PONs Overview The First Mile of Metropolitan Area Networks August/7/2007YWC study team @ NCU Tasuka@Gmail.com
Metropolitan Area Networks Network Infrastructure Ethernet/ATM Internet SwitchxDSL xDSL CPE BRAS DSLAM Edge Router Metro Network Ethernet/ATM Edge Router ONT Splitter Switch BRASFTTx OLTxPON Core Network SGSN Ethernet/ATM Cable Modem SwitchHFC CMTS PSTN RAN MSC CS/IMS RNCMobile3G Customer Physical Aggregation Network Aggregation Edge Router and Transport Core Router and Transport
Point to Point Connection Point to Point Connection Network1 Network2The term point-to-point telecommunications is includes technologies such as laser fortelecommunications but in all cases expects that the transmission medium is line of sightand capable of being fairly tightly beamed from transmitter to receiver. Thetelecommunications signal is typically bi-directional, either time division multiple access(TDMA) or channelized.In hubs and switches, a hub provides a point-to-multipoint (or simply multipoint) circuitwhich divides the total bandwidth supplied by the hub among each connected client node. Aswitch on the other hand provides a series of point-to-point circuits, via microsegmentation, which allows each client node to have a dedicated circuit and the addedadvantage of having full-duplex connections.So, what is point-to-point? It means a single connection between two locations. So from onepoint send a information out of that connection, it must goto the other side of connection,and only that location can received that information, it work like a bidirectional pipe.
Point to Multi-Point Connections PVC100 PVC200Point-to-multipoint communication is a termthat is used in the telecommunications ﬁeldwhich refers to communication which isaccomplished via a speciﬁc and distinct type ofmultipoint connection, providing multiple pathsfrom a single location to multiple locations.Point-to-multipoint is often abbreviated asP2MP or PTMP.A Point to multipoint work like a hub andspoke or a bus scenarios T-Type Connector 50 ohm Terminator
FTTx• FTTP:Fiber To The Premises• FTTH:Fiber To The Home• FTTB:Fiber To The Building (Basement)• FTTC:Fiber To The Curb• FTTN:Fiber To The Node (Neighborhood/Cabinet) Service Provider Neighborhood Building Home Node FTTC FTTB FTTP FTTH FTTN FTTx is a describe for How the Fiber spread to customer, only.
What is FTTx OLT ONT FTTH FIber FTTB/C ONU NT Fiber Copper FTTCab Fiber ONU NT Copper Service User Network Access Network Network SNI UNIAt each customers premises is a special type of network interface device (NID). This deviceis called either an optical network terminal (ONT) or an optical network unit (ONU). Itconverts the optical signal into some format understandable to the customers devices.Optical network units use thin ﬁlm ﬁlter technology to convert between optical andelectrical signals.The connection between the optical network terminal at the customers premises and theequipment at the providers central ofﬁce is called an optical distribution network (ODN).Optical distribution networks can have several different implementations.
What is FTTxThe simplest optical distribution network is called home run ﬁber. In this architecture, eachﬁber leaving the central ofﬁce goes to exactly one customer. Such networks can provideexcellent bandwidth since each customer gets their own dedicated ﬁber extending all the wayto the central ofﬁce. However, this approach is extremely costly due to the amount of ﬁberand central ofﬁce machinery required. It is usually used only in instances where the servicearea is very small and close to the central ofﬁce.More commonly each ﬁber leaving the central ofﬁce is actually shared by many customers. Itis not until such a ﬁber gets relatively close to the customers that it is split into individualcustomer-speciﬁc ﬁbers. There are two competing optical distribution network architectureswhich achieve this split: active optical networks (AONs) and passive optical networks(PONs).
