Optical networks

TPCT’s College of Engineering
Osmanabad
Department of Electronics and Telecommunication
Presentation
on
Unit-5 Optical Networks
Subject- FOC Ele-II Class- BE(ECT)
AY-2019-20 Sem-II
Presented by- Prof A P Mane
1

Contents
• Optical Network Concepts
• Optical Network Topologies
• SONET/SDH
• SONET/SDH Frame/Format
• Photonic Switching/Optical Cross Connect (OXC)
• WDM Network (Covered in Unit-4)
• Passive Optical Networks(PON)
• Optical Ethernet
2

Network- Is an assemblage of transmission link/s and other equipments
that provide a mean of exchanging information with in a group of end user.
In Comp/Comm. Network the info. is carried over in electrical form using
Cu wire/Coaxial cable/atmosph. Channel.
But ON is based on optical technology in which info. is exchanged
between end users in the form of light/optical signal through Optical Fiber.
Generally it uses LASER to carry info. and OF for Propagation.
Different forms of ONs are – P-to-P, P-to-MP and MP-to MP.
Need of Optical Networking
-ON brought a new revolution in telecom industry with the use of ON
components- OF- has gradually increased n/w data rate/bandwidth.
-Over past couple of decades OF has been used to make connections
between communication devices such as switches and computers.
-Now-a-days to increase capacity, speed of data transfer is achived
using optical devices along with OF technology.
3 Optical Network Concept

The use of Light/optical communication had long been started with Fire
beacons to convey info. to peoples.
However full fledged use of optical technology in optical networking was
started in 18th century.
Developments in op. technology- LASER in 1960, Low loss OF in 1970,
Optical amp in 1980, WDM in 1990 & Optical accessories in 1990, etc.
Depending upon coverage area in that end users accommodate, there
are three types
- LAN
- MAN
- WAN
4 History of Optical Networking
Broad Types of Optical Networks

Optical Network Topologies
- N/w Topology-Is a logical arrangement of links and end uses/host
computers to get exchange of info./data.
- Common topologies used in ONs are Bus(Linear Bus), Ring and Star.
Each has advantages and limitations in terms of reliability, expandability
and performance characteristics.
Bus Topology-In this the different nodes
(stations / users) are connected to each
other using common Bus(Bus trunk line
/main OF) through coupling elements
(optical couplers)(active or passive).
And using this element optical power/data
is coupled into or out of the main OF link.
5

Optical Network Topologies Contd…
Ring Topology-In this consecutive nodes
(stations / users) are connected by point-
to-point links that are arranged to form a
Single closed path. Information in the form
of data packets is transmitted from node to
Node. Each node is active with ability to
recognize its own address in the data pack-
et in order to accept message & to forward
remaining packet on ring.
Star Topology-In this all nodes are joined
to a single point called central node/Hub
(Star coupler). Hub can be active/passive
device. Active hub-can control all routing
of messages in the n/w. Passive hub- It is
a power splitter to divide the incoming data.
6

SONET/SDH
Technologies for Optical Networking- 1) SONET/SDH
2) DWDM
SONET/SDH is a standardized digital TDM protocol that transmits
information over optical fiber using LASER or LED.
SONET (Synchronous Optical Network) is a US standard for optical
network or FOC system specification is provided by the ANSI.
SDH (Synchronous Digital Hierarchy) is a International standard for
fiber transmission whose specification is provided by ITU.
SONET/SDH uses TDM scheme for the best utilization of BW. i.e. BW
of OF is considered as a channel divided in to multiple sub channels
(time slots) where the transmission of bits in these sub channels is
controlled by a master clock with very high accuracy.
7

Why SONET/SDH ?
The main aim of this std. was to create a technology that is capable of
transmitting the traffic of all existing digital channels using high speed
fiber optics. i.e. it also ensured data rate of several Gbps.
It also holds proposals for the standardization of Fiber–Optic
Transmission system equipments from different manufacturers all over
the world.
As a result, these stds were developed to make a compatible universal
network that can multiplex input streams from different users and
provide that streams to called user/s.
8

