V5 interface

The V5 interface is a standardized interface for connecting a digital local switch to an access network. Via this interface, all narrowband services for analog (PSTN) and digital subscriber (ISDN) can offer to connected to the access network participants. The international standardization of the V5 interface and the disclosed network protocols on this interface, the V5 protocols, make it possible to connect components of the access network from different network operators to exchanges. Alternative network operators therefore need not establish its own nationwide networks with switches, but can be limited to establish local access networks, which can then use on V5 interfaces, the switching performance of the existing network of exchanges. The disclosed V5 interface is therefore an important tool of deregulation of the telephone market.

  • 3.1 logs to the V5.2 interface
  • 3.2 Layer 2
  • 3.3 Layer 3

V5 protocols

The V5 protocols control facilities of the access network, the so-called "access nodes" that can be connected via a V5.1 or V5.2 interface to a digital exchange.

Characteristic of the V5.1 interface

  • 2-Mbit/s-Schnittstelle (E1 ) to the exchange
  • Permanently assigned traffic channels: for every subscriber on the access network are permanently assigned traffic channels at the V interface
  • Maximum of 30 analog subscribers or 15 ISDN user with basic access

Protocols on the V5.1 interface

Characteristic of the V5.2 interface

  • Up to 16 2-Mbit/s-Schnittstellen (E1)
  • Analog or ISDN subscriber ( basic access )
  • Dynamically assigned traffic channels: for example, 4:1 ( 480 participants are 120 channels available )

Protocols on the V5.2 interface

Layer 2

  • Envelope function sublayer (EF - Layer)
  • Data Link Sublayer (DL- Layer)


  • PSTN protocol
  • ISDN protocol
  • Control Protocol
  • Port Control Protocol
  • Common protocol
  • Bearer Channel protocol
  • Protection Protocol
  • Link Control Protocol


The relevant standards are:

  • Interface (Software)
  • Network protocol
  • Telephone network