PONs Overview

The First Mileof

Metropolitan Area Networks

Tasuka@Gmail.comAugust/7/2007

YWC study team @ NCU

Customer Physical Aggregation Network Aggregation Edge Router and Transport Core Router and Transport

xDSL CPE

ONT

Cable Modem

Mobile

xDSL

FTTxxPON

HFC

DSLAM

OLT

CMTS

RAN

Ethernet/ATMSwitch

Ethernet/ATMSwitch

Ethernet/ATMSwitch

BRAS

BRAS

Metro Network

CS/IMSRNC MSC

PSTN

Edge Router

Edge Router

SGSN

Core Network

Internet

Splitter

Network Infrastructure

3G

Metropolitan Area Networks

Point to Point Connection

The term point-to-point telecommunications is includes technologies such as laser for telecommunications but in all cases expects that the transmission medium is line of sight and capable of being fairly tightly beamed from transmitter to receiver. The telecommunications 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) circuit which divides the total bandwidth supplied by the hub among each connected client node. A switch on the other hand provides a series of point-to-point circuits, via micro segmentation, which allows each client node to have a dedicated circuit and the added advantage of having full-duplex connections.

So, what is point-to-point? It means a single connection between two locations. So from one point 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.

Network2Network1Point to Point Connection

Point to Multi-Point Connections

PVC100

PVC200

Point-to-multipoint communication is a term that is used in the telecommunications field which refers to communication which is accomplished via a specific and distinct type of multipoint connection, providing multiple paths from a single location to multiple locations.

Point-to-multipoint is often abbreviated as P2MP or PTMP.

A Point to multipoint work like a hub and spoke or a bus scenarios

50 ohm TerminatorT-Type Connector

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)

FTTx is a describe for How the Fiber spread to customer, only.

Service Provider Neighborhood Building Home Node

FTTC

FTTB

FTTH

FTTN

FTTP

What is FTTx

At each customer's premises is a special type of network interface device (NID). This device is called either an optical network terminal (ONT) or an optical network unit (ONU). It converts the optical signal into some format understandable to the customer's devices. Optical network units use thin film filter technology to convert between optical and electrical signals.

The connection between the optical network terminal at the customer's premises and the equipment at the provider's central office is called an optical distribution network (ODN). Optical distribution networks can have several different implementations.

Access NetworkUser

Network

OLT

ONUNT

NT

ONT

ONU

FTTH

FTTB/C

FTTCab

ServiceNetwork

FIber

Copper

Copper

Fiber

Fiber

SNI UNI

What is FTTx

The simplest optical distribution network is called home run fiber. In this architecture, each fiber leaving the central office goes to exactly one customer. Such networks can provide excellent bandwidth since each customer gets their own dedicated fiber extending all the way to the central office. However, this approach is extremely costly due to the amount of fiber and central office machinery required. It is usually used only in instances where the service area is very small and close to the central office.

More commonly each fiber leaving the central office is actually shared by many customers. It is not until such a fiber gets relatively close to the customers that it is split into individual customer-specific fibers. There are two competing optical distribution network architectures which achieve this split: active optical networks (AONs) and passive optical networks (PONs).

Active Optical NetworksActive optical networks rely on some sort of electrically powered equipment to distribute the signal, such as a switch, router, or multiplexer. Each signal leaving the central office is directed only to the customer for which it is intended. Incoming signals from the customers avoid colliding at the intersection because the powered equipment there provides buffering. Network 3

Network 1 Network 2

As of 2007, the most common type of active optical networks are called active ethernet, a type of ethernet in the first mile (EFM). Active ethernet uses optical ethernet switches to distribute the signal, thus incorporating the customers' premises and the central office into one giant switched ethernet network. Such networks are identical to the ethernet computer networks used in businesses and academic institutions, except that their purpose is to connect homes and buildings to a central office rather than to connect computers and printers within a campus. Each switching cabinet can handle up to 1,000 customers, although 400-500 is more typical. This neighborhood equipment performs layer 2/layer 3 switching and routing, offloading full layer 3 routing to the carrier's central office. The IEEE 802.3ah standard enables service providers to deliver up to 100 Mbit/s full-duplex over one single-mode optical fiber to the premises depending on the provider.

