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TRENDnet User's Guide
IP Header Type of Service: 8 bits
The Type of Service provides an indication of the abstract parameters of the quality of
service desired. These parameters are to be used to guide the selection of the actual
service parameters when transmitting a datagram through a particular network. Several
networks offer service precedence, which somehow treats high precedence traffic as
more important than other traffic (generally by accepting only traffic above certain
precedence at time of high load). The major choice is a three way tradeoff between low-
delay, high-reliability, and high-throughput.
Bits 0-2:
Precedence.
Bit 3:
0 = Normal Delay,
Bits 4:
0 = Normal Throughput,
Bits 5:
0 = Normal Reliability,
Bit 6-7:
Reserved for Future Use.
0
1
2
3
4
5
6
7
+-----+-----+-----+-----+-----+-----+-----+-----+
| PRECEDENCE | D | T | R | 0 | 0 |
+-----+-----+-----+-----+-----+-----+-----+-----+
Precedence
111 - Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
The use of the Delay, Throughput, and Reliability indications may increase the cost (in
some sense) of the service. In many networks better performance for one of these
parameters is coupled with worse performance on another. Except for very unusual cases
at most two of these three indications should be set.
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1 = Low Delay.
1 = High Throughput.
1 = High Reliability.
The type of service is used to specify the treatment of the datagram during its
transmission through the internet system. Example mappings of the internet type of
service to the actual service provided on networks such as AUTODIN II, ARPANET, SATNET,
and PRNET is given in "Service Mappings".
The Network Control precedence designation is intended to be used within a network
only. The actual use and control of that designation is up to each network. The
Internetwork Control designation is intended for use by gateway control originators only.
If the actual use of these precedence designations is of concern to a particular network,
it is the responsibility of that network to control the access to, and use of, those
precedence designations.
DSCP
Priority
DSCP
0
0
1
60
0
31
63
0
Example:
IP Header
➔ 45 C8 . . .
DSCP=50
Queuing Algorithms
Queuing algorithms allow switches to maintain separate queues for packets from each
individual source or flow and prevent a source from monopolizing the bandwidth.
⚫
Strict-Priority (SPQ)
The packets on the high priority queue are always service firstly.
⚫
Weighted round robin (WRR)
Managed Industrial L2 Switch
Priority
DSCP
Priority
0
2
0
0
62
0
46
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