METRODATA NetTESTER FAMILY USER MANUAL
76-02-107 Rev.A
Page 33 of 133
6 VLANS AND TAGGING
IEEE 802.1Q [2] defines the concept of a Virtual LAN (VLAN), a mechanism for
partitioning traffic that is carried over a physical LAN so that it appears as a number
of separate LAN connections. This is done by adding an extra 4-byte 'tag' near the
start of each packet, which identifies the VLAN to which it belongs using a number in
the range 1-4095 (the VLAN ID).
Each VLAN tag contains a priority (or 'PCP') field. This is used by several functions
within the unit; for example: to implement the priority-based queuing system, for
colour-marking associated with SLAs and service activation testing, for rate-limiting
and policing, etc.
