Fibre ink superframe format

#This invention relates to a method for communicating data from a transmission facility to a receiving facility over a serial link and to a communication system for utilising a pair of serial links.

#Optical fibre cables provide high speed serial data links. DS-512 is a known protocol for sending data over an optical fibre cable. According to this protocol, transmissions comprise frames of data, each frame consisting of 512 words. Each word is a ten bit payload word which is expanded to twelve bits prior to transmission in order to embed clock information in the word for extraction by the receiver. Words of like rank in each frame (e.g., the fifty-fourth word in each frame) comprise data from one channel (e.g., one telephone connection). The first word of each frame (i.e., channel 0) is a framing word. The framing word comprises a set pattern, which in the standard for 12 bit code is unique and is the hexadecimal number "782". A receiver uses the framing word to ensure it stays in synchronisation with the transmitter during a transmission.

#In the case of an alarm situation (e.g., a loss of synchronisation or a failure of one of the transmitter or receiver), the transmitting end may flood the channel data with specific codes, overwriting the payload data words of the channels.

#In the drawings which illustrate example embodiments of the invention,

#FIG. 1 is a schematic diagram of a communication system for utilising a pair of serial links,

#FIG. 2 is a detail view of a portion of FIG. 1,

#Turning to FIG. 1, a communication system generally illustrated at 10 comprises a first transceiver facility 12a and a second transceiver facility 12b linked by a link 17 which comprises a pair of optical fibres 16a, 16b. Fibre 16a is for sending data from facility 12a to 12b and fibre 16b is for sending data from facility 12b to 12a. Facility 12a is connected to a data source/sink 18a, and facility 12b is connected to a data source/sink 18b. Each transceiver 12a, 12b comprises a processor 20a, 20b which is connected for two-way communication with a link controller (LC) 22a, 22b. It is the LC of the facility which is connected between the link 17 and the data source/sink 18a, 18b.

#Turning to FIG. 2, which details a portion of FIG. 1, each LC 22a, 22b includes a two word transmit buffer 30a, 30b and an eight word first-in-first-out (FIFO) receive buffer 32a, 32b. The transmit buffer receives words from the processor on bus 34a, 34b. Each FIFO receive buffer 32a, 32b sends words to its processor 20a, 20b on bus 34a, 34b. As will be explained hereinafter, the transmit buffer holds information facility data words for transmission and the FIFO receive buffer holds received information facility data words for passing to the processor 20a, 20b at the receiving end.

#When an LC 22a, 22b of a facility 12a, 12b receives data from the data source/sink 18a, 18b to which it is connected, it organises the data into superframes for transmission over a serial link 17. More particularly, each current communication channel established between the data source/sink and the LC has, or is given, a channel number between 1 and 511. Turning to FIG. 3, received data words are organised serially into consecutive frames, with words from channel 1 allocated to rank 1 in each frame, words from channel 2 allocated rank 2 in each frame, and so on up to words from channel 511, which are allocated to the final rank of the frame. Consequently, there is one word per channel accommodated in each frame. The data words received from the data source/sink may be described as payload data words since they comprise words which are for communication between remote stations. As explained more fully hereinafter, the zeroth rank of each frame is reserved for a non-payload word.