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Subject: FIBER-OPTIC COMMUNICATIONS SYSTEM Course Teacher: Dr. Mohammad Nasir Uddin, P. Eng., Associate Professor & Head of EEE Dept.(Graduate Program), AIUB. Name of the students: 1. Md. Arifur Rahman, ID: 21-91960-1 2. Ripon  Kabiraj , ID: 21-92089-2 3. Md. Shakil Ahmed, ID: 20-91700-2 4.  Rasedur  Rahman Rashed, ID: 21-92056-2

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What Is PON  History of PON  Architecture & Function of PON  Passive Optical Network  VS  Active Optical Network  Types of passive optical networks (APON, BPON, EPON, GPON)  Benefit  Drawbacks

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Passive Optical Network (PON) is a FTTX ( Fiber  to the X) technology deployed in both domestic and commercial consumers. It is called a passive network since it does not require a power equipment to amplify or process signals. A PON implements point – to – multipoint architecture, where a single optical line is divided into many optical splitters to serve multiple customers. It is used in the last mile of the network connection between an ISP and a user.

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BPON
>proposed by F S AN
and standardized by
Standard roost
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Used in US and
Japan
> To be replaced
PON
EPON
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802. Bah
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GPON
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standardized by —
encapsulation
Standard on going
F ese vendors

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Fit*r cables
OLT
Optical Slitter /
Combiner
ONU
ONU

The passive optical network has three parts − Optical Line Terminator (OLT) − This is the end office of the service provider. Optical Distribution Network (ODN) − This contains the  fibers  and splitters, enabling point – to – multipoint connection. Optical Network Unit (ONU) − This terminates the PON and provides services for interface with the customer.

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A PON system consists of an optical line terminal (OLT) at the communication company's central office and several optical network units (ONUs) near end users. Typically, up to 32 ONUs can be connected to a single OLT. The word passive simply describes the fact that optical transmission has no power requirements or active electronic parts once the signal is being transmitted across the network. This is in contrast to active optical networks, which require electrically powered switching hardware to pass cells or frames across the  fiber  cabling.

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This image shows how redundant OLT hardware commonly sits in the telecommunications service provider's central  office.  It  provides two main  functions: 1 . To perform conversion between the electrical signals  2 . To coordinate the multiplexing between the conversion devices on the other end of  that  network.

Active Optical Network (AON)
Routed
to 500 ONTs.
up to 70 Km
Passive Optical Network (PON)
up to 20 Krn
ONT
ONT
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ONT
ONT
ONT
ONT
ONT
BO
OLT
Key:
split
to 32 ONTs.
split
to 32 ONTs.
up to 20 Km
- Data or voice for a single customer.
O - Video for multiple customers.

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An innovation that is integral to PON operation is  wave division multiplexing  (WDM), used to separate data streams based on the wavelength (color) of the laser light. One wavelength can be used to transmit downstream data while another is used to carry upstream data. These dedicated wavelengths vary depending on the PON standard in use and can be present simultaneously on the same fiber.

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WDM-PON is an access network technology that has the potential to significantly alter carrier infrastructures. WDM-PON creates a wavelength-based logical point-to-point architecture upon a physical point-to-multipoint  fiber  topology.

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Time-division multiplexing (TDM) allows multiple end devices to transmit and receive independent signals across a single  fiber  by reserving time slots in a stream of data. PON uses two such technologies: TDM for downstream traffic and time-division multiple access (TDMA) for upstream traffic.

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1. Arrayed waveguide gratings (AWG) are commonly used as optical (de)multiplexers in wavelength division multiplexed (WDM) systems. These devices are capable of multiplexing many wavelengths into a single optical  fiber , thereby increasing the transmission capacity of optical networks considerably.

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2.W avelength  Selective Switch A WSS comprises a switching array that operates on light that has been dispersed in wavelength without the requirement that the dispersed light be physically demultiplexed into separate ports. This is termed a ‘disperse and switch’ configuration. For example an 88 channel WDM system can be routed from a “common”  fiber  to any one of N  fibers  by employing 88 1 x N switches.

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3.Fiber  Optic Splitter: Generally speaking, when the light signal transmits in a single mode  fiber , the light energy cannot be entirely concentrated in the  fiber  core.

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The key difference between AON and PON is how the signal is split between the multiple  fibers  going to each customer. AONs use active, electrically powered devices to direct the appropriate signal only to the relevant customer .  In contrast, a PON uses optical splitters, which require no electrical power, to send the signal to each customer. Each switching cabinet can handle up to 128 end users.

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The first PON standard was based on ATM cells. It consists of:  –Downstream Channel @ 155 Mbps or 622 Mbps  	–Upstream Channel @ 155 Mbps  It supported different services:  	–Digital Broadband Video (No Analog Video) ‏  	–Multimedia Services  	–ATM Services  Those were the ATM days!

