Avaya P580 - Manual (Page 133)

Avaya P550R, P580, P880, and P882 Multiservice Switch User Guide, Version v5.3.1 4-3
Using VLANs, Spanning Tree, Hunt Groups, and VTP Snooping
A switch that is strictly port based needs additional information to
separate traffic passing from one VLAN to another. Since each port is
dedicated to a particular VLAN, there is no need to analyze the
traffic arriving on a port to determine its VLAN membership. As an
example, (Figure 4-1) two switches with two VLANs, Sales and
R&D, would need a dedicated switch to switch connections (Trunk)
for both VLANs between switches. Therefore all traffic arriving on
that port must belong to the VLAN assigned to that port since, in this
case, no unique identifiers are sent with the frames.
Figure 4-1. Vlans No Tagging
The Avaya Multiservice switch is able to separate VLAN traffic
between switches across a single Trunk links. In order to accomplish
this, the switch implements VLAN Tagging and Trunking. VLAN
Tagging is enabled on a switch port by selecting a Trunk mode for
that port; clear, IEEE 802.1Q or Cisco-Multi Layer mode. A trunk
port can send frames in clear mode, with no VLAN ID, or the VLAN
ID, over the same trunk. A frame is classified as belonging to a
particular VLAN based on the value of the VLAN Identifier (VID)
that is included in the Tag Header. Therefore using our example,
and implementing VLAN tagging, we need only one connection
(trunk) between the two switches to carry the traffic from both
VLANs.(Figure 4-2)