1. INTRODUCTION TO OPTICAL NETWORKS

2. Presentation Overview
Why Optical Networks..?!
Generations of Optical Networks
The Classical Layered Hierarchy
The Optical Layer
Functions of Optical Layer
Advantages of Layering
Architectures Of Networks
Access Networks: Introduction
Why Passive Optical Networks..?!
Passive Optical Access Network
Ethernet Passive Optical Network (EPON)
Downstream and Upstream Operation
WDM-Passive Optical Network (WDM-PON)
Ring-Based WDM-PON Architecture

3. Why Optical Networks ...?? Dramatic changes in the telecommunication
industry.
Need for more capacity in the network.
Tremendous growth of the Internet and the World Wide Web in terms of
number of users & the amount of time
bandwidth taken by each user – internet traffic growing rapidly.
Businesses rely on high speed networks.
Need for more bandwidth.
Deregulation of the telephone industry.
Need of providing quality of service(QoS) to carry performance sensitive applications ( real-time voice, video etc.)
Businesses  high speed networks to conduct their businesses - these networks are used to interconnect multiple locations within
a company as well as between companies for business to business transactions.
Need for more bandwidth  phone calls get cheaper –people spend more times on the phone.
Deregulation of the telephone industry :
monopolies companies can take their time adapting to changes and have no increase to reduce costs and provide new services.
Deregulation of these monopolies has stimulated competition in the marketplace which in turn has resulted in lower costs to end users and faster deployment of new technologies and services.
resulted also of a new start-up companies providing equipment to these service providers.
Also traffic in a network is dominated by data opposed to traditional voice traffic.
In the past, the reverse was true and so legacy networks were designed to support voice rather data.

4. Optical Networks
Definition: An Optical Network is a telecommunication network
with transmission links that are optical fibers and
with an architecture that use designed to exploit the unique features if fibers.
High performance lightwave network –involve complex combination both optical and electronic devices.
Low-cost broadband services – Internet based applications continues to increase.
The “glue” that holds the purely optical network together consists of :
optical network nodes (ONN) connecting the fibers within the network
network access stations (NAS) interfacing user terminals and other non- optical end systems to the network
Critical role :
Reducing communications costs
Promoting competition among carriers & service providers
Increasing the demand for new services
Optical & lightwave network does not necessarily imply a purely optical network- more than a set of fibers interconnecting electronic switches

5. Generations of Optical Networks
First Generation:
Optics used for transmission & provide capacity
Switching & other intelligent network functions were handled by electronics
ex. SONET (synchronous optical network)
SDH ( synchronous digital hierarchy)
Second Generation:
have routing ,switching and intelligence in the optical layer
use multiplexing techniques – provide the capacity needed
When talking about optical networks  we really talking about two generations of optical networks

6. The Classical Layered Hierarchy
The OSI Model
Physical layer
Provides a “pipe” with a certain amount of bandwidth to the data link layer.
Data link layer
Framing
Multiplexing
Reliable transmission –acknowledgment frames
Error detection and correction
Flow control
Demultiplexing data send over the physical layer.
Physical layer  lowest layer in the hierarchy
Μετάδοση ακατέργαστων bits (0 or 1) από τον αποστολέα στον δέκτη
the physical layer may be optical , wireless or coaxial or twisted pair.
Data link layer  The next layer above physical layer
Τεμαχίζει τα δεδομένα σε πλαίσια δεδομένων (frames)
Επιβεβαιώνει ότι η επικοινωνία του Φυσικού στρώματος είναι αξιόπιστη (Πλαίσια επαλήθευσης -acknowledgement frames)
Ανίχνευση και επιδιόρθωση λαθών (Error detection and correction).
Έλεγχος ροής (flow control).

7. The Classical Layered Hierarchy
Network Layer
Performs the end-to-end routing function of taking a message at its source
And delivering it to its destination
Controls congestion
Transport Layer
Ensuring the end-to-end
In-sequence
Ensuring error-free delivery of the transmitted messages
Network Layer  above data link layer resides the Network Layer
Δρομολόγηση πακέτων
Έλεγχος συμφόρησης
Έκδοση λογαριασμών (billing)
Transport layer  Resides on top of the network layer –Responsible for :
Τεμαχίζει τα μηνύματα σε μικρότερες μονάδες
Επιβεβαιώνει ότι όλες οι μονάδες φτάνουν στο άλλο άκρο και επανασυναρμολογεί το μήνυμα.
Πολυπλεξία συνδέσεων/συρμών (steams)
Υπηρεσίες μεταφοράς πακέτων από άκρο σε άκρο (end-to-end). (π.χ., αξιόπιστη μεταφορά δεδομένων στον δέκτη).
Έλεγχος συμφόρησης (congestion) και ροής πακέτων

