NETWORKING by xiagong0815


									Section A


ANS :--Modem (modulation/demodulation)
A device that allows computer information to be transmitted and receving over a
telephone line. The transmitting modem translates digital computer data into analog
signals that can be carried over a phone line the reveving modem translates the analog
signals back to addition to digital/analog signal conversion,modem control
other aspects of establishing maintaining,and terminating data communication protocol
with the remote modem,and error detection/correction.

ANS:-Hypertext Markup Language (HTML)
A simple markup language used to create hypertext documents that are portable from one
platform to another. HTML files are simple ASCII text files with codes embedded
(indicated by markup tags) to denote formatting and hypertext links
ANS:       authentication

The process for verifying that an entity or object is who or what it claims to be. Examples include
confirming the source and integrity of information, such as verifying a digital signature or verifying
the identity of a user or computer.

ANS:Data communication
Data communication is the process of sending data electronically from one location to another.
linking one computer to another permits the power and resources of that computer to be
also makes possible the updating and sharing of data at different locations.

Ans:      UTP

Unshielded twisted pair (utp) cable is composed of a set ot twisted paris with a simple plastic
encasement. it is widely available and has been largely standardized.the electical
Industries association (eia) category 3 and category 5 utp are commonly used in computer
netrworking utp may support data transfer rated from 1 to 100 mbps at distances up to 100m.

Q6 explain MAN
Ans: MAN
A metropolitan area network (man) is a network that is larger than a lan. Is is called metropolitan
since it normally covers the area of a city. Different hardware and transmission media are often
used in mans because they must efficiently cover these distances(a few tens to about one hundred
kilometers) or because they don’t reuire complete access to loations between the networked sites.

Q7 function of bridges
Ans:        Bridge

A bridge interconnects two networks that use the same technology (such as Ethernet or arcnet) a
bridge is more sophisticated than a repeater. for example assume a bridge interconnects two
networks called “eastside” and “westside” the bridge will examine all packets on ech network data
bus. in addition to interconnecting networks, bridges often boost performance,reliability,and

Q8    explain DHCP

Ans:Dynamic Host Configuration Protocol (DHCP)
A TCP/IP service protocol that offers dynamic leased configuration of host IP addresses and
distributes other configuration parameters to eligible network clients. DHCP provides safe, reliable,
and simple TCP/IP network configuration, prevents address conflicts, and helps conserve the use of
client IP addresses on the network.
DHCP uses a client/server model where the DHCP server maintains centralized management of IP
addresses that are used on the network. DHCP-supporting clients can then request and obtain lease
of an IP address from a DHCP server as part of their network boot process.

Q9 what is routing
Ans:         ROUTING

The process of forwarding a packet through an internetwork from a source host to a destination
host. For Message Queuing, a communications link established between Windows sites for routing
Q 10 What is Switching?

                 Every time you access the internet or another network outside your immediate
location,your messages are sent through a maze of transimission media and connection
devices.the mechnasim for moving informations between diffrent networks and network segment
is called switching.For example :- whenever a telephone called is placed, there are numerous
juncations in the communication path that perform this movment of data from one network onto
another network.

Q 11. explain space-switching.

        Time space switching:-
                 A time space(ts) switch takes the outputs of several time-division switches,for
example , TSI switches and connects them as inputs as a space division switch. the effect of this
paired arrangment is that packets can be swaped between diffrent output lines. If there were two
outputs on a time division switch contending for the same output, the space-division switch
delivers one of the two outputs to another output path.This arrangment also reduces the number
of crosspoints required.
Q 12. What is attenuation

         The weakening of a signal as it is transferred across a communication medium. There
are limits to how far signals can travel down a copper,fiber-optic, or atmospheric media before the
signal becomes too weak and /or noisy to be able to properly extract the data from the signal.This
property is called attenuation.

Q13. Expalin Hybrid Topology.

         It is a combination of a bus and a is designed to take advantages both of star and
bus network this topology several buses can be connected together in a star
There are number of logical examples of hybrid networks, such as ATM and Frame Relay.

Q14. what is Distrributed Processing.

       Disributed Processing :-
                 Distributed processing is the combination of two terms.The "distributed
Processing" is used to describe systems with multiple processors. A distributed processing
system allows the use of many smaller, more specillized computers that can be tailored to
complete a particular task or tasks efficiently and cost effectively
       Three advantages of using distributed processing are:-
                1. Cost efficiency.
                2. Shared Resources.
                3. User control of computer facillities.
Q1. What is Simplex Transmmision?
Ans. Communications network can provide many types of service. The most basic type
of service is known as simplex. This service provides one-way communication.
Examples of this type of service are TV distribution.

Q2. Distinguish between router and gateway?

