[PWE3] Re: comments on draft-ietf-pwe3-frame-relay-05.txt
Luca Martini <lmartini@cisco.com> Tue, 13 December 2005 00:47 UTC
Received: from localhost.cnri.reston.va.us ([127.0.0.1] helo=megatron.ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1ElyKc-0001ZR-SB; Mon, 12 Dec 2005 19:47:50 -0500
Received: from odin.ietf.org ([132.151.1.176] helo=ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1ElyKa-0001YU-Se for pwe3@megatron.ietf.org; Mon, 12 Dec 2005 19:47:48 -0500
Received: from ietf-mx.ietf.org (ietf-mx [132.151.6.1]) by ietf.org (8.9.1a/8.9.1a) with ESMTP id TAA28843 for <pwe3@ietf.org>; Mon, 12 Dec 2005 19:46:44 -0500 (EST)
Received: from rtp-iport-2.cisco.com ([64.102.122.149]) by ietf-mx.ietf.org with esmtp (Exim 4.43) id 1ElyLL-0007xA-NU for pwe3@ietf.org; Mon, 12 Dec 2005 19:48:36 -0500
Received: from rtp-core-1.cisco.com ([64.102.124.12]) by rtp-iport-2.cisco.com with ESMTP; 12 Dec 2005 19:47:26 -0500
X-IronPort-AV: i="3.99,245,1131339600"; d="scan'208"; a="77627176:sNHT35319520"
Received: from [209.245.27.1] ([10.32.241.115]) by rtp-core-1.cisco.com (8.12.10/8.12.6) with SMTP id jBD0lI4X024388; Mon, 12 Dec 2005 19:47:24 -0500 (EST)
Message-ID: <439E1A16.6060602@cisco.com>
Date: Mon, 12 Dec 2005 17:47:18 -0700
From: Luca Martini <lmartini@cisco.com>
User-Agent: Mail/News 1.4 (X11/20050929)
MIME-Version: 1.0
To: Stewart Bryant <stbryant@cisco.com>
References: <42CEC167.6080804@cisco.com>
In-Reply-To: <42CEC167.6080804@cisco.com>
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 7bit
X-PMX-Version: 4.7.1.128075
X-from-outside-Cisco: [10.32.241.115]
X-Spam-Score: 0.0 (/)
X-Scan-Signature: 90e8b0e368115979782f8b3d811b226b
Content-Transfer-Encoding: 7bit
Cc: pwe3 <pwe3@ietf.org>
Subject: [PWE3] Re: comments on draft-ietf-pwe3-frame-relay-05.txt
X-BeenThere: pwe3@ietf.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Pseudo Wires Edge to Edge <pwe3.ietf.org>
List-Unsubscribe: <https://www1.ietf.org/mailman/listinfo/pwe3>, <mailto:pwe3-request@ietf.org?subject=unsubscribe>
List-Post: <mailto:pwe3@ietf.org>
List-Help: <mailto:pwe3-request@ietf.org?subject=help>
List-Subscribe: <https://www1.ietf.org/mailman/listinfo/pwe3>, <mailto:pwe3-request@ietf.org?subject=subscribe>
Sender: pwe3-bounces@ietf.org
Errors-To: pwe3-bounces@ietf.org
Stewart, Replies below. Thanks. Luca Stewart Bryant wrote: > Please remember to address Carlos Pignataro's comments at > > http://www.ietf.org/mail-archive/web/pwe3/current/msg07089.html > Done. > ------- > > - Backward direction. > > In frame relay it is the direction opposite to the direction > taken by a frame being forwarded (see also forward direction). > > - Forward direction. > > The forward direction is the direction taken by the frame being > forwarded. > > It would read better if you reversed the order of these definitions > Ok. > ------ > Although different layer 2 protocols > require different information to be carried in this encapsulation, an > attempt has been made to make the encapsulation as common as possible > for all layer 2 protocols. Other layer 2 protocols are described in > separate documents. [ATM] [ETH] [PPP] > > As before not sure of the value of this > The point is to make sure the reader realizes that we strive to use the same CW, and that we have other documents for the other layer2 protocols... I do not think this text is bad .... So I would like to keep it. > ------ > > Two mapping modes can be defined between frame relay VCs and pseudo > wires: The first one is called "one-to-one" mapping, because there > is a one-to-one correspondence between a frame-relay VC and one > Pseudo Wire. The second mapping is called "many-to-one" mapping or > "port mode" Because multiple frame-relay VCs assigned to a port are > s/"port mode" Because/"port mode", because/ > one-to-one either all in "" or all not? > > ------- > Ok. > +-------------------------------+ > | | > | MPLS Transport header | > | (As required) | > +-------------------------------+ > | Pseudo Wire (PW) Header | > +-------------------------------+ > | Control Word | > +-------------------------------+ > | FR Service | > | Payload | > +-------------------------------+ > > same comment as for ATM - you have PW header when you really mean > PW label > what does rfc3985 say ? This is aligned with it. I added text to make it a little better. I identified an MPLS label as the PW label which is the PW header .... > -------- > > > 6.5. PW packet