Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-08-07
2003-01-28
Ton, Dang (Department: 2732)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S241000
Reexamination Certificate
active
06512767
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device through which plural bus type transmission media are connected to one another and packets are exchanged, and also to a controlling device and a controlled device which are used under a situation where such plural transmission media are connected to the devices.
2. Related Art of the Invention
At present, as a digital interface which is useful in a digital AV apparatus or a computer peripheral apparatus, known is an IEEE 1394 interface which is an interface standardized by IEEE (I-triple-E) as the generation of a multimedia high-speed serial interface (see IEEE Std 1394-1995 High Performance Serial Bus).
Apparatuses which are to be connected to an IEEE 1394 interface (hereinafter, such an apparatus is referred to as a node) are connected in the form of a tree structure having branches, so that a data output from any node is transmitted to all the other nodes. Although the configuration has a tree structure, therefore, it actually functions as a bus. An identifier which is called a node ID is assigned to each of apparatuses which are connected to a bus in this way. A node ID can have a value in the range from 0 to 62. As a result, 63 apparatuses can be connected to one bus. In view of the tree structure, the connection between two arbitrary apparatuses can be performed by 16 hops at most, and the maximum length of a cable between apparatuses is 4.5 m. In the case where 64 or more apparatuses are to be connected or the connection length is longer than 4.5 m, a bus bridge which assigns IDs to busses and through which the busses are connected to one another can be used. According to this configuration, 1,023 busses can be connected to one another. At present, IEEE proceeds the standardization of such a bus bridge.
By contrast, an IEEE 1394 interface is an interface in which a node can be connected or disconnected during operation. The node IDs are automatically assigned by an operation initializing a bus which is performed when a new node is connected to the bus or conversely when a node is disconnected from the bus (hereinafter, such an operation is referred to as a bus reset). Therefore, a node can be connected or disconnected without requiring the user to set an ID. On the other hand, such a node ID is used as an address for transmission and reception of a packet, and node IDs are changed as a result of a bus reset. When a bus reset once occurs, therefore, the source node must check the node ID of the destination node at the present timing, before a packet is transmitted.
In the bus reset process, each of connected nodes transmits a self ID packet containing information relating to its own functions, in an order which is defined under a certain rule. The self ID packet further contains information indicative of the branching state, that indicative of the ability of the node relating to the bus management, and that relating to the transmission speed to which the node corresponds. In IEEE 1394, three transmission speeds, i.e., 100 Mbps, 200 Mbps, and 400 Mbps are defined. It is guaranteed that all nodes correspond to the transmission speed of 100 Mbps. When two nodes which perform transmission and reception of a packet and all relay nodes between the two nodes correspond to speeds of 200 Mbps and higher, the packet transmission can be performed by using a transmission speed of 200 Mbps or higher. According to information contained in the self ID packet, it is possible to judge whether a transmission speed of 200 Mbps or higher can be used or not. When the self ID packet is received, it is possible to know the number of nodes connected to the bud, the connection state of the bus, etc. Therefore, information such as a delay time for propagation which depends on the connection state of the bus can be known.
IEEE 1394 defines two kinds of packets. One of the packets is used for transmitting a data which must be processed in real time, such as video and audio, and called an isochronous packet. The other packet is used for transmitting a usual data which is not required to be processed in real time, and called an asynchronous packet. An isochronous packet is guaranteed to be transmitted in a reserved bandwidth, but cannot be subjected to processes such as retransmission. On occasions when such a process is necessary, an error correction process is performed. In advance of transmission, as described above, a bandwidth to be used must be reserved. By contrast, with respect to an asynchronous packet, processes such as retransmission can be performed, but the time period for transmission of the packet is not guaranteed because retransmission may be performed.
Among the two kinds of packets, an asynchronous packet undergoes transmission and reception processes as an access to a CSR (Control and Status Register) address space which is defined in ISO/IEC 13213 (Control and Status Register Architecture for Microcomputer Buses) and IEEE 1394 and which the corresponding node has. In other words, in IEEE 1394, all nodes connected to a bus have a virtual 48-bits address space and communication between nodes is realized as a writing or reading operation on the respective address space. In an asynchronous packet, therefore, a packet for performing a writing or reading operation on an address space is defined.
When a data which is not required to be processed in real time is to be transmitted from a node, the node transmits a packet for writing the data into the destination address space. The reception side judges the kind and type of the data from the written address, and returns a response indicating whether the reception has been normally performed as a result of the writing operation or not (a write request and a write response). By contrast, when a node requests a data, a request for reading out the address of the request destination is transmitted. In this case, the node which receives the data request judges the kind and contents of the requested data, from the address of the read request, and then transmits an appropriate data as a response to the reading operation (a read request and a read response). In this way, the data transfer is realized by writing a data into an address space, a read request, and a response to the request.
FIGS. 1 and 2
show such an asynchronous packet. The portions of the same contents are designated by the same reference numeral.
FIG.
1
(
a
) shows a packet for performing a write request, and FIG.
1
(
b
) shows a packet for performing a response to the write request. FIG.
2
(
a
) shows a packet a packet for performing a read request, and FIG.
2
(
b
) shows a packet for performing a response to the read request. The write request, the read request, and the responses to the requests are distinguished from one another by a kind
106
.
The write request is transmitted with using a packet of a write request packet
101
, and writing the node ID of the destination to which the write request is to be transmitted into a destination ID
103
, the ID of the node which performs the write request into a source ID
108
, the leading address into which the data is to be written, into a write leading address
109
, the size of the data to be written, into a write size
110
, and the data to be transmitted into a data to be written
111
. A label
104
is used by the transmission node in order to associate the request with the response, an rt
105
indicates whether retransmission is to be performed or not, and a pri
107
indicate the priority of the packet.
In the response to the write request, a write response packet
102
is used, and it is indicated whether the data has been normally received or not, by using a result
112
. A label
104
of the packet for the response uses the same value as the packet for the request. According to this configuration, it is possible to associate the request with the response.
By contrast, the read request is transmitted with using a packet of a read request packet
201
, and writing the node ID of the destination to which the read request is to be tra
Hamamoto Yasuo
Takeda Hidetoshi
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Ton Dang
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