2 Marks

2 MARKS QUESTIONS – OPTICAL COMMUNICATION AND NETWORKS

UNIT – I OPTICAL NETWORKING COMPONENTS

1. What is an optical network?

An optical network is not necessarily all-optical: the transmission is certainly optical, but

the switching could be optical, or electrical, or hybrid Also, an optical is not necessarily

packet-switched.

2. What are the advantages of optical network?

Huge bandwidth,

Low signal attenuation (as low as 0.2 dB/km),

Immunity to electromagnetic interference,

High security of signal because of no electromagnetic radiation,

No crosstalk and interferences between fibers in the same cable,

Low signal distortion, suitable for carrying digital information,

Low power requirement,

Low material usage, small space requirement, light weight, non-flammable, cost-

effective and high electrical resistance.

3. Give an example for the First generation and second generation optical networks?

First generation optical networks,

FDDI (Fiber Distributed Data Interface)

SONET/SDH (Synchronous optical network/ Synchronous digital hierarchy)

ESCON (Enterprise serial connection).

Second generation optical networks,

Services

Transparency.

WDM Architecture.

Optical Components.

4. Why is WDM technique preferred over TDM?

WDM is the favorite multiplexing technology for practical optical communication

networks since all of the end-user equipment needs to operate only at the bit rate of a

WDM channel, which can be chosen arbitrarily, e.g., peak electronic processing speed.

5. Why do you need multiplexing? What are the different types of multiplexing?

The need for multiplexing is driven by the fact that it is much more economical to

transmit data at higher rates over a single fiber than it is to transmit at lower rates over

multiple fibers, in most applications.

There are three types of multiplexing,

Time division multiplexing (TDM)

Optical time division multiplexing (OTDM)

Wavelength division multiplexing (WDM)

6. Define transparency.

Transparency can be defined as the lightpaths can carry data as a variety of bit rates,

protocols, and so forth, and can, in effect, be made protocol insensitive.

Transparency can be defined as an operator can provide a variety of different services

using a single infrastructure. The infrastructure is future-proof in that if protocols or

bit rates change, the equipment deployed in the network is still likely to be able to

support the new protocols and bit rates without requiring a complete overhaul of the

entire network.

7. What is the function of couplers? What are the different types of optical couplers?

A coupler is a device which is used to combine and split signals in an optical network.

Different types of couplers,

Directional coupler,

Star coupler,

Fused fiber coupler,

2 x 2 coupler.

8. What are the requirements of good couplers?

Good optical couplers should have low insertion losses.

Good optical couplers should have low polarization-dependent loss.

Insensitive to temperature.

Reliability.

9. What is the function of isolators?

An isolator is a device used to allow transmission in one direction through it but block all

transmission in the other direction. Isolators are used in systems at the output of optical

amplifiers.

Types of isolators,

A polarization-dependent isolator,

A polarization-independent isolator.

10. What is an isolator? List the two important key parameter of an isolator?

An isolator is a device used to allow transmission in one direction through it but block all

transmission in the other direction. Isolators are used in systems at the output of optical

amplifiers.

Key Parameter:-

Insertion Loss

Isolation Loss

11. What is the function of circulators?

A circulator is similar to an isolator, except that it has multiple ports, typically three or

four ports. In a three-port circulator, an input signal on port 1 is sent out on port 2, an

input signal on port 2 is sent out on port 3, and an input signal on port 3 is sent out on

port 1.

Types of circulators,

Three-port circulator,

Four-port circulator.

12. What is the function of filter? List the different types of filter.

A filter is a device used to select on particular wavelength and reject all other

wavelengths.

Types of filters,

Fixed filter

Tunable filter.

Fixed filter:-

Gratings

Bragg gratings

Tunable filter:-

Fabry perot filter.

Mach zehnder interferometer.

13. What are the requirements of a good filter?

Good optical filters should have low insertion losses.

The loss should be independent of the state of polarization of the input signals.

The passband of a filter should be insensitive to variations in ambient

temperature.

The passband skirts should be sharp

14. Define grating.

The term grating is used to describe almost any device whose operation involves

interference among multiple optical signals originating from the same source but with

different relative phase shifts. An exception is a device where the multiple optical signals

are generated by repeated traversals of a single cavity; such devices are called etalons.

Type of gratings,

A transmission grating,

A reflection grating.

