| 7.1 | X.25 | ||
| 7.1.3 | X.25 DTE and DCE |
| Data terminal equipment (DTE)
and data communications equipment (DCE) for X.25 identify the
responsibilities of the two stations on an X.25 attachment. The X.25
protocol implements virtual circuits between the X.25 DTE and X.25
DCE.
Although the terms DTE and DCE occur at all three layers associated with the X.25 stack, the use shown in the Figure identifies responsibilities that are independent of the physical-layer DTE/DCE. The terms DTE/DCE are independent of the typical plug-gender and clock-source definitions used at the physical layer. The X.25 DTE is typically a router or a packet assembler/disassembler (PAD). The X.25 packet-level DCE typically acts as a boundary function to the public data network (PDN) within a switch or concentrator. The X.25 switch at the carrier site may also be called data switching equipment (DSE). The X.25 use of DTE/DCE terminology differs from the usual physical layer interpretation. The way X.25 traffic is carried within the carrier cloud depends on the implementation. In some cases, X.25 is also used within the cloud. X.25 DTE is usually a subscriber's router or PAD. X.25 DCE is usually a PDN switch or concentrator.
|