Data network planning
PTP 450 Configuration and User
pmp-0815 (August 2015)
4-35
As an additional exception, the BHM does not flood downward the unknown unicast frames
to the BHS. A VLAN configuration in Layer 2 establishes a logical group within the
network. Each computer in the VLAN, regardless of initial or eventual physical location,
has access to the same data. For the network operator, this provides flexibility in network
segmentation, simpler management, and enhanced security.
Special case VLAN numbers
This system handles special case VLAN numbers according to IEEE specifications:
Table 46
Special case VLAN IDs
VLAN
Number
Purpose
Usage Constraint
0
These packets have 802.1p priority, but are
otherwise handled as untagged.
Must not be used as a
management VLAN.
1
Although not noted as special case by IEEE
specifications, these packets identify traffic that
was untagged upon ingress into the BHS and
must remain untagged upon egress. This policy
is hard-coded in the BHM.
Must not be used for
system VLAN traffic.
4095
This VLAN is reserved for internal use.
Must not be used at all.
BHS membership in VLANs
With the supported VLAN functionality, the radios determine bridge forwarding on the
basis of not only the destination MAC address, but also the VLAN ID of the destination.
This provides flexibility in how BHSs are used:
Each BHS can be a member in its own VLAN.
Each BHS can be in its own broadcast domain, such that only the radios that are
members of the VLAN can see broadcast and multicast traffic to and from the BHS.
The network operator can define a work group of BHSs, regardless of the BHM(s)
to which they register.