15. What is the transfer function of fabry perot filter?

The power transfer function of a filter is the fraction of input light power that is

transmitted by the filter as a function of optical frequency f, or wavelength. The transfer

function is given by,

This can also be expressed in terms of the optical free-space wavelength λ as,

16. What is the transfer function of Mach-Zehnder interferometer?

The power transfer function of the Mach-Zehnder interferometer is given by,

17. What is the transfer function of Acousto-optic tunable filter?

The power transfer function of the Acousto-optic tunable filter is given by,

18. What is Multiplexer? List the different types of multiplexer.

A multiplexer combine signals at different wavelength on its input port onto a common

output port and demultiplexer performs the opposite function.

Types of multiplexers,

Gratings

Bragg gratings

Multilayer dielectric thin film filter.

Arrayed waveguide grating.

19. What is the function of an optical amplifier?

The main function of the optical amplifier is to strengthen the weak signal without being

any conversion.

Three different types of optical amplifiers:

Erbium-doped fiber amplifiers,

Raman amplifiers, and

Semiconductor optical amplifiers.

20. Write the principle of operation of EDFA.

Stark splitting

Three of the energy levels of erbium ions in silica glass are labeled El, E2, and E3 in

order of increasing energy. Each energy level that appears as a discrete line in an isolated

ion of erbium is split into multiple energy levels when these ions are introduced into

silica glass. This process is termed Stark splitting.

Thermalization

Within each energy band, the erbium ions are distributed in the various levels within that

band in a nonuniform manner by a process known as thermalization.

21. State the important parameters used to characterize the suitability of a switch for optical

networking.

Extinction ratio,

Insertion loss,

A latching,

The reliability of the switch is an important factor,

Switches should have a low polarization-dependent loss (PDL).

22. What are the main considerations in building large switches?

Number of switch elements required.

Loss uniformity.

Number of crossovers.

Blocking characteristics.

23. What are the different types of architecture available in large switches?

Crossbar

Clos

Spanke

Benes

Spanke-Benes

24. What is the function of wavelength converters?

A wavelength converter is a device that converts data from one incoming wavelength to

another outgoing wavelength.

There are four fundamental ways of achieving wavelength conversion:

(1) Optoelectronic approach,

(2) Optical gating,

(3) Interferometric, and

(4) Wave mixing.

25. What is the need of wavelength conversion?

Wavelength converters are useful components in WDM networks for three major reasons.

Data may enter the network at a wavelength that is not suitable for use within the

network.

Wavelength converters may be needed within the network to improve the

utilization of the available wavelengths on the network links.

Wavelength converters may be needed at boundaries between different networks

if the different networks are managed by different entities.

UNIT II SONET AND SDH NETWORKS

SECTION - I

1. What is SONET?

Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH) are

standardized multiplexing protocols that transfer multiple digital bit streams over optical

fiber using lasers or light-emitting diodes (LEDs). Lower rates can also be transferred via

an electrical interface.

2. What are the advantages of TDM?

It is possible to transmit more number of signals through a single channel.

It is immune to amplitude non-linearities.

Equal time slot is allocated for more number of users, hence the traffic gets reduced.

More number of signals can be transmitted in a single wavelength with equal time

slot, since the bandwidth utilization is more efficient.

3. What is statistical time division multiplexing?

Statistical time division multiplexing (STDM) is one method for transmitting several

types of data simultaneously across a single transmission cable or line (such as a T1

or T3 line).

STDM is often used for managing data being transmitted via a local area network

(LAN) or a wide area network (WAN). In these situations, the data is often

simultaneously transmitted from any number of input devices attached to the network,

including computers, printers, or fax machines.

The concept behind STDM is similar to TDM, or time division multiplexing.

4. What is PDH? List the draw backs.

The Plesiochronous Digital Hierarchy (PDH) is a technology used in

telecommunications networks to transport large quantities of data over digital

transport equipment such as fibre optic and microwave radio systems.

The basic data transfer rate is a data stream of 2048 kbit/s.

Drawbacks:-

In PDH it is difficult to pick low bit rate stream from high bit rate stream.

In PDH it is very difficult to connect one vendor's equipment to another's via a

transmission link.

Service restoration time is several seconds to minutes.

Network Management is totally failure in PDH.

5. List out different layers in SONET architecture?

Line Layer

Path Layer

Section Layer

Photonic Layer

6. What is the function of Line layer?

The main function of the line layer is to provide synchronization and to perform

multiplexing for the path layer.

Its functions include protection switching, synchronization, multiplexing, line

maintenance, and error monitoring.

7. What is the function of Path layer?

The main function of the path layer is to map the signals into a format required by the

line layer.

Its functions include reading, interpreting, and modifying the POH for performance

and APS.

8. What is the function of Section layer?

The section layer deals with the transport of an STS-N frame across the physical

medium.

Its main functions are framing, scrambling, error monitoring, and section

maintenance.

