The Message Contains Two Destination Addresses

The message therefore contains two destination addresses: * Address of the final destination * Address of the node which is the next "hop" The way these addresses are used in message propagation depends on the network topology, as follows:Star Topology All messages are routed via the Co-ordination. Both addresses are needed and the "next hop" address is that of the Co-ordination. Tree Topology A message is routed up the tree until it reaches a node that can route it back down the tree to the destination node.

Both addresses are needed and the initial "next hop" address is hat of the parent of the sending node. The parent node then resends the message to the next relevant node - if this is the target node itself, the "final destination" address is used. The last step is then repeated and message propagation continues in this way until the target node is reached. Mesh Topology In this case, the propagation path depends on whether the target node is in range: * If the target node is in range, only the "final destination" address is used. If the target node is not in range, the initial "next hop" address is that of the first node in the route to the IANAL destination. The message propagation continues in this way until the target node is reached. I I Application programs in intermediate nodes are not aware of the relayed message or its contents - the relaying mechanism is handled by the Gibe stack. I I The message propagation methods for the different topologies are illustrated by the animations below. Star Topology Tree Topologies Topology I Click "Next Page" to continue.

I Previous Page | 1 12 13 14 15 16 17 I Negotiate o connecting 1 Route Discovery The Gibe stack network layer supports a "route discovery' facility in which a mesh outwork can be requested to find the best available route to the destination, when sending a message. Route discovery is initiated when requested by a data transmission request. Route Discovery Options There are three options related to route discovery for a mesh network (the required option being indicated in the message): SUPPRESS route discovery: The message is routed along the tree.

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ENABLE route discovery: The message is routed along an already discovered mesh route, if one exists, otherwise the Router initiates a route discovery. Once this is complete, the message will be sent along the calculated route. If the Router does not have the capacity to store the new route, it will direct the message along the tree. FORCE route discovery: If the Router has the route capacity, it will initiate a route discovery, even if a known route already exists. Once this is complete, the message will be sent along the calculated route.

If the Router does not have the route capacity, it will route the message along the tree. Use of this option should be restricted, as it generates a lot of network traffic. Route Discovery Mechanism The mechanism for route discovery between two End Devices involves the following . A route discovery broadcast is sent by the parent Router of the source End steps: Device. This broadcast contains the network address of the destination End Device. 2. All Routers eventually receive the broadcast, one of which is the parent of the destination End Device. 3.

The parent Router of the destination node sends back a reply addressed to the parent Router of the source. 4. As the reply travels back through the network, the hop count and a signal quality measure for each hop are recorded. Each Router in the path can build a routing table entry containing the best tat to the destination End Device. 5. Eventually, each Router in the path will have a routing table entry and the route from source to destination End Device is established. Note that the corresponding route from destination to source is not known - the route discovered is unidirectional.

I The choice of best path is usually the one with the least number of hops, although if a hop on the most direct route has a poor signal quality (and hence a greater chance that retries will be needed), a route with more hops may be chosen. Device and Service Discovery The Gibe specification provides the facility for devices to find out information about other nodes in a network, such as their addresses, which types of applications are running on them, their power source and sleep behavior.

This information is stored in descriptors on each node, and is used by the enquiring node to tailor its behavior to the requirements of the network. Discovery is typically used when a node is being introduced into a user-configured network, such as a domestic security or lighting control system. Once the device has Joined the network, its integration into the outwork may require the user to start the integration process by pressing a button or similar. The first task is to find out if there are any other devices that it can talk to.

For example, a device implementing the switch conforming to the HOC profile tries to find devices containing HOC load controllers to which it could potentially send its switch state information (the process of associating the switch with a particular load controller is handled by the binding process, presented earlier in this course). There are two types of discovery, Device and Service Discovery: Device Discovery Device Discovery involves interrogating a remote node for address information.

The retrieved information can be either: * the MAC (IEEE) address of the node with a given network address * the network address of the node with a given MAC address. If the node being interrogated is a Router or Co-ordination, it may optionally supply the addresses of all the devices that are associated with it, as well as its own address. In this way, it is possible to discover all the devices in a network by requesting this information from the Co-ordination and then using the list of addresses corresponding to the children of the Co-ordination to launch queries about their child nodes.

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