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Host Access Protocol (HAP) specification: Version 2 (RFC1221) Disclosure Number: IPCOM000002035D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2000-Sep-12

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

W. Edmond: AUTHOR


The Host Access Protocol (HAP) is a network layer protocol (as is X.25). ("Network layer" here means ISO layer 3 lower, the protocol layer below the DoD Internet Protocol (IP) layer [3] and above any link layer protocol.) HAP defines the different types of host-to- network control messages and host-to-host data messages that may be exchanged over the access link connecting a host and the network packet switch node. The protocol establishes formats for these messages, and describes procedures for determining when each type of message should be transmitted and what it means when one is received.

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Network Working Group W. Edmond

Request for Comments: 1221 BBN

Updates: RFC 907 April 1991

Host Access Protocol (HAP) Specification - Version 2

Status of this Memo

This memo describes the Host Access Protocol implemented in the

Terrestrial Wideband Network (TWBNET). It obsoletes most but not all

of RFC 907. This memo provides information for the Internet

community. It does not specify an Internet standard. Distribution

of this memo is unlimited.


This memo specifies the Host Access Protocol (HAP). HAP is a Network

layer (OSI Layer 3 lower) access protocol that was first implemented

about a decade ago for the DARPA/DCA sponsored Wideband Packet

Satellite Network (WBNET), the precursor of the current Terrestrial

Wideband Network (TWBNET). This version of the specification

obsoletes references [1] and [2] in addition to most of RFC 907.

HAP is a developmental protocol, and will be revised as new

capabilities are added and unused features are eliminated or revised.

One reason that HAP is being revised now is that, unlike the original

WBNET's satellite channel, the TWBNET's T1 fiber links are not a

broadcast medium. This has prompted some changes to the protocol

that will permit greater efficiency in a mesh topology network.

Another cause of revision is the need to make HAP able to support a

variety of OSI layer 3 upper protocols, such as DECNET Phase V, ST,

and CLNP, where before only Internet Protocol (IP) was used.

Appendix B describes how backward compatibility with the older IP-

only version of HAP is achieved. A third cause of protocol changes

is the desire to simplify interaction between ST2 protocol (RFC 1190)

agents and the TWBNET. This has mainly affected the way certain

setup errors are handled. These changes are expected to be backward

compatible. Appendix A describes two capabilities that may be added

to HAP in the future.

One of the protocol enhancements, "Group Streams", described in

reference [2] has been eliminated. There are no known applications

that use the feature. As described in Appendix A, a new mechanism,

to be called "shared streams", capable of providing equivalent

capabilities will be implemented if needed. Changes in [2] that have

been retained include various query/reply control messages that

permit a host to determine what resources it owns (mostly useful for

cleanup following a host reboot or crash).

This document assumes the reader is familiar with DoD internetworking