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gateways_02_terms.fm
Terms
Key Words
8
•
Untagged
•
Priority Tagged
•
VLAN Tagged
Some IP equipment vendors only allow priority bits to be used when
VLAN ID > 0 is set.
When tagging is being used, the IPDA components always use priority
tagging, but allow a setting of VLAN ID > 0
The priority bits are fixed according to the traffic type.
The values are specified in Table 2, "TOS values".
TOS byte
The Type Of Service byte is a component of the header for all IP
packets in accordance with RFC 791.
According to RFC 791 (Internet Protocol), the byte is split up as follows
(most significant -> least significant bit)
3 bits for precedence
111 - Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
According to RFC 2474 (Differentiated Services), the six high-order
bits are used as DiffServ Code Point (DSCP), while the two least
significant bits are reserved.
Some of the values to be set are specified as 6-bit values without the
2 reserved bits, and others as 8-bit values (with the 2 reserved bits =
0).
With IPDA, the entire TOS byte is always specified. The two least
significant bits are always set to zero.
A pure DiffServ Code Point must therefore be moved 2 bits to the left
or multiplied by 4 in order to obtain the TOS byte setting for IPDA.
HiPath 4000 V5, IP Solutions - HG 3500 & HG 3575, Service Documentation
Normal Ethernet frames without tagging
Ethernet frames with tagging
The priority bits are used
The VLAN ID is 0.
Ethernet frames with tagging
The priority bits are 0,
The VLAN ID is > 0.
3 bits for priority
2 bits reserved
D-T-R
for future use
Slight delay:
0 = Normal, 1 = Low
Throughput:
0 = Normal, 1 = High
Reliability:
0 = Normal, 1 = High
A31003-H3150-S104-2-7620, 03/2009
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