9. What is the function of Photonic layer?

Its main function is the conversion between STS-N and OC-N signals.

Its functions include wavelength launching, pulse shaping, and modulation of power

levels.

10. What are the elements of STS-1 frame?

The STS level 1 (STS-1) is the basic building block of SONET optical interfaces with

a data rate of 51.84 Mbps.

The STS consists of two parts: the STS payload and the STS overhead.

STS-1 frame consisting of 9 rows and 90 columns.

First 3 bytes of each row is TOH and the remaining bytes are POH and Payload.

11. How is STS-1 frame organized?

As shown in Figure, the first three columns of the STS-1 frame are for the Transport

Overhead. The three columns each contain nine bytes. Of these, nine bytes are

overhead for the Section layer (for example, Section Overhead), and 18 bytes are

overhead for the Line layer (for example, Line Overhead). The remaining 87 columns

constitute the STS-1 Envelope Capacity (payload and path overhead).

The basic signal of SONET is the Synchronous Transport Signal level 1, or STS-1.

The STS frame format is composed of 9 rows of 90 columns of 8-bit bytes, or 810

bytes.

12. Define TOH.

TOH is transport overhead. It contains two layers such as SOH and LOH.

SOH provides communication between adjacent network elements such as

regenerators.

LOH is used for communication between STS-N signals and STS Mulitiplexer and

demultiplexer.

13. Define LOH.

The line overhead (LOH) of the SONET STS-1 frame consists of 18 bytes found in

rows 4 to 9 of columns 1, 2, and 3 of the SONET frame. The LOH is processed by all

SONET NEs except for regenerators or repeaters.

The LOH is responsible for performance monitoring of the individual STS-1s,

carrying express orderwire communications information, data channels for OAM&P,

pointers to indicate the start of the SPE, protection switching information.

14. Define POH.

The POH is assigned to and transported with the SONET payload. It is created by the

PTE as part of the SPE until the payload is demultiplexed at the terminating path

equipment.

The STS POH is responsible for performance monitoring of the STS SPE, signal

labeling (equipped or unequipped), carrying the path status, and path trace.

15. What is the actual data rate of the SPE of a SONET STS-1 frame?

The actual data rate of the SPE can be computed as follows:

Data Rate = 87 columns * 9 rows * 8 bits/byte * 8000 frames/sec = 50.112 Mbps

16. What are VT’s?

The sub STS-1 signals are called as VT’s. VT is virtual tributaries.

Four types of VT’s defined in SONET

VT 1.5 (DS-1: 1.544 Mbit/s)

VT 2 (E-1: 2.048 Mbit/s)

VT 3 (DS-1C: 3.152 Mbit/s)

VT 6 (DS-2: 6.312 Mbit/s)

An STS - SPE 1 which is sub divided into lower data rate blocks are called virtual

tributaries.

It is of 108 bytes each bit rate is 108*8*8000 = 6.912 Mbps.

17. Define SONET alarms.

SONET alarms are defined as anomalies, defects, and failures.

An anomaly is the smallest discrepancy that can be observed between the actual and

desired characteristics of an item.

If the density of anomalies reaches a level at which the ability to perform a required

function has been interrupted, it is termed a defect.

The inability of a function to perform a required action persisted beyond the

maximum time allocated is termed a failure.

18. What are the different types of Network elements used in SONET architecture?

Regenerator

Terminal Multiplexer

Add/Drop Multiplexer

Broadband Digital Cross-Connect

Wideband Digital Cross-Connect

Digital Loop Carrier

19. What are the different types of Topologies available in SONET architecture?

Point to point topology.

Point-to-Multipoint Topology

Hub Topology

Ring Topology

Mesh Topology

20. Differentiate Unidirectional and Bidirectional Rings in SONET standards.

Unidirectional Ring Bidirectional Ring

The working traffic is routed over the

clockwise direction.

The working traffic is routed over the

anticlockwise direction.

Data is always passed on the working path

and not on the protection path.

Data is passed on both working path and

the protection path.

Large round trip delay Less delay

Single time slot is allocated to both

working and protection fiber path.

It estabishes fullduplex path for connection

over shortest path in a ring.

21. What is function of Network management in SONET architecture?

The functions of the NM’s are as follows,

Fault management (FM),

Performance management (PM),

Accounting management (AM),

Security management (SM),

Configuration management (CM),

Trouble ticketing, and

Billing applications and all is the function of the operations support system

(OSS).

22. What is the difference between SONET and SDH?

SONET SDH

Synchronous Optical Networking. Synchronous Digital Hierarchy.