8. The Classical Layered Hierarchy
Session Layer
Sessions restoration
Token management
Synchronization
Presentation Layer
Encoding data
Application Layer
Compatibility between
applications
Session layer :
Αποκατάσταση συνόδων μεταξύ διαφόρων μηχανών (sessions)
Διαχείριση σκυτάλης (token management)
Συγχρονισμός (synchronization)
Presentation Layer:
Κωδικοποίηση δεδομένων
Application Layer :
Συμβατότητα μεταξύ εφαρμογών

9. The Optical Layer Layered View of the Optical Network
The architecture is composed of an
underlying optical infrastructure
Physical layer
Contains optical components executing linear(transparent)operations on optical signal.
provides basic communication services to a number of independent logical networks (LNs).
LNs are residing in the Logical layer.
Contains electronic components executing nonlinear operations on electrical signal
The classical layered view of networks needs some embellishment to handle the variety of network and protocols that are proliferating.
The optical networks do not fit exactly in the 7 OSI layer model  distinguish as the physical /logical applications (services) layers.
Today’s and tomorrow’s optical networks must provide the capacity ,connectivity and intelligence necessary to link together a global community of information providers and consumers.
A well-designed network performs this function efficiently and reliable.
Networks that achieve this goal – use a generic model in the form of Multiwavelength Network Architecture (MWNA).
MWNA must be structured to offer a special set of features adapted to each service it supports.
Network in terms of its constituent layers  with client-server relations between the neighboring layers.
Each LN organizes the raw capacity offered by the physical layer adapting it to the needs of the clients it serves, shown in the services layer of the previous figure.

10. The Optical Layer Layered View of the Optical Network
Description of the multilayered network
For example the SONET network uses optical wavelength channels provided by the physical layer, transmits optical signals on them
and carries multiplexed communication channels on those signals .
The SONET channels can be tailored to support a wide variety of services, two services shown in the figure are plain old telephone service (POTS) and a VPN.
In our example, the SONET layer also is supported directly by the physical layer providing a telemedicine service, VoIP and music/video file-sharing service.
In addition, the physical layer provides purely optical connection directly to end-users via demand-assigned wavelengths (also known as clear channels) thereby bypassing the logical layer altogether.

11. Functions Of The Optical Layer
Multiplexes lightpaths into a single fiber.
Allows individual lightpaths to be extracted efficiently from the composite multiplex signal at the network nodes.
Incorporates sophisticated service restoration techniques.
Incorporates management techniques.
Provides lightpaths – used by SONET and IP network elements.
The functions performed by the optical layer are in many ways analogous to those performed by the SONET layer.
The SONET layer multiplexes low-speed circuit switched streams into higher-speed streams –which are then carried over lightpaths.
The IP layer performs statistical multiplexing of packet-switched streams into high-speed streams , which are also carried over lightpaths.

12. Advantages of Layering
Independently control and manage each logical network simplifying these functions.
Share the total resources of the physical layer among several logical network  exploiting them more efficiently.
Customize each logical network to provide specialized user services  improving the QoS.
Dynamically reconfigure each logical network  equipment failures and changing traffic patterns.
Use both optical and electronic degrees of freedom provide flexibility, survivability, manageability and capacity for growth and change.

13. Architectures Of Networks
Backbone Networks
networks in the same building, in different buildings in a campus environment, or over wide areas.
exchange of information between different LANs
Metro Area Networks (MAN)
network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN).
Access Networks
Distributed EPON architectures
Distributed ring-based WDM-PON architectures
Converged Optical/Wireless Access Networks

14. Architecture Of Networks

15. Access Networks : Introduction
Tremendous growth in both backbone and Metro Access Network (MAN) capacity.
End users are becoming more sophisticated
Rich multimedia
Real-time services
The “Last Mile” remains a bottleneck.
Current “Last Mile” capacity has increased from 56Kb/s (dialup modem) to a few Mb/s (cable modem or digital subscriber line (DSL) connection).
Still far short of the Gigabit line speed necessary to support rich multimedia and real-time services.

