pwe3 Working Group R. Zheng Internet-Draft H. Li Intended status: Informational Huawei Technologies Expires: January 27, 2011 July 26, 2010 Multisegment Pseudowires in Passive Optical Networks draft-li-pwe3-ms-pw-pon-01 Abstract This document describes the application of multi-segment pseudowires (MS-PWs) in a Passive Optical Network (PON). Static configuration of at least one PW segment is a typical case for a MS-PW. This is often one of the end segments and, in the case of mobile backhaul, it is the segment closest to the aggregation device. But, when MS-PW is implemented in a PON, there may be a very large number of PW Terminating Provider Edge nodes (T-PEs). This makes provisioning a heavy burden for the network manager. Making use of a Gigabit-capable Passive Optical Network (GPON) management protocol helps to reduce the labor of configuration, simplify and speed up the PW provision procedure to a great extent, and notify to switching PE (S-PE) (which is the Optical Line Termination node (OLT)) of the status of the AC at the T-PE (which is the Optical Network Unit (ONU)). This document describes how to end-to-end MPLS MS-PWs can be provided through the integration of MPLS and GPON provisioning and control protocols, and describes how the MPLS-PW can be carried by the link layer of the GPON. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." Zheng & Li Expires January 27, 2011 [Page 1] Internet-Draft MS-PW-PON July 2010 This Internet-Draft will expire on January 27, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Zheng & Li Expires January 27, 2011 [Page 2] Internet-Draft MS-PW-PON July 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Specification of Requirements . . . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Multi-Segment Pseudowire over PON Network Reference Model . . 7 5. MS-PW in PON for Mobile Backhaul . . . . . . . . . . . . . . . 9 6. Label Provisioning for Pseudowires over PON . . . . . . . . . 9 7. MPLS-PW in PON network . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 10.2. Informative References . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Zheng & Li Expires January 27, 2011 [Page 3] Internet-Draft MS-PW-PON July 2010 1. Introduction RFC 5659 [RFC5659] defines the architecture for multi-segment pseudowires (MS-PWs) satisfying requirements in RFC 5254 [RFC5254]. Draft-ietf-pwe3-segmented-pw [draft-ietf-pwe3-segmented-pw] provides more detail on MS-PW. MS-PW is a typical technology for certain applications, e.g. mobile backhaul. Among all technologies in access and metro networks, Passive Optical Network (PON) provides longer distance, higher bandwidth with better economy than other technologies like point-to-point Ethernet or Digital Subscriber Line (DSL) in many scenarios. Mobile backhaul with PON is already at its dawn. In a Passive Optical Network, the Optical Network Unit (ONU) and Optical Line Termination (OLT) are adjacent nodes connected by Optical Distribution Network (ODN), which consists of optical fibers and optical splitters in a tree topology. Link between each ONU and OLT is simulated as point to point, and there is no redundant path between them. OLT resides in the central office, while ONUs reside in customer premises. ONUs are deployed with a huge number and cost sensitive. Figure A depicts the physical infrastructure of an ODN and more information about ODN can be found in [G.984.1]. In a mobile backhaul network, many 2G and 3G base stations still use legacy interfaces like TDM and ATM. Therefore, PWs have to start from devices directly connected with base stations. In the case of mobile backhauling with PON, ONUs connected with base stations are T-PEs, while OLT is the switching point. Routing protocols and dynamic label allocation protocols like LDP will extremely increase ONUs' cost as it influences both hardware and software. Besides coding and maintenance of these new protocols, a much powerful CPU and more memory are also necessary for them to run smoothly. As there is no redundant link between each ONU and the OLT, routing and path selection are not necessary between the ONUs and the OLT. This will greatly reduce the cost of an ONU when it acts as a PW PE node. Therefore, static provision of PW labels between ONUs and the OLT is preferred. However, if provision PW labels on ONUs by Network Management System directly, it requires a network manager touching each ONU once for each PW, and there may be very many PWs. This brings a large amount of OPEX. Additionally, there must be a concern that the configuration at the ONU and the OLT will be inconsistent because for any PW, both the ONU and the OLT must be configured. According to ITU-T G.984.4amd2 [G.984.4amd2] and G.988 [G.988], the management protocol of GPON can also configure variant PWs on a ONU. OMCI is a prerequisite protocol for all GPON systems. Hereby using Zheng & Li Expires January 27, 2011 [Page 4] Internet-Draft MS-PW-PON July 2010 OMCI to configure PWs on an ONU doesn't require to upgrade an ONU's hardware and cost of coding is neglectable. This provides a cost- saving method of static provisioning of PW in GPON. MPLS-PW may be either carried by PSNs as defined in RFC3985 [RFC3985], or by GPON link layer according to ITU-T G.984.3amd1 [G.984.3amd1]. 