Telesis PX24 IP PBX Business Phone System
Design and manufacture IP PBX Business Phone System, Switching System, VoIP Gateway, and Signaling Converter  

V5.2 Protocol

Telesis Systems Offering V5.2 Protocol

  • Telesis Business Phone Systems:
    • PX24X Hybrid IP PBX Business Phone System
  • Telesis Switching Systems:
    • X1 Large Capacity TDM - IP Telephony Switch
  • Combined VoIP Gateway and Signaling Converters:
    • Stillink 200
    • Stillink 800
    • Stillink 3200

V5.2 Protocol In General

The V5.2 protocol stack is used for the connection of an Access Network (AN) to a Local Exchange (LE). It enables for various access methods, like analog telephone access and ISDN basic rate access. A V5.2 interface may use up to 16 E1 interface links. For analog access, the PSTN user port is converted into a functional part of the V5.2 protocol for signaling to the AN side. In principle, the V5.2 interface uses a concentrator type, whereby up to 16 E1 links, each carrying 30 channels (480 channels in all), may serve up to 1,920 subscribers with 1/4 concentration. There is no limit in principle, to the number of V5.2 interfaces that can exist between the access network and the local exchange. A channel is allocated to a subscriber dynamically when he or she makes or receives a call.

V5.2 includes a protection protocol, allowing for redundancy in the signaling. Usually, the signaling for the 16 E1s is carried on one channel on one link (the primary link). If the signaling link fails, a secondary link is set to take over. This is similar in principle to SS7`s multiple point codes. In order to support more traffic through dynamic allocation of channels, the V5.2 protocol has several additions:

  • A bearer channel connection (BCC) protocol establishes and de-establishes bearer connections required on demand, identified by the signaling information, under the control of the Local Exchange.
  • A link control protocol is defined for the multi-link management to control link identification, link blocking, and link failure conditions. 
  • A protection protocol, operated on two separate data links for security reasons, is defined to manage the protection switching of communication channels in case of link failures.

Access Network

The term AN (access network) refers to the network between the local exchange (or Central Office) and the subscriber. In many countries, this network is still predominantly made up of the copper-cable-based point-to-point connections. However, conventional point-to-point copper cabling has some limitations:

  • It offers limited bandwidth, which is difficult to overcome.
  • Inflexibility: both in time and types of service provided.
  • Due to star topology (from the exchange to the subscriber), reliability is limited.
  • Installation time is long.
  • It is maintenance intensive due to possible cable damage and thus costly.
  • Largely passive, making it difficult to manage.
  • Loop length limitations( ~ 10 km ).
  • Uneconomical in remote, isolated areas with low telephone densities.
  • Prone to electromagnetic interference.


PX24X as a V5.2 Access Network

Telesis systems may be the remote of Local Exchanges with using V5.2 protocol

To overcome the above-mentioned issues, several vendors developed AN (access network) technologies, almost all which support the V5.2 protocol in connecting to the voice-switching Local Exchanges. Some examples of new technologies based on AN with V5.2 protocol are mentioned below:

DSLAM (Digital Subscriber Line Access Multiplexer) or Broadband Access Network Technology

A family of technologies that have begun to transform the narrow-band copper access network into a broadband network is the xDSL family of technologies. The term DSL, or digital subscriber line, refers to the modem that, when connected at either end of a normal twisted-wire pair line, converts it into a digital line capable of handling data rates well into broadband. By using higher frequencies, DSL technologies enable much higher speeds over the twisted-pair lines.

WLL (Wireless Local Loop) Technology

Bringing telephone access to subscribers in remote and isolated areas with low telephone densities by laying down a copper network may be uneconomical. WLL technology makes installation in such areas easy and more economical by utilizing radio to access subscriber premises. WLL equipment may be connected to Telesis systems with V5.2 protocol to access rural areas via radio.

Telesis systems have E1 interfaces with V5.2 protocol support. An example for WLL connection.

Wireless Local Loop ANs may connect to Telesis systems with V5.2 protocol

DLC (Digital Loop Carrier) Technology

Optical fibers, clearly the preferred technology for transmission media, are beginning to find their place in the subscriber`s loop. The tremendous advantages in terms of the information capacity of fiber, its small weight, and its size compared to copper cable are making it a very attractive technology with which to replace copper in the subscriber loop. To access to the same number of subscribers that one fiber cable can carry, we would need hundreds of twisted-wire copper cables, which makes DLC the preferred technology in many installations. DLC equipment may be connected to Telesis systems with V5.2 protocol to access rural areas via copper.