Active Optical NetworksActive optical networks rely on some sort of Network 1 Network 2electrically powered equipment to distribute thesignal, such as a switch, router, or multiplexer. Eachsignal leaving the central ofﬁce is directed only to thecustomer for which it is intended. Incoming signalsfrom the customers avoid colliding at the intersectionbecause the powered equipment there providesbuffering. Network 3As of 2007, the most common type of active optical networks are called active ethernet, a typeof ethernet in the ﬁrst mile (EFM). Active ethernet uses optical ethernet switches to distributethe signal, thus incorporating the customers premises and the central ofﬁce into one giantswitched ethernet network. Such networks are identical to the ethernet computer networksused in businesses and academic institutions, except that their purpose is to connect homesand buildings to a central ofﬁce rather than to connect computers and printers within acampus. Each switching cabinet can handle up to 1,000 customers, although 400-500 is moretypical. This neighborhood equipment performs layer 2/layer 3 switching and routing, ofﬂoadingfull layer 3 routing to the carriers central ofﬁce. The IEEE 802.3ah standard enables serviceproviders to deliver up to 100 Mbit/s full-duplex over one single-mode optical ﬁber to thepremises depending on the provider.
Active Optical Networks Active Optical Network (AON) Up to 20KM Up to 70KM ONT ONT ONT ONTONT ONTONT ONTONT ONTONT ONT
Passive Optical NetworksPassive optical networks do not use electrically powered components to split the signal.Instead, the signal is distributed using beam splitters. Each splitter typically splits a ﬁber into 16,32, or 64 ﬁbers, depending on the manufacturer, and several splitters can be aggregated in asingle cabinet. A beam splitter cannot provide any switching or buffering capabilities; theresulting connection is called a point-to-multipoint link. For such a connection, the opticalnetwork terminals on the customers end must perform some special functions which wouldnot otherwise be required. For example, due to the absence of switching capabilities, eachsignal leaving the central ofﬁce must be broadcast to all users served by that splitter (includingto those for whom the signal is not intended). It is therefore up to the optical networkterminal to ﬁlter out any signals intended for other customers. In addition, since beam splitterscannot perform buffering, each individual optical network terminal must be coordinated in amultiplexing scheme to prevent signals leaving the customer from colliding at the intersection.Two types of multiplexing are possible for achieving this: wavelength-division multiplexing andtime-division multiplexing. With wavelength-division multiplexing, each customer transmits theirsignal using a unique wavelength. With time-division multiplexing, the customers "take turns"transmitting information. As of early 2007, only time-division multiplexing was technologicallypractical.
Passive Optical NetworksIn comparison with active optical networks, passive optical networks have signiﬁcant advantagesand disadvantages. They avoid the complexities involved in keeping electronic equipmentoperating outdoors. They also allow for analog broadcasts, which can simplify the delivery ofanalog television. However, because each signal must be pushed out to everyone served by thesplitter (rather than to just a single switching device), the central ofﬁce must be equipped with aparticularly powerful piece of transmitting equipment called an optical line terminal (OLT). Inaddition,because each customersoptical network terminalmust transmit all the way tothe central ofﬁce (ratherthan to just the nearestswitching device), customerscant be as far from thecentral ofﬁce as is possiblewith active opticalnetworks.
Passive Optical Networks Passive Optical Network (PON) Up to 20KM ONT Splitter Splitter Splitter Splitter OLT ONT ONT ONT ONT Splitter ONT Splitter ONT ONTONT ONT Splitter SplitterONT ONTONT ONT ONTONT ONT ONT ONT ONT
Advantages of PONs• Conserves ﬁber resources• Low cost of equipment per subscriber• There is only one optical port at the Central Ofﬁce (instead of multiple ports)• Passive components require little maintenance and have a high MTBF• Additional buildings can be added to the network easily and inexpensively• Supports a broad range of applications including triple play (voice, data, video) over a single ﬁber and FTTB, FTTC, FTTH• Offers a large amount of high speed bandwidth providing greater ﬂexibility for adding future services• Flexible and scalable bandwidth assignment
Advantages of PONsPoint to Point Network Curb-Switched Network MUX Passive Optical Network
Disadvantages of PONs• Optical ﬁber only• Fixed location install only• Optical ﬁber price still higher than copper• Difﬁcult to deployment when mass installation will be limited Optical Fiber network spread range• Require installed extra splitter when network spread• Splitter and bandwidth ratio cause the network size be limited• Bandwidth limited on OLT capability• No dedicate protected solutions on wire redundancy• Shared bandwidth network topology• QoS issues
