[L2tpext] TDM over L2TPv3
Carlos Pignataro <cpignata@cisco.com> Thu, 02 August 2007 20:45 UTC
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Date: Thu, 02 Aug 2007 16:45:02 -0400
From: Carlos Pignataro <cpignata@cisco.com>
Organization: cisco Systems, Inc.
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Subject: [L2tpext] TDM over L2TPv3
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Please find some review comments on draft-ieft-l2tpext-tdm-03 All, please note that there was a typo in the filename of early versions of this draft, as draft-ieft-l2tpext-tdm. We had this fixed through the Secretariat, and the current version -03 has been corrected (s/ieft/ietf/). Please use the second filename/link onwards (the first one for the rev history): http://tools.ietf.org/wg/l2tpext/draft-ieft-l2tpext-tdm/ http://tools.ietf.org/wg/l2tpext/draft-ietf-l2tpext-tdm/ ^^ More substantive: ================ 2. L2TP Extension ... [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]. Is the recommendation not to use "Set-Link-Info (SLI)" message, or not to use the "Circuit Status AVP in Set-Link-Info (SLI)"? Please note that the Circuit Status AVP is a MUST for ICRQ/ICRP in RFC3931, and that should probably be clarified as well (i.e., what does the Circuit Status mean in ICRQ/ICRP for TDM PWs). Additionally, the RFC2119 keyword is "NOT RECOMMENDED" instead of "RECOMMENDED to not" --- 2.1 TDM PW AVP (ICRQ, OCRQ) ... Bit Rate is defined in [RFC4446]. Its usage for all types of TDM PWs ... CEP/TDM Payload Bytes has been defined in [RFC4446]. It can be used Are the "TDM Payload Bytes" and "TDM Bit-Rate" defined in RFC4446? RFC4446 seems to assign their parameter id number for the Interface Parameters Sub-TLV, but not define them. Are these two actually defined in draft-ietf-pwe3-tdm-control-protocol-extensi-03, Sections 3.1 and 3.2 (and in rfc4842 Sections 12.1 and 12.2 for CEP)? --- 2.1 TDM PW AVP (ICRQ, OCRQ) ... Bit Rate is defined in [RFC4446]. Its usage for all types of TDM PWs I think it would help with clarity to explicitly mention that the Bit Rate is specified in units of 64kbps/DS0s, even if the definition is a pointer to a normative reference. Also, the place where they are actually defined (which appears to be draft-ietf-pwe3-tdm-control-protocol-extensi-03) should likely be normatively referenced, since it defines the syntax and semantics of the fields. --- 2.4 Changes in the Session Connection AVPs ... TDM pseudowires use their own control word. Therefore the L2- Specific Sublayer AVP MUST either be omitted or set to zero. Does this imply that TDM PWs cannot use PW Frag and VCCV, which use bits in the L2-Specific Sublayer? It seems not: Frag: The SAToP CW and the CESoPSN CW both seem to contain the two "FRG" bits, so this could be clarified in this paragraph. VCCV: Both rfc4553 and draft-ietf-pwe3-cesopsn say something like: An ACH is needed if the state of the SAToP PW is being monitored using Virtual Circuit Connectivity Verification [PWE3-VCCV]. So basically the SAToP/CESoPSN CW is used as the L2SS. I think it would help to mention this. Or alternatively, would it be an option to define the SAToP/CESoPSN CW as the L2SS (with a new L2SS enumeration value for the L2SS AVP), and have a MUST be signaled? Maybe it's too late for this? --- 3. Creation of the TDM Pseudowire Session ... 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. What happens when the two sides differ in the timestamping mode (absolute or differential) --- Security Considerations There are no additional security considerations on top of the ones discussed in [RFC3931] Do the additional security considerations listed in rfc4553 and CESoPSN apply? --- 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 and 2. L2TP Extension ... [PWE3-CESoPSN] and [RFC4553] describe how to transfer the End Point status via the data plane. ... 2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP) ... 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 ... The C bit indicates the ordering of the RTP header and the control word as following: ... 2.4 Changes in the Session Connection AVPs ... 