16. Access Networks …
Central
Office
End
Users
Last/First Mile

17. Access Networks …
Copper-based access networks will soon no longer be able to meet the ever-growing consumer demand for bandwidth.
PON-based fiber-to-the-curb/home (FTTC/FTTH) systems are considered as possible successors to current copper-based access solutions.
Two most viable architectures:
Single channel Time-Division Multiplexed PON (TDM-PON)
Multi-channel Wavelength-Division Multiplexed PON (WDM- PON)

18. Why Passive Optical Networks? A natural step in access evolution
Point-to-Point links CO SC
Passive Star Coupler
PON
Minimum fiber usage/ N+1 transceivers
Path transparency
Passive network elements
Much longer distance (~20km) than DSL (~5.5 km).
Higher bandwidth due to deeper fiber penetration.
Downstream video broadcasting.
Concentration Switch in the neighborhood
PON
~20 km
~1 km

19. Passive Optical Access Network

20. Multiplexing Techniques
Time Division Multiplexing (TDM) :
A type of multiplexing that combines data streams by assigning each stream a different time slot in a set. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel.
Wavelength Division Multiplexing (WDM):
A technique of sending signals of several different wavelengths of Light into the Fiber simultaneously. In fiber optic communications, wavelength-division Multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single Optical Fiber by using different wavelengths (colors) of Laser light to carry different signals.WDM is similar to frequency-division multiplexing (FDM).

21. Optical Network Terminal and Optical Network Unit
ONT (Optical Network Terminal):
An ONT is a media converter that is installed either outside or inside your premises, during fiber installations.
The ONT converts fiber-optic light signals to copper/electric signals.
Three wavelengths of light are used between the ONT and the Optical Line Terminal :
1310 nm voice/data transmit
1490 nm voice/data receive
1550 nm video receive Each ONT is capable of delivering:
Multiple POTS (plain old telephone service) lines
Internet data
Video
ONU (Optical Network Unit):
An Optical Network Unit (ONU) converts optical signals transmitted via fiber to electrical signals.
These electrical signals are then sent to individual subscribers. ONUs are commonly used in fiber-to-the-home (FTTH) or fiber-to-the-curb (FTTC) applications.

22. Transmission between ONT and ONU Example …
Using different wavelengths for each service makes it possible to transmit high-speed Internet and video services at the same time.
The 1310nm and 1490nm bands are used for Internet transmissions on the uplink and downlink, respectively,
The 1550nm band is used for multi-channel video broadcasts.
Wavelength multiplexing is performed at the central office and a wavelength demultiplexing mechanism is provided at the customer's house.

23. OLT – Optical Line Terminal
OLTs are located in provider’s central switching office.
This equipment serves as the point of origination for FTTP (Fiber-to-the- Premises) transmissions coming into and out of the national provider’s network.
An OLT, is where the PON cards reside. The OLT's also contain the CPU and the GWR and VGW uplink cards. Each OLT can have a few or many dozens of PON cards.
PON = Passive Optical Network GWR = Gateway Router VGW = Voice Gateway
Each PON card transmits 1490nm laser data signal to the ONT, and receives the ONT transmission of the 1310nm laser data signal.
The one-way 1550nm laser video signal to the ONT is injected into the fiber at the CO.

24. Optical Splitter and Combiner
Fiber optic splitter is used to split the fiber optic light into several parts at a certain ratio.
For example, a 1X2 50:50 fiber optic splitter will split a fiber optic light beam into two parts, each get 50 percent of the original beam.
An optical combiner is a passive device that combines the optical power carried by two input fibers into a single output fiber.

25. Ethernet PON (EPON) Architecture
Downstream:
Operates as Broadcast & Select Network
Each ONU extracts those packets that contain the ONU’s unique MAC address
Upstream:
ONUs employ arbitration mechanism to avoid collisions.
OLT arbitrates transmissions via a Dynamic Bandwidth Allocation (DBA) module.
A Multi-point Control Protocol (MPCP) was developed.OLT and ONUs exchange control messages, namely, REPORT and GATE messages.
REPORT message contains the ONU’s bandwidth requirements. GATE message has the start time and the duration of the granted time slot.
The average dedicated bandwidth per user is limited to a few percent of the channel capacity, i.e., a few tens of Mb/s.
Passive Optical
Splitter/Coupler
10-20 km
Downstream operation
In the upstream direction (from the ONUs to the OLT), the ONUs need to employ some
arbitration mechanism to avoid data collisions and fairly share the channel capacity. This is achieved by
the OLT allocating (either statically or dynamically) non-overlapping, variable-sized transmission
windows (timeslots) to each ONU. To enable timeslot assignment, a Multi-point Control Protocol (MPCP) was developed.
MPCP uses two MAC control messages: GATE and REPORT
The GATE message is sent from the OLT to an ONU and is used to assign a timeslot to the
ONU. The REPORT message is sent from an ONU to the OLT to request another timeslot by reporting
the amount of queued data. Each message is a standard 64-byte MAC Control frame. MPCP is only a
message-exchange protocol. IEEE 802.3ah specifically does not specify any algorithm for bandwidth
allocation.
The main content of the MPCP protocol is: upstream bandwidth assignments to different ONUs; discovery and register processes of ONUs; reporting bandwidth requirements to the upper layer protocol entities and performing dynamic bandwidth assignment achieve statistical multiplexing.
Upstream operation

