Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-06-25
2003-08-12
Holloway, III, Edwin C. (Department: 2635)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S438000
Reexamination Certificate
active
06606320
ABSTRACT:
TECHNICAL FIELD
This invention relates to a data transmission system, a data transmission method, a data transmitting apparatus, and a data transmitting method, and more particularly to a data transmission system, a data transmission method, a data transmitting apparatus, and a data transmitting method which are capable of more efficiently carrying out transmission of data.
BACKGROUND ART
FIG. 1
represents an example of packet transmission format of the Institute of Electrical and Electronics Engineers, inc. (hereinafter referred to as IEEE) 1394 serial bus. As shown in this figure, packet is subjected to transmission at Isochronous Cycle of 125 &mgr;sec. At leading portions of respective isochronous cycles, Cycle start arbitration
101
-
1
,
101
-
2
, . . . ,
101
-n are disposed (allocated), and Cycle start packet
102
-
1
,
102
-
2
, . . . ,
102
-n are disposed (allocated) subsequently to Data prefix
111
at the next thereto. At the next of these Cycle start packet
102
-
1
,
102
-
2
, . . . ,
102
-n, Iso_gap
110
is disposed (allocated) subsequently to Data end
109
.
In this case, Cycle start constituted by Cycle start arbitration
101
-
1
,
101
-
2
, . . . ,
101
-n and Cycle start packets
102
-
1
,
102
-
2
, . . . ,
102
-n is packet sent by cycle master node within IEEE 1394 serial bus (hereinafter simply abbreviated as 1394 serial bus or bus according as occasion may demand) and indicating start of isochronous cycle. Data prefix
111
indicates start of acknowledge packet in data packet or asynchronous transfer, and Data end
109
indicates end of acknowledge packet in data packet or asynchronous transfer. Iso.gap
110
represents idle of 1394 serial bus and sub action of the isochronous transfer is separated by Iso_gap
110
.
At the next of Iso_gap
110
, arbitration
103
-
1
,
103
-
2
, . . . ,
103
-n are disposed (allocated). At the portion next thereto, there are disposed (allocated) isochronous packet
104
-
11
,
104
-
12
, . . . ,
104
-nn of n number of channels with respect to client terminals connected to the 1394 serial bus. At leading portions of respective isochronous packets
104
-
11
,
104
-
12
, . . . ,
104
-nn, Data prefix
111
are respectively disposed (allocated).
In the isochronous transfer, broadcast transmission is carried out with respect to the client terminal by using channel No. represented by 8 bits. The receiving side takes thereinto only data of channel No. that the own side desires.
At the last portions of the n-th isochronous packet
104
-
1
n,
104
-
2
n, . . . ,
104
-nn, Data end
109
are respectively disposed (allocated). At the portions next thereto, Subaction_gap
112
is disposed (allocated). At the next of Subaction_gap
112
, arbitration
105
-
1
,
105
-
2
, . . . ,
105
-n are disposed (allocated). Further, Asynchronous Transfer
106
-
1
,
106
-
2
, . . . ,
106
-n which are asynchronous packet are disposed (allocated) through Data prefix
111
and Data end
109
are respectively disposed (allocated) subsequently thereto. At the portion next thereto, Ack Transfer
107
-
1
,
107
-
2
, . . . ,
107
-n as acknowledge packet are disposed (allocated) subsequently to Data prefix
111
, and Data end
109
are respectively disposed (allocated) subsequently thereto.
Subaction_gap
112
indicates idle of 1394 serial bus. Respective terminals monitor this gap time to thereby judge whether or not transmission can be made. When idle of a fixed time or more (longer than Iso_gap
110
) is lasted (continued), the node which desires asynchronous transfer judges that bus can be used to execute arbitration (arbitration
105
-
1
,
105
-
2
, . . . ,
105
-n) for the purpose of bus acquisition. The node which has acquired use right of bus transmits data of asynchronous transfer (Asynchronous Transfer
106
-
1
,
106
-
2
, . . . ,
106
-n). The node which has received data of asynchronous transfer transmits acknowledge packet (Ack Transfers
107
-
1
,
107
-
2
, . . . ,
107
-n) as reception result with respect to node of sending source of its data which has been transmitted.
