RFC 935 (rfc935) - Page 1 of 13
Reliable link layer protocols
Alternative Format: Original Text Document
Network Working Group J. Robinson
Request for Comments: 935 BBN
January 1985
RELIABLE LINK LAYER PROTOCOLS
Status of This Memo
This RFC discusses protocols proposed recently in RFCs 914 and 916,
and suggests a proposed protocol that could meet the same needs
addressed in those memos. The stated need is reliable communication
between two programs over a full-duplex, point-to-point communication
link, and in particular the RFCs address the need for such
communication over an asynchronous link at relatively low speeds.
The suggested protocol uses the methods of existing national and
international data link layer standards. This RFC suggests a
proposed protocol for the ARPA-Internet community, and requests
discussion and suggestions for improvements. Distribution of this
memo is unlimited.
Introduction
This RFC is motivated by recent RFCs 914 and 916, which propose new
standards for protocols that transfer serial data reliably over
asynchronous communication lines. In this note, I summarize
widely-used standards that have been in existence for some time that
might be appropriate for this environment. I hope that the existing
standards will be found to meet the needs the new proposals seek to
address.
In both the US and international standards areas, there are two major
categories of serial data communication standards for the link layer.
These categories are character-oriented and bit-oriented. The first
is the older class; it is standardized in the US standard ANSI
X3.28-1976 (which superseded the original version of 1971), and in
the ISO standards IS 1745, IS 2111, IS 2628 and IS 2629. Although
frequently used in synchronous environments, wherein the name binary
synchronous (or bisynch) is used, these standards use the term "basic
mode" to describe their procedures. The latter class is standardized
in the US standard ADCCP (Advanced Data Communication Control
Procedures), ANSI X3.66- 1979, and in the ISO standard HDLC
(High-level Data Link Control procedures), in IS 3309, IS 4335 and IS
7809.
Other international standards, draft standards and vendor standards
follow the ADCCP/HDLC procedures. Among these are SDLC (IBM), X.25
LAPB (CCITT), IEEE 802.2/ISO 8802.2 LLC (LAN Logical Link Control)
and ISDN LAPD (CCITT). Many vendors have built equipment which meets
Robinson