PON’s TERMs• OAN: Optical Access Network• ODN: Optical Distribution Network• OLT: Optical Line Termination• ONU: Optical Network Unit• ONT: Optical Network Termination• Beam Splitter: Split optical beam and power to different path.• GFP: Generic framing Procedure
OLT - Optical Line TerminationA PON consists of a central ofﬁce node, called an optical line terminal (OLT), one or moreuser nodes, called optical network units (ONUs) or optical network terminals (ONTs), andthe ﬁbers and splitters between them, called the optical distribution network (ODN). AnONU is a single integrated electronics unit, while an ONU is a shelf with plug-in circuitpacks. In practice, the difference is frequently ignored, and either term is used generically torefer to both classes of equipment.The OLT provides the interface between the PON and the backbone network. Thesetypically include: • Standard time division multiplexed (TDM) interfaces such as SONET/SDH or PDH at various rates • Internet Protocol (IP) trafﬁc over Gigabit or 100 Mbit/s Ethernet • ATM UNI at 155-622 Mbit/s
OLT’s FeaturesOLTs include the following features: • A downstream frame processing for receiving and churning an asynchronous transfer mode cell to generate a downstream frame, and converting a parallel data of the downstream frame into a serial data thereof. • A wavelength division multiplexing for performing an electro/optical conversion of the serial data of the downstream frame and performing a wavelength division multiplexing thereof. • A upstream frame processing for extracting data from the wavelength division multiplexing means, searching an overhead ﬁeld, delineating a slot boundary, and processing a physical layer operations administration and maintenance (PLOAM) cell and a divided slot separately. • A control signal generation for performing a media access control (MAC) protocol and generating variables and timing signals used for the downstream frame processing means and the upstream frame processing means. • A control for controlling the downstream frame processing and the upstream frame processing by using the variables and the timing signals from the control signal generation.
ONU - Optical Network UnitThe ONT terminates the PON and presents the native service interfaces to the user. Theseservices can include voice (plain old telephone service (POTS) or voice over IP – VoIP), data(typically Ethernet or V.35), video, and/or telemetry (TTL, ECL, RS530, etc.). Often, the ONTfunctions are separated into two parts: • The ONU, which terminates the PON and presents a converged interface – such as xDSL or multi-service Ethernet – toward the user, and • Network Termination Equipment (NTE), which provides the separate, native service interfaces directly to the userA PON is a converged network, in that all of these services are typically converted andencapsulated in a single packet type for transmission over the PON ﬁber. BPON is ATM-based.EPON is Ethernet-based. Although GPON allows for a mix of TDM, ATM and GEM, GEM is theusual transport mechanism. GEM, which stands for GPON Encapsulation Method, is a variationon Generic Framing Procedure (GFP), adapted for use on a PON. It uses variable-length framesover a synchronous physical layer.A PON is a shared network, in that the OLT sends a single stream of downstream trafﬁc that isseen by all ONTs. Each ONT only reads the content of those packets that are addressed to it.Encryption is used to prevent eavesdropping on downstream trafﬁc.
Beam SplitterA beam splitter is an optical device that splits a beam of light in two or more. It is the crucial part ofmost interferometers.In its most common form, it is a cube, made from two triangular glass prisms which are glued togetherat their base using Canada balsam. The thickness of the resin layer is adjusted such that (for a certainwavelength) half of the light incident through one "port" (i.e. face of the cube) is reﬂected and theother half is transmitted. Polarizing beam splitters, such as the Wollaston prism, use birefringentmaterials, splitting light into beams of differing polarization.
BPON/APON ITU-T G.983Broadband PON standardHistorically, The Broadband Passive Optical Network (BPON) standard was introducedﬁrst. It was accepted by ITU-T in 1999. The standard was endorsed by a number ofnetwork providers and equipment vendors which cooperated together in the FullService Network Access (FSAN) group.The FSAN group proposed the ATM protocol should be used to carry user data, hencesometime access networks based on this standard are referred to as APONs.The Architecture of BPON is ﬂexible and adapts well to different scenarios. Theunderlying ATM protocol provides support for different types of service by means ofAAL. The small size of ATM cells and the use of virtual channels and links allowallocating available bandwidth to the end users with a ﬁne granularity. Moreover, thedeployment of ATM in a backbone of metropolitan networks and easy mapping intoSONET/SDH containers allows the use of only one protocol from one end user toanother.