2. Specification of Requirements 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]. Although this document is not a protocol specification, this convention is adopted for clarity of description of requirements. 3. Terminology The terminology specified in RFC3985 [RFC3985] and RFC5659 [RFC5659] applies. In addition, we defined the following terms related with PON according to ITU-T G.984.1 [G.984.1]: o Gigabit-capable Passive Optical Network (GPON): A variant of the Passive Optical Network (PON) access technology supporting transmission rates in excess of 1Gbps and based on the ITU-T G.984 series of Recommendations. o GPON Encapsulation Method (GEM). A data frame transport scheme used in GPON systems that is connection-oriented and that supports fragmentation of the user data frames into variable sized transmission fragments. o GEM Port. An abstraction on GPON adaptation layer representing a logical connection associated with a specific client packet flow between the OLT and the ONU. o Optical Distribution network (ODN). In the PON context, a tree of optical fibers in the access network, supplemented with power or wavelength splitters, filters, or other passive optical devices. o Optical Line Termination (OLT). A device that terminates the common (root) endpoint of an ODN, implements a PON protocol, such as that defined by ITU-T G.984 series, and adapts PON PDUs for uplink communications over the provider service interface. The OLT provides management and maintenance functions for the Zheng & Li Expires January 27, 2011 [Page 5] Internet-Draft MS-PW-PON July 2010 subtended ODN and ONUs. In this draft, OLT is actually a network element with multiple PON ports and uplinks. o Optical Network Termination (ONT). A single subscriber device that terminates any one of the distributed (leaf) endpoints of an ODN, implements a PON protocol, and adapts PON PDUs to subscriber service interfaces. An ONT is a special case of an ONU. o Optical Network Unit (ONU). A generic term denoting a device that terminates any one of the distributed (leaf) endpoints of an ODN, implements a PON protocol, and adapts PON PDUs to subscriber service interfaces. In some contexts, an ONU implies a multiple subscriber device. o ONT management and control interface (OMCI). The management and control channel between OLT and ONT in PON. The OMCI protocol runs across a GEM connection between the OLT Controller and the ONT Controller that is established at ONT initialization. The OMCI protocol is asymmetric: the Controller in the OLT is the master and the one in the ONT is the slave. A single OLT Controller using multiple instances of the protocol over separate control channels may control multiple ONTs. The OMCI protocol is used to manage the ONT in areas of configuration, fault, performance and security. o Passive Optical Network (PON). An OLT connected using an ODN to one or more ONUs or ONTs. Zheng & Li Expires January 27, 2011 [Page 6] Internet-Draft MS-PW-PON July 2010 | | |<--Optical Distribution Network-->| | | | branch main | +-----+ fibers fiber Base ------| | | | Stations ------| ONU |\ | | ------| | \ V | +-----+ \ | \ +----------+ | +-----+ \| | | +-----+ Base ------| | | Optical | V | | Stations ------| ONU |---------| Splitter |-------------| OLT | ------| | /| | | | +-----+ / +----------+ +-----+ / +-----+ / Base ------| |/ Stations ------| ONU | ------| | +-----+ Figure A: Typical PON System Architecture 4. Multi-Segment Pseudowire over PON Network Reference Model RFC5659 [RFC5659] provides several pseudowire emulation edge-to-edge (PWE3) reference architectures for the multi-segment case, which are general models extended from RFC3985 [RFC3985] to enable point-to- point pseudowires through multiple PSN tunnels. A Gigabit-capable Passive Optical Network consists of an Optical Line Termination (OLT), an Optical Distribution Network (ODN) and multiple Optical Network Units (ONU). The ODN is actually a fiber tree that provides physical connections between the OLT and the ONUs. GPON has its own physical layer and link layer. GEM Port is a logical point- to-point connection between the OLT and each ONU over GPON Transmission Convergence (GTC) layer. There could be more than one GEM port between the OLT and an ONU. Each GEM port could be assigned different QoS and bandwidth. Zheng & Li Expires January 27, 2011 [Page 7] Internet-Draft MS-PW-PON July 2010 Native |<------Multi-Segment Pseudowire------>| Native Service | GEM PSN | Service (AC) | |<--Port-->| |<-Tunnel->| | (AC) | V V V V V V | | +----+ +-----+ +----+ | +----+ | |TPE1|===========|S-PE |==========|TPE2| | +----+ | |------|..... PW.Seg't1....X....PW.Seg't3.....