ISO/IEC 7776:1995/Amd 1:1996 PDF

Information technology — Telecommunications and information exchange between systems — High-level data link control procedures — Description of the X.25 LAPB-compatible DTE data link procedures — Amendment 1: Modulo 32 768 and multi-selective reject option

Название (английский):

ISO/IEC 7776:1995/Amd 1:1996

Статус документа:: Действующий
Формат:: Электронный (PDF)
Количество страниц:: 28
Дата публикации:: 21 ноября 1996 г.
Издание:: ISO/IEC IS 7776 edition 2 version 1
ICS:: 35.100.20

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Описание (английский):

Adds the multi-selective reject option (option 3.3) and modulo 32 768 (option 10.2) from ISO/IEC 7809:1993.

Технические детали

Технический комитет: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
SKU: ISO/IEC 7776:1995/Amd 1:1996

Abstract

Overview

ISO/IEC 7776:1995/Amd 1:1996 is an amendment to the ISO/IEC 7776:1995 description of X.25 LAPB‑compatible DTE data link procedures. It adds two options from ISO/IEC 7809:1993: the multi‑selective reject option (SREJ, option 3.3) and modulo 32 768 operation (option 10.2). The amendment improves recovery efficiency for errored or lost I‑frames and enables operation over high‑throughput or long‑delay links by increasing the sequence number modulus.

Key topics and technical requirements

Multi‑selective reject (SREJ)
- Allows a DTE to request retransmission of one or more non‑contiguous I‑frames with a single SREJ frame.
- The SREJ control field N(R) contains the earliest I‑frame to be retransmitted; the information field lists additional sequence numbers or span lists.
- If the SREJ F bit = 1, frames up to N(R)−1 are considered acknowledged; if F bit = 0, N(R) does not indicate acknowledgement.
- Encoding differs by modulo: for extended (mod 128) there is one octet per standalone frame and two‑octet span lists; for modulo 32 768 there are two octets per standalone and four‑octet span lists.
- Lists truncated to fit within the parameter NI (maximum bits in an I‑frame).
Modulo 32 768 operation
- Introduces a much larger modulus for sequence numbering to support many outstanding frames on high‑delay or high‑rate links.
- Control field lengths differ by mode: basic (modulo 8) uses 1 octet, extended (modulo 128) uses 2 octets for numbered frames, and modulo 32 768 uses 4 octets for numbered frames.
- The maximum number of outstanding I‑frames can be as large as modulus − 1.
Mode selection and recovery mechanism rules
- Basic (mod 8): may be supported; REJ is required if supported; SREJ‑with‑span‑list prohibited.
- Extended (mod 128): may support REJ and/or SREJ‑with‑span‑list but only one recovery mechanism is used at a time.
- Modulo 32 768: must support SREJ‑with‑span‑list; REJ is prohibited.
- Mode choice is fixed at subscription time for DTE/DCE and by bilateral agreement for DTE/DTE.

Applications and who uses it

Implementers of X.25 / LAPB DTE and DCE stacks (network equipment vendors, embedded modem/terminal firmware).
Network operators and systems integrators working with packet‑switched, high‑latency, or high‑throughput links where selective retransmission improves efficiency.
Software developers building data link layer protocol implementations, especially where backward compatibility with X.25 / LAPB is required.

Related standards

ISO/IEC 7776:1995 (base standard)
ISO/IEC 7809:1993 (source of the SREJ and modulo 32 768 options)
X.25 and LAPB specifications (context for packet‑switched, DTE/DCE link operation)

Keywords: ISO/IEC 7776:1995/Amd 1:1996, ISO/IEC 7776, X.25 LAPB, multi‑selective reject, SREJ, modulo 32768, data link control, selective retransmission, DTE/DCE.

Overview

Key topics and technical requirements

Multi‑selective reject (SREJ)
- Allows a DTE to request retransmission of one or more non‑contiguous I‑frames with a single SREJ frame.
- The SREJ control field N(R) contains the earliest I‑frame to be retransmitted; the information field lists additional sequence numbers or span lists.
- If the SREJ F bit = 1, frames up to N(R)−1 are considered acknowledged; if F bit = 0, N(R) does not indicate acknowledgement.
- Encoding differs by modulo: for extended (mod 128) there is one octet per standalone frame and two‑octet span lists; for modulo 32 768 there are two octets per standalone and four‑octet span lists.
- Lists truncated to fit within the parameter NI (maximum bits in an I‑frame).
Modulo 32 768 operation
- Introduces a much larger modulus for sequence numbering to support many outstanding frames on high‑delay or high‑rate links.
- Control field lengths differ by mode: basic (modulo 8) uses 1 octet, extended (modulo 128) uses 2 octets for numbered frames, and modulo 32 768 uses 4 octets for numbered frames.
- The maximum number of outstanding I‑frames can be as large as modulus − 1.
Mode selection and recovery mechanism rules
- Basic (mod 8): may be supported; REJ is required if supported; SREJ‑with‑span‑list prohibited.
- Extended (mod 128): may support REJ and/or SREJ‑with‑span‑list but only one recovery mechanism is used at a time.
- Modulo 32 768: must support SREJ‑with‑span‑list; REJ is prohibited.
- Mode choice is fixed at subscription time for DTE/DCE and by bilateral agreement for DTE/DTE.

Applications and who uses it

Implementers of X.25 / LAPB DTE and DCE stacks (network equipment vendors, embedded modem/terminal firmware).
Network operators and systems integrators working with packet‑switched, high‑latency, or high‑throughput links where selective retransmission improves efficiency.
Software developers building data link layer protocol implementations, especially where backward compatibility with X.25 / LAPB is required.

Related standards

ISO/IEC 7776:1995 (base standard)
ISO/IEC 7809:1993 (source of the SREJ and modulo 32 768 options)
X.25 and LAPB specifications (context for packet‑switched, DTE/DCE link operation)

Keywords: ISO/IEC 7776:1995/Amd 1:1996, ISO/IEC 7776, X.25 LAPB, multi‑selective reject, SREJ, modulo 32768, data link control, selective retransmission, DTE/DCE.

ISO/IEC 7776:1995/Amd 1:1996 PDF

Технические детали

Abstract

Overview

Key topics and technical requirements

Applications and who uses it

Related standards

Похожие стандарты

Abstract

Overview

Key topics and technical requirements

Applications and who uses it

Related standards

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