Source: http://www.google.com/patents/US6314097?dq=inventor:%22Arthur+R.+Hair%22
Timestamp: 2017-11-24 10:06:20
Document Index: 478965052

Matched Legal Cases: ['art 34', 'art 34', 'art 34', 'art 22', 'art 39', 'art 22', 'art 39', 'art 39', 'arts 61', 'art 64', 'art 65', 'art 65', 'art 68', 'art 65', 'art 68', 'art 65']

Patent US6314097 - Transmission device - Google Patents
A transmission device to which transmission lines over which signals including overhead information are transferred, includes a first part which gathers and transfers the overhead information of the signals transferred over the transmission lines to a second part, and the second part which terminates...http://www.google.com/patents/US6314097?utm_source=gb-gplus-sharePatent US6314097 - Transmission device
Publication number US6314097 B1
Application number US 08/908,064
Publication number 08908064, 908064, US 6314097 B1, US 6314097B1, US-B1-6314097, US6314097 B1, US6314097B1
Inventors Katsuichi Ohara
US 6314097 B1
A transmission device to which transmission lines over which signals including overhead information are transferred, includes a first part which gathers and transfers the overhead information of the signals transferred over the transmission lines to a second part, and the second part which terminates the overhead information of the signals.
1. A transmission device which sends and receives signals, including overhead information, over transmission lines,
the transmission device comprising:
a first part which adds and drops overhead information every N bytes for each of the transmission lines where N is an integer greater than 2;
a second part which assembles the overhead information concerning the transmission lines dropped by the first part into a first packet and extracts overhead information to be added from a second packet; and
a third part which extracts the overhead information from the first packet and assembles the overhead information into the second packet,
said third part comprising:
a fourth part that converts data forming the overhead information terminated into continuous data;
a memory that stores the overhead information supplied from the second part; and
a digital PLL circuit including a counter generating a read clock applied to the memory from which the overhead information is read, and a controller which controls the counter in accordance with a frequency variation in the overhead information so that the frequency of the read clock is changed based on the frequency variation.
2. The transmission device as claimed in claim 1, wherein the second part includes an asynchronous transfer system in which the overhead information of the signals is transferred to the third part in asynchronism with the signals transferred over the transmission lines.
First, a description will be briefly given of the SONET. The SONET is described in, for example, William Stallings, “ISDN and Broadband ISDN, Macmillan Publishing Company, 1992, pp. 546-558.
In the SONET, a multiplexed optical carrier (OC) is transmitted. The transmission device converts the optical signal (carrier) into an electric signal and vice versa. The electric signal is called a synchronous transport signal (STS). The basic bit rate of the SONET is 51.84 Mbps. The optical carrier having the above basic bit rate is expressed as OC-1. Generally, an optical carrier or signal is expressed as OC-N where N (optical carrier level N) is an integer, and a corresponding electric signal is expressed as STS-N (synchronous transport carrier level N). For example, the optical carrier OC-12 is an optical carrier or signal having a bit rate of 622.080 Mbps (=12×51.84 Mbps). In the SONET, signals having bit rates which are integer multiples of the basic bit rate. The optical carrier OC-12 is obtained by multiplexing 12 STS-1 signals at the byte level to thereby generate an STS-12 signal and by converting the STS-12 signal into an optical signal. Generally, the multiplexing of STS-N signals employs a byte-level interleave process.
FIG. 1 is a block diagram showing the outline of a network of the SONET. Electric signals from terminals 1 and 2 are respectively multiplexed by transmission devices 3 and 7, and resultant multiplexed signals are converted into light signals, which are then sent to transmission paths 8 formed of optical fiber cables. Repeaters 4, 5 and 6 are provided in the transmission paths 8. Particularly, the repeater 5 has a function of terminating the optical signals (the above function is called an add/drop function). As shown in FIG. 1, terms “section”, “line” and “path” are defined in the SONET. The section corresponds to an optical transmission part between transmission devices, between repeaters or between a transmission device and a repeater. The line corresponds to an optical transmission part between transmission devices, between repeaters or between a transmission device and a repeater, each having the terminating function. The path indicates the end-to-end optical transmission part.