|-------| | | CE1| | | | | | | | | |CE2 | | |------|..... PW.Seg't2....X....PW.Seg't4.....|-------| | +----+ | | |===========| |==========| | | +----+ ^ +----+ +-----+ +----+ ^ | Provider Edge 1/ ^ Provider Edge 2 | | ONU | | | PW switching point/ | | OLT | | | |<------------------ Emulated Service --------------->| Figure B: MS-PW over PON Network Reference Model Network is partitioned into access segment and metro/core segment with a hub & spoke topology. MS-PW is recommended when extending PW technology to ONUs. This removes the need of full mesh. It minimizes the number of PSN tunnels and signaling adjacencies terminating on T-PEs and reduces the routing information processed by T-PEs. Thus it can enhance the scalability and lower the complexity of the network. The OLT is recommended as a S-PE so that PWS can be optimized within each segments. Figure B applies the MS-PW architecture in a PON and shows the specific technologies usages. The Terminating PE1 (T-PE1) is an Optical Network Unit (ONU), while Switching PE1 (S-PE1) is an Optical Line Termination (OLT). GEM ports replace PSN tunnels between ONU (T-PE1) and OLT (S-PE) across Optical Distribution Network (ODN), and a PSN tunnel extends from S-PE to T-PE2 across PSN. In a Passive Optical Network, the ONUs and the OLT are adjacent nodes connected by Optical Distribution Network (ODN), which consists of optical fibers and optical splitters in a tree topology. Routing or path selection is unnecessary, as there is only one unique path between each ONU and the OLT. It should be noted that all PW segments are of the same technology, which is packet encapsulated. It is only the tunneling technology that changes at the S-PE. Zheng & Li Expires January 27, 2011 [Page 8] Internet-Draft MS-PW-PON July 2010 5. MS-PW in PON for Mobile Backhaul As stated in RFC5254 [RFC5254], when a TDM access network is replaced with a packet-based infrastructure, initiating PWs closer to the end- user and converging multiple services onto a single access network may reduce expenses. Backhauling 2G Base Stations (BS) by a packet network is a typical use case that may benefit from moving pseudowire PEs closer to the end-user and requires pseudowires to be extended into the access network. In case the access network is a PON, pseudowires are expected to extend to Optical Network Units (ONUs). Mobile services are backhauled from base stations all the way back to a mobile network Controller via pseudowires. PEs are attached by base stations and the Controller on both ends respectively. This means each ONU acts as an edge PE that terminates attachment circuits (ACs) from base stations, and encapsulates native data in them to pseudowires. MS-PW is particularly preferred in this case according to RFC5659 [RFC5659], as an edge PE (connected to the Controller) terminates N PWs to/from N different remote PEs (connected to base stations), which attach to a single intermediate PE. The intermediate PE switches PWs In the network depicted in figure A, CE1 is the base station and CE2 is the controller. ONUs are PW Terminating Provider Edge (T-PE) where Access Circuits are attached, while OLT is the PW Switching Provider Edge (S-PE). PON is a network with a tree topology that fits the infrastructure described above. The OLT aggregates a large number of ONUs, which terminate ACs from base stations. For economic reasons, ONUs are built to be low cost and without powerful routing or IP capabilities. The cost of ONUs will evidently increase if they are required to support similar PW setup and maintenance mechanisms as that used in the core network. Multi-segment PW enables PW in PON to use a different setup mechanism than that in the metro and core network, with the OLT performing an intermediate PE switching PWs between ONUs and the Controller. For example, the core could use a dynamic control plane (T-LDP PWs over RSVP-TE tunnels), while the access network could be provisioned through the management plane using the Network Management Station. 