[PWE3] comments on draft-ietf-pwe3-frame-relay-05.txt
Stewart Bryant <stbryant@cisco.com> Fri, 08 July 2005 18:10 UTC
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Date: Fri, 08 Jul 2005 19:09:43 +0100
From: Stewart Bryant <stbryant@cisco.com>
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Cc: pwe3 <pwe3@ietf.org>
Subject: [PWE3] comments on draft-ietf-pwe3-frame-relay-05.txt
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Please remember to address Carlos Pignataro's comments at http://www.ietf.org/mail-archive/web/pwe3/current/msg07089.html ------- - 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 ------ 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 ------ 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? ------- +-------------------------------+ | | | 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 -------- 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 ------- - 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. ---------- - The sequence number field is processed if the PW uses sequence numbers. Perhaps a forward reference --------- 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. ---------- 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 - 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. - 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. ------- - It processes the length and sequence field, the details of which are in the subsequent sub-sections. reference would be helpful to the reader ------ - It generates the frame relay information field from the contents of the PW packet payload after removing any padding. s/generates/copies/ ? ------ Once the above fields of a FR frame have been generated, the FCS has to be computed, s/computes/appended/ ? 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. ---------- 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" --------- 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? --------- 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 ----------- 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. 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 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 ? , 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 --------- _______________________________________________ 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