SIST-TP ETSI/TR 102 016 V1.1.1:2005

• Abstract:

  The purpose of this technical report is to identify the requirements and impacts on the network to support the transmission of PPP packets over the LAP-D of an ISDN access, e.g. based on the IETF RFC-1662 document PPP in the HDLC-like framing.

• Status: Published
• Publication Date: 31-Dec-2004
• ICS: 33.040.35 - Telephone networks
• ICS: 33.080 - Integrated Services Digital Network (ISDN)
• Technical Committee: SPN - Services and Protocols for Networks
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Jan-2005
• Due Date: 01-Jan-2005
• Completion Date: 01-Jan-2005
• Ref Project: ETSI TR 102 016 V1.1.1 (2001-11) - Services and Protocols for Advanced Networks (SPAN); Integrated Services Digital Network (ISDN); Potential solutions to support the transmission of PPP

ETSI TR 102 016 V1.1.1 is a Technical Report from ETSI, produced by the Services and Protocols for Advanced Networks (SPAN) committee, on ways to carry Point-to-Point Protocol (PPP) traffic over the D channel of an Integrated Services Digital Network (ISDN) access. It explains potential solutions for network designers and implementers who need to support PPP packets on ISDN without using the X.25 virtual circuit used in AO/DI.

What does ETSI TR 102 016 V1.1.1 specify?

ETSI TR 102 016 V1.1.1 gives guidance on two ways to transport internet protocols over LAPD in an ISDN access: PPP over LAPD (PPPoLAPD) and Multilink Protocol over LAPD (MPoLAPD). The report is about how to fit PPP traffic into the LAPD constraints of the ISDN D channel and what that means for framing and negotiation.

The document is organized into:

• Scope
• References
• Definitions and abbreviations
• Description
• LAPD restrictions
• PPP over LAPD (PPPoLAPD)
• MP over LAPD (MPoLAPD)
• Conclusion

What are the key requirements of ETSI TR 102 016 V1.1.1?

ETSI TR 102 016 V1.1.1 focuses on practical framing and size limits, because the ISDN LAPD layer is the main constraint. The report compares a simple PPP encapsulation approach with a multilink approach and explains what each means for packet size, negotiation, and implementation.

LAPD framing limits

The report states that the LAPD information field is limited to 260 octets, so internet packets have to fit within that size. It also points out that LAPD does not provide the same fragmentation mechanism as X.25, so the implementation has to work within the fixed LAPD frame structure. In practice, this is the core sizing issue for any device carrying PPP on the D channel.

Addressing on the D channel

ETSI TR 102 016 V1.1.1 says the LAPD address field uses SAPI and TEI values, and that a new SAPI codepoint is preferred for identifying internet traffic on an ISDN access. It also recommends non-automatic TEI assignment for transporting internet packets over the D channel. For implementers, this affects how the network recognizes the traffic and how address values are allocated.

PPPoLAPD size behavior

For PPP over LAPD, the report ties the PPP MRU to the LAPD payload limit and fixes it to 258 octets, with 2 octets reserved for the PPP protocol field. This means PPP negotiation and user data both have to stay within that payload size. In practice, small negotiation messages or IP datagrams may need attention so that authentication and control traffic still fit.

IP and higher-layer handling

The report explains that PPP itself does not fragment, so with PPPoLAPD the effective IP datagram size is limited by the PPP information field size. It notes that fragmentation then happens at the IP layer, which matters for TCP and UDP traffic because larger payloads have to be split before transmission over the D channel.

MPoLAPD behavior

ETSI TR 102 016 V1.1.1 describes MP as a way to fragment and reassemble messages over PPP and says it can be used on a single link to increase the effective MTU when needed. It introduces MRRU for reconstructed frames and says the negotiated MRRU is used as the MTU for network-layer interfaces. In practice, MPoLAPD lets the reconstructed IP datagram be much larger than the LAPD frame, while still sending fragments that fit the channel.

Fragment header choice

The report distinguishes between long and short sequence number fragment formats in MP, and says the short format is desirable because of the LAPD 260-octet limit. For implementers, this is a framing decision that affects overhead and how much user data fits in each fragment.

What terms does ETSI TR 102 016 V1.1.1 define?

• Always On/Dynamic ISDN (AO/DI) - A networking service that provides an always-available connection to TCP/IP based services.
• Point-to-Point Protocol (PPP) - The protocol used to carry network-layer traffic over a point-to-point link.
• Link Access Protocol on channel D (LAPD) - The ISDN data-link protocol used on the D channel.
• Link Control Protocol (LCP) - The PPP phase used to negotiate link parameters such as MRU.
• Network Control Protocol (NCP) - The PPP phase used to negotiate network-layer protocol settings.
• Multilink Protocol (MP) - The PPP mechanism for fragmenting and reassembling traffic across links.
• Maximum Receive Unit (MRU) - The largest PPP information field an implementation can receive.
• Maximum Receive Reconstructed Unit (MRRU) - The largest reconstructed frame size in multilink PPP.

Who uses ETSI TR 102 016 V1.1.1?

