L2TP TDM February 2007
Network Working Group A. Vainshtein
Internet Draft Axerra Networks
Document: draft-ieft-l2tpext-tdm-03.txt S. Galtzur
Rawflow
Intended Status: Proposed Standard
Expires: August 2007 February 2007
Layer Two Tunneling Protocol - Setup of TDM Pseudowires
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document defines extensions to the Layer Two Tunneling Protocol
(L2TP) for support of structure-agnostic [RFC4553] and structure-
aware [PWE3-CESoPSN] pseudowires.
Conventions used in this document
In this document we refer to control plane as the packets that
contain control information (via AVP) and the mechanism that handle
these packets.
In this document we refer to the data plane as the packets that
contain transported user data.
Vainshtein and Galtzur Expires - August 2007 [Page 1]
L2TP TDM February 2007
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
Table of Contents
1. Introduction...................................................2
2. L2TP Extension.................................................2
2.1 TDM PW AVP (ICRQ, OCRQ)...................................3
2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP)..........................4
2.3 Changes in the Control Connection AVPs.....................5
2.4 Changes in the Session Connection AVPs.....................5
3. Creation of the TDM Pseudowire Session.........................5
4. IANA Considerations............................................6
Security Considerations...........................................7
Copyright notice..................................................7
Normative references..............................................8
Informative references............................................8
Authors' Addresses................................................8
1. Introduction
This document defines extensions to the Layer Two Tunneling Protocol
(L2TP) for support of structure-agnostic [RFC4553] and structure-
aware [PWE3-CESoPSN] pseudowires. Setup of structure-aware
pseudowires using encapsulations described in [PWE3-TDMoIP] has been
left for further study.
2. L2TP Extension
The L2TP Control Connection is responsible for 3 main operations:
1. Establishment and validation of session.
2. Ending (tearing down) of session.
3. Transferring of End Point status.
Tearing down of session is identical to [RFC3931].
[PWE3-CESoPSN] and [RFC4553] describe how to transfer the End Point
status via the data plane. This is therefore RECOMMENDED to not use
the Set-Link-Info (SLI) described in [RFC3931].
The next sections describe the extensions to the L2TP for
establishment and validation of TDM pseudowire sessions.
There are 2 new AVPs for the Session Connection Messages. One AVP
describe the TDM pseudowire attributes. The second AVP describe the
RTP attributes for this TDM pseudowire.
Vainshtein and Galtzur Expires - August 2007 [Page 2]
L2TP TDM February 2007
2.1 TDM PW AVP (ICRQ, OCRQ)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|H| rsvd | Length | Vendor Id (IETF) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attribute Type (AVP-TBA-1) | Reserved |CAS|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bit Rate | CEP/TDM Payload Bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This AVP MAY be hidden (the H bit MAY be 0 or 1). The M bit for this
AVP SHOULD be set to 0. The Length (before hiding) of this AVP is
12.
Bit Rate is defined in [RFC4446]. Its usage for all types of TDM PWs
implies the following semantics:
1) Only the following values MUST be specified for structure-agnostic
emulation (see [RFC4553]):
a) Structure-agnostic E1 emulation - 32
b) Structure-agnostic T1 emulation:
i) MUST be set to 24 for the basic mode
ii) MUST be set to 25 for the "Octet-aligned T1" mode
c) Structure-agnostic E3 emulation - 535
d) Structure-agnostic T3 emulation - 699
2) For all kinds of structure-aware emulation, this parameter MUST be
set to the number of DS0 channels in the corresponding attachment
circuit.
Note: for structure-agnostic T1 emulation the value 24 does not
indicate the exact bit rate, and is used for convenience only.
CEP/TDM Payload Bytes has been defined in [RFC4446]. It can be used
for setup of all types of TDM PWs without any changes in its encoding
(see [RFC4446]) with the following semantics:
1) For Structure-agnostic emulation any value of the payload bytes can
be specified.
2) For CESoPSN PWs:
a) The specified value MUST be an integer multiple of number of
DS0 channels in the corresponding attachment circuit.
b) For trunk-specific NxDS0 with CAS, (Payload Bytes/number of DS0
channels) must be an integer factor of the number of frames per
corresponding trunk multiframe.