SONET standards are employed in North

America.

SDH standards are employed in Europe or

Japan.

Bit rate is 51.84 Mbps. Bit rate is 155.52 Mbps.

SONET uses VT, such as VT 1.5, 2, 3, 6. SDH uses VT, such as VC 11, 12, 2, 3, 4.

SECTION – II

23. What is SDH?

Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH) are

standardized multiplexing protocols that transfer multiple digital bit streams over optical

fiber using lasers or light-emitting diodes (LEDs). Lower rates can also be transferred via

an electrical interface.

24. Why do we need Multiplexing? Explain.

Multiplexing is needed in a network to avoid traffic problem. Multiplexing is a

process by which more number of signals is transmitted through a single fiber.

Multiplexing also reduces the number of laser sources required at the transmitter side

and number of detector sources at the receiver side.

If multiplexing is not done or employed,

Large bandwidth will be occupied.

Power consumption will be more.

Traffic problem is also increased.

Circuit become complex.

25. List out different layers in SDH architecture?

Path Layer

Multiplex Section Layer

Regenerator Section Layer

Photonic Layer

26. What is the function of Path layer?

The main function of the path layer is to map the signals into a format required by the

line layer.

Its functions include reading, interpreting, and modifying the POH for performance

and APS.

27. What is the function of Section layer?

The section layer deals with the transport of an STM-N frame across the physical

medium.

Its main functions are framing, scrambling, error monitoring, and section

maintenance.

28. What is the function of Photonic layer?

Its main function is the conversion between STM-N signals and light pulses on

the fiber media.

Its functions include wavelength launching, pulse shaping, and modulation of

power levels.

29. What are the elements of STM-1 frame?

The STM-1 base frame is structured with the following characteristics:

Length: 270 column x 9 row = 2430 bytes

Duration (Frame repetition time): 125 μs i.e. 8000 frame/s

Rate (Frame capacity): 2430 x 8 x 8000 = 155.520 Mbit/s

Payload = 2349bytes x 8bits x 8000frames/sec = 150.336 Mbit/s

30. Define TOH.

TOH is transport overhead. It contains two layers such as SOH and LOH.

SOH provides communication between adjacent network elements such as

regenerators.

LOH is used for communication between STM-N signals and STM Mulitiplexer and

demultiplexer.

31. Define LOH.

The line overhead (LOH) of the SDH STM-1 frame consists of 18 bytes found in

rows 4 to 9 of columns 1, 2, and 3 of the SDH frame. The LOH is processed by all

SDH NEs except for regenerators or repeaters.

The LOH is responsible for performance monitoring of the individual STM-1s,

carrying express orderwire communications information, data channels for OAM&P,

pointers to indicate the start of the SPE, protection switching information.

32. Define POH.

The POH is assigned to and transported with the SDH payload. It is created by the

PTE as part of the SPE until the payload is demultiplexed at the terminating path

equipment.

The STM POH is responsible for performance monitoring of the STM-N SPE, signal

labeling (equipped or unequipped), carrying the path status, and path trace.

33. What is the actual data rate of the SDH STM-1 frame?

The SDH STM-1 line rate of 155.520 Mbps can be computed as follows:

Line rate = 270 columns * 9 rows * 8 bits/byte * 8000 frames/sec = 155.520 Mbps

34. Define SDH alarms.

SDH alarms are defined as anomalies, defects, and failures.

An anomaly is the smallest discrepancy that can be observed between the actual and

desired characteristics of an item.

If the density of anomalies reaches a level at which the ability to perform a required

function has been interrupted, it is termed a defect.

The inability of a function to perform a required action persisted beyond the

maximum time allocated is termed a failure.

35. What are the different types of Network elements used in SDH architecture?

Regenerator

Terminal Multiplexer

Add/Drop Multiplexer

Broadband Digital Cross-Connect

Wideband Digital Cross-Connect

Digital Loop Carrier

36. What are the different types of Topologies available in SDH architecture?

Point to point topology.

Point-to-Multipoint Topology

Hub Topology

Ring Topology

Mesh Topology

37. Differentiate Unidirectional and Bidirectional Rings in SDH standards.

Unidirectional Ring Bidirectional Ring

The working traffic is routed over the The working traffic is routed over the

clockwise direction. anticlockwise direction.

Data is always passed on the working path

and not on the protection path.

Data is passed on both working path and

the protection path.

Large round trip delay Less delay

Single time slot is allocated to both

working and protection fiber path.

It estabishes fullduplex path for connection

over shortest path in a ring.