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Fiber Type
Power Budget
Max Reach
Split Ratio
Transmission
U pstream
Downstream
G.652 (STD SMF)
Class B: 10-25 dB
Class C: 15-30 dB
20 km
16 or 32
Single Fiber
Dual Fiber
Single
Fiber
1310 nm
1550
Dual Fiber
1310 nm
1310 nm

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Downstream
1550 nm
Voice, Video and Data
100 nm
OLT
upstream
1310 nm
Voice and Data
100 nm
yoice. Video & Data
[Downstream
1550 nm
Optical
Couple
Upstream
1310 nm
Optical
Splitter
or
ONU
Video Data POTS

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Based on STM-1 (155 Mbps) line rate  Each frame (150 s) carries timeslots of 53B  	–The frame is long  		–56 slots (155 Mbps)  3.6 s timeslots  		–224 slots (622Mbps)  0.9 s timeslots  Each timeslot contains  		–a data cell (ATM) ‏  		–or a Physical Layer Operation & Management cell (PLOAM) ‏ 		–Every 28 slots a PLOAM cell is inserted.

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Downstream PLOAM cells are responsible for  		–allocating bandwidth (via grant fields),  		–frame synchronization,  		–error control,  		–ranging,  		–and maintenance.  Payload of 48 bytes  		–Carries 27 grants  		–Each grant, schedules 1 upstream ATM cell Downstream PLOAM Cell

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ONUs filter downstream ATM cells and receive only those that are addressed to them  Each ATM cell has a 12-bit addressing field associated with a virtual circuit  		–At most 4096 A TM circuits are allowed per PON

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VPI
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VCI
HEC
Information field

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Each frame (150 s) carries 53 slots of 56 bytes  		–53 bytes of ATM or PLOAM cell  		–3 overhead bytes per ATM cell  The 3 overhead bytes contain  		–at least 4 bits of guard time  * to prevent collisions with cells from other ONUs.  		–a preamble field for bit synchronization and amplitude recovery.  		–a delimiter field is used to indicate the start of an incoming cell.

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Upstream PLOAM cells carry  		–alarms,  		–alerts  		–ranging messages  		–receiver and transmitter status  Upstream PLOAM rate  		–Defined by the OLT for each 			ONU  		–Minimum is 1 PLOAM every 			100  ms  Upstream PLOAM Cell

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Coupled downstream and upstream timing  		–Both frames have equal length (150 s)  		–Synchronization is based on downstream frames  The OLT, by means of the ranging process, aligns all ONUs upstream frames to an unique downstream frame  The downstream frame carries grants for ONUs to allow upstream transmission  One grant = One cell  		–Data Grant  		–PLOAM Grant  		–Divide Slot Grant

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The OLT must compute the RTT for each ONU, and sends an equalization delay time to each of them  		–PLOAM cells are used for this purpose  ONUs implement the equalization delay to emulate an equidistant network

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OLT sends a Ranging Grant and waits for the ONU response  Once, the OLT has received all responses, it calculates the equalization delays and communicates this information to the ONUs, who adjust their transmission

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Allocation Downstream Bandwidth  	–bandwidth can be dynamically allocated by the OLT based on the ONU’s services Upstream Bandwidth  	 – bandwidth is allocated statically through grants  	– minislots  mechanism for reporting ONUs’ queues, but no dynamic 	bandwidth allocation  sheme  defined  	–No dynamic bandwidth allocation!

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PONs are similar to APONs, but add extra functionalities  Include APONs (G.983.1) ‏  Defined in the ITU-T G.983.3 (2001) ‏  Support higher rates  		–Downstream (155, 622 & 1244 Mbps) ‏  		–Upstream (155 & 622 Mbps) ‏  Defines  		–alternative wavelength plan including additional wavelength band  		*for downstream video broadcast,  		–dynamic upstream bandwidth allocation (G.983.4) ‏  		–protection mechanisms

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OLT
Upstream
Data
EDFA
Video
1550 nm
Voice & Data
Downstream
1490 nm
Coupler
Upstream
1310 nm
Downstream
14@0 nm
42 MHz
TV
Optical
1550 nm
Vid eo
550 MHz
TV
or
Cascade
MHz
ONU
Video Data POTS

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DBA is the process by which ONUs dynamically request upstream bandwidth, and the method the OLT reassign bandwidth accordingly BPON defines two DBA schemes  		–buffer status reporting (SR) ‏  		–idle cell monitoring, or no status reporting (NSR)

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R-ONUs explicitly report to its OLT PON interface  Since a number of ONUs and their T-CONTs may report queue lengths of T-CONT buffers, it is imperative to balance the amount of information with the upstream bandwidth consumption of these reports  Generally the OLT will generate divided slot grants to request a queue length for the specified ONU according to the service requirements

