View source for MAC Layer Address

Depends on the Physical layer technology:

Note: A MAC length of zero is allowed, since this indicates a broadcast, as long as the [[Network Number]] indicates the [[BACnet Network]] that the broadcast is aimed at.

MAC Address consists of a length, DLEN or SLEN and an ADR ( DADR, SADR )

'''MAC length of Zero

* Indicates broadcast

** If [[DNET]] is oxffff then it is a global broadcast

** If [[DNET]] is any other non-zero value, then it is a Remote Broadcast

See [[BACnet Broadcast]]



{| border="1" cellpadding="10" cellspacing="0"
|+ align="top" style="color:#e76700;" |'''SLEN/SADR Examples'''
|-
|'''Physical Layer'''
|'''SLEN'''
|'''Source of Address'''
| '''Example'''
|-
|MSTP
| 1 
|(Usually switch on device)
| 27
|-
|BACnet/IP
| 6 
|(IP Address:Port)
| 192.168.1.26:47808
|-
| LonTalk
| 6, 7
| Neuron ID
|
|-
| BACnet/IPv6
| 1-6
| [[VMAC]]
| 
|-
|}


=== Other MAC Layer Address Lengths ===

The BACnet Implementation guide recommends that devices handle MAC addresses up to 18 octets long. (Section 2.9)
[http://www.bacnetinternational.org/associations/8066/files/BTL%20Implementation%20Guidelines-v26.pdf BTL Implementation Guide]. This has been deemed "no longer relevant" (see below).

However, [http://www.bacnet.org/Addenda/Add-135-2008q.pdf BACnet 135-2008q-2] introduces the concept of a [[VMAC]], of length 6 (or less)

Addresses are expected to be no more than 6 bytes. Addendum 135-2008q-2 which describes the VMAC layer approach, addresses are expected to be no more than 6 bytes. So there is no longer a need for implementations to expect longer addresses. The support for LON addresses of length 7 is so restrictive; only usable as a DLEN and never as an SLEN, that only routers and devices that themselves will utilize the form of LON addresses of length 7, are required to support that. i.e. Routers that potentially route messages to Lon networks should support a length of 7 still.


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[[Category:2 OSI link layer]]