FIG. 2A is a diagram showing the frame format of the signal STS-1. As shown in FIG. 2A, the signal STS-1 consists of 810 octets, and is transferred every 125 μs. The 810 octets consists of nine rows arranged in a matrix formation, each of the rows consisting of 90 octets. In other words, the signal STS-1 has a 9×9 matrix formation. The first three columns (three octets×nine rows) forms an overhead in which a variety of control information concerning transmissions. The first three rows of the overhead forms a section overhead, and the remaining six rows forms a line overhead. The control information forming the overheads is also referred to as overhead information.
FIG. 4 is a block diagram of an example of the SONET. The SONET shown in FIG. 4 includes transmission devices 10A, 10B, 10C and 10D, each of which has a higher bit rate of the bit rates of other transmission devices provided in the SONET. The transmission devices 10A-10D are coupled by means of optical fiber cables 11 1 and 11 2 in a dual loop (ring) formation. Transmission devices having bit rates equal to or lower than the transmission devices 10A-10D can be coupled to the transmission devices 10A-10D. For example, transmission devices 12 a, 12 b, 12 c, 12 d, . . . are connected to the transmission device 10A. The transmission device 10A multiplexes signals transmitted from the transmission devices 12 a, 12 b, 12 c, 12 d and so on via optical fiber cables 13 a, 13 b, 13 c, 13 d and so on. Then, the transmission device 10A sends a resultant multiplexed signal to either the transmission device 10B or 10D or both thereof. For the sake of convenience, the terms “east” and “west” can be used to describe the directions in which the signals are transferred. In FIG. 4, the transmission device 10D is located at the east side of the transmission device 10A, and the transmission device 10B is located at the west side thereof.
The opto-electric signal converter 31 converts a light signal received via an optical fiber cable (which is, for example, the east side optical fiber cable 11 1) into an electric signal. The descrambler 32 descrambles the electric signal form the converter 31. The opto-electric signal converter 31 extracts a clock signal CLK from the converted electric signal, and sends the extracted clock signal CLK to the framer circuit 33. The framer circuit 33 produces a frame synchronizing signal from a descrambled signal (which is indicated as DATA in FIG. 6) and the clock signal CLK. The frame synchronizing signal indicates one frame, which corresponds to nine lines each consisting of 90 octets in the case of the signal STS-1. The frame synchronizing signal thus produced is applied to the overhead byte drop part 34 and the signal demultiplexer 35. The overhead byte drop part 34 separates the overhead and data from the above signal DATA. The overhead (DROPOHB) thus separated is output to the overhead terminator 26. The signal demultiplexer 35 demultiplexes, on the frame basis, the data supplied from the overhead byte drop part 34 in synchronism with the frame synchronizing signal. The dropped data is then output to the TSA part 22 via the multiplexer/demultiplexer 22. The above relates to a receive system of the line terminator 25 w.
A transmit system of the line terminator 25 w operates in synchronism with a master clock MCLK, which has the same frequency as that of the clock signal CLK extracted in the receive system. The frame pulse generator 38 generates a frame pulse from the master clock signal MCLK, and outputs the frame pulse to the overhead byte add part 39 and the signal multiplexer 40. The signal multiplexer 40 multiplexes data (ADD Data) received from the TSA part 22 via the multiplexer/demultiplexer 22 on the frame basis. The overhead byte add part 39 adds the overhead (ADD OHB) to the data multiplexed on the frame basis. In FIG. 6, the output signal of the overhead byte add part 39 is indicated as DATA. The descrambler 37 descrambles the signal DATA. The electro-optical signal converter 36 converts the scrambled signal from the scrambler 37 into a light signal, which is then output to the light fiber cable.
It is a general object of the present invention to provide a transmission device in which the above disadvantages are eliminated.
FIG. 9 is a block diagram of a transmission device according to an embodiment of the present invention. The transmission device shown in FIG. 9 includes line termination parts 61 1, 61 2, . . . , 61 n, a multiplexer/demultiplexer (MUX/DMUX) 62, a time slot assignment part (TSA) 63, an ATM relay/continuity protection part 64, and an overhead processing part 65. The overhead processing part 65 is connected to a CPU bus 67, to which a CPU 66 is connected. A data processing part 68 which processes DCC data is connected to the overhead processing part 65. As is well known, the term ATM is an abbreviation of Asynchronous Transfer Mode. The CPU 66 and the data processing part 68 shown in FIG. 9 can be provided inside of the transmission device or the outside thereof. As will be described later, the overhead processing part 65 is equipped with a plurality of ports (for example, a port for connection with a speech codec) other than a port via which the DCC data is output. However, these ports are omitted in FIG. 9 for the sake of simplicity.