SONET Layered Architecture
SONET follows a 4-layered architecture model. All the layers in
the SONET protocol stack are equivalent to the physical layer of OSI
model. In band operation Operation, administration, maintenance and
Provisioning i.e. OAMP is one of the great benefits of the SONET/SDH.
4-layered architecture (as shown in Fig.) consisting-
Path Layer- Carries info. end-to-end and
looks after the actual data transport across
the SONET.
Line Layer- Manages Sync. Transport Signal
Level n (STS-n) frame for adding or dropping
used data and deals with interfaces from ph-
-ysical layer. Also provides synchronization,
Multiplexing/Demultiplexing and protection switching.
9

Section Layer-Support the physical integrity of the n/w and build the
SONET frame from either lower SONET interfaces/electrical interfaces.
Physical Layer- It is a photonic interface which signifies the type of fiber
used and its charactristics.
10 SONET Layered Architecture contd..
SONET structure
SONET structure is multiplexed to form high speed transport circuit that
provide an alternative to existing signalling system. This is build around
the following 3 basic devices. (as shown if Fig. on next slide)
STS(Sync.Transport Signal)Mux and Demux- STSMux- Multiplexes
STS-1 signals from multiple sources in to an STS-n. Where as STS
Demux- Demultiplexes STS-n in to different STS-1 destination signals.
Regenerator- These are repeaters. Additionally it also functions at the
Data link Layer to replace some existing header info. with new info..
Add/Drop Mux- This adds signal coming from other sources in to a
given path or take away the desired signal from a path without Demux.

A simple network using SONET equipments11

Device–layer relationship in SONET12

Generally frame contains a header, a payload and a trailer and in
most of network technologies first header is transmitted then payload
followed by trailer.
SONET follows slightly different approach-
Basic SONET system is the STS-1 (Sync.Transport Signal-1) which is
lowest rate system. In this frame consists of 9 rows of 90 bytes each i.e.
total frame contains 810 bytes.
13 SONET Frame/Format
OH PL OH PL T
H PL T

14 SONET Frame/Format contd…
. . . . . . . .
90 coloums
Section
Overhead
9 rows
Line
Overhead
Total OH=SO+LO Path OH SPE(Sync.Pay Env)
=9 rows x 3 bytes =9 rows x 1 byte =Path OH + Pay Load
= 27 bytes = 9 bytes =9 bytes+774 bytes(user data)

STS overhead consisting 3 overheads-
i) SO- These bytes are accessed, generated and processed by section
terminal equipments (STEs). Another functions supported are controlling,
administration and providing another communication needs.
ii) LO- This locates SPE(Sync. Payload Env.) in the frame, Multiplexes or
De-multiplexes signals, monitor performance and provides automatic
protection switching.
iii) SPE(Sync.Payload Env.)- Is a container to hold actual data to be
transmitted across SONET. Out of 87 col. 1st col. is assigned to Path OH,
col. 30 & 59 (stuff col.) are not used to carry Payload and remaining are
for actual data.

The time taken to transmit one STS-1 frame is 125µsec. i.e. the rate of
transmission of STS-1 frame is 8000 frames/sec.
Therefore Bit rate of STS-1 frame = 9 x 90 x 8 x 8000 frames/sec
Rows in a frame Bytes in a row Bits in a byte
=51.84 Mbps
However to achive higher rate together multiple STS-1 frames can be
byte multiplexed to form STS-n (n indicates no. of STS-1 frames).
i.e. STS-2(2 times STS-1) and Bit rate of STS-2=2 x 51.84= 103.68Mbps
STS-3(3 times STS-1) and Bit rate of STS-3=3 x 51.84= 155.52Mbps
or STS-n(n times STS-1) and Bit rate of STS-n=n x 51.84Mbps

SDH basic frame is known as STM-1(Sync. Transport Module-1) which is
SONET STS-3 and functions 3 times faster than SONET STS-1.
The frame structure in STM-1 is as shown in Fig.
It consist 9 rows where as each row 1 ………..……..9 10……270
contains 270 bytes. First 9 col(bytes)
Are reversed for OH and next 261 col
(bytes) for payload. 9
OH-9 col, 9 rows Rows
-3 rows- Regen. Section OH
-1 row-Admin unit pointer signify location
of frame and 5 rows –Multiplex section OH.
SOH Payload
Path OH
17 SDH Frame
. . .

