Submitted to PPP Working Group Yves T'Joens
INTERNET DRAFT Paolo Crivellari
Laurent Hermans
<draft-ietf-pppext-l2tp-atmext-01.txt> Bernard Sales
Alcatel
June 1999
Expires December, 1999
Layer Two Tunnelling Protocol : ATM access network extensions.
Status of this memo
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Abstract
[L2TP] specifies a protocol which permits the tunnelling of the link
layer of PPP over packet based networks, to support remote access
(mainly) by ISDN and PSTN networks. This document augments the
procedures described in [L2TP] to further support ATM SVC or PVC
based access networks. The extensions defined within this document
allow for asymmetric bi-directional call establishment and service
selection in the ATM access network.
Table Of Contents
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1. Introduction
1.1 Conventions
2. Assumptions
2.1 Topology
2.2 Connection Establishment
2.3 LCP Negotiation
3. ATM access enhanced procedures
3.1 ATM connectivity
3.2 Tunnel establishment
3.3 call establishment
3.4 Framing
4. Service model issues
4.1 Authentication
4.2 Authorization
5. New and extended AVPs
5.1 New AVP Summary
5.2 New AVP definition
5.3 Changed AVP Definition
6. IANA considerations
7. Security considerations
8. Acknowledgements
9. References
10. Contacts
1. Introduction
[L2TP] is a tunnelling protocol that allows tunnelling of PPP
sessions between a so called L2TP Access Concentrator (LAC) and an
L2TP Network Server (LNS). The main focus of [L2TP] is on supporting
HDLC based ISDN/PSTN access networks.
This document augments the procedures described in [L2TP] to further
support ATM SVC or PVC based access networks. Support for ATM access
networks requires extensions to the present L2TP procedures along the
following lines :
(a) the traffic management aspects of ATM connections (e.g.
assymetric bandwidth allocation and service category selection
capabilities),
(b) the addressing format to be used in switched ATM networks [AESA]
and
(c) the limititations imposed on LCP negotiation by transporting PPP
over AAL5 over the access network segment of the PPP connection
[PPPoA].
Within this draft, the necessary extensions to [L2TP] are defined to
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cope with issues (a) and (b), issue (c) which is not specific to ATM
may be solved as described in [L2TP_link].
1.1 Conventions
Throughout this document, the words that are used to define the
significance of particular requirements are capitalised. These words
are:
o "MUST"
This word or the adjective "REQUIRED" means that the item is an
absolute requirement of this specification.
o "MUST NOT"
This phrase means that the item is an absolute prohibition of this
specification.
o "SHOULD"
This word or the adjective "RECOMMENDED" means that there may exist
valid reasons in particular circumstances to ignore this item, but
the full implications should be understood and the case carefully
weighed before choosing a different course.
o "SHOULD NOT"
This phrase means that there may exist valid reasons in particular
circumstances when the listed behaviour is acceptable or even useful,
but the full implications should be understood and the case carefully
weighed before implementing any behaviour described with this label.
o "MAY"
This word or the adjective "OPTIONAL" means that this item is truly
optional. One vendor may choose to include the item because a
particular marketplace requires it or because it enhances the
product, for example; another vendor may omit the same item.
2. Assumptions
In this section we describe some assumptions that have lead to the
extensions described in this draft.
2.1 Topology
The procedures as defined in [L2TP] apply mainly to access network
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technology such as PSTN and ISDN, which may be respectively asynch.
HDLC and synch HDLC based. The aim of this document is to extend L2TP
support to allow for user / LAC communication based on ATM access
network technology.
2.2 Connection Establishment
Due to the wide variety of existing signalling protocols and ATM
service categories, and their support or non-support within ATM based
access networks, this document takes as approach to provide for a
flexible identification of ATM connection characteristics while
establishing outgoing and incoming L2TP calls. The procedures as
defined within this document allow the allocation of asymmetric
bandwidth and service category selection in terms of real or non-real
time requirements on the ATM portion of the access network.
