[PWE3] comments on draft-ietf-pwe3-fc-encap-09
Stewart Bryant <stbryant@cisco.com> Fri, 15 May 2009 13:47 UTC
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Date: Fri, 15 May 2009 14:48:13 +0100
From: Stewart Bryant <stbryant@cisco.com>
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To: draft-ietf-pwe3-fc-encap@tools.ietf.org, pwe3 <pwe3@ietf.org>, BOCCI Matthew <Matthew.Bocci@alcatel-lucent.co.uk>, "ext Black_David@emc.com" <Black_David@emc.com>
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Subject: [PWE3] comments on draft-ietf-pwe3-fc-encap-09
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LC for this document finished some time ago. This document is pretty well there, but does need another pass to address the issues I highlight. To provide clarification about a couple of them. You need to make it much clearer earlier in the text why you need a new method of running FC over MPLS, since I am sure some reviewer will cite RFC3821 over MPLS as a viable solution to FC over MPLS. You do get there, but not before the reviewer will have asked themselves the question. You really need to address this up front. You can also point to the work on MPLS-TP to further enhance your case, since this needs to work without IP in the data-plane. You also need to address the statement about the about a lossless PSN path, since there is no such thing and the statement will get pounced on. Mostly the rest is minor stuff such as nits incorrect references and references needed. I don't think these needs another LC, but it does need another version. - Stewart Encapsulation Methods for Transport of Fibre Channel frames Over MPLS Networks draft-ietf-pwe3-fc-encap-09.txt Abstract A Fibre Channel pseudowire (PW) is used to carry Fibre Channel frames over an MPLS network. This enables service providers to offer "emulated" Fibre Channel services over existing MPLS networks. SB> This comment applies here and in the intro. SB> You can run RFC3821 over MPLS, so you need to add some SB> small amount of text saying why the additional mode is SB> needed. This document specifies the encapsulation of Fibre Channel PDUs within a pseudowire. It also specifies the common procedures for using a PW to provide a Fibre Channel service. The mechanisms controlling the reliable transport of Fibre Channel PW over MPLS networks are specified in a companion document [FC-flow]. 1. Introduction As metro transport networks migrate towards a packet-oriented network infrastructure, the PSN is being extended in order to allow all services to be transported over a common network infrastructure. This has been accomplished for services such as Ethernet [RFC4448], Frame Relay [RFC4619], ATM [RFC4717] and SONET/SDH [RFC4842] services. Another such service, which has yet to be addressed, is the transport of Fibre Channel (FC) frames over the PSN. This will allow network service providers to transparently carry FC services over the packet- oriented network, along with the aforementioned data and TDM services. SB> See above WRT why we need the new mode FC/IP, as described in [RFC3821] and [FC-BB], defines the mechanisms that allow the interconnection of islands of FC SANs over IP Networks. It provides a method for encapsulating FC frames employing FC Frame Encapsulation, as defined in [RFC3643], and addresses specific FC concerns related to tunneling FC over a pure IP network. Fibre Channel pseusowire (FC PW) is being proposed to provide a method for transporting FC frames over an MPLS network. SB> Again you can do this with the above method FC PW complements the currently available standardized methods for transporting FC frames over a PSN. Specifically, FC/IP addresses "only the requirements necessary to properly utilize a pure IP network as a conduit for FC Frames", whereas FC PW addresses the requirements necessary to transport FC over an MPLS PSN. An example of such a network might be a packet-oriented multi-service transport network, where MPLS is used as the universal method for encapsulating and transporting all type of services, including mission critical FC applications as well as other TDM and data services. Hence, a key benefit of FC PW is that it will enable the extension of FC applications to the carrier space. SB> You eventually get to the point. SB> I would restructure the intro so it's clear up front SB> why you need a new way to carry FC over MPLS. The following sections describe some of the key carrier requirements for transporting FC frames over an MPLS PSN. 1.1. Transparency Conventionally, the coupling (or pairing) of FC entities with those pertaining to specific encapsulation methods requires the protocol-specific entity to terminate the FC Entity. This, in most cases, would require global address synchronization to be performed by the operator. In addressing this requirement, and providing full transparency, FC PW defines a port-mode FC encapsulation into a PW. SB> The above is not clear. It's probably that I am unfamiliar SB> with FC, but then most of the next stage reviewers will be SB> similarly unfamiliar. This requires the creation of an FC pseudowire emulating an FC Link between two FC ports, appearing architecturally as being wired to those ports, similar to the approach defined for FC over GFPT in [FC-BB]. This results in transparent forwarding of FC frames over the MPLS PSN from both the FC Fabric and the operator's point of view. SB> OK - I get this, but it took a lot more thinking about SB> than it should have, could you look at rewording/rewording SB> the section to provide more clarity. 