Multiplex communications – Wide area network – Packet switching
Patent
1993-05-04
1995-01-31
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
375107, 375108, H04L 704
Patent
active
053864182
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a synchronous data communication network, and more particularly to a method of switching among a plurality of synchronizing signal sources.
BACKGROUND ART
Recently, as a consequence of a demand for standardization of digital communication networks, many of those networks are synchronous networks, and reliability of a synchronizing signal responsible for synchronization is called for. Known synchronous communication networks include the one using an optical fiber cable for performing transmissions of high-speed digital signals. In such a synchronous communication network, an oscillator for generating a main clock is provided in a system. This main clock is shared by both the transmitting side and the receiving side. Normally, a plurality of input signals, by being subjected to a plurality of times of hierarchical multiplexing processes, are converted into a high-speed multiplexed signals before transmission. The input signals are multiplexed in a byte unit. Upon each multiplexing, signal transmission rate increases.
One of the known high-speed transmission network utilizing byte-multiplexing is SONET (synchronous optical network). As shown in FIG. 1, an STS-1 signal of this SONET system is configured such that one frame is constructed of 6480 bits (=90 bytes.times. 8 rows.times.8 bits), where 1 byte represents 8 bits. The duration of one frame is 125 .mu.s, and the bit rate is 51.84 MHz. The frame format of the STS-1 signal shown in FIG. 1 is provided in each channel. The headmost 2 bytes of the frame format are frame synchronizing patterns A1, A2, and the next 1 byte is a channel identification pattern C1. SOH (section overhead), LOH (line overhead), and POH (path overhead) are control data added to the information to be transmitted.
A plurality of STS-1 signals having the above frame format are subjected to a simple byte-multiplexing (meaning that no format conversion is carried out). FIG. 2 shows how three STS-1 signals are byte-multiplexed. The STS-1 signals for three S channels #1, #2 and #3 are byte-multiplexed so that an STS-3 signal having 155.52 MHz rate is generated. This STS-3 signal is standardized as an STM-1 signal according to the CCITT recommendation. It is assumed that an STS-1 signal is transmitted as an optical signal. At the head of the data in the three channels #1-#3, the 2-byte frame synchronizing patterns A1, A2 and the 1-byte channel identification pattern C1 are added. As indicated by broken lines, the STS-3 signal is formed by byte-multiplexing. It is to be noted that no frame patterns unique to the resultant STS-3 signal are inserted. Byte-multiplexing in this system is carried out such that the heads of the signals on the channels #1-#3 are in sync with each other, with the result that the frame-multiplexed synchronizing pattern of an STS-3 signal is of a 6-bit construction.
The frame synchronizing patterns A1, A2 are the same for the channels #1-#3, A1 being "11110110" and A2 being "00101000". The channel identification patterns C1 for the channels #1-#3 are set to be different from channel to channel.
Referring back to FIG. 1, B1-B3 are byte interleave parities; C2 is a signal label byte indicative of the presence or absence of information; D1-D12 are data communication bytes for transporting, for example, information relating to the state of different units; E1, E2 are order wire bytes; F1, F2 are user channel bytes; G1 is a path status byte for detecting a parity error of an input signal and returning the detected error to the originating unit; H1, H2 are pointers having a stuffing function for incorporating an asynchronous system; H3 is a pointer having a variable slot function in stuffing; H4 is a multi-frame indication byte; J1 is a trace byte; K1, K2 are automatic protection switch bytes; and Z1-Z5 are reserved bytes.
At the receiving side, frame synchronization is effected by detecting the 6-byte frame multiplexed synchronizing pattern of the STS-3 signal as shown in FIG. 2. As indicated by the broken lines, th
REFERENCES:
patent: 4794596 (1988-12-01), Gloyne et al.
patent: 4847836 (1989-07-01), Keilholz
patent: 5068877 (1991-11-01), Near et al.
Komuro Yasuko
Yajima Noboru
Yoshida Hiroshi
Fujitsu Limited
Safourek Benedict V.
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