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BPON defines different protection schemes  		–Based on Automatic Protection Switching (APS) ‏  		–Duplication of transceivers (TR), splitters and optical fiber sections  Similar to metro/core networks

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Redundant Cost-effective Redundant OLT transceivers Most secure and expensive Redundant feeder and drops Redundant transceivers

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All data packets carried in EPON are encapsulated in Ethernet frames  		–Support for variable size packets  Use of Ethernet frames without modification makes it possible to use existing low-cost Ethernet parts  Similar wavelength plan to BPON  Maximum bit rate is 1Gbps (1.25 Gbps 8B/10B) ‏  Minimum number of splits is 16  Maximum reach is 10 km or 20km  Different configurations are allowed

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OLT
802.3 trame
reader
FCS
ONU 1
ONU 2
ONU 3
USER 1
USER 2
USER 3

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OLT
time Slot
.3 frarne
ONU 1
ONU 2
ONU 3
USER 1
USER 2
USER 3
EEacser
Payload
FCS

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‏ PON devices implement a logical topology emulation (LTE) function  		–To preserve the existing Ethernet MAC operation, LTE must reside 			below the MAC sublayer  Emulation relies on tagging Ethernet frames  		–Logical Link Identification (LLID)  		–Replaces 2 bytes of 8 of the Ethernet preamble

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Unicast LLID  		–Established between the OLT and each ONU  		–Point-to-point links  		–ONUs filter frames by their assigned LLID  Universal LLID  		–Used to define a broadcast service  		–Received by all ONUs  		–Exploits downstream broadcast nature of PONs!

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Original Ethernet MAC protocol cannot operate properly in the upstream channel (no collision detection) ‏  MPCP (Multi-Point Control Protocol)  		–In-band  signalling 		– Messages (64 bytes) ‏  			*GATE 			*REGISTER  			*REGISTER_REQUEST 			*REGISTER_ACK  			*REPORT

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Auto Discovery Mode  		–Detects newly connected ONUs and learns the round-trip delay and MAC address of that ONU  		–Messages: GATE, REGISTER, REGISTER_REQUEST, REGISTER_ACK  Bandwidth Assignment Mode 		–Assigns transmission opportunities to registered ONUs  		–Messages: GATE, REPORT

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The OLT sends a GATE message (grant) and schedules upstream transmission for a specific time interval  ONUs send REPORT messages with their queue status claiming grants

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Both the OLT and the ONU have 32-bit counters that increment every 16 ns  		–These counters provide a local timestamp  MPCP messages contain a timestamp field  When the ONU receives a MPCP message, it sets its counter according to the value in the timestamp of the received message  		–Local clock is then “synchronized” with the OLT one

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When either device transmits a MPCP message, it maps its counter to the timestamp field  		–Useful for the ranging process

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REPORTs are generated at the ONU  A REPORT message may contain queue reports (DBA) ‏  REPORT messages can be used with timestamps only (Ranging) ‏  The OLT must  		–process REPORT messages  		–consider the REPORT when allocating bandwidth  REPORTs must be issued periodically

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Gigabit Passive Optical Networks is a  fiber  optic technology (GPON Technology) that allows a higher speed of transmission and reception of data through a single  fiber . With a point-to-multipoint architecture, it will enable optical  fiber  to the home, or a building. It allows access to Video, Voice, and Data and arose with the need to enhance copper networks. Now, copper and state-of-the-art  fiber  optic offer solutions adapted to each need.

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GPON supports triple – play services, providing competitive all-services solutions. GPON supports high-bandwidth transmission. GPON supports the long-reach (up to 20 km). With complete standards and high technical requirements, GPON supports integrated services in a good way. GPON is the choice of large carrier in the international market GPON is a fully optical architecture option that offers the best of all worlds A GPON system consists of an optical line terminal (OLT) that connects several optical network terminals (ONTs) together using a passive optical distribution network (ODN).

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Efficient Use of Power: No powering requirements for the access network. Power is only required at the source and at the receive ends. Simplified Implement: No need for wiring closets, cooling infrastructure, or midspan electronics. Convenient Maintenance: It's quite easy to identify the failure caused by the PON passive and active components, better for maintaining and troubleshooting. Easier for Upgrades: If there is upgrading need, only the endpoint devices (OLT, ONT/ONU) require to upgrade or replacement while the optical  fiber  and the splitter will remain the same. Lower Budgets: On the one hand, the cost of passive elements themselves are much lower than active ones. On the other hand, PON networking has largely reduced the cost of active elements installation.

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Limited Transmission Distance: The range for PON is limited to between 20 to 40 km, whereas an active optical network may reach up to 100 km. Potential Breakdown Risks: The feeder line and the OLT service multiple end-users may be potentially up to 128 in the P2MP architecture. With little redundancy, an accidental  fiber  cut or a faulty OLT are possible to happen.

Passive Optical Network (PON)

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