BPON/APON ITU-T G.983Yet, the advantages of ATM proved to be the main obstacle in deployment of BPON anddespite many ﬁeld trails BPON did not gain much popularity. The complexity of the ATMprotocol was hard to implement and in many cases superﬂuous. Much simpler, data onlyoriented Ethernet protocols found a widespread use in local area networks and startedto replace ATM in many metropolitan area and backbone networks.Further improvements to the original APON standard – as well as the gradual falling outof favor of ATM as a protocol – led to the full, ﬁnal version of ITU-T G.983 being referredto more often as broadband PON, or BPON. A typical APON/BPON provides 622megabits per second (Mbit/s) of downstream bandwidth and 155 Mbit/s of upstreamtrafﬁc, although the standard accommodates higher rates
APON Scenario ATM SDH/SONET 622Mbps T1/E1 Ethernet APON OLT 1:N Splitter ONT Data Voice POTS Phone ONT POTS PhoneUsing ATM Adaption Layers to carrier different type of trafﬁcs, such Voice with AAL1/2 and Data with AAL5.The trafﬁc QoS is based on ATM, so APON can management each port’s rate based on ATM Cell.
ONT Protected Ring ScenarioUse a 1:2 Splitter for two optical ring to connect to all ONTs, it can provide protected link butrequired more interfaces for different splitter on each ONTs.
Point to Point Emulation OLT OLTMAC MAC MAC MAC MAC MAC P2PE P2PEP2PE P2PE P2PE P2PE P2PE P2PEMAC MAC MAC MAC MAC MACONU1 ONU2 ONU3 ONU1 ONU2 ONU3
Shared Medium Emulation OLT BridgeMAC MAC MAC P2PEP2PE P2PE P2PEMAC MAC MACONU1 ONU2 ONU3
Broadcast from OLT Broadcast OLT BridgeMAC MAC MAC P2PEP2PE P2PE P2PEMAC MAC MACONU1 ONU2 ONU3
Broadcast from ONU OLT Bridge MAC MAC MAC P2PE P2PE P2PE P2PE MAC MAC MAC ONU1 ONU2 ONU3Broadcast
EPON/GEPON IEEE 802.3ahThe Ethernet Passive Optical Network (EPON) standard has been endorsed by theEthernet in the First Mile Alliance (EFMA). The ﬁnal version of the new protocol andnecessary amendments to the existing ones were accepted by Standard Body andreleased as IEEE 802.3ah in September 2004. The main goal was to archive a fullcompatibility with other Ethernet based networks. Hence, the functionality ofEthernet’s Media Access Control (MAC) layer is maintained and the extensions areprovided to encompass the features of PONs. The archived solution is simple andstraightforward, and the legacy equipment and technologies can be reused similar as in100Base-X and 1000Base-X networks.
EPON/GEPON IEEE 802.3ahThe IEEE 802.3 Ethernet PON (EPON or GEPON) standard was completed in2004 (http://www.ieee802.org/3/), as part of the Ethernet First Mileproject.EPON uses standard 802.3 Ethernet frames with symmetric 1 Gbps upstreamand downstream rates. EPON is applicable for data-centric networks, as wellas full-service voice, data and video networks.Recently, starting in early 2006, work began on a very high-speed 10Gigabit/second EPON (XEPON or 10-GEPON) standard (http://www.ieee802.org/3/av/).
GPON ITU-T G.984The ITU-T G.984 (GPON) standard represents a boost in both the total bandwidthand bandwidth efﬁciency through the use of larger, variable-length packets. Again, thestandards permit several choices of bit rate, but the industry has converged on 2.488Gbits per second of downstream bandwidth, and 1.244 Gbit/s of upstream bandwidth.GPON Encapsulation Method (GEM) allows very efﬁcient packaging of user trafﬁc,with frame segmentation to allow for higher Quality of Service (QoS) for delay-sensitive trafﬁc such as voice and video communications.
