VLAN Tagged Frames:
The 802.1q standard defines a 4-byte VLAN tag, which is
inserted into a standard Ethernet frame after the source address.
The VLAN tag identifies which VLAN the frame should be routed
to. It also carries additional information used for priority and
routing information. Because adding a VLAN tag adds 4-bytes to
the standard Ethernet frame, most 802.1q capable devices
remove it from the frame before delivering it to its final destination.
Ethernet has evolved significantly since the original thick-coax 10
Mb/s network of the 1980s. Several different versions of the Ethernet standard are in use today.
IEEE 802.3u is commonly referred to as Fast Ethernet or
100Base-T. Because Fast Ethernet offers a choice of 10 or 100
Mb/s bandwidth, the standard also allows for equipment that can
auto negotiate the two speeds. Fast Ethernet can be cabled over
either twisted-pair or fiber optic cables.
Gigabit Ethernet works much the same way as 10 Mb/s and100
Mb/s Ethernet, only faster. It uses the same frame format, full
duplex, and flow control methods. Additionally, it takes
advantage of CSMA/CD when in half-duplex mode, and it
supports Simple Network Management Protocol (SNMP) tools.
Gigabit Ethernet takes advantage of jumbo frames to reduce the
frame rate to the end host. Jumbo frames are between 64 and
9215 bytes. Gigabit Ethernet can be transmitted over twisted pair cables or optical fiber.