Active Optical Networks

ONT

ONT

ONT

ONT

ONT

ONT

ONT

ONT

ONT

ONT

ONT

ONT

Up to 20KM Up to 70KM

Active Optical Network (AON)

Passive Optical Networks

Passive 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 a single cabinet. A beam splitter cannot provide any switching or buffering capabilities; the resulting connection is called a point-to-multipoint link. For such a connection, the optical network terminals on the customer's end must perform some special functions which would not otherwise be required. For example, due to the absence of switching capabilities, each signal leaving the central office must be broadcast to all users served by that splitter (including to those for whom the signal is not intended). It is therefore up to the optical network terminal to filter out any signals intended for other customers. In addition, since beam splitters cannot perform buffering, each individual optical network terminal must be coordinated in a multiplexing scheme to prevent signals leaving the customer from colliding at the intersection. Two types of multiplexing are possible for achieving this: wavelength-division multiplexing and time-division multiplexing. With wavelength-division multiplexing, each customer transmits their signal using a unique wavelength. With time-division multiplexing, the customers "take turns" transmitting information. As of early 2007, only time-division multiplexing was technologically practical.

Passive Optical NetworksIn comparison with active optical networks, passive optical networks have significant advantages and disadvantages. They avoid the complexities involved in keeping electronic equipment operating outdoors. They also allow for analog broadcasts, which can simplify the delivery of analog television. However, because each signal must be pushed out to everyone served by the splitter (rather than to just a single switching device), the central office must be equipped with a particularly powerful piece of transmitting equipment called an optical line terminal (OLT). In addition,

because each customer's optical network terminal must transmit all the way to the central office (rather than to just the nearest switching device), customers can't be as far from the central office as is possible with active optical networks.

Passive Optical Networks

ONTOLT

Splitter

ONT

ONT

ONT

Splitter

Splitter

ONT

ONT

ONT

ONT

Splitter

Splitter

ONT

ONT

ONT

ONT

SplitterONT

ONT

ONT

ONT

Up to 20KM

Passive Optical Network (PON)

SplitterONT

ONT

ONT

ONT

Splitter

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 PONs

Point to Point Network

Curb-Switched NetworkMUX

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 Market Analysis

Passive Optical Networks

Types of PONs

• BPON - Broadband PON

• APON - ATM based Broadband PON

• EPON - Ethernet based PON

• GPON - Gigabit PON

• GE-PON - Gigabit Ethernet PON

• 10GE-PON - 10 Gigabit Ethernet PON

• WDM-PON - Wavelength Division Multiplexing PON

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 Termination

A PON consists of a central office node, called an optical line terminal (OLT), one or more user nodes, called optical network units (ONUs) or optical network terminals (ONTs), and the fibers and splitters between them, called the optical distribution network (ODN). An ONU is a single integrated electronics unit, while an ONU is a shelf with plug-in circuit packs. In practice, the difference is frequently ignored, and either term is used generically to refer to both classes of equipment.

The OLT provides the interface between the PON and the backbone network. These typically 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 Features

OLT's 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 Unit

The ONT terminates the PON and presents the native service interfaces to the user. These services 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 ONT functions 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 user

A PON is a converged network, in that all of these services are typically converted and encapsulated 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 the usual transport mechanism. GEM, which stands for GPON Encapsulation Method, is a variation on Generic Framing Procedure (GFP), adapted for use on a PON. It uses variable-length frames over a synchronous physical layer.

A PON is a shared network, in that the OLT sends a single stream of downstream traffic that is seen 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 Splitter

A beam splitter is an optical device that splits a beam of light in two or more. It is the crucial part of most interferometers.

In its most common form, it is a cube, made from two triangular glass prisms which are glued together at their base using Canada balsam. The thickness of the resin layer is adjusted such that (for a certain wavelength) half of the light incident through one "port" (i.e. face of the cube) is reflected and the other half is transmitted. Polarizing beam splitters, such as the Wollaston prism, use birefringent materials, splitting light into beams of differing polarization.

BPON/APON ITU-T G.983

Broadband PON standardHistorically, The Broadband Passive Optical Network (BPON) standard was introduced first. It was accepted by ITU-T in 1999. The standard was endorsed by a number of network providers and equipment vendors which cooperated together in the Full Service Network Access (FSAN) group.The FSAN group proposed the ATM protocol should be used to carry user data, hence sometime access networks based on this standard are referred to as APONs.The Architecture of BPON is flexible and adapts well to different scenarios. The underlying ATM protocol provides support for different types of service by means of AAL. The small size of ATM cells and the use of virtual channels and links allow allocating available bandwidth to the end users with a fine granularity. Moreover, the deployment of ATM in a backbone of metropolitan networks and easy mapping into SONET/SDH containers allows the use of only one protocol from one end user to another.

