PPP Over AAL5
RFC 2364
Network Working Group G. Gross
Request for Comments: 2364 Lucent Technologies
Category: Standards Track M. Kaycee
Paradyne
A. Lin
Shasta Networks
A. Malis
Ascend Communications
J. Stephens
Cayman Systems
July 1998
PPP Over AAL5
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 Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links.
This document describes the use of ATM Adaptation Layer 5 (AAL5) for
framing PPP encapsulated packets.
Applicability
This specification is intended for those implementations which desire
to use the facilities which are defined for PPP, such as the Link
Control Protocol, Network-layer Control Protocols, authentication,
and compression. These capabilities require a point-to-point
relationship between the peers, and are not designed for the multi-
point relationships which are available in ATM and other multi-access
environments.
Gross, et. al. Standards Track [Page 1]
RFC 2364 PPP Over AAL5 July 1998
1. Introduction
ATM AAL5 protocol is designed to provide virtual connections between
end stations attached to the same network. These connections offer a
packet delivery service that includes error detection, but does not
do error correction.
Most existing implementations of PPP use ISO 3309 HDLC as a basis for
their framing [3].
When an ATM network is configured with point-to-point connections,
PPP can use AAL5 as a framing mechanism.
2. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [10].
3. AAL5 Layer Service Interface
The PPP layer treats the underlying ATM AAL5 layer service as a bit-
synchronous point-to-point link. In this context, the PPP link
corresponds to an ATM AAL5 virtual connection. The virtual
connection MUST be full-duplex, point to point, and it MAY be either
dedicated (i.e. permanent, set up by provisioning) or switched (set
up on demand). In addition, the PPP/AAL5 service interface boundary
MUST meet the following requirements:
Interface Format - The PPP/AAL5 layer boundary presents an octet
service interface to the AAL5 layer. There is no provision for
sub-octets to be supplied or accepted.
Transmission Rate - The PPP layer does not impose any
restrictions regarding transmission rate or the underlying ATM
layer traffic descriptor parameters.
Control Signals - The AAL5 layer MUST provide control signals to
the PPP layer which indicate when the virtual connection link
has become connected or disconnected. These provide the "Up"
and
"Down" events to the LCP state machine [1] within the PPP layer.
Gross, et. al. Standards Track [Page 2]
RFC 2364 PPP Over AAL5 July 1998
4. Multi-Protocol Encapsulation
This specification uses the principles, terminology, and frame
structure described in "Multiprotocol Encapsulation over ATM
Adaptation Layer 5" [4].
The purpose of this specification is not to document what is already
standardized in [4], but to specify how the mechanisms described in
[4] are to be used to map PPP onto an AAL5-based ATM network.
Section 1 within [4] defines the two mechanisms for identifying the
Protocol Data Unit (PDU) payload field's protocol type: virtual
circuit based multiplexing, and Logical Link Control (LLC)
encapsulation. In the former technique, the payload's protocol type
is implicitly agreed to by the end points for each virtual circuit
using provisioning or control plane procedures. When using the LLC
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