This set of Optical Communications Questions and Answers for Aptitude test focuses on “Optical Network Transmission Modes, Layers and Protocols”.
1. Electrical devices in optical network are basically used for _____________
a) Signal degradation
b) Node transfer
c) Signal control
Explanation: The optical infrastructure in networks constitutes a transparent network in which electronic devices are present. They are basically used for signal control. The other use includes providing interconnection to other networks.
2. Signals are defined as ________________ if their significant instants occur at nominally the same rate, any variation being constrained within specific limits.
Explanation: With any multiplexing strategies, come some setbacks. This includes the differentiation in the frequencies occurring throughout a network. This is called as plesiochronous transmission.
3. The bit stuffing in the plesiochronous digital hierarchy is complex and uneconomic.
Explanation: The bit stuffing is a complex process as it does not provide individual channel extraction. For individual channel extraction, the whole de-multiplexing procedure is to be performed again. This is both uneconomic and complex.
4. A ____________ digital hierarchy was required to enable the international communications network to evolve in the optical fiber era.
Explanation: The plesiochronous digital hierarchy was uneconomic and complex in execution. To reduce the complexity and efficient bit stuffing purpose, a synchronous digital hierarchy was required. It transformed the international communications into an optical fiber era.
5. The standardization towards a synchronous optical network termed SONET commenced in US in _______
Explanation: Synchronous optical network mechanism was efficient and its standardization process mainly started in 1985. Some modifications in the plesiochronous hierarchy were retained and some new features were added in the optical era to achieve efficient bit stuffing.
6. ______________ is a packetized multiplexing and switching technique which combines the benefits of circuit and packet switching.
a) Synchronous mode
b) Asynchronous transfer mode
c) Circuit packet
d) Homogeneous mode
Explanation: ATM transfers the information in fixed size units called cells. Each cell contains the information identifying the source of the transmission. It generally contains less data than packets.
7. The ___________ sits at the top of hierarchy of the OSI layer model.
a) Session layer
b) Transport layer
c) Application layer
d) Data link layer
Explanation: Application layer is the seventh layer and sits at the top of the hierarchy. It provides a means for a user to access information on or utilize the network by receiving a service.
8. The ____________ controls the dialogs between intelligent devices.
a) Physical layer
b) Transport layer
c) Application layer
d) Session layer
Explanation: The session layer is fifth in the OSI layer model. It controls the sessions between the devices and manages the connections between the remote and local application.
9. The network layer looks after the flow and error control mechanism.
Explanation: The network layer is the third level in the OSI layer model. It provides procedural and functional method for transferring data sequences from source to destination.
10. The physical layer is located at the bottom of the OSI model.
Explanation: The physical layer defines all the electrical, optical and media specifications for devices. Hence, it is located at the bottom of the OSI model. It establishes and terminates the connection between the media devices.
11. In order to access for end-to-end networking of optical channels to transparently convey information, the _____________ is employed in the OTN structure.
a) Presentation layer
b) Session layer
d) OCh layer
Explanation: The OCh stands for optical channel. It provides end-to-end access in networking of optical channels. It includes the multiplexing section to support multi-user networking.
12. An advanced type of reconfigurable OTN is referred to as an _______________
a) Automatic OTN
b) Auto-generated photon
c) Automatically switched optical network
d) Optical reimbursement
Explanation: Automatically switched optical network (ASON) is capable of switching the optical channels automatically when requested. It is specified in the ITU-T Recommendation G.8080 and it is basically a transport layer.
13. The __________ is a network layer that contains both addressing and control information to enable packets to be routed within a network.
b) Internet protocol (IP)
d) SONET/SDH protocol
Explanation: Internet protocol forms a part of the network layer. It controls the logical architecture within the network and addresses the issues accordingly. It routes the packets within a network.
14. The mapping of IP frames in SDH/SONET is accomplished in ___________ stages.
Explanation: Mapping requires three stages. In the first stage, point-to-point protocol is used. The second and the third stage includes synchronous mapping of data onto the SDH/SONET frame.
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