The Reserved bits are reserved. They MUST be set to 0 on transmission
and MUST be ignored on reception.
Vainshtein and Galtzur Expires - August 2007 [Page 3]
L2TP TDM February 2007
CAS bits define the trunk type for trunk-specific CESoPSN services
with CAS. These bits:
1) MUST be set to 0 for all pseudowire types excluding trunk-specific
CESoPSN with CAS
2) For trunk-specific CESoPSN with CAS these bits bust be set to:
a) '01' in the case of an E1 trunk
b) '10' in the case of a T1/ESF trunk
c) '11' in the case of a T1/SF trunk.
2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|H| rsvd | Length | Vendor Id (IETF) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attribute Type (AVP-TBA-2) |D| PT |C| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Timestamp Clock Frequency |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This AVP MUST appear if and only if the RTP header is used in the TDM
pseudowire encapsulation. This AVP MAY be hidden (the H bit MAY be 0
or 1). The M bit for this AVP SHOULD be set to 0. The Length
(before hiding) of this AVP is 16.
The D bit indicates the timestamping mode (absolute or differential)
in the RTP header. These modes are described in, e.g., in [RFC4553],
Section 4.3.2. If the D bit is set to 1 then the differential
timestamping mode is used, otherwise absolute timestamping mode is
used. Differential mode can be used only if both sides use RTP and
use differential time stamping.
The C bit indicates the ordering of the RTP header and the control
word as following:
o If the C bit is set to 1 the RTP header appears after the control
word in the data channel of the TDM pseudowire. This mode is
described as SAToP/CESoPSN encapsulation over IPv4/IPv6 PSN with
L2TPv3 demultiplexing in [RFC4553] and [PWE3-CESoPSN] respectively.
o If the C bit is set to 0 the RTP header appears before the control
word. This mode described as the old mode of the SAToP/CESoPSN
encapsulation over L2TPv3 in [RFC4553], Appendix A, and [PWE3-
CESoPSN], Annex C, respectively.
Vainshtein and Galtzur Expires - August 2007 [Page 4]
L2TP TDM February 2007
PT is the payload type expected in the RTP header. Value of zero
indicates that the payload type is ignored and will not be used to
detect malformed packets.
Timestamp Clock Frequency is the clock frequency used for the time
stamping in 8 KHz.
SSRC indicates the expected value of SSRC ID in the RTP header. A
zero in this field means that SSRC ID will not be used for detecting
misconnections. Since L2TP provides an alternative security mechanism
via the cookies, if the cookie length is larger then zero the SSRC
SHOULD be zero.
2.3 Changes in the Control Connection AVPs
Control Connection that support TDM MUST add the appropriate PW Type
value to the list in the Pseudowire Capabilities List AVP. The exact
value is TBA by IANA and is listed in the next section.
2.4 Changes in the Session Connection AVPs
PW Type AVP should be set to one of the following values:
1. Structure-agnostic emulation [RFC4553] of:
a. E1 circuits - TBA-SAToP-E1 by IANA. The value 0x0011 is
suggested for alignment with [RFC4446]
b. T1 circuits - TBA-SAToP-T1 by IANA. The value 0x0012 is
suggested for alignment with [RFC4446]
c. E3 circuits - TBA-SAToP-E3 by IANA. The value 0x0013 is
suggested for alignment with [RFC4446]
d. T3 circuits - TBA-SAToP-T3 by IANA. The value 0x0014 is
suggested for alignment with [RFC4446]
2. Structure-aware emulation [PWE3-CESoPSN] of:
a. CESoPSN basic mode - TBA-CESoPSN-Basic by IANA. The value
0x0015 is suggested for alignment with [RFC4446]
b. Trunk-specific CESoPSN service with CAS - TBA-CESoPSN-CAS by
IANA. The value 0x0017 is suggested for alignment with
[RFC4446].
TDM pseudowires use their own control word. Therefore the L2-
Specific Sublayer AVP MUST either be omitted or set to zero.
TDM pseudowires use their own sequencing. Therefore the Data
Sequencing AVP MUST either be omitted or set to zero.