6. Label Provisioning for Pseudowires over PON In a PON with MS-PW, where OLT acts as a switching point and ONU as a PE, provision of PWs between OLT and ONU may be performed through static configuration, e.g. from a NMS. However, it incurs heavy burden of management if each ONU has to be touched to set up PW from ONUs to OLT and configure forwarding information on ONUs. The huge Zheng & Li Expires January 27, 2011 [Page 9] Internet-Draft MS-PW-PON July 2010 number of ONUs makes this method quite forbidding. Using a management protocol over PON to provision pseudowire labels on ONUs largely reduces labor of static label configuration, while keeping simplicity of ONU by not implementing a dynamic control plane. Thanks to the management protocol in GPON system, ONT management and control interface (OMCI), a semi-static mechanism could be used to set up PWs from ONUs to OLT. OMCI, running between the OLT and the ONUs, is the channel that OLT manages and controls ONUs. All GPON physical layer and data GTC layer configuration on ONUs are installed via OMCI. It also has the capability to configure MPLS-PW labels and related forwarding information on ONUs per ITU-T G984.4amd2 [G.984.4amd2] and G.988 [G.988]. When using OMCI to provision PWs on ONU, the network manager only needs to send all configurations to the OLT, which will send all parameters to ONUs automatically through OMCI. There is no need to touch each ONU. OMCI now supports configuration of variant types of PWs, e.g. TDM, ATM and Ethernet. Besides, OMCI can act as a signaling mechanism between ONU and OLT, which enables the ONU to notify AC status to OLT. 7. MPLS-PW in PON network Expanding PW to the ONU requires some form of routing hierarchy. The approach taken here is to divide the network into access segments and Metro/Core segments. The OLT is the interconnecting point of Hub and Spokes. Spoke tunnels locate PSNs or GPON in the access segment are spoke tunnels, while hub tunnels PSNs locate in the core segment are hub tunnels. +--------------+ +----------------------------+ | +----------+ | | | | | TDM/ATM | | | | | +----------+ | | +----------+ +----------+ | | | PW | |<----------------->| | PW | | PW | | | +----------+ | | +----------+ +----------+ | | | GEM | | | | GEM | | MPLS | | | +----------+ | | +----------+ +----------+ | | | GPON-PHY | | | | GPON-PHY | |Link Layer| | | +----------+ | | +----------+ +----------+ | | | | | PHY | | | ONU | | +----------+ | +--------------+ | | | OLT | +----------------------------+ Zheng & Li Expires January 27, 2011 [Page 10] Internet-Draft MS-PW-PON July 2010 Figure C: Protocol Stacks on OLT for PWE3 over GEM Port According to ITU-T G.984.3amd1 [G.984.3amd1], MPLS-PW can be carried by GEM Port. Figure C illustrates protocol stacks of GPON ONU and OLT where MPLS-PW is carried directly by GEM Ports. Multiple GEM Ports are supported for each pair of OLT and ONU, which enables multiple PSNs for each ONU. According to current GPON system specification, one GPON port supports maximum 4096 GEM Ports shared by all ONUs connected to it. One GPON port can aggregate maximum 64 ONUs, but typically no more than 8 ONUs for bandwidth reason, when the ONU is a Multi-Dwelling Unit (MDU) or a Multi-Tenant Unit (MTU) that serves multiple subscribers. There should be no scalability problem for GEM Ports to carry MPLS-PWs between ONU and OLT. When backhauling TDM services in a packet network, almost 50% of payload are shorter than 64 bytes. Reducing protocol stacks and overhead of packets can obviously improve transmission efficiency. Besides the simplified protocol stacks described in this section, other PSN technologies are also valid to transmit PWs in GPON. 8. IANA Considerations No new options or messages are defined in this document. 9. Security Considerations GPON has its own security mechanism to guarantee each ONU are isolated on GPON link layer. There are no other security issues concerned. 10. References 10.1. Normative References [G.984.1] ITU-T, "Gigabit-capable passive optical networks (GPON): General characteristics", March 2008, . [G.984.3amd1] ITU-T, "Gigabit-capable Passive Optical Networks (G-PON): Transmission convergence layer specification", February 2009, . Zheng & Li Expires January 27, 2011 [Page 11] Internet-Draft MS-PW-PON July 2010 [G.988] ITU-T, "ONU management and control interface (OMCI) specification", 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to- Edge (PWE3) Architecture", March 2005. [RFC5254] Bitar, N., Bocci, M., and L. Martini, "Requirements for Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)", October 2008. [RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi- Segment Pseudowire Emulation Edge-to-Edge", October 2009. [draft-ietf-pwe3-segmented-pw] Martini, L., Nadeau, T., Metz, C., and M. Bocci, "Segmented Pseudowire", June 2010. 10.2. Informative References [G.984.4amd2] ITU-T, "Gigabit-capable passive optical networks (G-PON): ONT management and control interface specification", November 2009, . Authors' Addresses Ruobin Zheng Huawei Technologies Huawei Industrial Base Shenzhen China Email: robin@huawei.com Hongyu Li Huawei Technologies Huawei Industrial Base Shenzhen China Email: lihy@huawei.com Zheng & Li Expires January 27, 2011 [Page 12]