Passive Optic Networks

1. PONs Overview
The First Mile
of
Metropolitan Area Networks
August/7/2007
YWC study team @ NCU Tasuka@Gmail.com

2. Metropolitan Area Networks
Network Infrastructure
Ethernet/ATM Internet
Switch
xDSL xDSL CPE BRAS
DSLAM
Edge Router
Metro Network
Ethernet/ATM Edge Router
ONT Splitter Switch
BRAS
FTTx OLT
xPON Core Network
SGSN
Ethernet/ATM
Cable Modem Switch
HFC CMTS
PSTN
RAN MSC CS/IMS
RNC
Mobile
3G
Customer Physical Aggregation Network Aggregation Edge Router and Transport Core Router and Transport

3. Point to Point Connection
Point to Point Connection
Network1 Network2
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.

4. 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
T-Type Connector
50 ohm Terminator

5. 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.

6. 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 UNI
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.

7. 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).

8. Active Optical Networks
Active optical networks rely on some sort of Network 1 Network 2
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
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.

9. Active Optical Networks
Active Optical Network (AON)
Up to 20KM Up to 70KM
ONT
ONT
ONT
ONT
ONT
ONT
ONT
ONT
ONT
ONT
ONT
ONT

10. 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.

11. Passive Optical Networks
In 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.

12. Passive Optical Networks
Passive Optical Network (PON)
Up to 20KM
ONT
Splitter Splitter Splitter Splitter OLT
ONT
ONT
ONT
ONT
Splitter
ONT
Splitter
ONT
ONT
ONT ONT
Splitter Splitter
ONT ONT
ONT ONT ONT
ONT ONT ONT
ONT
ONT

13. 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

14. Advantages of PONs
Point to Point Network
Curb-Switched Network
MUX
Passive Optical Network

15. 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

16. PON Market Analysis

21. Passive Optical
Networks

22. 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

23. 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

24. 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

25. 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.

26. 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.

27. 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.

28. BPON/APON ITU-T G.983
Broadband PON standard
Historically, 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.

29. 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

30. APON Scenario
ATM
SDH/SONET 622Mbps T1/E1
Ethernet
APON OLT 1:N Splitter
ONT
Data
Voice
POTS Phone
ONT
POTS Phone
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.

31. 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.

32. Point to Point Emulation
OLT OLT
MAC MAC MAC MAC MAC MAC
P2PE P2PE
P2PE P2PE P2PE P2PE P2PE P2PE
MAC MAC MAC MAC MAC MAC
ONU1 ONU2 ONU3 ONU1 ONU2 ONU3

33. Shared Medium Emulation
OLT
Bridge
MAC MAC MAC
P2PE
P2PE P2PE P2PE
MAC MAC MAC
ONU1 ONU2 ONU3

34. Broadcast from OLT
Broadcast
OLT
Bridge
MAC MAC MAC
P2PE
P2PE P2PE P2PE
MAC MAC MAC
ONU1 ONU2 ONU3

35. Broadcast from ONU
OLT
Bridge
MAC MAC MAC
P2PE
P2PE P2PE P2PE
MAC MAC MAC
ONU1 ONU2 ONU3
Broadcast

36. 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.

37. 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/).

38. 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.

39. 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.

40. 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.

41. WDM PON - Wavelength Division Multiplexing PON
4 wavelength with 2.448Gb each
OLT with WDM
10Gb
Single Fiber
2.448Gb
ONT with WDM
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.

42. ITU-T G.984 GPON

43. 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.

44. 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 layer
G.984.4 defines the OMCI on the system.

45. 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

46. 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.

47. 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.

48. 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.

49. 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.

50. 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.

51. GTC Framing
Downstream
Upstream

52. Protocol stack for C/M planes

53. 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).

54. Protocol stack for U planes

55. 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.

56. 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 Yes No Yes
GEM No Yes Yes
Mixed Yes Yes Yes

57. GPON Multiplexing Services
Payloads with ATM cells only to Multiple ONUs

58. GPON Multiplexing Services
Payload with GEM only to Multiple ONUs

59. GPON Multiplexing Services
Payloads mixed ATM cells and GEM to multiple ONUs

60. GPON Multiplexing Services
Payloads mixed with ATM cells and GEM to single ONU

61. 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.

62. 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.

63. GFP - Generic Framing Procedure Layers Relation

64. GFP format
Frame format
A GFP frame consists of:
•
a core header 16 bit payload length indicator
•
a payload header cHEC (CRC-16)
•
an optional extension header Core Header 4 bytes
•
a GFP payload
•
an optional payload frame check
sequence (FCS).
Payload Headers (4-64 bytes) Payload Area 4~65535
16 bit payload type field
tHEC (CRC-16)
Client Payload Information Field 1 2 3 4 5 6 7 8
Extension Header
(0-58 bytes)
Optional
Optional Payload FCS (CRC-32)
eHEC (CRC-16)

65. Ethernet MAC frame in GFP Frame

66. SONET PDU in GFP Frame

67. PPP/HDLC-line Frame in GFP

68. MPLS PDU in GFP Frame

69. 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 ?

70. 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

71. 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

72. 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