38. What is function of Network management in SDH architecture?

The functions of the NM’s are as follows,

Fault management (FM),

Performance management (PM),

Accounting management (AM),

Security management (SM),

Configuration management (CM),

Trouble ticketing, and

Billing applications and all is the function of the operations support system

(OSS).

UNIT III BROADCAST AND SELECT NETWORKS

1. What is broadcast and select Networks?

The Network sends the signal received from each node to all the nodes. Thus no routing function is provided by the network.

Information stream from multiple sources are optically combined by the star coupler and the signal power of each stream is equally split and forward to all of the nodes on their received fiber.

Ex: - Ethernets, Token Rings, FDDI Networks.

2. Name any 2 network topologies for Broadcast and select Network?

Star topology

Bus topology

3. What is star topology?

All nodes are connected by a central unit (or) hub

It requires less no of couplers.

Propagation loss is given by

Lstar = 10 log10n – (2n-1) 10 log10 γ

4. What is Bus topology?

In bus topology nodes transmit into the bus througha coupler and received from the bus via another coupler.

All nodes are directly connected to the bus

It requirs more no of couplers

Propagation loss is given by

Lbus = α2 (1-α) 2n-3γ2n-1

5. What is single-hop network?

Single hop refers to networks where information transmitted in the form of light

reaches its destination without being converted to an electrical form at any

intermediate point.

6. What is multi-hop network?

There is an electro optical conversion takes place between transmitter and receiver.

There is no direct connection of nodes in this network.

The transmission of data’s in this network purely depends on the signal wavelength.

7. Compare Single-hop and Multi-hop Networks.

SINGLE HOP MULTI HOP

There is no electro optical conversion between transmitter and receiver.

Nodes are directly connected.

There is an electro optical conversion takesplace between transmitter and receiver.

There is no direct connection between Nodes.

8. List the importance of Media Access control protocol.

To resolve contentions.

Avoid or minimize collisions.

To improve the level of system performance.

9. List the three (any) Media access control protocol.

The three types of Media Access control protocols are

Slotted Aloha / Slotted Aloha protocol

DT – WDMA protocol

Scheduling protocol.

12. What is synchronisation in Broadcast and select network?

Synchronisation means that all nodes have a suitable time reference so that signals

transmitted in diferent slots do not collide anywhere in the network.

13. What is SA/SA protocol?

Whenever a node, say x, has a data packet to send, it sends a control packet in a control slot

and the data packet in the data slot immediately following it.

14. What is DT-WDMA protocol?

On the data channels as well as the control channel, time is divided into slots, but the size of

a data slot is n times that of a control slot. Unlike SA/SA the data slots do not overlap in

time and control slots are (-1,0),(0,1), (1,2)…… data slots can be (-n,o),(o,n),(n,2n).

15. What is scheduling protocol?

Scheduling protocol is defined as that all nodes that have packets to transmit to the same

destination node schedule their transmissions in different data slots so that they never

contend with each other.

16. Define Access delay in SA/SA protocol.

The Access delay is defined as the delay between the time at which a packet is available for

transmission at a Node and the time at which it is first transmitted.

17. What is Media Access control protrocol?

To resolve contentions and avoid or minimize, wasteful collisions, some co-ordination is

required between the various nodes in the network. A mechanism that provides this co-

ordination is called MAC protocol.

18. What is matching algorithm? What are its different types?

Matching is a subset of packets such that no packets in the subset have the same source

node (or) destination node. The algorithm used for matching is called matching algorithm.

Types of matching algorithm

Maximum matching algorithm

Maximal matching algorithm.

19. Write notes on Lambdanet testbed.

Developed by - Bellcore

Topology - Star

Number of Wavelength - 18

Wavelength Spacing - 2 nm

Bit rate per wavelength - 1.5 Gb/s

20. Write notes on NTT’s testbed.

Topology - Star



Bit rate per wavelength - 622 Gb/s

21. Write notes on Rainbow-I testbed.

Topology - Star




22. Write notes on Rainbow-II testbed.

Topology - Star




23. Write notes on STARNET-I testbed.

Topology - Star


Wavelength Spacing - 10 GHZ


24. Write notes on BBC testbed.

Topology - Interconnected Star




UNIT IV WAVELENGTH ROUTING NETWORKS

1. What is a wavelength routing network?

The nodes in the network are capable of routing different wavelengths at an input port to

different output ports. This enables to setup many simultaneous lightpaths using the same

wavelength in the network; (i.e,) the capacity can be reused spatially.

2. What is meant by ‘wavelength reuse’ in wavelength routing networks?

The number of wavelengths available may be limited; the network can still provide

enormous capacities, since wavelengths can be spatially reused in the network. Here two

separate lightpaths are both carried at the same wavelength λ1. Thus the number of

lightpaths that the network can support can be much larger than the number of

wavelength available.

