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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, 1 = Low Delay.
Bits 4: 0 = Normal Throughput,
1 = High Throughput.
Bits 5: 0 = Normal Reliability,
1 = High 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.
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.
Summary of Contents for NGI-M08C4POE8-2
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