More particularly, if the output signal of the comparator 204 (the difference between the current count value and the previous count value) falls within a given range corresponding to a tolerable frequency range, the output signal of the comparator 204 passes through the filter 205 and is output to the up/down counter 206. If the output signal of the comparator 204 is out of the given range, the filter 205 blocks the output signal of the comparator 204. If the output signal of the comparator 204 falls within the given range and the value obtained by subtracting the previous count value from the current count value is a positive value, the output signal of the comparator 204 functions to decrement the count value of the up/down counter 206 by value “1” corresponding to one cycle of the master clock MCLK. If the output signal of the comparator 204 falls within the given range and the value obtained by subtracting the previous count value from the current count value is a negative value, the output signal of the comparator 204 functions to increment the count value of the up/down counter 206 by value “1” corresponding to one cycle of the master clock MCLK. The clock signal CLK thus generated by the up/down counter 206 is applied to the FIFO memory 207 from which the overhead byte is read at the timing defined by the clock signal CLK.
It will now be assumed that one overhead byte is input every 125 μs, as shown in part (a) of FIG. 16. For example, the ATM cell generating timing will vary within a maximum range of ±95 μs. It is required to detect the line frequency variation even if a maximum deviation of the line frequency (equal to ±95 μs) occurs. Hence, the comparator 204 is operated in synchronism with a pulse signal of 2 kHz (having a cycle of 250 μs), as shown in part (d) of FIG. 16. Part (c) of FIG. 16 shows 125 μs intervals synchronized with the pulse signal shown in part (d) of FIG. 16.
Overhead bytes #1, #2 and #3 shown in part (a) of FIG. 16 have frequency variations. The operation of the comparator 204 is carried out every 250 μs. Under the above condition, if the overhead bytes shown in part (a) of FIG. 16 are indicated by using a pulse signal which changes when two overhead bytes are detected, such a pulse signal indicates the overhead bytes, as shown in part (b) of FIG. 16. A pulse signal shown in part (e) of FIG. 16 indicates the difference between the phase shown in part (b) of FIG. 16 and the phase shown in part (d) thereof, and corresponds to the output of the clock counter 201 shown in FIG. 15. Letters “k”, “l”, “m” and “n” shown in part (f) of FIG. 16 denote the count values of the clock counter 201.
If the up/down counter 206 is controlled in response to a frequency deviation as large as the maximum deviation equal to ±95 μs, the count value thereof will be changed greatly, and the continuity of data will be destroyed. The input timing deviation of the DPLL circuits 133 obtained when there is no deviation of the ATM cell generating timing is equal to 40 ppm. Hence, in the case where the overhead byte is input every 125 μs, the overhead byte will deviate only by 5 ns. Since the comparing operation of the comparator 204 is carried out every 250 μs, the overhead byte have a deviation of 10 ns. The time 10 ns corresponds to 0.4 if the overhead byte is sampled by a clock signal having a frequency of 38.88 MHz. When taking into account an accumulation of deviation, the up/down counter 206 is controlled when the count value of the clock counter 201 indicates falls within a range of (the previous number of samples)±2. That is, the count value of the up/down counter 206 can be incremented or decremented by 1 every 250 μs by the master clock MCLK.
In other words, when (the current number of samples)−(the previous number of samples)=+n (n=2 in the above example), the count value of the up/down counter 206 is decremented by 1 only for the next time. When (the current number of samples)−(the previous number of samples)=−n, the count value of the up/down counter 206 is incremented by 1 only for the next time. Hence, if (the current number of samples)−(the previous number of samples) is out of the range of ±n, the difference between the current number of samples and the previous number of samples is discarded, and the count value of the up/down counter 206 is not changed.
In the case shown in FIG. 16, the difference (1−m) or (m−1) is calculated and it is determined whether the difference falls in the range of ±2. Based on the result of the above determination, the count value of the up/down counter 206 is controlled.
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U.S. Classification 370/392, 370/397, 398/9
International Classification H04L12/951, H04Q3/00, H04Q11/04, H04J3/00, H04J3/08
Cooperative Classification H04L2012/5649, H04Q11/0478, H04J3/085, H04L2012/5672
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:OHARA, KATSUICHI;REEL/FRAME:008756/0878