3. Creation of the TDM Pseudowire Session
When LCCE wants to open a Session for TDM PW it MUST include the TDM
PW AVP (in any case) and the RTP AVP (if RTP and only if the RTP
header is used) in the ICRQ or OCRQ message. The LCCE peer must
validate the TDM PW AVP and make sure it can meet the requirements
Vainshtein and Galtzur Expires - August 2007 [Page 5]
L2TP TDM February 2007
derived from the RTP AVP (if it exist). If the peer agrees with the
TDM AVP it will send an appropriate ICRP or OCRP message with the
matching RTP AVP (if needed). The Initiator need to validate that it
can supply the requirements derived from the received RTP AVP.
The two peers MUST agree on the values in the TDM PW AVP:
1. Bit Rate values MUST be equal on both sides. If they are
different, the connection will be rejected with return code RC-
TBD-1 and error code EC-TBD-1.
2. In the case of trunk-specific CESoPSN with CAS, the trunk type (as
encoded in the CAS bits of the TDM AVP) MUST be the same for the
two sides. Otherwise the connection will be rejected with return
code RC-TBD-1 and error code EC-TBD-2.
3. If one side does not support the payload bytes value proposed by
the other one, the connection will be rejected with return code
RC-TBD-1 and error code EC-TBD-3.
4. If one side cannot send RTP header requested by the other side,
the connection will be rejected with return code RC-TBD-1 and
error code EC-TBD-4.
5. If one side can send RTP header but not with the requested
timestamp clock frequency, the connection will be rejected with
return code RC-TBD-1 and error code EC-TBD-5.
4. IANA Considerations
This draft requires assignment of the following values by IANA:
PW types listed in Section 2.1 above. It is RECOMMENDED to use the
same values as defined in [RFC4446].
New attribute value pair IDs:
1. AVP-TBD-1 - TDM Pseudowire AVP
2. AVP-TBD-2 - RTP AVP
New return codes and error codes:
1. RC-TBD-1 - return code to indicate connection refused because of
TDM PW parameters. The exact error code is as follows.
2. EC-TBD-1 - indicate Bit Rate values disagree.
3. EC-TBD-2 - indicate different trunk types in the case of trunk-
specific CESoPSN with CAS
4. EC-TBD-3 - requested payload size too big or too small.
5. EC-TBD-4 - RTP header cannot be generated.
6. EC-TBD-5 - requested timestamp clock frequency cannot be
generated.
Vainshtein and Galtzur Expires - August 2007 [Page 6]
L2TP TDM February 2007
Security Considerations
There are no additional security considerations on top of the ones
discussed in [RFC3931]
Copyright notice
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
IPR Validity Disclaimer
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Vainshtein and Galtzur Expires - August 2007 [Page 7]
L2TP TDM February 2007
Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
[RFC3931] J. Lau, M. Townsley, I. Goyret, Layer Two Tunneling
Protocol - Version 3 (L2TPv3), March 2005
Informative references
[PWE3-CESoPSN] A. Vainshtein et al, Structure-aware TDM Circuit
Emulation Service over Packet Switched Network
(CESoPSN), Work in progress, May 2006, draft-ietf-
pwe3-cesopsn-07.txt
[RFC4553] A. Vainshtein, Y. Stein, Structure-Agnostic TDM over
Packet (SAToP), RFC 4553, June 2006
[PWE3-TDMoIP] Y. Stein et al, TDM over IP, Work in progress, draft-
ietf-pwe3-tdmoip-06.txt, December 2006.
[RFC4446] L. Martini, M. Townsley, IANA Allocations for pseudo
Wire Edge to Edge Emulation (PWE3), RFC 4446,
April 2006
Authors' Addresses
Sharon Galtzur
Rawflow Inc.
The Old Pump House, 19 Hooper St.,
London E1 8BU,
UK
Email: sharon@rawflow.com
Alexander Vainshtein,
Axerra Networks,
24 Raoul Wallenberg St.,
Tel Aviv, Israel
Email: sasha@axerra.com
Vainshtein and Galtzur Expires - August 2007 [Page 8]