PDF Archive

Easily share your PDF documents with your contacts, on the Web and Social Networks.

Share a file Manage my documents Convert Recover PDF Search Help Contact

network viva questions and answers .pdf

Original filename: network_viva_questions_and_answers.pdf

This PDF 1.5 document has been generated by Microsoft® Word 2016, and has been sent on pdf-archive.com on 24/11/2015 at 19:14, from IP address 117.198.x.x. The current document download page has been viewed 661 times.
File size: 892 KB (28 pages).
Privacy: public file

Download original PDF file

Document preview

Questions by REVA IT Dept of Information Science & Engg

Viva Questions
1. What are functions of different layers?
Functions of each Layer:
Physical Layer(Layer 1):This layer defines the physical and electrical characteristics of the network.
Helps to pass strings(data) of ones and zeros down the wire.
Device:Hub, NIC, Repeater.. etc
Data Link Layer:
It defines the acess strategy for sharing the physical medium. Helps convert the bits into frame.
Devices: Bridge, Switch
Network Layer:
Layer 3 is the Network Layer, providing a means for communicating open systems to establish,
maintain and terminate network connections.
Transport Layer:
The main function of this Layer is to ensure data reliability and integrity.
Session Layer:
It provides two communicating presentation entities to exchange data with eachother.
Presentation Layer:
Application data is either unpacked or packed only in this layer. Protocol conversions,
encryption/decryption and graphics expansion all takes place here.
Application Layer:
This is where you find your end-user and end-application protocols, such as telnet, ftp, and
mail(pop3 and smtp).
2. Differentiate between TCP/IP Layers and OSI Layers
The Session layer permits two parties to hold ongoing communications called a session across a
Not found in TCP/IP model
In TCP/IP,its characteristics are provided by the TCP protocol.
(Transport Layer)
The Presentation Layer handles data format information for networked communications. This is
done by converting data into a generic format that could be understood by both sides.
Not found in TCP/IP model
In TCP/IP, this function is provided by the Application Layer.
e.g. External Data Representation Standard (XDR)
Multipurpose Internet Mail Extensions (MIME)

Answers by S.Raaj Nishanth

1 / 28

Questions by REVA IT Dept of Information Science & Engg

The Application Layer is the top layer of the reference model. It provides a set of interfaces for
applications to obtain access to networked services as well as access to the kinds of network
services that support applications directly.
Although the notion of an application process is common to both, their approaches to constructing
application entities is different

It takes the information to be sent and breaks it into individual packets that are sent and
reassembled into a complete message by the Transport Layer at the receiving node
Transport Layer protocols include the capability to acknowledge the receipt of a packet; if no
acknowledgement is received, the Transport Layer protocol can retransmit the packet or time-out
the connection and signal an error
Defines two standard transport protocols: TCP and UDP
TCP implements a reliable data-stream protocol
connection oriented
UDP implements an unreliable data-stream
TCP is responsible for data recovery
by providing a sequence number with each packet that it sends
TCP requires ACK (ackowledgement) to ensure correct data is received
Packet can be retransmitted if error detected

Like all the other OSI Layers, the network layer provides both connectionless and connectionoriented services. As for the TCP/IP architecture, the internet layer is exclusively connectionless.

3. Why header is required?
(answer below)
4. What is the use of adding header and trailer to frames?

IPv4 Packet Header
The Internet Protocol (IP) uses a Datagram service to transfer packets of data between end systems using
The IPv4 packet header consists of 20 bytes of data. An option exists within the header that allows
further optional bytes to be added, but this is not normally used (with the occasional exception of
something called "Router Alert"). The full header is shown below:
Answers by S.Raaj Nishanth

2 / 28

Questions by REVA IT Dept of Information Science & Engg

The header fields are discussed below:

