Browse Prior Art Database

JANUS interface specifications (RFC0745) Disclosure Number: IPCOM000003792D
Original Publication Date: 1978-Mar-01
Included in the Prior Art Database: 2019-Feb-14
Document File: 10 page(s) / 14K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M. Beeler: AUTHOR

Related Documents

10.17487/RFC0745: DOI

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 16% of the total text.

NWG/RFC# 745 MDB2 30-MAR-78 43649 JANUS Interface Specifications

Network Working Group Michael Beeler Request for Comments 745 BBN NIC 43649 30 March 1978 PRTN 245

JANUS Interface Specifications

(Symmetrical, 1822-like Interface)

1. INTRODUCTION 1.1. Motivation

A need arose in the Packet Radio project for specification of an interface between Packet Radio units and other equipment. This paper is to meet BBN’s responsibility to supply that specification. It is our hope that it will find application in other areas as well.

1.2. Historical Relationship to 1822

The ARPANET employs a network of switching nodes, called IMPs, to provide interconnection among user equipment, called hosts. A uniform means of connecting a host to an IMP is specified in BBN Report Number 1822. Consequently, this interface has become known as an 1822 interface.

As the need to interconnect new types of devices has grown, it has become attractive to implement an 1822-like interface on each end of pairs of devices which are to communicate. The devices are then connected electrically, and communication can take place in spite of differences in processing speed, word length, signal levels and so forth in the two devices. A part of Report 1822 reads as follows.

"The technique of transferring information between the Host and the IMP is identical in each direction; we will, therefore, refer to the sender and the receiver without specifying the Host or IMP explicitly." [BBN Report Number 1822, 12/75 revision, page 4-2.]

Unfortunately, Report 1822 does not specify a completely symmetrical interface. Although there is a high degree of symmetry, some aspects are peculiar to the IMP side and some to the host side. Therefore, two interfaces constructed to connect to IMPs may not function connected to each other. In what follows, the unsymmetrical aspects are respecified in a way which will accomplish full interchangeability.

The interface specified here is called the JANUS interface, to distinguish it from the Report 1822 interface.

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NWG/RFC# 745 MDB2 30-MAR-78 43649 JANUS Interface Specifications

1.3. Terminology

The terms, "IMP" and "host," are not relevant in the present context. Sections of Report 1822 such as Appendix B are conveniently re-interpreted by substituting "foreign interface" and "home interface," respectively.


Report 1822 addresses two aspects of the connection of a host to the ARPANET, the hardware requirements and the software protocols. Since the JANUS interface will typically be used in applications other than connection to the ARPANET, the higher level software protocols are beyond the scope of this paper. They are properly addressed by documentation specific to each application. Concern here is only for electrical specification of the JANUS interface. The various areas which differ from Report 1822 are as follows.

2.1. Low-level Protocol

Certain aspects of the JANUS interface and its operation may be implemented in hardware, software of a...