BPON/APON ITU-T G.983

Yet, the advantages of ATM proved to be the main obstacle in deployment of BPON and despite many field trails BPON did not gain much popularity. The complexity of the ATM protocol was hard to implement and in many cases superfluous. Much simpler, data only oriented Ethernet protocols found a widespread use in local area networks and started to replace ATM in many metropolitan area and backbone networks.Further improvements to the original APON standard – as well as the gradual falling out of favor of ATM as a protocol – led to the full, final version of ITU-T G.983 being referred to more often as broadband PON, or BPON. A typical APON/BPON provides 622 megabits per second (Mbit/s) of downstream bandwidth and 155 Mbit/s of upstream traffic, although the standard accommodates higher rates

APON Scenario

Using 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.

POTS Phone

POTS Phone

Data

Voice

SDH/SONET 622Mbps T1/E1

Ethernet1:N Splitter

ONT

ONT

APON OLT

ATM

ONT Protected Ring Scenario

Use a 1:2 Splitter for two optical ring to connect to all ONTs, it can provide protected link but required more interfaces for different splitter on each ONTs.

Point to Point Emulation

MAC MAC MAC

P2PE

P2PE

MAC

P2PE

MAC

P2PE

MAC

OLT

ONU1 ONU2 ONU3

MAC MAC MAC

P2PE

P2PE

MAC

P2PE

MAC

P2PE

MAC

OLT

ONU1 ONU2 ONU3

Shared Medium Emulation

MAC MAC MAC

P2PE

P2PE

MAC

P2PE

MAC

P2PE

MAC

OLT

ONU1 ONU2 ONU3

Bridge

Broadcast from OLT

MAC MAC MAC

P2PE

P2PE

MAC

P2PE

MAC

P2PE

MAC

OLT

ONU1 ONU2 ONU3

Bridge

Broadcast

Broadcast from ONU

MAC MAC MAC

P2PE

P2PE

MAC

P2PE

MAC

P2PE

MAC

OLT

ONU1 ONU2 ONU3

Bridge

Broadcast

EPON/GEPON IEEE 802.3ah

The Ethernet Passive Optical Network (EPON) standard has been endorsed by the Ethernet in the First Mile Alliance (EFMA). The final version of the new protocol and necessary amendments to the existing ones were accepted by Standard Body and released as IEEE 802.3ah in September 2004. The main goal was to archive a full compatibility with other Ethernet based networks. Hence, the functionality of Ethernet’s Media Access Control (MAC) layer is maintained and the extensions are provided to encompass the features of PONs. The archived solution is simple and straightforward, and the legacy equipment and technologies can be reused similar as in 100Base-X and 1000Base-X networks.

EPON/GEPON IEEE 802.3ah

The IEEE 802.3 Ethernet PON (EPON or GEPON) standard was completed in 2004 (http://www.ieee802.org/3/), as part of the Ethernet First Mile project. EPON uses standard 802.3 Ethernet frames with symmetric 1 Gbps upstream and downstream rates. EPON is applicable for data-centric networks, as well as full-service voice, data and video networks. Recently, starting in early 2006, work began on a very high-speed 10 Gigabit/second EPON (XEPON or 10-GEPON) standard (http://www.ieee802.org/3/av/).

GPON ITU-T G.984

The ITU-T G.984 (GPON) standard represents a boost in both the total bandwidth and bandwidth efficiency through the use of larger, variable-length packets. Again, the standards permit several choices of bit rate, but the industry has converged on 2.488 Gbits 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 PON

Wavelength Division Multiplexing Passive Optical Network (WDM-PON) are the next generation in development of access networks. Ultimately, they can offer the largest bandwidth at the lowest cost. In principle, the architecture of WDM-PON is similar to the architecture of the PON. The main difference is that ONTs operate on different wavelengths and hence higher transmission rates can be archived.The main problem with WDM-PONs is that usually the wavelength is assigned to an ONT in a fixed manner. This makes upgrades in the network topology difficult as they require manual reconfiguration of the equipment in the customer’s premise, which significantly increases the cost of maintenance. The solution to this is the development of so called “colorless” ONTs. In such a scheme the ONT detects what wavelength is used in the downstream direction and sends its data on the wavelength in the upstream direction. The disadvantage of WDM-PONs is the high cost of equipment. Much research was focused on enhancing WDM-PONs ability to serve large number of customers in attempt to increase revenue from invested resources and its cost efficiency.

