 1,544-Mbps T1-links that carry 24 channels, see ITU-T G.733. Links with larger capacity are also possible, according to the multiplexing hierarchy defined by PDH. Again, another possibility is to use SDH links. Both PDH and SDH are defined by ITU-T recommendations in the G-series. 3 Logical Network Modelling To establish CN connections between terminal systems might require that the TE-DNCP also negotiate with other switching nodes in the operator network. The teleservice distribution protocol used for that is ISUP, according to ITU-T Q.761-766. CCS is a packet-switched logical network for supporting ISUP and other net- work protocols. The CCS logical node in the model comprises only MTP and SCCP of the CCS standard (CCS has a wider definition). CCS provides both connection-oriented services (SCCP) and connection-less services (MTP and SCCP). For connection control purposes, ISUP uses MTP. Control of resources that are needed for handling connections between the CNUs in terminal systems is performed by TE-DNCPs over resource control- lers. The model shows only controllers for the switches. The routing analyser is used by the TE-DNCP as a kind of server. When the TE-DNCP gets a setup message from either the access side (over the ITU-T Q.931 protocol) or the network side (over the ISUP protocol), it provides the destination-SAPI to the routing analyser and asks for suggestions for suitable outgoing links. The answer is then used by the TE-DNCP to give switching orders to the switch controllers. Users of CN connections between terminal systems are protocol elements that are instantiated in CNUs. The protocol elements are called TE-UDT, since they are units that provide teleservices over TE-SAPs to teleservice users (TEU). TE-UDTs communicate by means of teleservice protocols directly between ter- minal systems, or via protocol converters that are connected to 64K CSs some- where in the operator network. For example, for voice communication, the TE- UDT is an analog-digital