American Fibertek SM24p-PoE Manuel d'instructions télécharger pdf (Page 46)

User Manual

Rev.A1

1-Mar-11

A frame, carrying a tag field following the source MAC address, is four bytes

long and contains VLAN protocol ID and tag control information composed of user

priority, Canonical Format Indicator (CFI) and optional VLAN identifier (VID).

Normally, the maximal length of a tagged frame is 1522 bytes.

802.1Q VLAN-tagged Ethernet frame

6 6 2 2 2

DA SA

VLAN Protocol

Tag Control

Information

Length/

Type

VLAN Protocol ID =

0x8100

User Priority CFI VLAN identifier

Fig.3-9 Tag Format

VLAN Protocol ID: 8100 is reserved for VLAN-tagged frame.

User Priority: 3 bits long. User priority is defined to 7 – 0. 0 is the lowest

priority.

CFI: Canonical Format Indicator. 1 bit long. It is used to encapsulate a

token ring packet to let it travel across the Ethernet. Usually, it is

set to 0.

VLAN ID: 12 bits long. 0 means no VLAN ID is present. 1 means default

VLAN,

4095 reserved.

VLAN-tagged frame:

An Ethernet frame, carrying VLAN tag field, contains VLAN identification

without the value of 0 and 4095, and priority information.

Priority-tagged frame:

An Ethernet frame, carrying VLAN tag field, contains VLAN identification with

the value of 0 and priority information.

Untagged frame:

An Ethernet frame carries no VLAN tag information.

VLAN Identifier:

Also referred to as VID. It is used to identify a member whether it belongs to

the VLAN group with the VID. The assignable number is 1- 4094. If VID=0, the

tagged frame is a priority packet. Both the value of 0 and 4095 also cannot be

assigned in VLAN management.

Port VLAN Identifier:

1 2 ... 41 42 43 44 45 46 47 48 49 50 51 ... 124 125

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American Fibertek SM24p-PoE Manuel d'instructions Page 46