Raisecom ISCOM2600G-HI (A) Series - Figure 7-1 Traffic Classification; Figure 7-2 Structure of an IP Packet Header; Figure 7-3 Structures of the Tos Priority and DSCP; Figure 7-4 Structure of a VLAN Packet

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ISCOM2600G-HI (A) Series Configuration Guide
7 QoS
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Figure 7-1 Traffic classification
IP precedence and DSCP
Figure 7-2 shows the structure of the IP packet header. The head contains an 8-bit ToS field.
Defined by RFC 1122, IP priority (IP Precedence) uses the highest 3 bits (0–3) with value
range of 0–7; RFC2474 defines ToS field again, and applies the first 6 bits (0–5) to DSCP
with value ranging from 0 to 63, the last 2 bits (bit-6 and bit-7) are reserved. Figure 7-3 shows
the structure of ToS and DSCP.
Figure 7-2 Structure of an IP packet header
Figure 7-3 Structures of the ToS priority and DSCP
CoS
IEEE802.1Q-based VLAN packets are modifications of Ethernet packets. A 4-byte 802.1Q
header is added between the source MAC address and protocol type, as shown in Figure 7-4.
The 802.1Q header consists of a 2-byte Tag Protocol Identifier (TPID, valuing 0x8100) filed
and a 2-byte Tag Control Information (TCI) field.
Figure 7-4 Structure of a VLAN packet