26. EPON - Frame Transmission
EPON employs a point-to-point emulation mechanism, which makes the EPON medium behave as a collection of point-to-point links.
Emulation mechanisms rely on tagging Ethernet frames with a unique value called the Logical Link ID (LLID).
To allow point-to-point emulation, the OLT must have N MAC ports (interfaces), one for each logical link .
When sending a frame downstream (from the OLT to an ONU), the emulation function in the OLT will insert the LLID associated with a particular MAC port on which the frame arrived. Even though the frame will be delivered to each ONU, only one ONU will match that frame’s LLID with its own assigned value, and thus accept the frame and pass it to its MAC layer for further verification.
MAC layers in all other ONUs will never see that frame. (discard it)

27. EPON – Logical Link ID (LLID)
The LLID replace two bytes in the preamble. The OLT could distinguish frames of different ONUs by the LLIDs and thus the LLID equals the logical identification of the ONU.
EPON frame

28. WDM-PONs
Separate pair of dedicated upstream/downstream wavelength channels to each subscriber (≥1 Gb/s of dedicated bandwidth per subscriber).
Provide dedicated optical connectivity to each subscriber with bit rate and protocol transparencies, guaranteed QoS, and increased security.
WDM-PON systems’ capacity is still too high compared to the access capacity needed. However, as bandwidth demand increases, the economics change. In terms of cost per bit rate, WDM-PON is more efficient and economical.
1530 to 1565 nm C-band
1565 to 1625 nm L-band
Maximum number of wavelengths in WDM PONs:
The system utilized 32 WDM channels : 16 for downstream and 16 for upstream.

29. WDM-PONs Simple Architecture
WDM-PON assigns a wavelength to each subscriber (wavelength-divide) whereas TDM-PON assigns specific time slots (time-divide).
WDM-PON can be regarded as an aggregation of point-to-point connections between each subscriber and the Central Office (CO).  
This means that each user can send data to the OLT at any time , independent of what the other users are doing.
No interaction between or coupling between the subscribers on a WDM-PON.
According to ITU-TG :
the upstream wavelengths of PON systems range from 1260 to 1360 nm {( )/2=1310nm}
the downstream from1480 to 1500 nm.
The wavelength for video use is defined as 1550 to 1560 nm.
BRIEF EXPLANATION - DATA TRANSPORT BETWEEN SUBSCRIBERS ..!!

30. WDM-PON Limitations
Traditional tree-based WDM-PON architectures suffer from several limitations including:
Inability to efficiently utilize network resources. The unused dedicated channel capacities of lightly-loaded/idle subscribers cannot be shared by any of the other heavily-loaded users attached to the PON.
Inability to provide private networking capability within a single PON
Lack of simple and cost-effective protection and/or restoration capabilities.
Benefits of WDM-PON : large transmission capacity, network security, and data transparency.

31. Ring-Based WDM-PON Architecture
Olt
Trunk
Ring
Onu

32. Ring-Based WDM-PON Architecture
Efficiently utilizes network resources. Provides dynamic allocation of unused capacities of lightly loaded/idle wavelengths to heavily loaded channels
Provides truly shared LAN capability among PON end-users.
Utilizes a fully distributed control plane among the ONUs that enables distributed provisioning and fault restoration by the ONUs
Eliminates the OLT's centralized task of bandwidth provisioning and failure recovery
Reduction of processing complexities and delays at the OLT.

33. Downstream & Upstream Operation (Without Sharing)
An upstream flow
from ONU-1 to OLT
An upstream flow
from ONU-2 to OLT λ1 λ2 λ1
A downstream flow to ONU-1 λ2
Scheduler
A downstream flow to ONU-2

34. LAN Operation (ONU-ONU Communication)

35. Arrival of a downstream
Downstream & Upstream Operation (With Sharing)
Congestion at downstream buffer, Q1
ONU2 determines new flow as ONU1’s downstream flow and forwards it to ONU1 over λLAN
More downstream
flows to ONU1
(i.e, Rin>Rout) λ1 λ2
λLAN
Arrival of a downstream
flow destined to ONU1
Scheduler
Scheduler runs SWS algorithm searching for a lightly loaded downstream buffer to send ONU1’s newly arriving excess flows (Assume Q2 is lightly loaded )
OLT discards all excess downstream traffic

36. Upstream Scheduling Algorithm (USA)
Arrival of more upstream flows (i.e, Ri,up>λi,up)
Arrival of an
upstream flow λ1
λLAN
OLT processes all TUS flows and forwards them to their destinations