Ans. Gateway: A device connected to multiple physical TCP/IP networks capable of
routing or delivering IP packets between them. A gateway translates between different
transport protocols or data formats (for example, IPX and IP) and is generally added to a
network primarily for its translation ability. In the context of interoperating with Novell
NetWare networks, a gateway acts as a bridge between the server message block
(SMB) protocol used by Windows networks and the NetWare core protocol (NCP) used
by NetWare networks. A gateway is also called an IP router.

Router: In a Windows environment, hardware that helps LANs and WANs achieve
interoperability and connectivity, and can link LANs that have different network
topologies (such as Ethernet and Token Ring). Routers match packet headers to a LAN
segment and choose the best path for the packet, optimizing network performance. In
the Macintosh environment, routers are necessary for computers on different physical
networks to communicate with each other. Routers maintain a map of the physical
networks on a Macintosh internet (network) and forward data received from one physical
network to other physical networks. Computers running the Server version of Windows
with AppleTalk network integration can act as routers, and you can use other routing
hardware on a network with AppleTalk network integration.

Q2. What is FDM?

Ans. Frequency-division multiplexing (FDM) is a scheme in which numerous signals are
combined for transmission on a single communications line or channel. Each signal is
assigned a different frequency (sub channel) within the main channel. A typical analog
Internet connection via a twisted pair telephone line requires approximately three
kilohertz (3 kHz) of bandwidth for accurate and reliable data transfer. Twisted-pair lines
are common in households and small businesses. But major telephone cables, operating
between large businesses, government agencies, and municipalities, are capable of
much larger bandwidths.

Q3. What is ping utility?
Ans. Ping: Packet Internet Grouper, Ping is a basic Internet program that allows a user
to verify that a particular IP address exists and can accept requests. The verb ping
means the act of using the ping utility or command. Ping is used diagnostically to ensure
that a host computer you are trying to reach is actually operating. If, for example, a user
can't ping a host, then the user will be unable to use the File Transfer Protocol (FTP) to
send files to that host. Ping can also be used with a host that is operating to see how
long it takes to get a response back.

Q4. Explain Go-Back N ARQ?
Ans. Go-back-n ARQ is the most commonly used form of error control based on sliding-
window flow control. In this method, a station may send a series of frames sequentially
numbered modulo some maximum value. While no error occur, the destination will
acknowledge incoming frames with a ACK. If the destination station detects an error in a
frame, it sends a negative acknowledgment (NACK) for that frame. The destination
station will discard that frame and all future incoming frames until the frame in error
correctly received. When the source station receives a NACK, it must retransmit the
frame in error and all succeeding frames that were transmitted in the interim.

Q5. Explain ICMP?
Ans. ICMP (Internet Control Message Protocol) is a message control and error-reporting
protocol between a host server and a gateway to the Internet. ICMP uses Internet
Protocol (IP) datagrams, but the messages are processed by the IP software and are not
directly apparent to the application user.

Q6. What is IP telephony?
Ans. IP telephony (Internet Protocol telephony) is a general term for the technologies
that use the Internet Protocol's packet-switched connections to exchange voice, fax, and
other forms of information that have traditionally been carried over the dedicated circuit-
switched connections of the public switched telephone network (PSTN). Using the
Internet, calls travel as packets of data on shared lines, avoiding the tolls of the PSTN.
The challenge in IP telephony is to deliver the voice, fax, or video packets in a
dependable flow to the user. Much of IP telephony focuses on that challenge

Q7. Explain Windows XP Networking Features?
       1. Network Diagnostics Features
                    Network diagnostics features were added to Windows XP to
             support diagnosing network problems.

       2. Network Setup Wizard
                    Windows XP provides you with a Network Setup wizard to ease
             the task of setting up your network. This wizard allows you to configure
             the Internet connection the computers on your network will use, enable
             the Internet Connection Firewall, configure the network adapters on your
             computer and enable the Network Bridge if appropriate, share files and
             printers and name your computers.

       3. Quality of Service (QoS) Enhancement for Home Networks
                      When a home network is connected to a corporate or other
             network through a slow link, such as a dial-up line, a situation can exist
             that will increase the delay on traffic traversing the slow link.

       4. Internet Connection Firewall (ICF)
               When a computer is connected to the Internet or other pathway to the
       outside world, there is the threat of unauthorized attempts to access the
       computer and data.

       5. Internet Connection Sharing (ICS) Enhancements
                Windows 2000 included ICS to enable sharing of a single Internet
       connection among all of the computers on a home or small office network. The
       computer connected to the Internet would have ICS enabled and provide
       addressing and network address translation services for all of the computers on
       the network.
       Some other features are:-

       6. UPnP Client Support
       7. Network Location Awareness and Winsock API Enhancements
       8. Wireless LAN Enhancements
       9. IPv6 Development Stack

Q8. What is Subnetting?
Ans. The process of subnetting involves dividing a network up into smaller networks
called subnets or sub networks. To create these additional networks we use a subnet
mask. The subnet mask simply determines which portion of the IP address belongs to
the host. The subnet mask does not alter the class of the IP address; it simply "borrows"
bits from the host portion and uses these to create subnets. This naturally reduces the
maximum number of hosts your network can have, because you are using some of your
host bits for your subnet bits.
Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple
base Frequency-division multiplexing band signals are modulated on different
frequency carrier waves and added together to create a composite signal.