GPON Advantages• Triple Play: Transports Voice, Data and Video services over a single ﬁber in their native format. A variety of Ethernet services such as QoS,VLAN, pVLAN, IGMP and RSTP are supported.• Highest Bit Rates & Efﬁciency: Supports the highest bit rate PON available in the industry today, with an unprecedented 2.488/1.244 Gbps in the downstream/upstream. This allows a service provider to sell larger amounts of bandwidth to their customers while also supporting more ‘revenue bits’ per capital investment in optical plant.• Advanced Networking Capabilities: Supports long reach networks allowing 32 ONTs to be located as far as 20 Km from the Central Ofﬁce.• Availability: Supports sub-50ms protection switching and trafﬁc restoration in case of ﬁber failure, STM1/GbE facility failure, as well as PON I/F card failure.• Cost savings: Can provide a signiﬁcant CAPEX and OPEX savings vs. the deployment of SDH/SONET and other PON technologies in the access loops.
WDM-PON - Wavelength Division Multiplexing PONWavelength Division Multiplexing Passive Optical Network (WDM-PON) are the nextgeneration in development of access networks. Ultimately, they can offer the largestbandwidth at the lowest cost. In principle, the architecture of WDM-PON is similar tothe architecture of the PON. The main difference is that ONTs operate on differentwavelengths and hence higher transmission rates can be archived.The main problem with WDM-PONs is that usually the wavelength is assigned to anONT in a ﬁxed manner. This makes upgrades in the network topology difﬁcult as theyrequire manual reconﬁguration of the equipment in the customer’s premise, whichsigniﬁcantly increases the cost of maintenance.The solution to this is the development of so called “colorless” ONTs. In such a schemethe ONT detects what wavelength is used in the downstream direction and sends itsdata on the wavelength in the upstream direction.The disadvantage of WDM-PONs is the high cost of equipment. Much research wasfocused on enhancing WDM-PONs ability to serve large number of customers inattempt to increase revenue from invested resources and its cost efﬁciency.
WDM PON - Wavelength Division Multiplexing PON 4 wavelength with 2.448Gb each OLT with WDM 10Gb Single Fiber 2.448Gb ONT with WDMA PON takes advantage of wavelength division multiplexing (WDM), using one wavelength fordownstream trafﬁc and another for upstream trafﬁc on a single ITU-T G.652 ﬁber. Thespeciﬁcation calls for downstream trafﬁc to be transmitted on the 1490 nanometer (nm)wavelength and upstream trafﬁc to be transmitted at 1310 nm. The 1550 nm band is allocatedfor optional RF (analog) video.
Gigabit PONThe progress in the technology, the need for larger bandwidths and theunquestionable complexity of ATM forced the FSAN group to revise theirapproach. In the outcome a new standard called Gigabit Passive Optical Network(GPON) was released and adopted by ITU-T in 2003.The GPON’s functionality is heavily based on its predecessor, although it is nolonger reliant on ATM as an underlying protocol. Instead a much simpler GenericFraming Protocol Procedure (GFP) is used to provide support for both voice anddata oriented services. A big advantage of GPON over other schemes is thatinterfaces to all the main services are provided and in GFP enabled networkspackets belonging to different protocols can be transmitted in their nativeformats. The functionality is provided which allows seamless interoperability withother GPONs or BPONs. As in modern networks the security of transmitted datais a key issue. A sophisticated mechanism based on Advanced Encryption Standardand a complex exchange of unique keys is built into the GPON architecture.Also in comparison with the BPON standard, higher transmission rates arespeciﬁed making GPON capable of supporting transfer rates of up to 2.488 Gbpsin the downstream as well as the upstream direction.