processing > > 6.5.1. Generation of PW packets > > I am not sure generation is the right word to use. How > about FR PW encapsulation > Yes, this is not my terminology - I will fix it. > ------- > > - The DE bit of the frame relay frame is copied into the D bit > field. However if the D bit is not already set, it MAY be set as > a result of ingress frame policing. If not already set by the > copy operation, setting of this bit by a PE is OPTIONAL. The PE > MUST NOT clear this bit (set it to 0 if it was received with the > value of 1). > > I think that we could express this in some simpler way. > How about something like > > If the DE bit of the frame relay frame is set the D bit MUST be set. > The PE MAY set the D bit in response to ingress policing. Otherwise the > D bit MUST be clear. Setting the D in response to ingress policing is > OPTIONAL. > > Same for the other bits. > it is unclear to me why this is simpler .... the point that was critical here is not to clear the D bit. Some implementations actually cleared the D bit.... > ---------- > > - The sequence number field is processed if the PW uses sequence > numbers. > > Perhaps a forward reference > to CW ? yes . I'll add it. I will also edit the sequence number processing section to point to CW. > --------- > 6.6. Reception of PW packets > > Perhaps decapsulation. Whatever word is used it should be the opposite > of the word used to title the encapo process. > Ok decacapsulation it is. > ---------- > > When a PE receives a PW packet, it processes the different fields of > the control word in order to generate a new frame relay frame for > transmission to a CE on a frame relay UNI or NNI. The PE performs the > following actions (not necessarily in the order shown): > > - It generates the following frame relay frame header fields from > the corresponding fields of the PW packet. > - The C/R bit is copied in the frame relay header. > - The D bit is copied into the frame relay header DE bit. > - The F bit is copied into the frame relay header FECN bit. If the > F bit is set to zero, the FECN bit may be set to one, depending > on the congestion state of the PE device in the forward > direction. Changing the state of this bit by a PE is OPTIONAL. > - The B bit is copied into the frame relay header BECN bit. If the > B bit is set to zero, the BECN bit may be set to one, depending > on the congestion state of the PE device in the backward > direction. Changing the state of this bit by a PE is OPTIONAL. > > I think that a few MUSTs would be appropriate above something like > > - The C/R bit MUST be copied into the C/R bit in the frame relay header > > - The D bit MUST be copied into the D bit in the frame relay header > Ok . > - If the F bit is set, the FECN bit MUST be set in the frame relay > header. If the PE detects congestion in the forward direction, it > MAY set the set the FECN bit in the frame relay header. Otherwise > the FECN bit MUST be clear. Setting the FECN bit in response to > congestion is OPTIONAL. > The original section is a bit clearer then what you suggest. > - If the B bit is set, the BECN bit MUST be set in the frame relay > header. If the PE detects congestion in the backwards direction, it > MAY set the set the BECN bit in the frame relay header. Otherwise > the BECN bit MUST be clear. Setting the BECN bit in response to > congestion is OPTIONAL. > Ditto. > ------- > > - It processes the length and sequence field, the details of which > are in the subsequent sub-sections. > > reference would be helpful to the reader > The sections are immediately following a few lines of text, I do not think that it is necessary to mention the section name and number given that they are a few lines below ... > ------ > > - It generates the frame relay information field from the contents > of the PW packet payload after removing any padding. > > s/generates/copies/ ? > ok. > ------ > > Once the above fields of a FR frame have been generated, the FCS has > to be computed, > > s/computes/appended/ ? > ok. > HDLC flags have to be added and any bit or byte > stuffing has been performed (these final actions typically take place > in a hardware framer). The FR frame is queued for transmission on > the selected frame relay UNI or NNI interface. > > I think that there must be some simpler way of saying the above - > (FCS + bit stuffing + flags), but the words don't spring to mind > as a type this. Perhaps there are some