The time taken to transmit one STM-1 frame is 125µsec. i.e. the rate of
transmission of STM-1 frame is 8000 frames/sec.
Therefore Bit rate of STSM1 frame = 9 x 270 x 8 x 8000 frames/sec
Rows in a frame Bytes in a row Bits in a byte
= =155.52 Mbps
However to achive higher rate together multiple STM-1 frames can be
byte multiplexed to form STM-n (n indicates no. of STM-1 frames).
i.e. STM-2(2 times STM-1) and Bit rate of STM-2=2x155.52=311.04Mbps
STM-3(3 times STM-1) and Bit rate of STM-3=3x155.52=466.56Mbps
or STM-n(n times STM-1) and Bit rate of STM-n=nx155.52Mbps.
Multiple STM-1 i.e. STM-n is preferred in SDH.
270 bytes 270 x n bytes
9
bytes
STM-1 Frame STM-n Frame
18 SDH Frame contd…
2430 bytes 2430 x n bytes

To achive high degree of path modularity(routing/flow), capacity scaling
(BW/utilization) and flexibility in adding/dropping channels at a user site a
optical cross connect architecture(OXCs) is introduced in the physical
path structure(path layer) of an optical network.
These OXCs operates directly in the optical domain and can route very
high capacity WDM data streams over a n/w of interconnected optical
path/fiber.
This uses space switching without wavelength conversion and space
switch an be constructed by cascading of electronically controlled optical
directional couplers or by using semiconductor optical amplifier switching
gates.
19
Optical Cross Connect (OXC)
or Photonic/Optical Switching

Fig. shows a 12X12 Optical Cross-Connect (OXC)
20 Optical Cross Connect (OXC) contd…

Here each of the I/p fiber/s(here 2) carries M wavelengths (here λ1, λ2,
λ3, λ4) , any or all of which could be added/dropped at a node.
At I/p these wavelengths are amplified by using EDOPAs then
passively divided in to N streams by using power splitter (DeMux).
Then Tunnable filters select individual wavelengths and which are
directed to an optical switch matrix.(Alternatively a waveguide gating
Demux could be used to divide the incoming aggregate stream in to
individual W/L channel).
The switch matrix directs the channels either to one of the eight o/p
lines if it is a through - travelling signal (o/p lines 1 to 8). Or it directs the
channels to a particular receiver attached to OXC at the o/p ports 9 to 12.
if it has to be dropped to a user at that node.

Signals that are generated locally by a user get connected to an optical
transmitter via DXC and from here these signals are added in the switch
matrix which directs then to the appropriate o/p line.
Finally M o/p lines fed in to Mux to form a single aggregate stream
which is transmitted over trunk after amplification by EDOPA
Problem could arise when same wavelengths travelling on different i/p
fibers enters OXC and needs to be switched simultaneously to the same
o/p fiber. Solution-1) Assign a fixed W/L to each op path throughout n/w.
2) Or By dropping one of the channel and retransmitting it at another W/L.
Fig. shows 4x4 OXC using op space switches and W/L converters

Two type of OXCs are Optical Multiplex Section OXC and Optical
Channel OXC.
Optical Multiplex Section (OMS-OXC)- It is a multiplexed optical channel.
This switches WDM signals and also provides routing of WDM signal by
fiber switching for following reasons i) Fiber facility Management and
ii) Restoration against failure on optical fiber.
i.e. Many many i/ps WDM sinals I/P fibers O/P fibers
are allowed in this and switches
the connection between the i/p WDM
and o/p fibers. Signals
OMS OXC

Optical Channel(OCH-OXC)- It consist of a switch fabric in the center.
There is also Mux and Demux at both I/P and O/P ends of fabric and it is
used to switch individual wavelengths. i.e. it provides routing of individual
wavelengths for following reasons i) Bandwidth Management and
reconfiguration and ii) Restoration against failure on optical fiber.
I/P fibers O/P fibers
Different
individual
W/Lsignals
OMS OXC
De
Mux
De
Mux Mux
Mux

As the optical data moves across a fiber, there needs a way to separate
it and to route it to proper destination. Generally, there exist two essential
types of systems that make fiber-to-the-home broadband connections
possible, which are Active Optical Networks (AON) and Passive Optical
Networks (PON). Both provides ways to separate data and route it to the
proper destinations.
A PON is a system that brings optical fiber cabling and signals all or most
of the way to the end user. It implements a point-to-multipoint
architecture, in which passive optical splitters are used to enable a single
optical fiber to serve multiple end-points instead of providing individual
fibers between the hub and customer. The system can be described as
fiber-to-the-curb(FTTC), fiber-to-the-building(FTTB), or fiber-to-the-home
(FTTH).
Basic PON structure is as shown in Fig.
25 Passive Optical Network (PON)