An example for DLC V5.2 connection

Digital Subscriber Loop ANs may connect to Telesis systems with V5.2 protocol


V5.2 protocol implementation in Telesis systems follows ETSI Standard EN 300 347 (Version 2). The implemented protocol covers both LE (Local Exchange) and AN (Access Network) protocols and supports analog telephone access (PSTN) and ISDN basic-rate access.


Telesis systems support:

  • Both the Access Network (AN) and Local Exchange (LE) sides
    • Common control protocol
    • Protection control protocol
    • Link control protocol
    • Port control protocol
    • BCC protocol
    • ISDN messaging
    • PSTN messaging
  • Protocol conversion between the V5.2 LE protocol and any other signaling system provided by a Telesis system
  • ETSI FSK Caller ID transmission from an LE to an AN
  • Charge-pulse transmission from an LE to an AN
  • Mixed use of V5.2 LE and AN protocols and other signaling systems
  • Flexible assignment of selected subscribers to a dedicated AN while allowing the other ports (subscribers and trunks) to operate as usual.

For a V5.2 interface, the mapping of the logical (C-path) to the physical C-channel is stored in timeslot 16 of the primary link as default. This default profile cannot be modified while the V5.2 interface is in operation. If the V5.2 interface consists of more than one E1 link, then the protection protocol exists for both the primary and the secondary link in parallel. Time slots 16 in the primary link and the secondary link are always physical C-channels. If protection switching occurs, the C-path is restored at timeslot 16 of the secondary link. V5.2 protocol implementation in Telesis systems allows:

  • assignment of 16 E1 links to one V5.2 interface (if the system capacity allows)
  • assignment of Link Ids
  • assignment of Interface ID
  • assignment of logical C-channel ID
  • setting a primary link (which carries the C-path by default)
  • setting a secondary link

Frequently, service providers are hesitant to invest in a new switch in remote and isolated areas with low telephone densities. An attractive alternative is to install remote units in such areas that can act as part of an already existing switch. This solution offers ease of maintenance and operation as well as cost effectiveness. V5.2 protocol implementation in the Telesis X1 and PX24X enable them to serve as the remote units of any exchange that conforms to ETS 300 047 V5.2 protocol standards.


One unique feature of Telesis systems is their versatility: the V5.2 LE protocol and the V5.2 AN protocol and other signaling systems can co-exist within one system, such that:

  • Some subscribers may constitute an AN of a dedicated local exchange
  • Some E1 interfaces may utilize the V5.2 LE protocol so that other ANs may be connected
  • Some subscribers and trunks may continue to operate in conventional mode

Networking Telesis Systems

Networking Telesis systems is possible by utilizing the V5.2 protocol. Note that, because switching is actively done on the LE side, the number of bearer channels between the LE and the AN should be planned carefully in accordance with the expected telephone traffic. Erlang loss formula could be used as a service quality target. To illustrate, through a 60-channel (2 x E1) capacity V5.2 interface, total erlang traffic capacity is 44.75, with a lost-call probability of 0.005 at random traffic. Consequently, for a 250-subscriber capacity PX24X AN with a 60-channel V5.2 interface, erlang per subscriber is almost 0.2.

Networking Telesis systems with using V5.2 protocol. Master and Remote systems.

Networking Telesis systems is easy with using V5.2 protocol. Telesis supports both V5.2 LE and V5.2 AN protocols at the same time.

Protocol Conversion

With the interworking capability of Telesis algorithms, Telesis Stillink V5.2 protocol converters enable an exchange to adapt its existing equipment to the V5.2 protocol. This means Stillink V5.2 protocol converters:

  • allow V5.2 AN systems to be connected to LEs that do not support V5.2
  • allow AN vendors to facilitate the connection of their V5.2 ANs to existing non-compliant LEs.

V5.2 AN is connected to IP network via Stillink

Stillink V5.2 - VoIP Access Gateway allows V5.2 AN systems to be connected to IP network or softswitch

V5.2 AN is connected to an LE via Stillink

Stillink V5.2 protocol converters allow V5.2 AN systems to be connected to LEs that do not support V5.2

For more information about the Stilllink V5.2 protocol converters and V5.2-VoIP Access Gateways, visit the product web site


The physical layer of the V5.2 protocol in Telesis systems is an E1 (ITU-T G.703) interface. 120 ohm balanced terminations are supported on any E1 link. The line code is HDB3 or AMI programmable. CRC4 error checking may be enabled or disabled. The Telesis X1 supports up to 16 AN and/or LE V5.2 interfaces, each using up to 16 x E1 interface links, provided that the E1 capacity of the X1 allows it. The Telesis PX24X supports up to 4 AN and/or LE V5.2 interfaces each using up to four E1 interface links, provided that the E1 capacity of the PX24X allows it.

Related Readings

We recommend you to visit Telesis WiKi Pages for technical readings.


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