From Zenitel Wiki

The node number is the address of an Exchange. If several exchanges are interconnected (via the AlphaCom Data Protocol), then each exchange will have a unique node number. All ACDP data messages are addressed to a device. A device is always related to (owned by) a node. A full device address consists of <node> <device>.
<Node> is one byte.

Value (decimal) Value (Hex) Node Type
0 0x00 Node 0 is interpreted by the exchange which receives it as "own node", and it will replace the value 0 with it’s own node number before processing takes place.

Response messages will thus NOT contain any node 0 references

1 - 254 0x01 - 0xFE Exchanges in AlphaNet
255 0xFF Broadcast to all nodes

- All AlphaNet nodes will re-send messages addressed to 0xFF to all other AlphaNet signaling links. - The Network layer manages broadcast messages to avoid excessive signaling traffic and discards messages that has jumped too many times.

Virtual nodes

Node numbers are also used to address interface processes like SIP deamon, RingMaster deamon, M100 deamon. These interface processes appear as virtual nodes in the AlphaNet architecture, all though they are just Linux processes running on a AlphaCom exchange with an other node number. No specific node number range is defined for the virtual nodes, but we suggest using nodenumbers above 200.