                                       Section B

 Q1. What is e-commerce and it’s Advantages?
Ans. E-Commerce:-
       Electronic commerce is the paperless exchange of business information using
 electronic data interchange (EDI), e-mail, electronic bulletin boards, fax transmissions,
 and electronic funds transfer. It refers to Internet shopping, online stock and bond
 transactions, the downloading and selling of “soft merchandise” (software, documents,
 graphics, music, etc.), and business-to-business transactions. The concept of e-
 commerce is all about using the Internet to do business better and faster. It is about
 giving customers controlled access to your computer systems and letting people serve
 themselves. It is about committing your company to a serious online effort and
 integrating your Web site with the heart of your business. If you do that, you will see

Advantages of E-Commerce:
1. Catalog flexibility and Online fast updating

      Direct "link" capabilities to content information and visual displays already
       existing on other client web site. You can update your E-Catalog anytime,
       whether it's adding new products, or adjusting prices, without the expense and
       time of a traditional print catalog.
      Extensive search capabilities by item, corporate name, division name, location,
       manufacturer, partner, price or any other specified need.

2. Shrinks the Competition Gap
      Reduced marketing/advertising expenses compete on equal footing with much
       bigger companies; easily compete on quality, price, and availability.

3. Unlimited Market Place and Business Access Which Extend Customer Base

      The Internet gives customers the opportunity to browse and shop at their
       convenience and at their place. They can access your services from home,
       office, or on the road, 24 hours a day, 7 days a week.
      The Internet allows you to reach people around the world, offering your products
       to a global customer base.

4. A 24-hour Store Reduced Sale Cycle

      Reduce unnecessary phone calls and mailings.

5. Lower Cost of Doing Business

      Reduce inventory, employees, purchasing costs, order-processing costs
       associated with faxing, phone calls, and data entry, and even eliminate physical
       stores. Reduce transaction costs.

6. Eliminate Middlemen

      Sell directly to your customers.

7. Easier Business Administration

      With right software, store inventory levels, shipping and receiving logs, and other
       business administration tasks can be automatically stored, categorized and
       updated in real-time, and accessed on demand.

8. Frees Your Staff

      Reduce customer service and sales support.

9. Customers will love it

      Gives customers control of sales process. Builds loyalty.

10. More Efficient Business Relationships

      Better way to deal with dealers and suppliers.

11. Workflow automation
      Shipping, real time inventory accounting system which adjusts stock levels and
       site, location availability instantaneously
      Secured, automated registration verification, account entry and transaction
       authorization features
      Automated RFP and RTQ features for vendor bid development and selection.
      Banking and accounting features customized for pre-approved third party direct
       sales, vendor, consignment or internal transfer transactions.

12. Secure Payment Systems

      Recent advancements in payment technologies allow encrypted, secure payment

Q2. Distinguish between Datagram Packet switching and virtual Circuit switching?
Ans. Datagram packet switching
Conceived in the 1960's, packet switching is a more recent technology than circuit
switching which addresses a disadvantage of circuit switching: the need to allocate
resources for a circuit, thus incurring link capacity wastes when no data flows on a
circuit. Packet switching introduces the idea of cutting data on a flow into packets which
are transmitted over a network without any resource being allocated. If no data is
available at the sender at some point during a communication, then no packet is
transmitted over the network and no resources are wasted.

Figure 1.2: Datagram Packet Switching. Packets from a given flow are independent
and a router can forward two packets from the same flow on two different links.
Since each packet is processed individually by a router, all packets sent by a host to
another host are not guaranteed to use the same physical links. If the routing algorithm
decides to change the routing tables of the network between the instants two packets
are sent, then these packets will take different paths and can even arrive out of order. In
this Figure for instance, packets use two different paths to go from User 1 to User 5.
Second, on a network topology change such as a link failure, the routing protocol will
automatically recompute routing tables so as to take the new topology into account and
avoid the failed link. As opposed to circuit switching, no additional traffic engineering
algorithm is required to reroute traffic.
Virtual circuit packet switching