Version (always set to the value 4 in the current version of IP)
IP Header Length (number of 32 -bit words forming the header, usually five)
Type of Service (ToS), now known as Differentiated Services Code Point (DSCP) (usually set
to 0, but may indicate particular Quality of Service needs from the network, the DSCP defines
the way routers should queue packets while they are waiting to be forwarded).
Size of Datagram (in bytes, this is the combined length of the header and the data)
Identification ( 16-bit number which together with the source address uniquely identifies this
packet - used during reassembly of fragmented datagrams)
Flags (a sequence of three flags (one of the 4 bits is unused) used to control whether routers are
allowed to fragment a packet (i.e. the Don't Fragment, DF, flag), and to indicate the parts of a
packet to the receiver)
Fragmentation Offset (a byte count from the start of the original sent packet, set by any router
which performs IP router fragmentation)
Time To Live (Number of hops /links which the packet may be routed over, decremented by
most routers - used to prevent accidental routing loops)
Protocol (Service Access Point (SAP) which indicates the type of transport packet being carried
(e.g. 1 = ICMP; 2= IGMP; 6 = TCP; 17= UDP).
Header Checksum (A 1's complement checksum inserted by the sender and updated whenever
the packet header is modified by a router - Used to detect processing errors introduced into the
packet inside a router or bridge where the packet is not protected by a link layer cyclic
redundancy check. Packets with an invalid checksum are discarded by all nodes in an IP
Source Address (the IP address of the original sender of the packet)
Destination Address (the IP address of the final destination of the packet)
Options (not normally used, but, when used, the IP header length will be greater than five 32-bit
words to indicate the size of the options field)

5. What is encapsulation?
Encapsulation, closely related to the concept of Protocol Layering, refers to the practice of enclosing
data using one protocol within messages of another protocol.

Answers by S.Raaj Nishanth

3 / 28

Questions by REVA IT Dept of Information Science & Engg

To make use of encapsulation, the encapsulating protocol must be open-ended, allowing for arbitrary
data to placed in its messages. Another protocol can then be used to define the format of that data.
Encapsulation Example
For example, consider an Internet host that requests a hypertext page over a dialup serial connection.
The following scenario is likely:
First, the HyperText Transfer Protocol (HTTP) is used to construct a message requesting the page. The
message, the exact format of which is unimportant at this time, is represented as follows:

Next, the Transmission Control Protocol (TCP) is used to provide the connection management and
reliable delivery that HTTP requires, but does not provide itself. TCP defines a message header format,
which can be followed by arbitrary data. So, a TCP message is constructed by attaching a TCP header to
the HTTP message, as follows:

Now TCP does not provide any facilities for actually relaying a message from one machine to another in
order to reach its destination. This feature is provided by the Internet Protocol (IP), which defines its
own message header format. An IP message is constructed by attaching an IP header to the combined
TCP/HTTP message:

Finally, although IP can direct messages between machines, it can not actually transmit the message
from one machine to the next. This function is dependent on the actual communications hardware. In
this example, we're using a dialup modem connection, so it's likely that the first step in transmitting the
message will involve the Point-to-Point Protocol (PPP):

5. Why fragmentation required?
Every packet-based network has an MTU (Maximum Transmission Unit) size. The MTU is the size
of the largest packet which that network can transmit.
Answers by S.Raaj Nishanth

4 / 28

Questions by REVA IT Dept of Information Science & Engg

Packets larger than the allowable MTU must be divided into multiple smaller packets, or fragments,
to enable them to traverse the network.

6. What is MTU?
In computer networking, the maximum transmission unit (MTU) of a layer of a communications
protocol is the size (in bytes) of the largest protocol data unit that it can pass onwards. MTU
parameters usually appear in association with a communications interface (NIC, serial port, etc.).
The MTU may be fixed by standards (as is the case with Ethernet) or decided at connect time (as is
usually the case with point-to-point serial links). A higher MTU brings greater efficiency because
each packet carries more user data while protocol overheads, such as headers or underlying perpacket delays remain fixed, and higher efficiency means a slight improvement in bulk protocol

7. Which layer imposes MTU?
Layer 2 (Data Link Layer)

Differentiate between flow control and congestion control.
Flow control vs. congestion control:
Flow control mean preventing the source from sending data that the sink will end up dropping
because it runs out of buffer space.
This is fairly easy with a sliding window protocol--just make sure the source's window is no larger
than the free space in the sink's buffer. TCP does this by letting the sink advertise its free buffer
space in the window field of the acks.
Congestion control means preventing (or trying to prevent) the source from sending data that will end
up getting dropped by a router because its queue is full. This is more complicated, because
packets from different sources travelling different paths can converge on the same queue.
In a connection-oriented network:
Admission control and policers can be used to avoid congestion. Before a source starts sending data,
it sets up a connection, which requires permission from the routers/switches along the path. If
the requested resources are unavailable, the connection is not set up. Once the connection is set up,
policers at the edge of the network can make sure the source does not send more than it was
allowed to.
In a connectionless network:
Congestion is unavoidable, because the routers are not warned ahead of time that a source will be
sending packets along some path.