Gigabit PONBeginning with the BPON technology base, the participants of FSAN and ITU-T Question2/15 undertook to deﬁne a new PON system, named GPON. The approximate goals of thiswork were:To design a PON that operates at Gigabit and higher data rates.To craft the physical layer speciﬁcations to suit these higher speeds.To deﬁne the most bandwidth efﬁcient protocol that reﬂects the data-centric trends incustomer trafﬁc. A choice was made to not require backwards compatibility with the BPONsystem, because this would prevent the achievement of the goals as laid out above. However,the GPON system uses the teachings of the BPON standards, with the schemes for ONTActivation & ranging, Dynamic Bandwidth assignment (DBA), and ONT management controlinterface (OMCI) largely reused.The results of this effort have been a series of four basic recommendations.G.984.1 describes the service provider requirements for the system.G.984.2 speciﬁes the physical layer for all the data rate combinations in G-PON.G.984.3 deﬁnes the transmission convergence layerG.984.4 deﬁnes the OMCI on the system.
Gigabit PONBasically, GPON aims at transmission speeds greater than or equal to 1.2 Gbit/s. However,in the case of FTTH or FTTC with asymmetric xDSL, such a high-speed upstream bit ratemight not be needed. Accordingly, GPON identiﬁes 7 transmission speed combinations asfollows: Upstream Downstream 155.52 1244.16 622.08 1244.16 1244.16 1244.16 155.52 2488.32 622.08 2488.32 1244.16 2488.32 2488.32 2488.32 In Mbit/s, ITU-T G984.2 March/2003
OLT’s Functions BlockPON core shell: This block consists of two parts, the ODN interface function speciﬁed in ITU-T Rec. G.984.2, and the PON TCfunction speciﬁed in this Recommendation. PON TC function includes framing, media access control, OAM, DBA, and delineation ofProtocol Data Unit (PDU) for the cross-connect function, and ONU management. Each PON TC selects one mode of ATM, GEMand Dual mixed.Cross-connect shell: The Cross-connect shell provides a communication path between the PON core shell and the Serviceshell. Technologies for connecting this path depends on services, internal architecture in OLT and other factors. OLT providescross-connect functionality according to selected modes, such as GEM, ATM or Dual mixed.Service shell: This shell provides translation between service interfaces and TC frame interface of the PON section.
ONU’s Functions BlockThe functional building blocks of the G-PON ONU are mostly similar to the functional buildingblocks of the OLT. Since the ONU operates with only a single PON Interface (or maximum 2interfaces for protection purposes), the cross-connect function can be omitted. However, instead ofthis function, service MUX and DMUX function is speciﬁed to handle trafﬁc. Each PON TC selects one mode of ATM,GEM and Dual.
Protocol stack for the overall GTC layer systemG-PON TC (GTC) layer system. The GTC layer is comprised of two sub-layers, the GTC Framingsub-layer and the TC adaptation sub-layer.From another point of view, GTC consists of a C/M plane, which manages user trafﬁc ﬂows, security, and OAM features, anda U plane which carries user trafﬁc. As shown in Figure 7-1, in the GTC framing sub-layer, ATM partition, GEM partition,Embedded OAM and PLOAM partitions are recognized according to location on a GTC frame. Only Embedded OAM isterminated at this layer for control over thissub-layer, because information of Embedded OAM is embedded in GTC frame header directly.
GTC layer systemPLOAM information is processed at PLOAM block located as a client of this sub-layer. SDUs(Service Data Unit) in ATM and GEM partitions are converted from/to conventional PDUs(Protocol Data Unit) of ATM and GEM at each adaptation sub-layer, respectively. Moreover,these PDUs include OMCI channel data. This data is also recognized at this sub-layer, and isinterchanged from/to OMCI entity. Embedded OAM, PLOAM and OMCI are categorized intoC/M planes. SDUs except for OMCI on ATM and GEM partitions are categorized into U plane.The GTC framing layer has global visibility to all data transmitted, and the OLT GTC framinglayer is a direct peer of all the ONU GTC framing layers. Moreover DBA control block isspeciﬁed as a common functional block. Currently, this block has responsibility for whole ONUreport DBA.In GTC system, OLT and ONU do not always have two modes. Recognition of which modesare supported are invoked at the time of system installation. The ONU reports its basicsupport of ATM or GEM modes via the Serial_Number message. If the OLT is capable ofinterfacing to at least oneof the offered modes, it proceeds to establish the OMCI channel, and the ONU equipment isdiscovered in the usual manner. If there is a mismatch, the ONU is ranged, but declared to beincompatible to the operations support system.