ETSI TR 102 016 V1.1.1 is relevant to ISDN equipment manufacturers, telecom network engineers, and service providers that handle TCP/IP traffic over ISDN access. It is also useful for implementers working on PPP framing, D-channel transport, and interworking with AO/DI-style services. Quality and integration teams can use it when checking whether a device or network design matches the LAPD size and addressing constraints.

Which standards are used with ETSI TR 102 016 V1.1.1?

The report relies on:

• IETF draft-ietf-pppext-aodi-02, AO/DI - the service model used as the reference for always-on/dynamic ISDN behavior.
• IETF RFC 1548, The Point-to-Point Protocol (PPP) - the base PPP definition used for PPP framing and negotiation.
• IETF RFC 1990, The PPP Multilink Protocol (MP) - the basis for MP fragmentation and reassembly.
• ITU-T Recommendation Q.921 - the LAPD data-link layer specification that sets the ISDN framing constraints.

What does the ETSI TR 102 016 V1.1.1 document contain?

ETSI TR 102 016 V1.1.1 contains frame-structure tables for LAPD, PPPoLAPD, and MPoLAPD, plus a figure showing how LAPD, IP, and TCP/UDP layers fit together. It also includes a negotiation-oriented explanation of PPP MRU and MP MRRU, which helps readers understand how size limits are set during link setup. The document uses these examples to show how internet packets can be carried over the ISDN D channel.

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Services and Protocols for Advanced Networks (SPAN); Integrated Services Digital
Network (ISDN); Potential solutions to support the transmission of PPP
Ta slovenski standard je istoveten z: TR 102 016 Version 1.1.1
ICS:
33.040.35 Telefonska omrežja Telephone networks
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

Technical Report
Services and Protocols for Advanced Network (SPAN);
Integrated Services Digital Network (ISDN);
Potential solutions to support the transmission of PPP

2 ETSI TR 102 016 V1.1.1 (2001-11)

Reference
DTR/SPAN-130248
Keywords
ISDN, transmission
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All rights reserved.
ETSI
3 ETSI TR 102 016 V1.1.1 (2001-11)
Contents
Intellectual Property Rights.4
Foreword.4
1 Scope.5
2 References.5
3 Definitions and abbreviations.5
3.1 Definitions.5
3.2 Abbreviations.5
4 Description.6
5 LAPD restrictions.6
6 PPP over LAPD (PPPoLAPD).6
7 MP over LAPD (MPoLAPD).7
8 Conclusion.9
History .10

ETSI
4 ETSI TR 102 016 V1.1.1 (2001-11)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
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Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Services and Protocols for Advanced
Networks (SPAN).
ETSI
5 ETSI TR 102 016 V1.1.1 (2001-11)
1 Scope
The present document gives guidance on potential solutions to support the tranmission of Point-to-Point Protocol (PPP)
packets over the D channel of an ISDN access without the need of an X.25 virtual circuit as used and defined in the
Always On/Dynamic ISDN (AO/DI) [1] networking service.
2 References
For the purposes of this Technical Report, the following references apply:
[1] IETF, PPP extensions, draft-ietf-pppext-aodi-02: "Always On/Dynamic ISDN (AO/DI)"
(http://www.ietf.org/proceedings/00jul/I-D/pppext-aodi-02.txt)
[2] IETF, RFC1548: "The Point-to-Point Protocol (PPP)".
[3] IETF, RFC1990: "The PPP Multilink Protocol (MP)".
[4] ITU-T Recommendation Q.921: "ISDN User-Network interface - Data link layer specification".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following term and definition applies:
Always On/Dynamic ISDN (AO/DI): networking service that provides an always-available connection to TCP/IP
based services
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AO/DI Always On/Dynamic ISDN
IETF Internet Engineering Task Force
IP Internet Protocol
ISDN Integrated Services Digital Network
LAPD Link Access Protocol on channel D
LCP Link Control Protocol
MP Multilink Protocol
MPoLAPD Multilink Protocol over LAPD
MRRU Maximum Receive Reconstructed Unit
MRU Maximum Receive Unit
MTU Maximum Transfer Unit
NCP Network Control Protocol
PPP Point-to-Point Protocol
PPPoLAPD Point-to-Point Protocol over LAPD
RFC Request For Comment
SAPI Service Access Point Identifier
TCP/IP Transmission Control Protocol/IP
TCP/UDP Transmission Control Protocol/UDP
TEI Terminal End-point Identifier
UDP User Data Protocol
ETSI
6 ETSI TR 102 016 V1.1.1 (2001-11)
4 Description
AO/DI [1] is a networking service that provides an always-available connection to TCP/IP based services. This service
is provided to ISDN subscribers; an ISDN D channel permanent logical link is established between the subscriber and a
packet handler, a X.25 virtual circuit is then established between the subscriber and his Internet service provider. This
virtual circuit is used to establish an Internet connection, when bandwidth is required for the transmission of Internet
data (downstream and/or upstream), one or two B channels are established.
The present document gives guidance on potential solutions to support the transmission of Point-to-point Protocol (PPP)
packets over the D channel of an ISDN access without the need of an X.25 virtual circuit as used
...