Reference document

Transit Services
The Transit Services enable the processes related to connecting IP based Transport Services together, Frame Transport Services together and TDM Transport Services together, either point to point, point to multipoint or multipoint to multipoint over metro and wide area networks. They involve the interaction of different transmission bearers of the same or different types at different nodes. These routing or switching nodes can be on the terrestrial communications segment, a terrestrial wireless segment or even the SATCOM space segment (e.g. carrier, frame or packet switching occurring on a regenerative transponder onboard the satellite payload). Communications equipment deployed for these Transit Services (e.g. routers, switches, radio relays, SATCOM transponders, etc.) may operate at different points across the core of the network. The Transit Services support standalone routing or switching elements (i.e. without attached Communications Access Services) and only connect to Transmission Services (one or more services, when routing/switching across different bearers is involved), or connect with Communications Access Services to Packet-, Frame- and Circuit-based Transport Services. Nonetheless, Transit Services are not concerned with emulated Communications Access Services or Packet-, Frame- and Circuit-based Transport Services, by virtue of the single-hop end-to-end nature of the tunnelling mechanisms supporting the virtualisation of protocols over higher-layer protocols. Transit Services are closely associated with WAN routing/switching topologies (point-to-multipoint, mesh of point-to-point links or multipoint-to-multipoint). The topology is defined when the Transit Service is specified and will form part of the Service Level Specification (SLS).
Transport Services