3. What is meant by Virtual Topology?

The virtual topology is the graph consisting of the netwok nodes, with an edge between

two nodes if there is a lightpath between them. The virtual topology thus refers to the

topology seen by the higher layers using the optical layer, the lightpaths look like links

between ATM switches.

4. What is static network?

In static network, the set of lightpaths that can be established between users is fixed.

A static network does not have any switches or dynamic wavelength converters in it.

Otherwise, the routing pattern at the nodes is fixed and it cannot be changed.

A static network uses no switches inside the WXC nodes.

5. What is reconfigurable network?

A reconfigurable network contains switches or dynamic wavelength converters,

giving it the capability to change the routing pattern at the nodes.

In reconfigurable network, the set of lightpaths that can be changed, by changing the

states of the switch or wavelength converters at the WXC nodes.

A reconfigurable network uses switches inside the WXC nodes or wavelength

converters.

6. What are the different types of regeneration techniques for digital data in node design?

3R – Regeneration with retiming and reshaping.

2R – Regeneration with reshaping and without retiming.

1R – Retransmitted without reshaping and retiming.

7. What is fixed and full wavelength conversion in node design?

In fixed wavelength conversion, a signal entering the node on wavelength λi must

always leave the node on wavelength λj, regardless of its input or output ports.

In full wavelength conversion, a signal entering the node on λi can leave the node on

any wavelength λj.

8. What is degree of transparency in node design?

The degree of transparency offered by an electronic implementation depends on the type

os signal regeneration employed within the node. If the implementation is fully analog, it

can offer almost the same level of transparency as the optical one. If the implementation

is digital, it clearly cannot support analog traffic.

9. Compare optical and electronic wavelength cross connects.

Optical WXC Electronic WXC

Transparency Yes Difficult

Wavelength Conversion Difficult Easier

Bit rates > 10 Gb/s ≤ 2.5 Gb/s

Cross connect size Small Large

10. What are the issues in Network design and operation of wavelength routing networks?

Equipment cost

Number of wavelengths required

Capacity of the network

Number of wavelength converters required

Regeneration and retransmission steps

Routing and Wavelength assignment of lightpaths.

11. What is online and offline lightpath in network design?

In online lightpath, the demands of lightpaths arise one at a time, and each lightpath

must be provided on demand without waiting for future lightpath demand.

In offline lightpath, the entire set of lightpaths that are to be routed up front. the

offline is equal to the online case with the additional freedom of rerouting existing

lightpaths when new demands for lightpath arise.

12. Define Routing and wavelength assignment.

The routing and wavelength assignment can be defined as a set of end to end lightpath

requests, determine a route and wavelengths for the requests, used the minimum possible

number of wavelengths.

13. What are the conditions essential for a network with undirected lightpaths and undirected

edges in wavelength assignment?

Two lightpaths must not be assigned the same wavelength on a given link.

If no wavelength conversion is available, then a lightpath must be assigned the same

wavelength on all the links in its route.

14. Write the steps for wavelength assignment using greedy algorithm.

Number the wavelength from 1 to L. Start with the first lightpath from the left and

assign to it wavelength 1.

Goto the next lightpath starting from the left and assign to it the least numbered

wavelength possible, untill all lightpaths are colored.

15. What is meant by chromatic number in wavelength assignment?

The minimum number of colors needed to color the nodes of a graph is called the

chromatic number of the graph.

16. List the different types of RWA algorithms.

Random-1 For a lightpath request between two nodes, choosen at random.

Random-2 Fix two shortest paths between every pair of nodes.

Max-used-1 For a lightpath request between two nodes. Among the available

wavelength.

Max-used-2 Fix two shortest paths between every pair of nodes.

17. Define wavelength routing testbeds.

Wavelength routing testbeds have been realized because of cooperative efforts

involving several companies, both network operators and network equipment

suppliers.

With the help of these testbeds it is possible to build operational networks based on

existing components and have brought up a number of issues that need to be solved

before these networks can be commercialized.

