Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output command process
Reexamination Certificate
1999-04-22
2003-12-02
Lee, Thomas (Department: 2185)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output command process
C710S007000, C710S020000, C710S033000, C709S250000, C709S251000
Reexamination Certificate
active
06658495
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a data communication apparatus and a method for performing data communications effectively, and a data recording/reproducing apparatus and a method.
BACKGROUND ART
As one of the communication specification, for example, there is a fibre channel developed by ANSI (American National Standards Institute). It is spelled ‘fibre’ in the fibre channel different from ‘fiber’ as in so-called optical fiber.
An apparatus performing communications via the fibre channel is called a node and, each node performs transmitting and receiving data via a port (communication port). In the fibre channel, cables connecting between the ports are not especially limited. For example, optical fibers (fiber cable), coaxial cables (copper cable) or twisted pair cables may be used.
Further, the fibre channel is one of serial communication methods, and the transmission speed is faster and the transmission distance is longer comparing with other serial communication methods. Further, it is assumed that the fibre channel may be applied in the data transmission between various kinds of apparatuses hereafter since TCP/IP (Transmission Control Protocol/Internet Protocol) which has recently grown very rapidly and other various kinds of protocols can be used in addition and, further, its usage can be broadly extended to be connected.
Here, in the fibre channel at the moment, 128 Mbps (bit per second), 256 Mdps, 512 Mbps, -Gbps are defined as the transmission speed and, in the near future, extending it to 2 Gbps and 4 Gbps is expected. Further, the transmission distance varies depending on the transmission speed, however, it is defined as about 0.175 km to 10 km in the fiber cable, about 10 m to 100 m in the copper cable and about 50 m to 100 m in the twisted pair cable respectively.
Further, a port of the fibre channel as shown in
FIG. 15
, for example, has a transmitter which transmits information and a receiver which receives information respectively. Further, as substantial connecting forms of the fibre channel, as being classified broadly there is a point-to-point topology as shown in FIG.
16
and an arbitrated loop topology as shown in FIG.
17
.
In the point-to-point topology as shown in
FIG.16
, one of the transmitter is connected to the other receiver, and one of the receiver is connected to the other transmitter using only two ports. In the topology, the transmission speed, the transmission medium (cable connecting the both) and the protocol of the two ports and so on are required to be the same.
As shown in
FIG.17
, the arbitrated loop topology is formed with three or more ports, and a transmitter of one port is connected to a receiver of the other port so that a ring network is formed.
FIG. 17
shows an arbitrated loop topology formed with four ports A to D. Here, a transmitter of the port A and a receiver of the port B, a transmitter of the port B and a receiver of the port C, a transmitter of the port C and a receiver of the port D, and a transmitter of the port D and a receiver of the port A are connected respectively. In the arbitrated loop topology, the up to 127 ports can be connected so far.
In the point-to-point topology, transmitting and receiving data are performed subjecting to the other port, other than the transferring port itself since it is formed with two ports. However, in the arbitrated loop topology, there may be a case where transmitting and receiving data are performed via the port which is not the subject of the transmission and reception of the data.
That is, in
FIG. 17
, for example, when data is transmitted from the port A to the port C, data addressed to the port C is transmitted from the transmitter of the port A to the receiver of the port B. When the port B receives data addressed to the port C by the receiver, then, the data is transmitted from the transmitter of the port B to the receiver of the port C. In the port C, data addressed to the port C itself from the port A is received as described above. In this case, the port B functions as so-called repeater which only transmits data as it is received by the receiver from the transmitter.
By the way, in the specification of the fibre channel, a jitter (deviation) of ±100 ppm (parts per million; 1 ppm=1/100 million) is allowed in clocks of the transmitter of each port. Further, in the fibre channel, receiving data is performed synchronizing with the clock obtained from data so that data can be received reliably by the receiver even if there is a jitter in the clock of the transmitter as mentioned.
That is, a receiver of one port operates synchronizing with the clock of a transmitter of the other port being connected. Accordingly, for example, as shown in
FIG. 18
, the transmitter of the port A and the receiver of the port B, the transmitter of the port B and the receiver of the port C, the transmitter of the port C and the receiver of the port D and the transmitter of the port D and the receiver of the port A are synchronized with the identical clocks respectively.
Here, in the following description, an operation clock of the transmitter or the receiver forming the same port is called a transmitter clock or a receiver clock respectively where appropriate. The receiver clock is identical to the transmitter clock of the transmitter of other port connected to the receiver.
As described above, a receiver of one port operates synchronizing with the transmitter clock of the transmitter of the other port connected to the receiver. In one port, there is a deviation of 200 ppm in maximum between the transmitter clock and the receiver clock since a jitter of ±100 ppm is allowed in the transmitter clock.
In
FIG. 19
, in regard to a standard clock, a clock with a deviation of 100 ppm (FIG.
19
(A); transmitter clock or receiver clock) and a clock with a deviation of −100 ppm (FIG.
19
(B); receiver clock or transmitter clock) are shown. Accordingly, a deviation of 200 ppm in maximum occurs in the two clocks. Further, 1 clock of skew (clock skew) per 5000 clocks occurs between the two clocks having the deviation of 200 ppm.
On the other hand, in the arbitrated loop topology, the port transmitting data is required to obtain the right to use a bus (arbitrated loop) before transmitting data when transmitting data from a port to the other port. The competition to obtain the right to use the bus is called arbitration.
The port transmitting data is required to perform transmission of data after obtaining the right to use the bus by arbitration and, further, opening the port to which data is transmitted.
In the fibre channel, as a command to open the port connected in the arbitrated loop topology, OPNyx, OPNyy, OPNfr, OPNyr and so on, called order set are defined.
Here, OPNyx is used in a full duplex and OPNyy is used in a half duplex respectively. Further, OPNfr is used when opening all the ports forming the arbitrated loop topology and OPNyr is used when opening a plurality of ports among the all respectively.
FIG. 20
shows a format of the order set OPNyr, defined in the fibre channel.
The order set OPNyr, is formed with 1 transmission word (TW) as shown in FIG.
20
. Here, 1 transmission word is a data volume transmitted and received in 1 clock in the fibre channel and is 4 bytes (32 bits) so far.
In the fibre channel, a 8B/10B converted data is transmitted and received for decreasing transmission errors. In the first byte (the 31st bit to the 24th bit) of the order set OPNyr, a special code called K28.5 which is a code being 8B/10B converted is allocated. The special code is used to obtain word synchronism when reproducing a parallel data from a serial data.
In the second byte from the forefront (the 23rd bit to the 16th bit), a special code called D17.4 which is a code being 8B/10B converted is allocated. This shows that the order set is the order set of OPNyr. In the third byte (the 15th bit to the 8th bit), a port address AL_PD of the port to be opened is allocated. In the fourth byte (the last 1 bit), (the 7th bit to the 0th bit), a special code called D
Bell Boyd & Lloyd LLC
Cao Chun
Lee Thomas
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