3 to 6 ended
● If a single comms channel fails, or if a terminal is r
econfigured out of service, comms can be re-routed the
other way around the ring
● If 2 channels fails – No protection
2.5 FIBRE TELEPROTECTION SCHEME TERMINAL ADDRESSING
In Fibre Teleprotection schemes, commands are packaged together with other important data for transmission
ov
er communications channels to the other devices. The packages of information are generally called ‘messages’.
These messages are created for a specific destination where they will be acted upon to realise the overall scheme
protection. It is critical that they are only used by the intended device. Making the correct channel connections
may not always ensure that the messages get to the correct destination; there may be a possibility that
communication paths may become cross-connected or looped back during telecommunications network
switching operations. To avoid incorrect scheme operation, extra security is needed to ensure that messages are
acted upon only by their intended recipient. This is achieved by means of an address field in the messages. The
address field is used to individually match connected devices. A transmitting device includes the address of the
intended recipient in the message. If the receiving device matches the address, the message will be used. If it does
not match, it is discarded.
The address field is an 8-bit field in the message. It can carry any 8-bit value, but certain values have been chosen
for maximum security. For convenience they have been arranged into 32 groups. All devices in a scheme must
share the same group. For addressing, the different devices are referenced as ‘A’, ‘B’, and ‘C’ for three-terminal
schemes. Their addresses should recognise the referencing.
So for a two-terminal scheme, if one device has the address set to ‘5-A’ the other should have the address to ‘5-B’.
Similarly, in a three-terminal scheme if one device has address ‘1-A’, the other devices would have addresses ‘1-B’
and ‘1-C’. The address is set using the address setting in the PROT COMMS/IM64 column.
2.6 PHYSICAL CONNECTION
The protection communications into and out of the products are fibre-optic. Connections are made using BFOC/2.5
connector
s (BFOC/2.5 connectors are commonly referred to as “ST” connectors where “ST” is a registered
trademark of AT&T).
According to application, different fibre-optic interfaces are available described in the following table:
Wavelength of light (nm) Fibre type Maximum transmission distance (km)
850 Multi-mode 1
1300 Multi-mode 50
1300 Single-mode 100
1550 Single-mode 150
Connections are made using appropriate fibre-optic cables terminated with BFOC/2.5 connectors. The transmitter
of one device (for example T
x1) is connected to the receiver of another (Rx1 or Rx2 according to the scheme set-
up)
Products can be supplied with the following fibre-optic channel arrangements:
Ch 1 Ch2
850 nm 850 nm
1300 nm multi-mode Not fitted
1300 nm multi-mode 1300 nm multi-mode
1300 nm single-mode Not fitted
1300 nm single-mode 1300 nm single-mode
Chapter 15 - Fibre Teleprotection P54A/B/C/E
320 P54xMED-TM-EN-1
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