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. This document (draft-ietf-l2tpext-tdm-03) does not define or explicitly depicts the dataplane encapsulation for TDM PWs over L2TPv3. Instead, it relies on the definition of RFC4553 (for SAToP) and draft-ietf-pwe3-cesopsn (for CESoPSN), and cites those two. Since the SAToP/CESoPSN references are needed to implement TDM PWs (as they define the PW encapsulation), it seems to me that they should be Normative references rather than Informative references. http://www.ietf.org/IESG/STATEMENTS/iesg-statement-normative-informative-references.txt One issue here however is that the Intended Status of "TDM over L2TPv3" is Proposed Standard, and that of CESoPSN is Informational, resulting in a downref. But are those defining the PW encapsulation that TDM PWs need to use? Further, I think it would help significantly with clarity if the "TDM over L2TPv3" document points to the specific sections and figures in those citations (e.g., Figure 2b, Section 4.3 and Appendix A of RFC4553; Figure 1c., Section 4.1 and Appendix C of [PWE3-CESoPSN]) where the encapsulation is depicted/defined. More editorial: ============== Abstract This document defines extensions to the Layer Two Tunneling Protocol (L2TP) for support of structure-agnostic [RFC4553] and structure- aware [PWE3-CESoPSN] pseudowires. There shouldn't be citations in the Abstract. http://www.ietf.org/ID-Checklist.html#anchor6 --- 2.1 TDM PW AVP (ICRQ, OCRQ) ... 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. For consistency with previous paragraph in this section, I think that numbered bullet "2)" could say "For Structure-aware" instead of "For CESoPSN PWs". --- 2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP) ... This AVP MUST appear if and only if the RTP header is used in the TDM pseudowire encapsulation. Nit: Shouldn't the logic in this sentence be inverse (the AVP signaling what the dataplane needs to do)? Like "Presence of this AVP indicates that the RTP header is used in the encapsulation". --- 2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP) ... 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 There's an extraneous "e.g., ". --- 2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP) ... misconnections. Since L2TP provides an alternative security mechanism via the cookies, if the cookie length is larger then zero the SSRC SHOULD be zero. Typo: s/then/than/. Also, this Section 2.2 does not define the "Reserved" field (e.g., MBZ sending, ignored receiving) --- 3. Creation of the TDM Pseudowire Session When LCCE wants to open a Session for TDM PW it MUST include the TDM WOuld it be needed to narrow down when the LCCE actually wants to open the session? e.g., when configured, When admin up or When out of alarm. --- 2.2 RTP AVP (ICRQ, OCRQ, ICRP, OCRP) ... used. Differential mode can be used only if both sides use RTP and use differential time stamping. ... 3. Creation of the TDM Pseudowire Session ... 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 ... 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 ... 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. The four paragraphs listed above confused me a bit regarding two things: Can the RTP usage be unidirectional, or does it need to match? Does the presence of the RTP AVP means that the sending of the AVP wants to send the RTP header in the dataplane, or that it requests the peer sends the RTP header? --- 4. IANA Considerations ... PW types listed in Section 2.1 above. It is RECOMMENDED to use the same values as defined in [RFC4446]. Could you please list them here as well, with suggested values, and clarifying that these are "L2TPv3 PW Types" from http://www.iana.org/assignments/l2tp-parameters --- 4. IANA Considerations ... New return codes and error codes: Could you please add/clarify that the "Result Code values" are "for the CDN message"? Thanks, -- --Carlos Pignataro. Escalation RTP - cisco Systems _______________________________________________ L2tpext mailing list L2tpext@ietf.org https://www1.ietf.org/mailman/listinfo/l2tpext
- [L2tpext] TDM over L2TPv3 Carlos Pignataro
- [L2tpext] RE: TDM over L2TPv3 Sasha Vainshtein
- [L2tpext] Re: TDM over L2TPv3 Carlos Pignataro