Virtual 1394 Bus

In February of 1999 Subrata Banerjee, from Philips, presented a study about how to connect portals without using wires. A Firewire with this characteristic receives the denomination "Wireless Firewire", Virtual Firewire or Virtual IEEE 1394.

First, the Virtual Firewire was motivated by the limitation of the specification 1394-1, where a bus can unite only 2 portals. In its virtual configuration, you can have a topology with a bus uniting multiple portals, as shown in Figure 4.

Figure 4: Example of topology with a Virtual Firewire uniting the portals "a", "c" and "e".

As relevant Virtual Firewire operation characteristics, you have:

• It is allowed the concurrent transmission between multiple pairs of nodes connected to a Virtual Firewire, that is, the bus congesting characteristic is very reduced, that limits a lot the capacity of a communication network;
• Nodes not connected to the Virtual Firewire virtual (examples: "N1" or portal "d", in Figure 4) can be seen or not by the other connected nodes;
• Isochronal packets are sent only to the nodes that have been listed by devices as possible packet source/destination;
• The routing way of nodes and portals in a virtual bus is very flexible; so, not every node connected to the virtual bus can communicate directly with one another; sometimes it will be necessary the use of an intermediate node to temporarily store the packets to retransmit them afterwards;
• The packets communicated in a Virtual Firewire Virtual can be segmented, if necessary;
• You can have the node simulation by software.

Besides, still in study, among many other characteristics:

• The existence of portal a
• Inclusion, in a configuration ROM, of topology and speed maps;
• Guarantee of precision in the distribution of clock frequency;
• Transmission of asynchronous blocks of, at least, 512 bytes;
• Support to size of packets that are allowed in buses of 100 Mb/s or more;
• Support to all kinds of serial bus packets.

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