A Tutorial

The Faster Serial Interface.

Basically, V.35 is a high-speed serial interface designed to support both higher data rates and connectivity between DTEs (data-terminal equipment) or DCEs (data-communication equipment) over digital lines.

V.35 is an interface (V.35 is the ITU - formerly CCITT standard termed "Data Transmission at 48 Kbps Using 60-108 KHz Group-Band Circuits") commonly used on higher speed circuits of 56kbps and above. Recognizable by its blocky, 34-pin connector; V.35 combines the bandwidth of several telephone circuits to provide the high-speed interface between a DTE or DCE and a CSU/DSU (Channel Service Unit/Data Service Unit). To achieve such high speeds and great distances, V.35 combines both balanced and unbalanced voltage signals on the same interface. Transmission is usually a synchronous protocol (note clocking pins i.e. receive and transmit clock). Although V.35 is commonly used to support speeds ranging anywhere from 48 to 64 Kbps, much higher rates are possible [ ISDN (64 or 128Kbps), Factional T1@ 128 Kbps to 1.544Mbps T1, ATM and Frame Relay]. V.35 cable distances theoretically can range up to 4000 feet (1200 m) at speeds up to 100 Kbps. Actual distances will depend on your equipment and the quality of the cable . Lan routers often come equipped with a V.35 electrical interface but many today are using a HSSI interface at speeds higher than T1 and above (typical T3 45Mbps).

jump to V.35 on a DB25 used by some manufactures 

V.35 cable cross-over for tail circuits

V.35 cable cross-over for tail circuits

V.35 cable 18 pin layout

V.35 cable Pin # Source Description
* indicates if source is DTE or DCE

V.35 cable Connector pin layout