Post on 25-Aug-2014
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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
Number of Wavelength - 100
Wavelength Spacing - 1 nm
Bit rate per wavelength - 622 Gb/s
21. Write notes on Rainbow-I testbed.
Topology - Star
Number of Wavelength - 12
Wavelength Spacing - 1 nm
Bit rate per wavelength - 300 Gb/s
22. Write notes on Rainbow-II testbed.
Topology - Star
Number of Wavelength - 4
Wavelength Spacing - 1 nm
Bit rate per wavelength - 1 Gb/s
23. Write notes on STARNET-I testbed.
Topology - Star
Number of Wavelength - 2
Wavelength Spacing - 10 GHZ
Bit rate per wavelength - 1.25 Gb/s
24. Write notes on BBC testbed.
Topology - Interconnected Star
Number of Wavelength - 16
Wavelength Spacing - 4 nm
Bit rate per wavelength - 2.5 Gb/s
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
Channel Spacing - 0.8
Bit Rate - 622 Mb/s
Distance - 120 Km
22. Write notes on Alcatel testbed.
Architecture - OEADM
Topology - Ring
Router ports - 2
Wavelengths - 4
Channel Spacing - 1.6
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
Channel Spacing - 1.6
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
Channel Spacing - 3.2
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.