WDM PON - Wavelength Division Multiplexing PON

A PON takes advantage of wavelength division multiplexing (WDM), using one wavelength for downstream traffic and another for upstream traffic on a single ITU-T G.652 fiber. The specification 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 allocated for optional RF (analog) video.

OLT with WDM

ONT with WDM

4 wavelength with 2.448Gb each

2.448Gb

Single Fiber

10Gb

ITU-T G.984 GPON

Gigabit PON

The progress in the technology, the need for larger bandwidths and the unquestionable complexity of ATM forced the FSAN group to revise their approach. 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 no longer reliant on ATM as an underlying protocol. Instead a much simpler Generic Framing Protocol Procedure (GFP) is used to provide support for both voice and data oriented services. A big advantage of GPON over other schemes is that interfaces to all the main services are provided and in GFP enabled networks packets belonging to different protocols can be transmitted in their native formats. The functionality is provided which allows seamless interoperability with other GPONs or BPONs. As in modern networks the security of transmitted data is a key issue. A sophisticated mechanism based on Advanced Encryption Standard and a complex exchange of unique keys is built into the GPON architecture.Also in comparison with the BPON standard, higher transmission rates are specified making GPON capable of supporting transfer rates of up to 2.488 Gbps in the downstream as well as the upstream direction.

Gigabit PON

Beginning with the BPON technology base, the participants of FSAN and ITU-T Question 2/15 undertook to define a new PON system, named GPON. The approximate goals of this work 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 in customer traffic. A choice was made to not require backwards compatibility with the BPON system, 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 ONT Activation & ranging, Dynamic Bandwidth assignment (DBA), and ONT management control interface (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 PON

Basically, 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 rate might not be needed. Accordingly, GPON identifies 7 transmission speed combinations as follows:

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 Block

PON core shell: This block consists of two parts, the ODN interface function specified in ITU-T Rec. G.984.2, and the PON TC function specified in this Recommendation. PON TC function includes framing, media access control, OAM, DBA, and delineation of Protocol Data Unit (PDU) for the cross-connect function, and ONU management. Each PON TC selects one mode of ATM, GEM and Dual mixed. Cross-connect shell: The Cross-connect shell provides a communication path between the PON core shell and the Service shell. Technologies for connecting this path depends on services, internal architecture in OLT and other factors. OLT provides cross-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 Block

The functional building blocks of the G-PON ONU are mostly similar to the functional building blocks of the OLT. Since the ONU operates with only a single PON Interface (or maximum 2 interfaces for protection purposes), the cross-connect function can be omitted. However, instead of this 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 system

G-PON TC (GTC) layer system. The GTC layer is comprised of two sub-layers, the GTC Framing sub-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, and a 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 is terminated at this layer for control over this sub-layer, because information of Embedded OAM is embedded in GTC frame header directly.

GTC layer system

PLOAM 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 is interchanged from/to OMCI entity. Embedded OAM, PLOAM and OMCI are categorized into C/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 framing layer is a direct peer of all the ONU GTC framing layers. Moreover DBA control block is specified as a common functional block. Currently, this block has responsibility for whole ONU report DBA. In GTC system, OLT and ONU do not always have two modes. Recognition of which modes are supported are invoked at the time of system installation. The ONU reports its basic support of ATM or GEM modes via the Serial_Number message. If the OLT is capable of interfacing to at least one of the offered modes, it proceeds to establish the OMCI channel, and the ONU equipment is discovered in the usual manner. If there is a mismatch, the ONU is ranged, but declared to be incompatible to the operations support system.

GTC framing sub-layer

GTC framing sub-layer has three functionalities as follows. Multiplexing and demultiplexing: PLOAM, ATM and GEM portions are multiplexed into a downstream TC frame according to boundary information indicated in frame header. Each portion is abstracted from an upstream according to header indicator. Header creation and decode: TC frame header is created and is formatted in a downstream frame. Header in upstream frame is decoded. Moreover, Embedded OAM is performed. Internal routing function based on Alloc-ID: Routing based on Alloc-ID is performed for data from/to ATM and GEM TC Adapters.

