WAN Physical Layer Standards
WAN physical-layer protocols describe how to provide electrical, mechanical, operational, and functional connections for WAN services. The WAN physical layer also describes the interface between the DTE and the DCE. The DTE/DCE interface uses various physical layer protocols, including:
EIA/TIA-232-This protocol allows signal speeds of up to 64 kb/s on a 25-pin D-connector over short distances. It was formerly known as RS-232. The ITU-T V.24 specification is effectively the same.
EIA/TIA-449/530-This protocol is a faster (up to 2 Mb/s) version of EIA/TIA-232. It uses a 36-pin D-connector and is capable of longer cable runs. There are several versions. This standard is also known as RS422 and RS-423.
EIA/TIA-612/613-This standard describes the High-Speed Serial Interface (HSSI) protocol, which provides access to services up to 52 Mb/s on a 60-pin D-connector.
V.35-This is the ITU-T standard for synchronous communications between a network access device and a packet network. Originally specified to support data rates of 48 kb/s, it now supports speeds of up to 2.048 Mb/s using a 34-pin rectangular connector.
X.21-This protocol is an ITU-T standard for synchronous digital communications. It uses a 15-pin D-connector.
These protocols establish the codes and electrical parameters the devices use to communicate with each other. Choosing a protocol is largely determined by the service provider's method of facilitation.
Click the WAN Cable Connectors button in the figure to see the types of cable connectors associated with each physical layer protocol.