Answers by S.Raaj Nishanth

5 / 28

Questions by REVA IT Dept of Information Science & Engg

Congestion can, however, be managed, if sources are informed when their packets encounter
congestion and they slow down.

8. Differentiate between Point-to-Point Connection and End-to-End connections.
In networking, the Point-to-Point Protocol, or PPP, is a data link protocol commonly used to
establish a direct connection between two networking nodes. It can provide connection
authentication, transmission encryption privacy, and compression. PPP is used over many types of
physical networks including serial cable, phone line, trunk line, cellular telephone, specialized radio
links, and fiber optic links such as SONET. Most Internet service providers (ISPs) use PPP for
customer dial-up access to the Internet

The end-to-end principle states that, whenever possible, communications protocol operations should be
defined to occur at the end-points of a communications system, or as close as possible to the resource
being controlled. According to the end-to-end principle, protocol features are only justified in the lower
layers of a system if they are a performance optimization.
Example : example is that of file transfer. Every reliable file transfer protocol and file transfer program
should contain a checksum, which is validated only after everything has been successfully stored on
disk. Disk errors, router errors, and file transfer software errors make an end-to-end checksum


What are protocols running in different layers?
7 Application
Web Browser, Email, Print Serivces, SIP, SSH and SCP, NFS, RTSP, Feed, XMPP, Whois, SMB; DNS;
6 Presentation
5 Session
TLS, SSH, X.225, RPC, NetBIOS, ASP, Winsock, BSD
4 Transport
Gateway, Advanced Cable Tester, Brouter
3 Network
Brouter, Router, Frame Relay Device, ATM Switch, Advanced Cable Tester, DDP
2 Data Link
Ethernet, Token ring, StarLAN, HDLC, Frame relay, ISDN, ATM, 802.11 WiFi, FDDI, PPP, Bridge, Switch,
ISDN Router, Intelligent Hub, NIC, Advanced Cable Tester, ARCNET, LocalTalk, FDDI, ATM. NIC Drivers:
Open Datalink Interface (ODI), Network Independent Interface Specification (NDIS)
1 Physical

Answers by S.Raaj Nishanth

6 / 28

Questions by REVA IT Dept of Information Science & Engg

NIC, Twisted Pair, Coax, Fiber Optic, Wireless Media, Repeater, Multiplexer, Hubs, (Passive/Active), TDR,
Oscilloscope, Amplifier, Carrier pigeon
4 Application (OSI - Layers5 through 7)
(Routing protocols like BGP and RIP, which for a variety of reasons run over TCP and UDP respectively,
may also be considered part of the Internetwork layer)
3 Transport (OSI - Layers4 and 5)
(Routing protocols like OSPF, which run over IP, may also be considered part of the Internetwork layer)
2 Internetwork (OSI - Layer 3)
For TCP/IP this is the Internet Protocol (IP)
(Required protocols like ICMP and IGMP run over IP, but may still be considered part of the Internetwork
layer; ARP does not run over IP)
1 Link
(OSI - Layers 1 and 2)
Ethernet, Wi-Fi, MPLS, etc.

Answers by S.Raaj Nishanth

7 / 28

Questions by REVA IT Dept of Information Science & Engg

10.What is Protocol Stack?
A protocol stack (sometimes communications stack) is a particular software implementation of a
computer networking protocol suite. The terms are often used interchangeably. Strictly speaking,
the suite is the definition of the protocols, and the stack is the software implementation of them.
In practical implementation, protocol stacks are often divided into three major sections: media,
transport, and applications. A particular operating system or platform will often have two welldefined software interfaces: one between the media and transport layers, and one between the
transport layers and applications.

Answers by S.Raaj Nishanth

8 / 28

Questions by REVA IT Dept of Information Science & Engg

Answers by S.Raaj Nishanth

9 / 28

Related documents

homework6 7 8
network viva questions and answers
18i14 ijaet0514242 v6 iss2 724to729
untitled pdf document 1
mpls network as the new1058

Related keywords