As such, the detailed signalling protocol specific information
elements that are necessary for switched VC service, are not
negotiated during call establishment over the L2TP tunnel.
In order to identify the endpoint of the ATM connection within the
ATM access network, SVCs can be established on the basis of the ATM
end system addressing format [AESA]. For PVC based services, the PVC
can either be referred to by using the ATM end system addressing
procedure (Dialed Number), or by making use of a textual name
(Service Name). The latter is inspired by the procedures defined
within [Auto_PVC].
2.3 LCP negotiation
The procedures described within this draft may be combined with the
procedures described in [L2TP_link] to limit LCP negotiation between
LNS and user, so as to enforce PPP over AAL5 specific LCP negotiation
[PPPoA].
3. ATM access enhanced procedures
In order to illustrate the procedures specified within this draft,
this section will provide a description of what might happen when a
Virtual dial-up client initiates access through a (switched) ATM
access network. Note that the emphasis is on the changes proposed
within this draft relative to [L2TP].
3.1 ATM connectivity
Prior to initiating the PPP protocol layer, a Virtual Connection (VC)
MUST be established between the user and the Network Access Server
(LAC). This virtual connection MAY either be a preconfigured
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Permanent VC(PVC), where the access network provider, NAS and user
agree beforehand on the characteristics of the PVC, or MAY be an on-
demand switched VC(SVC), where the negotiation between user, network
and NAS takes place by means of an ATM signalling protocol. Note that
for establishing PVCs, alternative use may be made of the procedures
as described in [Auto_PVC].
In both cases, the user is referred to as the Virtual dial-in user.
Prior to accepting the switched connection from the Virtual dial-in
user, the LAC MAY check with the LNS whether the call should be
accepted. In the latter situation, the LAC MAY determine based upon
parameters available within the call establishment message that this
concerns a virtual dial in user, or MAY undertake a partial
authentication of the end system/user, in order to bind the end
system/user with a specific LNS.
3.2 Tunnel establishment
If no tunnel connection currently exists to the desired LNS, one is
initiated. During the tunnel establishment, LNS and LAC indicate
bearer and framing capabilities to each other, according to normal
procedures.
The bearer capability is extended to allow the identification of ATM
devices in the LAC. This allows the LNS to use the extensions as
defined within this draft to support ATM based outgoing calls.
If no compatibility between LNS and LAC exists according to the
extensions defined within this draft, no tunnel establishment can
take place. This would be because the LAC does not support any bearer
capability which is expected by the LNS, or vice versa. It is however
encouraged that LAC or LNS implementations would allow for seamless
interworking with peer devices which do not implement the extensions
defined within this draft. This could be implemented by allowing a
gracefull fallback to Digital bearer capability.
3.3 call establishment
During incoming and outgoing broadband call establishment, the
following extensions are defined to existing procedures.
During OCRQ, the LNS MUST indicate to the LAC minimum and maximum
speeds for receive and transmit traffic (from the LAC perspective).
This is to allow for the bi-directional asymmetric nature of ATM
traffic contracts. Note that in order to support UBR connections
between LAC and user, the Minimum BPS MUST be set to zero.
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Further during OCRQ, the LNS MAY indicate to the LAC the required
service category, i.e., real time (rt) or non-real time (nrt)
transport services. The combination of minimum and maximum receive
and transmit speed, and the indication of the required service
category allows the LAC to establish an ATM connection according to
its own capabilities, and the ATM access network capabilities,
however within the service requirement for the PPP layer.
Real time connectivity can be provided by either CBR or rt-VBR ATM
service categories, non-real time connectivity can be provided by
UBR, nrt-VBR, ABR or GFR ATM service categories.
Further the LNS MUST indicate to the LAC in OCRQ message the dialed
number according to the format described in this document (NSAP
format). When the dialed number carries an all zero payload, the LAC
SHOULD look at the Service Name AVP to bind the tunnel call to an
PVC.
