Device Connections
Here you'll find:
Topology, Routes, Cycle Master
Hot Plugging
Bus-Reset
Calculating the Number of Hops and Cable Length
Further reading

Each device in a mLAN-network is called a "node". "Topology" refers to the overall shape of the connected nodes. Types of topology include daisy-chain, star, and tiered star.

Three different types of topology: daisy-chain, star and tiered star

In these topologies, it is possible for any node to be seen from any other node as being in a "tree" structure. In this case, the single selected node is called the "root node". As the name suggests, the tree structure is similar to the branched form of a tree, but is normally drawn upside down from an actual tree. Thus, the "root" will be depicted at the top of the diagram. As shown in the following diagrams, any node in the topology can be the root node.

A star topology can be seen as a tree structure - any node in the topology can be the root node

A tiered-star topology can be seen as a tree structure, too

The above diagrams show the frequently-used tiered star (multiple stars that are connected) as a tree structure. In a tree structure, nodes that are not connected to another node in the direction away from the root are called "leaf nodes". In the above diagrams, these nodes are shown in gray.

Since Firewire treats all topologies as tree structures, a specific node will automatically be selected as the root node. It is also possible for the user to specify a specific node as the root.

In order to transfer realtime data such as audio and MIDI, the clocks that are built into each device to measure data timing must be synchronized; i.e., the devices must be synchronized. The node containing the clock used as the master is called the "cycle master", and the root node fulfills this role.

The cycle master node is indispensable when transferring realtime data such as audio and MIDI. If the power of the cycle master node is turned off, or if the cable is disconnected from it, it will no longer be possible to transfer data. Consequently, the sound will be interrupted. If this occurs another node will be selected as the root node, and data transfer will resume.

By using Fireiwre (IEEE 1394) compatible extending and relaying devices, bus connections can be branched and extended in an efficient manner. Such devices are collectively called "repeaters".

Of the different types of topology, "loops" cannot be interpreted as a type of tree; thus, it is not permitted to create a loop within the topology.

It is possible to create loops in a topology - but it is not allowed

Firewire allows cables to be freely plugged and unplugged even if the power is turned on. Since IDs are assigned automatically when the topology is modified, the user does not need to reset the IDs. The system can be used immediately after it has been connected.

One feature of mLAN is that after nodes are connected, the MIDI and audio signal flow can be routed freely without having to actually change physical connections. No particular care need be taken regarding the order of connections.

When a cable is connected or disconnected within a network, or when the power of a node is turned on or off, the bus will be initialized and the network will be reconfigured. There are two types of bus reset: long bus reset and short bus reset.

Bus is a technical term indicating a system by which multiple electronic devices share a single communication route to transfer data. IEEE 1394 or Firewire is a "bus" specification. In the document, the term "bus" refers to the portion that is operating according to IEEE 1394.

Long bus reset

This will occur when the topology has been changed or broken without leaving the previous root, or if the power of the root node has been turned off.

This will also occur if a device that does not support short bus reset (such as an IEEE 1394-1995 compatible DV camcorder) is connected. Since a certain amount of time is required for reconfiguration, audio data etc. will be interrupted.

After the bus has been initialized, the following processes are performed:

• The parent/child relationships between each node are determined, and after the root node has been decided, self-identifying packets (basic data) for each node will be transmitted. This is called "tree identification".
• The root node will be assigned as the cycle master.

Short bus reset
This will occur if the change in topology does not involve the root, and since it requires less time than the long bus reset, audio data etc. will not be interrupted. This will occur when a leaf node is added or removed, or if the power of a leaf node is turned on or off.

The number of hops indicates the distance between two nodes in the bus (system), and expressed by the number of cables between the two nodes.

The maximum number of hops is not the number of cables in the network; it simply means the maximum number of hops between any two nodes (not necessarily from the root). At present, the maximum is 16 hops. Even by using shorter cables such as 1 meter, it is not possible to increase the number of nodes or hops that can be used. Standard Firewire cables are 4.5 metres long, but today there are already Firewire cables of 20 m length. For bigger distances there are fibre optical solutions to transport the data.

Maximum dimensions of a mLAN-network

At present, a maximum of 63 nodes can be connected. In the future, devices called "bridges" will make it possible to connect up to 63 x 1023 devices.