18. Write notes on MWTN testbed.

Architecture - OWXC

Topology - Ring/Mesh

Router ports - 4

Wavelengths - 4

Channel Spacing - 4

Bit Rate - 622 Mb/s

Distance - 230 Km

19. Write notes on AON testbed.

Architecture - Static

Topology - Star

Router ports - 8

Wavelengths - 20

Channel Spacing - 0.4

Bit Rate - 2.5 Gb/s

Distance - 100 Km

20. Write notes on ONTC testbed.

Architecture - OWXC

Topology - Linked Rings

Router ports - 2

Wavelengths - 4

Channel Spacing - 4

Bit Rate - 155 Mb/s

Distance - 150 Km

21. Write notes on NTT testbed.

Architecture - OADM

Topology - Ring

Router ports - 2

Wavelengths - 15


Bit Rate - 622 Mb/s

Distance - 120 Km

22. Write notes on Alcatel testbed.

Architecture - OEADM

Topology - Ring

Router ports - 2

Wavelengths - 4


Bit Rate - 2.5 Gb/s

Distance - 160 Km

23. Write notes on MONET testbed.

Architecture - OWXC

Topology - Mesh/ Ring

Router ports - 4

Wavelengths - 8


Bit Rate - 10 Gb/s

Distance - 2000 Km

24. Write notes on NTONC testbed.

Architecture - OADM

Topology - Dual ring

Router ports - 2

Wavelengths - 4

Channel Spacing - 4

Bit Rate - 2.5 Gb/s

Distance - 700 Km

25. Write notes on PHTON testbed.

Architecture - OWXC

Topology - Mesh

Router ports - 2

Wavelengths - 8


Bit Rate - 2.5/10 Gb/s

Distance - 500 Km

26. What is the function of simple network management protocol?

Configuration management.

Performance management.

Fault management.

Security management.

Accounting management.

UNIT V HIGH CAPACITY NETWORKS

1. Write the concept of SDM.

In SDM, bit rate is kept constant with use of more number of fibers.

It has two main drawbacks. It requires more fibers and the cost of laying new fibers

varies widely.

2. Write the concept of TDM.

In TDM, the transmission bit rate is increased on the fiber.

The two major disadvantages are the chromatic dispersion and polarization mode

dispersion (PMD).

3. Write the concept of WDM.

In WDM, bit rate is kept constant with addition of more wavelengths, each operating

at the original bit rate over the same fiber.

4. How WDM approach differ from TDM approach?

Because of the lower bit rates, the distance limit due to chromatic dispersion is much

larger for WDM systems than for equivalent TDM systems.

In WDM transparent capacity can be increased in a modular manner by adding

additional wavelengths.

WDM system can be designed to be transparent systems.

In WDM, network design is less complicated.

5. What is meant by photonic packet switching Networks?

The optical Networks that are capable of providing packet switched service at the

optical layer are known as photonic packet switching networks.

The main purpose of PPS networksa is to provide much highet speed of data

transmission with good accuracy.

6. Define synchnonization

Synchnonization can be defined as the process of alighing two signal streams in time. In

PPS networks, it refers to the alignment of an incoming pulse stream and a locally

available clock pulse stream or to the relative alignment of two incoming pulse streams.

7. What is switching in PPS networks?

It is the process of switching the incoming packet to the appropriate output port

determined by the forwarding process.

8. Define OTDM

At the inputs to the network, lower speed data streams are multiplexed optically in to

a higher speed stream and at the outputs of the network.

At the output side the lower speed streams must be extracted from the higher speed

stream optically by means of a demultiplexing Function.

In OTDM, the multiplexing and demultiplexing operations are performed entirely

optically at high speeds.

9. What is meant by bit-interleaving?

Optical signals representing data streams from multiple sources are interleaved in

time to produce a single data stream. The interleaving can be done on a bit by bit

basis. In bit-interleaving, framing pulses plays a major role. If n input data streams

are to be multiplexed a framing pulses are used for demultiplexing individual packets

from a multiplexed stream of packets.

10. What is meant by packet-interleaving?

Optical signals representing data streas from multiple sources are interleaved in time to

produce a single data stream. The interleaving can be done on a packet by packet basis.

In packet interleaving, framing pulses plays a major role which is used for demultiplexing

individual packets from a multiplexed stream of packets. In packet interleaving, Framing

pulses mark the boundary between packets.

11. Define Fire bit-interleaved data stream

A bank of five AND gates is used to break up the incoming high speed stream into fire

parallel streams each with Five times the pulse spacing of the multiplexed stream. This

procedure is called as five bit interleaved data stream.

12. Write short notes on NOLM.

NOLM Non-linear optical Loop mirror.

The Non-linear optical loop mirror consists of 3-dB directional coupler, a fiber loop

and a non-linear element (NLE) located asymmetrically in the fiber loop.

13. What is meant by NALM?

NALM Nonlinear amplifying Loop mirror.

When the pulse travelling in the fiber loop clockwise direction is amplified by an

EDFA shortly after it leaves the directional coupler. The use of an amplifier inside

the Fiber loop is known as nonlinear amplifying loop mirror.