3.4 Framing
Within this document the PPP PDU refers to the concatenation of PPP
protocol ID, PPP Information and PPP padding fields.
In the direction of user to LNS, the PPP PDU will be carried on top
of an AAL5 connection between user and LAC. The LAC MUST strip off
the AAL5 specific fields based on the encapsulation mechanism in use
on the ATM connection, i.e. VC multiplexed or LLC encapsulated
[PPPoA], and MUST encapsulate the PPP PDU with address and control
field, as per HDLC procedures, on the L2TP tunnel.
In the direction of LNS to user, the PPP PDU will be carried on top
of an AAL5 connection between LAC and user. The LAC MUST strip the
PPP PDU from the address and control field on the L2TP tunnel, and
insert the AAL5 specific fields based on the encapsulation mechanism
in use on the ATM connection, i.e. VC multiplexed or LLC
encapsulated.
4. Service model issues
4.1 Authentication
In case of ATM switched VC establishment, calling party number
information may be used for first level authentication much in the
same way as for PSTN or ISDN access. In case of permanent VC
establishment, authentication may not be an issue from the LAC side,
because of the permanent character of the VC. Bilateral agreement
between LAC and LNS providers may eliminate the authentication phase
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in the latter case.
4.2 Authorization
Because of the flexibility of establishing ATM connections with
varying parameters, some authorization may be required prior to
accepting the establishment of a switched ATM connection from the
user with certain ATM traffic parameters. This authorization may be
performed against the ATM specific authentication information (e.g.
calling line id), or may be performed after partial authentication of
the user at the PPP level. Non authorized access requests result in
connection release.
5. New and extended AVPs
5.1 New AVP Summary
The following table lists the extra AVPs that are defined within this
document. The "attr" column indicates the integer value assigned to
this attribute. Note that the attribute value is relative compared
to the vendor ID. The "M" column indicates the setting of the
"Mandatory" bit of the AVP header for each attribute. The "LEN"
column indicates the size of the AVP including the AVP header. A "+"
in this column indicates that the length varies depending upon the
length of the actual contents of the value field.
The usage list for each entry indicates the message types that
utilize each AVP. An abbreviation shown in mixed or upper case
letters indicates that the corresponding AVP MUST be present in this
message type. All lower case indicates that the AVP MAY optionally
appear in this message type. Some AVPs MAY be present only when a
corresponding optional AVP or specific setting within the AVP is
present, these AVPs are shown in lower case as well.
Attr M Len Attribute Name (usage)
x 0 10 Rx Minimum BPS (OCRQ)
32-bit integer indicating the lowest acceptable line speed for the
call in the receive direction. Rx indicates the user to LAC
direction.
x 0 10 Rx Maximum BPS (OCRQ)
32-bit integer indicating the highest acceptable line speed for
call in the receive direction. Rx indicates the user to LAC
direction.
x 0 6+ ATM Cause Code (cdn)
16-bit cause code, 1 octet cause message, and optional ASCII
advisory message.
x 0 8 Service Category (ocrq, icrq)
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The Service Category indicates the service expected for the call,
e.g., real time or non-real time.
x 0 6+ Service Name (ocrq, icrq)
The Service Name indicates the service name linked to a
preestablished PVC.
5.2 New AVP definition
The following lists the new AVPs defined within this draft, and
describes the expected behaviour when this AVP would be present
within a message.
Rx Minimum BPS
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | BPS (H) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BPS (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Rx Minimum BPS AVP encodes the lowest acceptable line speed
for this call in the receive direction, for these cases where
asymmetric transmission is required. This AVP MAY be included
within the OCRQ, and SHOULD only be included when the LAC
indicated ATM support in the bearer capabilities AVP during
tunnel establishment.