In
FIG. 1
, the case where transmission of one asynchronous packet is carried out is taken as an example. Subaction_gap
114
is last disposed (allocated) and Cycle start arbitration
108
-
1
,
108
-
2
, . . . ,
108
-n of the next isochronous cycle are disposed (allocated) subsequently thereto. In this case, Cycle start arbitration
108
-
1
of isochronous cycle #
1
is Cycle start arbitration
101
-
2
located (in point of time) at the leading portion of the isochronous cycle #
2
.
Moreover, after isochronous transfer, asynchronous transfer can be executed until the next cycle. Even if this asynchronous transfer is continued until transmission time point of the next cycle start, that asynchronous transfer is not interrupted to stand by idle of the next bus, whereupon cycle start is caused to undergo transmission by the cycle master node. In the case where one cycle is continued for more than 125 &mgr;sec, the next cycle is shortened accordingly.
Lengths of respective isochronous channels (isochronous packets) are caused to be equal lengths calculated from the transmission band allocated to isochronous channels every respective isochronous cycles.
At respective isochronous packets, there are required overhead corresponding to time for Data prefix required at Physical Layer of IEEE 1394 (the number of bits corresponding to time corresponding to 16 clocks of BASE_RATE of 100 Mbps (precisely speaking, 98.304 Mbps) as basic rate (speed), overhead corresponding to time for Data end (the number of bits corresponding to time corresponding to 24 clocks of the BASE_RATE), and header for application for taking matching of isochronous packet header and application layout. In this case, according as length of isochronous packet is shortened, i.e., according as band required for isochronous channel becomes smaller, the ratio of these overheads becomes great.
For example, in the case where stream of AAL (ATM Adaptation Layer) 5-PDU (Protocol Data Unit) containing MPEG (Moving Picture Experts Group)-PS packet having the same length of 32 K bytes with respect to respective client terminals through IEEE 1394 serial bus from video server on ATM (Asynchronous Transfer Mode) network is caused to undergo transmission by CBR (Constant Bit Rate) service of 2 Mbps (2.048×10
6
bps), ATM/1394 Bridge which carries out interface processing between ATM and IEEE 1394 is adapted so that isochronous packet length to be transmitted with respect to respective client terminals becomes equal to 32 bytes (=2.048×10
6
/8000/8) when IP/ATM (IP over ATM) header prescribed at the IP (Internet Protocol) and RFC (Request For Comments) 1483 is excluded.
In this case, overheads in the respective isochronous packets become equal to 22 bytes in total because it is required that overhead of Data prefix is about 16 bits (=2 bytes), isochronous header and CRC (Cyclic Redundancy Check) field prescribed at the Link Layer of IEEE 1394 are 12 bytes, and header for application is at least 8 bytes. In this case, since the overhead of Data end is reversely proportional to the number of isochronous packets transmitted within one isochronous cycle, it becomes very small value in the case of the prior art. For this reason, this is neglected. As a result, from ATM/1394 Bridge, with respect to isochronous packet to respective client terminals, 41% (=22 bytes/(22 bytes+32 bytes)) of the entirety serves as overhead, and very high rate is obtained.
Moreover, in the case where transmission speed (rate) of the 1394 serial bus is 100 Mbps, the maximum value of transmittable isochronous packet becomes equal to 1024 bytes. However, at this time, since the number of containable (connectable) client terminals of ATM/1394 Bridge is calculated as follows. Since overhead of the layer of the link layer or more of the IEEE 1394 constitutes problem, 19 terminals are limit per one 1394 serial bus by the following formula when overhead of 20 bytes obtained by subtracting only Data prefi
Nomura Takashi
Takizuka Hiroshi
Frommer William S.
Frommer & Lawrence & Haug LLP
Holloway III Edwin C.
Smid Dennis M.
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