key words in an HDLC or FR spec > that someone can point to. > I'm re-writing this as it is clearly not clear. > ---------- > > If a packet passes the sequence number check, or is in order then, it > > Do you mean "if there is no sequence number, or if the packet is in > order" > section removed. > --------- > > If a PE router negotiated not to use receive sequence number > processing, and it received a non zero sequence number, then it > SHOULD send a PW status message indicating a receive fault, and > disable the PW. > > Now I remember some discussion about this being a security hole. > Was this the final resolution? > Section removed .. However this is no more a security hole then sending a packet with the wrong sequence number to make the PW loose many packets .... > --------- > > > If an egress PE receives an excessive number of out-of-sequence PW > packets, it SHOULD inform the management plane responsible for PW > setup/maintenance, and take the appropriate actions. The threshold > for declaring that out-of-sequence PW packets are excessive is not > defined in this document. > > Hang on this is inconsistent with the above > Removed. > ----------- > > > 6.7. MPLS Shim EXP Bit Values > > If it is desired to carry Quality of Service information, the Quality > of Service information SHOULD be represented in the EXP field of the > PW MPLS label. If more than one MPLS label is imposed by the ingress > LSR, the EXP field of any labels higher in the stack SHOULD also > carry the same value. > > > 6.8. MPLS Shim S Bit Value > > The ingress LSR, PE1, MUST set the S bit of the PW label to a value > of 1 to denote that the PW label is at the bottom of the stack. > > > 6.7 and 6.8 should be moved earlier > > > ------------- > > > 6.9. Control Plane Details for Frame Relay Service > > When emulating a frame relay service, the frame relay PDUs are > encapsulated according to the procedures defined herein. > > The PE MUST > provide frame relay PVC status signaling to the frame relay network. > If the PE detects a service-affecting condition for a particular > DLCI, as defined in [ITUQ] Q.933 Annex A.5 sited in IA FRF1.1, the PE > MUST communicate to the remote PE the status of the PW that > corresponds to the frame relay DLCI status. The Egress PE SHOULD > generate the corresponding errors and alarms as defined in [ITUQ] on > the egress Frame relay PVC. > > The above is out of place in this para. Should be a seperate para and > not in the middle of the encap stuff. > Not sure i follow, I will remove the top paragraph as it is not useful, but this one looks fine ... > There are two frame relay flags to > control word bit mappings described below. The legacy bit ordering > scheme will be used for a PW of type 0x0001 "Frame Relay DLCI > (Martini Mode)", while the new bit ordering scheme will be used for a > PW of type 0x0019 "Frame Relay DLCI". The IANA allocation registry of > "Pseudowire Type" is defined in [IANA] along with initial allocated > values. > > ------- > > > 6.9.1. Frame-Relay Specific Interface Parameters > > A separate document [CONTROL], describes the PW control, and > maintenance protocol in detail including generic interface > parameters. The interface parameter information, when applicable, it > > delete the trailing it > Ok. > MUST be used to validate that the PEs, and the ingress and egress > ports at the edges of the circuit, have the necessary capabilities to > interoperate with each other. The Interface parameter TLV is defined > in [CONTROL], the IANA registry with initial values for interface > parameter types is defined in [IANA], but the frame relay specific > interface parameters are specified as follows: > > - 0x08 Frame-Relay DLCI Length. > > An optional 16 bit value indicating the length of the frame relay > DLCI field. This OPTIONAL interface parameter can have value of 2 > > MUST have the value 2 or 4 ? > I do not see why I should use the MUST here ... > , or 4, with the default being equal to 2. If this interface > parameter is not present the default value of 2 is assumed. > > You descibe default behaviour twice > ??? this does not parse. > --------- > Thanks for all the comments ! Luca _______________________________________________ pwe3 mailing list pwe3@ietf.org https://www1.ietf.org/mailman/listinfo/pwe3
- [PWE3] comments on draft-ietf-pwe3-frame-relay-05… Stewart Bryant
- [PWE3] Re: comments on draft-ietf-pwe3-frame-rela… Luca Martini