GTC framing sub-layerGTC framing sub-layer has three functionalities as follows.Multiplexing and demultiplexing: PLOAM, ATM and GEM portions aremultiplexed into a downstream TC frame according to boundary informationindicated in frame header. Each portion is abstracted from an upstream according toheader indicator.Header creation and decode: TC frame header is created and is formatted in adownstream frame. Header in upstream frame is decoded. Moreover, Embedded OAMis performed.Internal routing function based on Alloc-ID: Routing based on Alloc-ID isperformed for data from/to ATM and GEM TC Adapters.
Protocol stack for C/M planesThe control and management planes in the GTC system consist of three parts: embedded OAM,PLOAM and OMCI.The embedded OAM and PLOAM channels manage the functions of the PMD and the GTC layers.The OMCI provides a uniform system of managing higher (service deﬁning) layers. The embeddedOAM channel is provided by ﬁeld-formatted information in the header of the GTC frame. Thischannel provides a low latency path for time urgent control information, because each informationpiece is deﬁnitely mapped into speciﬁc ﬁeld in the header of the GTC frame. The functions that usethis channel include: bandwidth granting, key switching, and Dynamic Bandwidth Assignmentsignaling. The PLOAM channel is a message-formatted system carried in a dedicated space of theGTC frame. This channel is used for all other PMD and GTC management information that is notsent via the embedded OAM channel. Messages for this OAM channel are formatted in a fashionsimilar to that found in ITU-T Rec. G.983.1. The OMCI channel is used to manage the servicedeﬁning layers that lay above the GTC. However, the GTC must provide a transport interface forthis trafﬁc, and there are two options for this transport: ATM or GEM. The GTC function providesthe means to conﬁgure these optional channels to ﬁt the capabilities of the equipment, includingspecifying the transport protocol ﬂow identiﬁers (VPI/VCI or Port-ID).
Protocol stack for U planesATM in GTC: In the downstream, the cells are carried in the ATM partition, and arrive at allthe ONUs. The ONU framing sub-layer extracts the cells, and the ATM TC adapter ﬁlters thecells based on their VPI. Only cells with the appropriate VPIs are allowed through to the ATMclient function. In the upstream, the ATM trafﬁc is carried over one or more T-CONTs. Each T-CONT is associated with only ATM or GEM trafﬁc, so there is no ambiguity of multiplexing. TheOLT receives the transmission associated with the T-CONT identiﬁed by Alloc-ID, and the cellsare forwarded to the ATM TC adapter, and then the ATM client.GEM in GTC: In the downstream, the GEM frames are carried in the GEM partition, and arriveat all the ONUs. The ONU framing sub-layer extracts the frames, and the GEM TC adapter ﬁltersthe cells based on their 12-bit Port-ID. Only frames with the appropriate Port-IDs are allowedthrough to the GEM client function. In the upstream, the GEM trafﬁc is carried over one or moreT-CONTs. Each T-CONT is associated with only ATM or GEM trafﬁc, so there is no ambiguity ofmultiplexing. The OLT receives the transmission associated with the T-CONT, and the frames areforwarded to the GEM TC adapter, and then the GEM client.