PON consists Optical Line Terminal(OLT) at the service provider’s central
office and number of Optical Network Terminations(ONTs) near end
users. Typically 32 ONTs can be connected to an OLT. It simply
describes the fact that optical transmission has no active electronic parts
once the signal is going through the network.
A Optical Splitter that takes signal from OLT and splits it to broadcast to
many users, which reduces the cost of links. PON splitters are bi-
directional, i.e. signals can be sent downstream from OLT to all users by
splitting at splitter and signals from the users can be sent upstream and
combined into one fiber to communicate with OLT.
26 Passive Optical Network (PON) contd…

Early 2009, PONs began appearing in corporate networks because these
networks were cheaper, faster, lower in power consumption, easier to
provision for voice, data and video, and easier to manage, since they
were originally designed to connect millions of homes for telephone,
Internet and TV services.
PON provide high-speed, high-bandwidth and secure voice, video and
data service delivery over a combined fiber network.
The main benefits of PON are listed below:
-Lower network operational costs
-Elimination of Ethernet switches and its recurring costs with in the n/w
-Less network infrastructure, Lower installation costs, Low Network
maintenance, Lower network energy costs and Less expensive.
-Provides increased distance between data center and users.
-Data is encrypted between the OLT and the ONTs.

APON (ATM Passive Optical Networks)
This was the first PON standards and was based on ATM (Asynchronous
Transfer Mode). ATM is a switching technique used by Telecom networks
that uses asynchronous TDM to encode data into small, fixed-sized cells.
This is different from Ethernet or internet, which use variable packet sizes
for data or frames. It was used for business applications.
BPON (Broadband PON)
This standard is based on APON. It adds support for WDM (Wavelength
Division Multiplexing), dynamic and higher upstream BW allocation and
survivability. It also create a standard management interface, called
OMCI (ONT Management Control Interface), between the OLT and ONT,
enabling mixed-vendor networks.
It offer 622 Mbps downstream and 155 Mbps upstream. However, its ATM
structure and bandwidth limits make it less than ideal for video
communication, otherwise, BPON networks will be converted to EPON or
GPON over time.

EPON (Ethernet PON)
It is a rival activity to GPON, which uses Ethernet packets instead of ATM
cells. It employs a single Layer 2 network that uses Internet Protocol (IP)
to carry data, voice, and video. It generally delivers 1 Gbps symmetrical
bandwidth, making it very popular in modern networks.
GE-PON (for Gigabit Ethernet PON)
It is still evolving; but, it requires the multiple protocols through translation
to support the native Generic Encapsulation Method (GEM) transport
layer. This emulation supports ATM, Ethernet and WDM protocols. It is
widely deployed in Asia and uses Ethernet as its native protocol and
simplifies timing and lowers the costs by using symmetrical 2.5 Gbps
data streams. The complexity is lower and cost is less than GPON.
GPON (Gigabit PON)
It provides three Layer 2 networks: ATM for voice, Ethernet for data and
proprietary encapsulation for voice. It offers 1.25 Gbps or 2.5 Gbps
downstream and upstream BWs scalable from 155 Mbps to 2.5 Gbps.

Ethernet is the most widely-installed local area network(LAN)
technology.. Technology- Ethernet was defined as an open standard in
the early 1980s by a consortium comprised of Digital Equipment Corp.,
Intel, and XEROX (DIX Ethernet Std.) The goal was to promote a
relatively high- performance and low-cost LAN implementation using
digital (baseband) signalling on a shared coaxial cable.
In 1983, the IEEE 802 LAN/MAN Standards Committee (LMSC)
released the IEEE 802.3 standard for Ethernet a shared medium for
LANs using a distributed media access control (MAC) mechanism called
carrier sense multiple access with collision detection(CSMA/CD).
31 Optical Ethernet

