The Multi-Class Extension to Multi-Link PPP (RFC2686)
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
This document proposes the fragment-oriented solution for the real-time encapsulation format part of the architecture. [STANDARDS-TRACK]
Network Working Group C. Bormann Request for Comments: 2686 Universitaet Bremen TZI Category: Standards Track September 1999
The Multi-Class Extension to Multi-Link PPP
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1999). All Rights Reserved.
A companion document describes an architecture for providing integrated services over low-bitrate links, such as modem lines, ISDN B-channels, and sub-T1 links . The main components of the architecture are: a real-time encapsulation format for asynchronous and synchronous low-bitrate links, a header compression architecture optimized for real-time flows, elements of negotiation protocols used between routers (or between hosts and routers), and announcement protocols used by applications to allow this negotiation to take place.
This document proposes the fragment-oriented solution for the real- time encapsulation format part of the architecture. The general approach is to start from the PPP Multilink fragmentation protocol  and provide a small number of extensions to add functionality and reduce the overhead.
As an extension to the "best-effort" services the Internet is well- known for, additional types of services ("integrated services") that support the transport of real-time multimedia information are being developed for, and deployed in the Internet.
The present document defines the fragment-oriented solution for the real-time encapsulation format part of the architecture, i.e. for the queues-of-fragments type sender . As described in more detail in the architecture document, a real-time encapsulation format is
Bormann Standards Track [Page 1]
RFC 2686 The Multi-Class Extension to Multi-Link PPP September 1999
required as, e.g., a 1500 byte packet on a 28.8 kbit/s modem link makes this link unavailable for the transmission of real-time information for about 400 ms. This adds a worst-case delay that causes real-time applications to operate with round-trip delays on the order of at least a second -- unacceptable for real-time conversation. The PPP extensions defined in this document allow a sender to fragment the packets of various priorities into multiple classes of fragments, allowing high-priority packets to be sent between fragments of lower priorities.
A companion document based on these extensions  defines a suspend/resume-oriented solution for those cases where the best possible delay is required and the senders are of type 1 .
1.1. Specification Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document ar...