1.3. Traffic Engineering FC PW defines the mapping of FC frames into a PW, implicitly assuming the use of MPLS-TE for the explicit provisioning of an FC PW over the MPLS PSN. This enables the operator to guarantee the performance and availability of the emulated FC link. SB> You use MPLS-TE to provision the LSP, not the PW. FC requires a reliable transmission mechanism between FC entities. This implicitly assumes a lossless media with high availability. This, however, cannot always be guaranteed in best effort networks where FC frames are at times transported over sub-optimal paths. Bearing this in mind, FC PW relies on MPLS-TE to create an emulated FC link over a packet-oriented network, effectively enabling network operators to establish an explicit path to enhance frame transmission performance. SB> First you just said you need TE SB> Second TE will not give you a lossless path. SB> TE gives you b/w reservation, a defined path, FRR, which SB> are useful to you, but not lossless path. SB> I think the point that you need to make is that TE SB> is a better appoximation to a lossless math than SB> conventional hop-by-hop routing and that this appox SB> is a sufficient approx to the required lossless SB> service to provide a satisfactor emulation of such SB> a path for these purposes. 2. Reference Model FC PW allows FC Protocol Data Units (PDUs) to be carried over an MPLS network. In addressing the issues associated with carrying a FC PDU over an MPLS network, this document assumes that a pseudowire has been set up by some means outside of the scope of this document. This MAY be achieved via static provisioning, or using the signaling protocol as defined in [RFC4447]. SB> I don't like the out of scope bit above - particularly SB> as you describe new RFC4447 types. SB> Surely you simply need to say the PW may be provisioned SB> statically, or through signaling as described in RFC4447. FC PW emulates a single FC link between exactly two endpoints. This SB> A FW PW.... document specifies the emulated PW encapsulation for FC. Figure 1 describes the reference models which are derived from [RFC3985] to support the FC PW emulated services. For the purpose of the discussion in this document PE1 will be defined as the ingress router, and PE2 as the egress router. A layer 2 PDU will be received at PE1, encapsulated at PE1, transported, decapsulated at PE2, and transmitted out on the attachment circuit of PE2. SB>Presumably you mean an FC PDU, or an FC L2 PDU? 3. Encapsulation This specification provides port to port transport of FC encapsulated traffic. The following FC connections (as specified in [FC-BB]) are supported over the MPLS network: - N-Port to N-Port - N-Port to F-Port - E-Port to E-Port FC Primitive Signals and FC-Port Login handling by the NSP function within the PE is defined in [FC-BB]. SB> You need to give the reader an idea what an N-Port and an E-Port is. 3.3. Mapping of FC traffic to PW PDU 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 +---------------------------------------------------------------+ | FC PW Control Word | +---------------------------------------------------------------+ | FC Encapsulation Header | +---------------+-----------------------------------------------+ | SOF Code | Reserved | +---------------+-----------------------------------------------+ | | +----- FC Frame ----+ | | +---------------------------------------------------------------+ | CRC | +---------------+-----------------------------------------------+ | EOF Code | Reserved | +---------------+-----------------------------------------------+ SB> Where is it defined how to calc the CRC and what it covers? Figure 4 - FC frame encapsulation within PW PDU 4. Signaling of FC Pseudowires [PWE3-CONTROL] specifies the use of the MPLS Label Distribution Protocol, LDP, as a protocol for setting up and maintaining pseudowires. This section describes the use of specific fields and error codes used to control FC PW. The PW Type field in the PWid FEC element and PW generalized ID FEC elements MUST be set to "FC Port Mode" as requested in section 8 below. SB> I think that it is section 7 4.1. Interface Parameters for FC PW 4.1.1. SR Poll Timeout (T1) The Selective Retransmission (SR) Poll Timeout (Parameter ID = TBA by IANA) is defined in section 6.3.5. The parameter length is 4 bytes. The parameter value indicates the poll timeout in units of 1 millisecond. SB> That must be section 6.3.5 of the other document SB> Same comment for T2, N2, k in sections below. SB> SB> Please run the verbose version of id-nits and make sure that all SB> issue are not-applicable or are addressed.
- [PWE3] comments on draft-ietf-pwe3-fc-encap-09 Stewart Bryant