And IEEE has approved 802.3 Ethernet in the First Mile (EFM) standard. The
first mile is the network infrastructure that connects business or residential
subscribers to the COof atelecom carrier or aserviceprovider.
OE is the technology that extends Ethernet beyond the LAN and into
MANs and WANs. While Ethernet LANs are almost exclusively used
within the enterprise and optical Ethernet technology can be used as a
service provider offering. Key components of OE are the abilities to
segregate traffic of different users and to deliver the particular service to
called user. They combine the flexibility, simplicity and cost effectiveness
of Ethernet with the reliability, speed and reach of optics to allow users to
extend their LAN environment across the MAN and WAN.
32 Optical Ethernet contd…

Three EFM physical transport schemes are: 1) Individual Point-to-Point links
2)A single Point-to-Point link to multiple users and 3)A single bidirectional PON

History and Developments
The First Optical Ethernet Repeaters- The first Ethernet standard
included a provision for a single 2-km optical repeater in an Ethernet LAN
that was expected to be used to link different buildings in a large LAN.
They were true Layer-1 repeaters.
Campus Optical Ethernet- This uses Ethernet “bridge,” now commonly
called an Ethernet “switch,”. The purpose of an Ethernet bridge is to
connect two/more different Ethernet LANs.
This required the development of the spanning-tree protocol (802.1D),
which works by disabling redundant paths and which implements a form
of path protection for the LAN.
In the early days, this was work in a few kilometers because LEDs
and MMFs were used, but this was still enough to enable large campuses
to be fully connected. The loss of collisions as a flow-control mechanism
required the development of a new protocol, 802.3x, to handle that need.

Optical Fast Ethernet-
As on the copper side ( ex-100BASE–TX using two Cat-5 UTPs), several
standards were ratified on the optical side.
The first standard was for medium-range MMF transmission at 1310 nm
(100BASE–FX), based upon the FDDI standards. This provided for a
normal range of about 2 km adequate for most campus environments.
100BASE-FX was part of the original 802.3u Fast Ethernet specification
back in 1994.
The second optical fast-Ethernet standard was 100BASE-SX, ratified in
June of 2000 (a full six years later). This standard was available both at
1310 nm (the wavelength used in 100BASE-FX, FDDI, and SONET
equipment) and 1550 nm (the wavelength used in WDM systems)
provides range about 10 km-100 km.

Optical Gigabit Ethernet-
The 802.3z gigabit Ethernet standard describes multiple optical
specification. 1000BASE–SX describes short wavelength (850 nm)
transmission using multimode fiber with a maximum range of 550 meters
on new fiber, or 220 meters on older fiber (with poorer dispersion
characteristics). 1000BASE–LX describes long-wavelength (1310 nm)
transmission using either multimode fiber (with a range of 550 meters) or
single-mode fiber (with a range of 5000 meters
The significant changes were the signalling rate, which was increased to
1.25 gigabits per second (Gbps) from fiber channel’s 1.06 Gbps, and the
frame content and size, which are the same as previous Ethernet
implementations.
This standard was available at 1550 nm and provides range about 5 km-
150 km without repeaters.

GBIC modules-
This standard is Originally specified for fiber channel and evolved to
support Gigabit Ethernet, and become the standard for gigabit Ethernet
interfaces. They provide hot-swappable modules that can be installed to
support LAN, CAN, MAN, and even WAN transport interchangeably, as
needed.
The modules themselves, by virtue of being small and plugging into a
standardized slot, challenged the transceiver manufacturers, who
responded with technological innovations and features beyond all
reasonable expectations. The chip manufacturers contributed readily
available chip sets that support these GBIC modules, simplifying and
speeding up the task of the hardware engineers.

Advantages of Optical Ethernet
- OE extends Ethernet beyond the LAN and into MAN and WAN. While
Ethernet LANs are almost exclusively used within the enterprise, optical
Ethernet technology can be used as a service provider offering.
- OE is beginning to revolutionize MAN by delivering very high
bandwidths 100Mbps to 1Gbps or even higher across cities and regions.
- OE can easily handle the needs of both data and circuit- switched or
voice applications.
- OE is well regarded for its simplicity, cost savings and ubiquity in LAN
environments.
- OE is 10 times less expensive than the SONET technology .
- OE is the best technology for carrying IP traffic because OE and IP
have grown up together.
- OE greatly reduces both equipments and power needed at CO.

Applications of Optical Ethernet
• Optical Ethernet Leased Line
• Multimedia Broadband with Optical Ethernet
• Optical Ethernet Switched Services
• Optical Ethernet for service provider
• Optical Ethernet for enterprises

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