Assigned link numbers
Assigning link numbers for ARPANET protocol connections
Postel, J., "Assigned link numbers", RFC 604, DOI 10.17487/RFC0604, December 1973, <https://www.rfc-editor.org/info/rfc604>.
@misc{rfc604,
series = {Request for Comments},
number = 604,
howpublished = {RFC 604},
publisher = {RFC Editor},
doi = {10.17487/RFC0604},
url = {https://www.rfc-editor.org/info/rfc604},
author = {J. Postel},
title = {{Assigned link numbers}},
pagetotal = 2,
year = 1973,
month = dec,
} RFC text
Contents
Network Working Group Jon Postel
RFC # 604 MITRE
NIC # 21186 26 December 1973
Assigned Link Numbers
This announcement modifies the official host-to-host protocol, and
updates the defining documents [NIC 8246, NIC 9347]. Please note that
the information on page 28 of "Host/Host Protocol for the ARPA Network"
about link number assignments is updated by this note, and that a
previous update [RFC 317, NIC 9347] is completely replaced. The
modification is minor and should have no effect on existing network
programs or usage. Four of the reserved link numbers are hereby
assigned for experimental use in the testing of an internetworking
protocol defined by Kahn and Cerf.
Description:
Control Link
Link 0 is assigned for use as the host-to-host protocol control
link.
Data Links
Links 2-71 are available for use in connections as provided by
the host-to-host protocol.
Internetworking Protocol
Links 155-158 are to be used for experiments with the
Internetworking Protocol.
Measurements
Links 159-191 are assigned for use in measurements under the
direction of the Network Measurement Center at UCLA.
Message Switching
Links 192-195 are to be used for experiments with the Message
Switching Protocol.
Private Experiments
Links 196-255 are available for private experimental use.
Reserved
Link 1, and links 72-154 are reserved for future developments
and experiments and currently are not to be used.
Table:
Link Number Assignment
0 Control Link
1 Reserved
2-71 Connections
72-154 Reserved
155-158 Internetworking Protocol
159-191 Measurements
192-195 Message Switching Protocol
196-255 Experimental
References:
Host-to-host Protocol NIC 8246
Internetworking Protocol NIC 18764
Message Switching Protocol NIC 9926
[ This RFC was put into machine readable form for entry ]
[ into the online RFC archives by Alex McKenzie with ]
[ support from GTE, formerly BBN Corp. 10/99 ]
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§1Link Numbers for the ARPANET
The ARPANET host-to-host protocol allows communication between computers using link numbers to distinguish different types and purposes of connections. Link 0 is reserved for control traffic. Links 2 through 71 are available for ordinary data connections between hosts. Other ranges are reserved for specific experiments, measurements, and future use.
This RFC officially assigns link number ranges and updates the earlier assignment in RFC 317.
Computers pick a link number to identify what they are talking about. Some numbers are for data, some for tests, and some for future experiments.
§2Link Number Assignments
Link 0 is the control link for protocol management. Links 1 and 72-154 are reserved for future development. Links 2-71 are available for normal connections. Links 155-158 are designated for experiments with the Internetworking Protocol developed by Kahn and Cerf. Links 159-191 are assigned for measurements conducted by the Network Measurement Center at UCLA. Links 192-195 are allocated for Message Switching Protocol experiments. Links 196-255 are open for private experimental use.
The range is divided up: some for normal traffic, some for testing new ideas, some for measuring the network, and some left over for anyone to use in their own experiments.
- 0Control Link — Host-to-host protocol control.
- 1Reserved — Reserved for future development.
- 2-71Connections — Data connections between hosts.
- 72-154Reserved — Reserved for future use.
- 155-158Internetworking — Experiments with Internetworking Protocol.
- 159-191Measurements — UCLA Network Measurement Center.
- 192-195Message Switching — Message Switching Protocol experiments.
- 196-255Private Experiments — Experimental use by anyone.
§3Why This Matters
Early ARPANET software needed to multiplex multiple logical conversations over a single host-to-host connection. The link number field in the protocol identified each logical conversation's purpose. By assigning ranges for control traffic, data, and experiments, this RFC provided structure that allowed hosts to distinguish and route different types of traffic correctly. The experiments in internetworking and message switching were especially important for testing new protocols that would eventually lead to the Internet.
Link numbers let one connection between two computers carry many different kinds of traffic at once, each marked so the computers know what each message is for.