Rx Maximum BPS
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | BPS (H) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BPS (L) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The Rx Maximum BPS AVP encodes the highest acceptable line speed
for this call in the receive direction, for these cases where
asymmetric transmission is required. This AVP MAY be included
within the OCRQ, and SHOULD only be included when the LAC
indicated ATM support in the bearer capabilities AVP during
tunnel establishment.
Service Category
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0| 8 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x |0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Service Category provides optional extra information on the
Quality of Service expected for the call establishment. The S
bit indicates either non real time (S bit set to 0) or real time
(S bit set to 1) service requirement. The other bit fields are
reserved for future use. The Service Category AVP MAY be present
in OCRQ and ICRQ messages, and SHOULD only be included when the
LAC indicated ATM support in the bearer capabilities AVP during
tunnel establishment.
Service Name
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0| 6+len name | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | name |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| name (ctd) ....
+-+-+-+-+-+-+-+-+-+-+-+-+-
The Service Name field allows for the exchange of a textual name
for referring to a PVC. The service name AVP MAY only be
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provided when the Dialed Number field is encoded as all zeros.
The service name AVP MAY be present in OCRQ and ICRQ messages,
and SHOULD only be included when the LAC indicated ATM support
in the bearer capabilities AVP during tunnel establishment.
ATM Cause Code
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0| 6 + len.Cause Code| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | Cause Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code (cont'd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The ATM Cause code AVP indicates the Cause Code as specified in
[UNI], for ATM connection establishment failures. The ATM Cause
Code AVP MUST be present in the CDN message.
5.3 Changed AVP Definition
The following AVPs see their contents changed relative to [L2TP] in
order to support ATM access awareness.
Bearer Capabilities
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 0x00 | 0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 |0|0|0|0|0|B|A|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The bearer Capabilities AVP within a SCCRQ or SCCRP indicates
the bearer capabilities that the sender of this message can
provide for outgoing calls. If bit B is set, broadband access is
supported (ATM), if bit A is set, analogue access is supported.
If bit D is set, Digital access is supported.
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This AVP provides the peer with an indication of the bearer
device types supported by the hardware interfaces of the sender
for outgoing calls. An LNS SHOULD NOT initiate an outgoing call
specifying a value in the Bearer Type AVP for a device type not
advertised in the Bearer Capabilities AVP it received from the
LAC during control connection establishment. Attempts to do so
will result in the call being rejected.
In these cases where the LAC only supports the B bit, and the
LNS would not recognize the B bit, no outgoing calls are
possible. Note that when the LAC only has ATM based devices, it
may still opt for fall back to digital bearer types.
(Tx) Minimum BPS
The (Tx) Minimum BPS AVP encodes the lowest acceptable line
speed for this call in the transmit direction. The (Tx) Minimum
BPS AVP MAY be used in OCRQ. If the Rx Minimum BPS is not
available in the message, then symmetric transmission is
implied, with both minimum receive and transmit bit-rates equal
to Minimum BPS.
(Tx) Minimum BPS is set in bits/second, and may be mapped to the
PCR in cells/second for ATM based traffic. Note that the PCR is
a mandatory parameter for all service capabilities in ATM
signalling. The exact mapping to signalling IEs is outside the
scope of this draft.
(Tx) Maximum BPS
(Tx) Maximum BPS AVP encodes the highest acceptable line speed
for this call in the transmit direction. The (Tx) Maximum BPS
AVP MAY be used in OCRQ. If the Rx Maximum BPS AVP is not
available in the message, then symmetric transmission is
implied, with both maximum receive and transmit bitrates equal
to Maximum BPS.
(Tx) Maximum BPS is set in bits/second, and may be mapped to the
PCR in cells/second for ATM based traffic. Note that the PCR is
a mandatory parameter for all service capabilities in ATM
signalling. The exact mapping to signalling IEs is outside the
scope of this draft.