GPON Multiplexing ServicesIn the G-PON TC layer, a T-CONT, that is identiﬁed by Alloc-ID, is the basic controlunit. The concept of a port, identiﬁed by Port-ID, is used for multiplexing trafﬁc ﬂowsover a T-CONT in GEM service. The concepts of Virtual paths/Virtual circuits, identiﬁedby VPIs/VCIs, are used for multiplexing trafﬁc ﬂows in ATM service. Moreover, mixtureconﬁgurations by two modes are possible.OLT and ONU are categorized into several types, such as ATM, GEM, and Dual mode.This Recommendation allows all types of equipment; however, there is a considerationto be made on the workable combinations of these types. There are no mandatorysupport modes for OLT and ONU, and interoperability will be managed by deploymentimplementation. ATM GEM Mixed ATM Yes No Yes GEM No Yes Yes Mixed Yes Yes Yes
GPON Multiplexing ServicesPayloads with ATM cells only to Multiple ONUs
GPON Multiplexing ServicesPayload with GEM only to Multiple ONUs
GPON Multiplexing ServicesPayloads mixed ATM cells and GEM to multiple ONUs
GPON Multiplexing ServicesPayloads mixed with ATM cells and GEM to single ONU
GFP - Generic Framing ProcedureGeneric Framing Procedure (GFP) is deﬁned by ITU-T G.7041. This allows mapping ofvariable length, higher-layer client signals over a transport network like SDH/SONET.The client signals can be protocol data unit (PDU) oriented (like IP/PPP or EthernetMedia Access Control) or can be block-code oriented (like ﬁber channel).There are two modes of GFP: Generic Framing Procedure - Framed (GFP-F) andGeneric Framing Procedure - Transparent (GFP-T). GFP-F maps each client frame into asingle GFP frame. GFP-T, on the other hand, allows mapping of multiple 8B/10B block-coded client data streams into an efﬁcient 64B/65B block code for transport within aGFP frame.GFP utilizes a length/HEC-based frame delineation mechanism that is more robust thanthat used by High-Level Data Link Control (HDLC), which is single octet ﬂag based.
GFP - Generic Framing ProcedureThere are two types of GFP frames: a GFP client frame and a GFP control frame. A GFPclient frame can be further classiﬁed as either a client data frame or a client managementframe. The former is used to transport client data, while the latter is used to transportpoint-to-point management information like loss of signal, etc. Client management framescan be differentiated from the client data frames based on the payload type indicator. TheGFP control frame currently consists only of a core header ﬁeld with no payload area.This frame is used to compensate for the gaps between the client signal where thetransport medium has a higher capacity than the client signal, and is better known as anidle frame.
Next Study• GPON, GE-PON, WDM GE-PON, or WDM G-PON will win ?• ITU-T 984.4 OMCI protocol implementation• Optical splitter ratio and wire speed.• WDM PON Network for Optical Exchange Center• TDM signaling and time sync in GEM• GPON Chips vendor already supported for GEM with TDM ?• VoIP cause TDM in GEM is not necessary ?• Is IEEE 802.16 WiMAX cause Fixed Optical network dead ?• Provide Backbone Transparent (PBT IEEE 802.1ah) with VLANs and MPLS cause PON network keep going ?
Reference Standard• ITU-T Recommendation G.983 Broadband optical access systems based on Passive Optical Networks (PON)• ITU-T Recommendation G.984 Gigabit-capable Passive Optical Networks (GPON)• ITU-T Recommendation G.7041 Generic framing procedure (GFP)• ITU-T Recommendation G.652 Characteristics of a single-mode optical ﬁber• ITU-T Recommendation G.985 100 Mbit/s point-to-point Ethernet based optical access system• ITU-T Recommendation Y.2001 Next Generation Network (NGN)• IEEE 802.3-2005 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method and physical layer speciﬁcations section 3 Page 243 64. Multipoint MAC Control (802.3ah)• IEEE 802.17 Telecommunications and information exchange between systems Local and metropolitan area networks speciﬁc requirements - Resilient packet ring (RPR) access method and physical layer speciﬁcations
Reference Documents• 開啟新世界之光纖網路 - 工研院 IKE 詹睿然 ITRI GPON Seminar July/31/2007• 光世代網路演進與 PON 技術發展 - 中華電信研究所 王井煦 ITRI GPON Seminar July/31/2007• Full Services Access Networks - FSAN http://www.fsanweb.org• ImmenStar Upcoming Solutions for MuLan EPON and Turandot G/EPON Switch Chipset• BroadLight GPON workshop Marketing• Overview of the Optical Broadband Access Evolution: A Joint Article by Operators in the IST Network of Excellence e-Photon/ONe - IEEE Communications Magaine August 2006
Reference Web sites• http://en.wikipedia.org/wiki/FTTH• http://en.wikipedia.org/wiki/Passive_optical_network• http://www.fsanweb.org• http://www.itu.int• http://www.gpon.com• http://www.standard802.org• Book: Ethernet Passive Optical Networks by Glen Kramer ISBN:0-07-244562-5