Issue 6.0 NEC SL1100
6 - 18 Network Design Considerations
User Priority - Defines user priority, giving eight priority levels. IEEE 802.1P
defines the operation for these three user priority bits.
CFI - Canonical Format Indicator is always set to zero for Ethernet switches.
CFI is used for compatibility reason between Ethernet type network and Token
Ring type network.
VID - VLAN ID is the identification of the VLAN, which is basically used by the
standard 802.1Q. It allows the identification of 4096 VLANs.
Length/Type - This field indicates either the number of MAC-client data bytes
that are contained in the data field of the frame, or the frame type ID if the
frame is assembled using an optional format.
Data - Is a sequence of bytes of any value. The total frame minimum is 64
bytes.
Frame Check Sequence (FCS) - This sequence contains a 32-bit cyclic
redundancy check (CRC) value, which is created by the sending MAC and is
recalculated by the receiving MAC to check for damaged frames.
Example Ethernet Frame with Layer 2 QoS Enabled
The example below shows an Ethernet Frame containing one RTP (speech)
packet. The Frame is VLAN tagged, has a VLAN ID of 99 and a VLAN Priority
of 5. It is also possible to see that the Layer 3 QoS has not been set.
Ethernet Frame Example - Layer 2 QoS Enabled
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