
Installation and Operation Manual Chapter 1 Introduction
Egate-100 Ver. 4.0 Functional Description 1-19
• DSCP (ToS byte).
IP Precedence / DSCP
The IP header is shown in
Figure
1-10
. ToS byte structure for IP Precedence is
shown in
Figure
1-11
and for DSCP in
Figure
1-12
.
Non-IP frames are mapped to the lowest-priority queue.
0
01234567890
1
0
2
0
3
1
VERSION IHL
TOS
TOTAL L ENGTH
IDENTIFICATION FLAGS FRAGMENT OFFSET
TIME TO LIVE PROTOCOL HEADER CHECKSUM
SOURCE ADDRESS
DESTINATION ADDRESS
123456789 123456789
OPTIONS PADDING
IP
HEADER
Figure
1-10. IP Header
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
P2 P1 P0 XX XX XX XX XX
P2–P0: Precedence value
Figure
1-11. ToS Byte IP Precedence Field
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
DS5 DS4 DS3 DS2 DS1 DS0 XX XX
DSCP: six bits (DS5–DS0)
Figure
1-12. ToS Byte DSCP Field
VLAN Priority
VLAN, according to IEEE 802.1p&q, adds four bytes to the MAC layer of the
Ethernet frame. The user can set the contents of these bytes, MAC layer priority
and VLAN ID.
Figure
1-13
shows the VLAN tag format.
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