14. What is TOAD?

TOAD – Terahentz optical asymmetric demultiplexer.

The configuration has the following two properties are called TOAD.

I. First Non-linear effects that works with shorter lengths of Fiber.

II. Second, to realize an AND gate, it require an NLE whose non-linear

properties can be conveniently controlled by the use of control pulses.

15. What is meant by soliton trapping?

The two pulses undergo wavelength shifts in opposite directions so that the group

velocity difference due to the wavelength shift exactly compensates the group velocity

difference due to birefringence. This phenomenon is called soliton trapping.

16. What is the need for tunable delay in PPS?

Tunable delay is very essential to achieve the synchronization.

A tunable delay line capable of realizing any delay in excess of a reference delay from

0 to T-2-k, in steaps of 2-k

The parameter k controls the resolution of the delay.

17. What is the need for phase lock loop?

A phase lock loop can be used to adjust the frequency and phase of a local clock source -

a mode locked laser of an incoming periodic stream.

18. How can we improve the effect of non-linearity in phase lock loop?

The two wavelengths can be choosen to lies symmetrically on either side of the zero

dispersion wavelength of the fiber so that the group velocities of the two pulse streams

are equal.

19. What is a Broadcast OTDM network?

The OTDM network is based on a star topology or a bus topology is known as

Broadcast OTDM networks.

In a star based network, all the nodes are connected by a pair of optical fibers to a

control star coupler.

In Broadcast OTDM networks, a multichannel media-access protocol is required so

that the nodes can decide how to tune transmitters and receivers.

20. What is switch based networks?

The electronic packet switched network is based on an arbitany mesh topology is

called a store and forward network. (Eg: ATM and IP networks)

In switch based networks, the links run at very high speeds (100 GB/s) and the signals

are handled entirely optically within each routing node.

21. List out the functions of a Routing node.

Synchnonization

Header Recognition

Buffering

22. Define Deflection Routing

Deflection routing was invented by Baran in 1964. It was implemented in the context of

processor interconnection networks in the 1980’s. In PPS, buffers are very expensive for

high transmission speeds; hence deflection routing is used as an alternative to buffering.

Deflection routing is also sometimes called Hot-potato routing.

23. What is meant by buffering?

Buffering is the process of store the packets from the incoming links before they can be

transmitted or forwarded on the outgoing links.

24. What are the reasons to store or buffer a packet before it is forwarded on its outgoing

link?

First to determine how the packet must be routed.

Second to find the free input and output switch port for avoiding the queue.

Third to making the packets wait for its turn.

25. What is meant by hot potato routing?

Deflection routing which doesn’t use buffers except for packet header processing is

called as hot potato routing.

26. Define Deadlock or Livelock.

When a network employs deflection routing, there is the possibility that a packet will be

deflected forever and never reach its destination. This phenomenon is called as dead

lock.

27. Define OTDM Testbeds

The main objective of the OTDM testbeds is the demonstration of certain key optical

TDM network Functions such as multiplexing, demultiplexing, routing/switching, header

recognition optical clock recovery, pulse generation, pulse compression and pulse

storage.

28. Write notes on KEOPS testbed.

Topology - Switch

Bit Rate - 2.5 Gb/s & 10 Gb/s

Functions Demonstrated - 4 x 4 Switch, Switching, Packet Synchronizer.

16 x 16 broadcast select and switching.

29. Write notes on FRONTIERNET testbed.

Topology - Switch

Bit Rate - 2.5 Gb/s

Functions Demonstrated - 16 X 16 tunable lasers.

30. Write notes on NTT testbed.

Topology - Switch

Bit Rate - 10 Gb/s

Functions Demonstrated - 4 x 4 broadcast select.

31. Write notes on Synchrolan testbed.

Topology - Bus

Bit Rate - 40 Gb/s

Functions Demonstrated - Bit-interleaved data transmission and reception.

32. Write notes on BT Labs testbed.

Topology - Switch

Bit Rate - 100 Gb/s

Functions Demonstrated - Routing in a 1 x 2 switch based on optical header recognition.

33. Write notes on Princeton testbed.

Topology - Switch

Bit Rate - 100 Gb/s

Functions Demonstrated - Packet Compression, TOAD based demultiplexing.

34. Write notes on AON testbed.

Topology - Helix

Bit Rate - 100 Gb/s

Functions Demonstrated - Optical phase lock loop, pulse generation.

35. Write notes on CORD testbed.

Topology - Star

Bit Rate - 2.5 Gb/s

Functions Demonstrated - Contention resolution.

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