Bearer Type
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 18 | 0x00 | 0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 |0|0|0|0|0|B|A|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The bearer type AVP encodes the bearer type for the requested
call. The bearer type AVP MUST be present in the OCRQ, and MAY
be present in the ICRQ. If bit B is set, broadband access is
requested (ATM), if bit A is set, analogue access is requested.
If bit D is set, Digital access is requested.
Note that in the OCRQ all 3 bits (B,A,D) may be set indicating
that the call may be of either type. The B bit SHOULD only be
set if the Broadband capability was indicated during tunnel
establishment.
Dialed Number
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|0|0|0| 26 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 21 | NSAP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NSAP (cont'd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NSAP (cont'd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NSAP (cont'd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NSAP (cont'd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NSAP (cont'd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Dialed Number AVP indicates the number that should be used
to address the virtual dial in user. The Dialed number AVP MUST
be present in OCRQ, and MAY be present in ICRQ. The Dialed
number AVP SHOULD be interpreted as binary encoded when the B
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bit is set in the Bearer Type AVP. The NSAP binary encoded
address provides a broader range of address encapsulation
methods than an ASCII field. In the NSAP field, which MUST have
the length of 20 octets, the addressing protocol used (E.164,
ICD, DCC) is specified as defined in [AESA].
If the Dialed Number AVP carries an all zero NSAP address, the
Service Name AVP MAY provide further information to bind the
L2TP call to a specific VC connection. See also [Auto_PVC].
Sub-Address
see Dialed Number. If the Dialed Number carries an all zero NSAP
address, the Sub-Address should be neglected on receipt.
6. IANA Considerations
This document requires 5 new type values for the following AVPs : -
Rx Minimum BPS - Rx Maximum BPS - ATM Cause Code - Service Category -
Service Name
This document further defines a new bit (B) in the bearer
capabilities and bearer type AVPs.
This document defines a flag field in the Service Category AVP, only
one bit in this flag has been assigned witin this document (S).
7. Security Considerations
No extra security risk outside these specified by [L2TP] are
foreseen.
8. Acknowledgements
The authors would like to thank Juha Heinanen (Telia) and David Allen
(Nortel Networks) for their constructive discussion on the draft
during the Minneapolis IETF meeting.
9. References
[L2TP] K. Hamzeh, T. Kolar, M. Littlewood, G. Singh Pall, J.
Taarud, A. Valencia, A. Rubens, W.M. Townsley, B. Palter, W. Verthein
"Layer Two Tunnelling Protocol (L2TP)", RFC xxxx, July 1999
[PPP] W. Simpson, "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994
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[PPPoA] G. Gross, M. Kaycee, A. Lin, A. Malis, J. Stephens, "PPP
over AAL5", RFC 2364, July 1998
[UNI] User-Network Interface (UNI) Specification, Version 4.0,
ATM Forum, July, 1996
[AESA] ATM Forum Addressing : Reference Guide, version 1.0, ATM
Forum, Final Ballot, January 1999
[PPP_HDLC] W. Simpson, "PPP in HDLC-like Framing", STD 51, RFC 1662,
July 1994
[L2TP_link] M. Townsley, W. Palter, "L2TP Link Extensions", Internet
Draft, November 1998, <draft-ietf-pppext-l2tp-link-00.txt>
[Auto_PVC] ATM Forum, "Auto-configuration of PVCs", af-nm-0122.000,
March 1999
10. Contacts
Yves T'joens
Alcatel Corporate Research Center
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 7890
E-mail : yves.tjoens@alcatel.be
Paolo Crivellari
Alcatel Access Systems Division
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 3319
E-mail : pcri@sebb.bel.alcatel.be
Laurent Hermans
Alcatel Corporate Research Center
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 8671
E-mail : hermanla@rc.bel.alcatel.be
Bernard Sales
Alcatel Corporate Research Center
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 9574
E-mail : bernard.sales@btmaa.bel.alcatel.be
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