GTC FramingDownstream

Upstream

Protocol stack for C/M planes

The 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 embedded OAM channel is provided by field-formatted information in the header of the GTC frame. This channel provides a low latency path for time urgent control information, because each information piece is definitely mapped into specific field in the header of the GTC frame. The functions that use this channel include: bandwidth granting, key switching, and Dynamic Bandwidth Assignment signaling. The PLOAM channel is a message-formatted system carried in a dedicated space of the GTC frame. This channel is used for all other PMD and GTC management information that is not sent via the embedded OAM channel. Messages for this OAM channel are formatted in a fashion similar to that found in ITU-T Rec. G.983.1. The OMCI channel is used to manage the service defining layers that lay above the GTC. However, the GTC must provide a transport interface for this traffic, and there are two options for this transport: ATM or GEM. The GTC function provides the means to configure these optional channels to fit the capabilities of the equipment, including specifying the transport protocol flow identifiers (VPI/VCI or Port-ID).

Protocol stack for C/M planes

Protocol stack for U planes

ATM in GTC: In the downstream, the cells are carried in the ATM partition, and arrive at all the ONUs. The ONU framing sub-layer extracts the cells, and the ATM TC adapter filters the cells based on their VPI. Only cells with the appropriate VPIs are allowed through to the ATM client 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. The OLT receives the transmission associated with the T-CONT identified by Alloc-ID, and the cells are 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 arrive at all the ONUs. The ONU framing sub-layer extracts the frames, and the GEM TC adapter filters the cells based on their 12-bit Port-ID. Only frames with the appropriate Port-IDs are allowed through to the GEM client function. In the upstream, the GEM 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. The OLT receives the transmission associated with the T-CONT, and the frames are forwarded to the GEM TC adapter, and then the GEM client.

Protocol stack for U planes

GPON Multiplexing Services

In the G-PON TC layer, a T-CONT, that is identified by Alloc-ID, is the basic control unit. The concept of a port, identified by Port-ID, is used for multiplexing traffic flows over a T-CONT in GEM service. The concepts of Virtual paths/Virtual circuits, identified by VPIs/VCIs, are used for multiplexing traffic flows in ATM service. Moreover, mixture configurations 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 consideration to be made on the workable combinations of these types. There are no mandatory support modes for OLT and ONU, and interoperability will be managed by deployment implementation.

ATM GEM Mixed

ATM

GEM

Mixed

Yes No Yes

No Yes Yes

Yes Yes Yes

GPON Multiplexing Services

Payloads with ATM cells only to Multiple ONUs

GPON Multiplexing Services

Payload with GEM only to Multiple ONUs

GPON Multiplexing Services

Payloads mixed ATM cells and GEM to multiple ONUs

GPON Multiplexing Services

Payloads mixed with ATM cells and GEM to single ONU

GFP - Generic Framing Procedure

Generic Framing Procedure (GFP) is defined by ITU-T G.7041. This allows mapping of variable 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 Ethernet Media Access Control) or can be block-code oriented (like fiber channel).

There are two modes of GFP: Generic Framing Procedure - Framed (GFP-F) and Generic Framing Procedure - Transparent (GFP-T). GFP-F maps each client frame into a single 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 a GFP frame.

GFP utilizes a length/HEC-based frame delineation mechanism that is more robust than that used by High-Level Data Link Control (HDLC), which is single octet flag based.

GFP - Generic Framing Procedure

There are two types of GFP frames: a GFP client frame and a GFP control frame. A GFP client frame can be further classified as either a client data frame or a client management frame. The former is used to transport client data, while the latter is used to transport point-to-point management information like loss of signal, etc. Client management frames can be differentiated from the client data frames based on the payload type indicator. The GFP 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 the transport medium has a higher capacity than the client signal, and is better known as an idle frame.

GFP - Generic Framing Procedure Layers Relation

GFP format

Payload Area

Core Header 4 bytes

4~65535

1 2 3 4 5 6 7 8

cHEC (CRC-16)

16 bit payload length indicator

Payload Headers (4-64 bytes)

Client Payload Information Field

Optional Payload FCS (CRC-32)

16 bit payload type field

tHEC (CRC-16)

eHEC (CRC-16)

Extension Header (0-58 bytes)

Optional

Frame format

A GFP frame consists of:

• a core header • a payload header • an optional extension header • a GFP payload • an optional payload frame check

sequence (FCS).

Ethernet MAC frame in GFP Frame

SONET PDU in GFP Frame

PPP/HDLC-line Frame in GFP

MPLS PDU in GFP 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