Network and node device

Details Network and node device Network and node device

1999-06-10

2003-11-25

Vanderpuye, Kenneth (Department: 2732)

Multiplex communications

Network configuration determination

Reexamination Certificate

active

06654353

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
The present invention claims priority from Japanese Patent Applications No. 10-165406 filed Jun. 12, 1998, No. 11-013273 filed Jan. 21, 1999 and 11-045406 filed Feb. 23, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to networks defined in IEEE 1394 (IEEE Std 1394-1995: IEEE Standard for High Performance Serial Bus, IEEE P1394.a, and others). It relates in particular to techniques for path restoration and avoidance of incorrect connection of links.
2. Description of Related Art
In a network based on IEEE 1394, the nodes are connected in a tree topology (which combines daisy-chains and branches). To communicate, the nodes therefore have to identify the tree topology and determine the connection relations among the nodes.
This tree identification process will now be described. At power-up and when a node is added to a bus, bus initialization takes place to determine the connection relations among the nodes. This involves sending a bus reset signal to all nodes. This signal results in all information relating to the configuration of node connections being cleared. At bus initialization, the only information that each node has is whether it is a branch node connected to two or more other nodes, or a leaf node connected to just one other node, or whether it is not connected to any other node at all.
FIG.
20
and
FIG. 21
give examples of how nodes identify a tree. When nodes A, B, C, D and E comprising a network are to start operating, a bus reset signal is sent to each node. The bus reset signal is a control signal for bus initialization. In these examples, if the nodes are connected by links AB, AC, BD and BE and a change occurs in the network configuration, each node detects the change and respectively sends a bus reset signal.
For example, if link AB is installed to connect node A and node B, nodes A and B each detect that link AB has been connected to it, and send a bus reset signal. If link AC is then installed to connect node A and node C, nodes A and C each detect that link AC has been connected to it, and send a bus reset signal.
Similarly, if link BD is installed to connect node B and node D, nodes B and D each detect that link BD has been connected to it, and send a bus reset signal. If link BE is installed to connect node B and node E, nodes B and E each detect that link BE has been connected to it, and send a bus reset signal.
Thus every time a new link is installed and a node is added, a bus reset signal is sent from the nodes which have detected this change. Because these bus reset signals reach each node, bus initialization takes place throughout the network. Conversely, every time an existing link is removed and the number of nodes decreased, a bus reset signal is sent from the nodes which have detected this change. Again, because these bus reset signals reach each node, bus initialization takes place throughout the network.
This process will be described in greater detail with reference to
FIG. 20
, where it will be seen that the first step is for signals notifying parent nodes from child nodes (parent_notify signals) are sent from all leaf nodes C, D and E to branch nodes A and B. The nodes which receive a parent_notify signal recognize the node which has sent this parent_notify signal as a child node, and send back a signal indicative of parent-to-child notification (a child_notify signal). This results in the parent-child relations among the nodes being determined.
After a fixed time has elapsed, a second step takes place. As shown in
FIG. 21
, this involves node A and node B each recognizing that despite having a port whereby link AB is connected, the node has received neither a parent_notify signal nor a child_notify signal, whereupon nodes A and B send a parent_notify signal to each other. When nodes A and B recognize that they have received a parent_notify signal, they each set an independent fixed time. A parent_notify signal is then sent from the node at which the fixed time first elapses. In the example of
FIG. 21
, it is assumed that node B has re-sent a parent_notify signal to node A. Since it is node A which has received this re-sent parent_notify signal, it constitutes the parent and sends back a child_notify signal to node B.
Thus each node receives a parent_notify signal or a child_notify signal, and thereby successively ascertains whether it is a leaf node or a branch node. Tree identification in the network takes place in this way.
FIG. 22
shows the connection relations of nodes among which a loop has been formed. If a loop forms among nodes A, B and C as shown in
FIG. 22
, normal connections do not hold among these nodes. That is to say, each such node has two ports at which neither a parent_notify signal nor a child_notify signal is received. Such nodes are unable to exchange parent_notify signals with the adjacent nodes to which they are mutually connected in the loop, and are unable to recognize their connection relations. If this state of affairs persists, a limited time (config_timeout) elapses and the bus is automatically reset.
This is because, in the second step described above, if a node has two ports at which neither a parent_notify signal nor a child_notify signal is received despite the relevant links being connected, that node comes under the application of a rule not to send a parent_notify signal.
The reason for this rule is that the procedure of sending parent_notify signals in the aforementioned second step has the purpose of enabling a higher-level node to be recognized. However, with a tree structure, a given node always has just one higher-level node and cannot have two. It follows that if a node has two ports at which neither a parent_notify signal nor a child_notify signal has been received despite the relevant links being connected, it judges that it is possible that there is a lower-level node which has not yet sent a parent_notify signal to it, with the result that it does not send a parent_notify signal.
Consequently, the tree identification procedure is repeated indefinitely and cannot be completed. As a result, since the initialization process cannot be completed, communication becomes impossible.
We now look at another problem.
FIG. 23
shows the connection relations of nodes among which a fault has occurred. If link AB between nodes A and B is disconnected as shown in
FIG. 23
, then as long as the network comprising nodes A and C, and the network constituted by nodes B, D and E remain separate, these networks will undergo independent bus initialization. The result is that the two networks operate independently and cannot intercommunicate.
However, given this scenario, if link BC has been present between node B and node C as shown by the broken lines in
FIG. 23
, a route which bypasses the fault can be formed and normal communication performed. However, as described with reference to
FIG. 22
, because link BC between node B and node C would result in a loop being formed among nodes A, B and C, it cannot be provided in advance. Thus in an IEEE 1394 based network the advance provision of redundant links for path restoration in the event of link faults is problematic.
SUMMARY OF THE INVENTION
In the light of the foregoing considerations, it is an object of the present invention to provide a network and a node device whereby communication is possible even when nodes are connected in a loop. It is another object of the present invention to provide a high-reliability IEEE 1394 based network and node device which, when a fault has occurred in a link, is capable of rapidly forming a route which bypasses the fault.
It is a particular feature of the present invention that it provides switching means for connecting and disconnecting a link between nodes, so that when an IEEE 1394 based network has a redundant link which forms a loop among nodes—this loop preventing normal connection relations being maintained—the connection relations can be made normal by controlling this swi

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