Figure: Virtual circuit packet switching. All packets from the same flow use the same
virtual circuit.
Virtual circuit packet switching (VC-switching) is a packet switching technique which
merges datagram packet switching and circuit switching to extract both of their
advantages. VC switching is a variation of datagram packet switching where packets
flow on so-called logical circuits for which no physical resources like frequencies or time
slots are allocated (see Figure). Each packet carries a circuit identifier, which is local to a
link and updated by each switch on the path of the packet from its source to its
destination. A virtual circuit is defined by the sequence of the mappings between a link
taken by packets and the circuit identifier packets carry on this link. In VC-switching,
routing is performed at circuit establishment time to keep packet forwarding fast. Other
advantages of VC-switching include the traffic engineering capability of circuit switching,
and the resources usage efficiency of datagram packet switching. Nevertheless, a main
issue of VC-Switched networks is the behavior on a topology change. As opposed to
Datagram Packet Switched networks which automatically recompute routing tables on a
topology change like a link failure, in VC-switching all virtual circuits that pass through a
failed link are interrupted. Hence, rerouting in VC-switching relies on traffic engineering
There are a number of important differences between virtual circuit and datagram
networks. The choice strongly impacts complexity of the different types of node. Use of
datagrams between intermediate nodes allows relatively simple protocols at this level,
but at the expense of making the end (user) nodes more complex when end-to-end
virtual circuit service is desired. The Internet transmits datagrams between intermediate
nodes using IP. Most Internet users need additional functions such as end-to-end error
and sequence control to give a reliable service (equivalent to that provided by virtual
circuits). This reliability may be provided by the Transmission Control Protocol (TCP),
which is used end-to-end across the Internet, or by applications such as the trivial file
transfer protocol (TFTP) running on top of the User Datagram Protocol (UDP)

Q3. Compare the efficiencies of ALOHA and CSMA/CD?
Ans. Aloha, also called the Aloha method, refers to a simple communications scheme in
which each source (transmitter) in a network sends data whenever there is a frame to
send. If the frame successfully reaches the destination (receiver), the next frame is sent.
If the frame fails to be received at the destination, it is sent again. This protocol was
originally developed at the University of Hawaii for use with satellite communication
systems in the Pacific. In a wireless broadcast system or a half-duplex two-way link,
Aloha works perfectly. But as networks become more complex, for example in an
Ethernet system involving multiple sources and destinations that share a common data
path, trouble occurs because data frames collide (conflict). The heavier the
communications volume, the worse the collision problems become. The result is
degradation of system efficiency, because when two frames collide, the data contained
in both frames is lost. To minimize the number of collisions, thereby optimizing network
efficiency and increasing the number of subscribers that can use a given network, a
scheme called slotted Aloha was developed. This system employs signals called
beacons that are sent at precise intervals and tell each source when the channel is clear
to send a frame. Further improvement can be realized by a more sophisticated protocol
called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is the protocol for carrier
transmission access in Ethernet networks. On Ethernet, any device can try to send a
frame at any time. Each device senses whether the line is idle and therefore available to
be used. If it is, the device begins to transmit its first frame. If another device has tried to
send at the same time, a collision is said to occur and the frames are discarded. Each
device then waits a random amount of time and retries until successful in getting its
transmission sent.

Q4. Explain Distance Vector routing in detail?
Ans. The distance-vector routing is a type of algorithm used by routing protocols to
discover routes on an interconnected network. The primary distance-vector routing
algorithm is the Bellman-Ford algorithm. Another type of routing algorithm is the link-
state approach. Routing protocols that use distance-vector routing include RIP (Routing
Information Protocol), Cisco's IGRP (Internet Gateway Routing Protocol), and Apple's
RTMP (Routing Table Maintenance Protocol). The most common link-state routing
protocol is OSPF (Open Shortest Path First). Dynamic routing, as opposed to static
(manually entered) routing, requires routing algorithms. Dynamic routing protocols assist
in the automatic creation of routing tables. Network topologies are subject to change at
any time. A link may fail unexpectedly, or a new link may be added. A dynamic routing
protocol must discover these changes, automatically adjust its routing tables, and inform
other routers of the changes. The process of rebuilding the routing tables based on new
information is called convergence. Distance-vector routing refers to a method for
exchanging route information. A router will advertise a route as a vector of direction and
distance. Direction refers to a port that leads to the next router along the path to the
destination, and distance is a metric that indicates the number of hops to the destination,
although it may also be an arbitrary value that gives one route precedence over another.
Inter network routers exchange this vector information and build route lookup tables from

Q5. What do you understand by MAC address? How is a MAC address translated
into an equivalent IP address?
Ans. In a local area network (LAN) or other network, the MAC (Media Access Control)
address is your computer's unique hardware number. (On an Ethernet LAN, it's the
same as your Ethernet address.) When you are connected to the Internet from your
computer (or host as the Internet protocol thinks of it), a correspondence table relates
your IP address to your computer's physical (MAC) address on the LAN. The MAC
address is used by the Media Access Control sub layer of the Data-Link Layer (DLC) of
telecommunication protocols. There is a different MAC sub layer for each physical
device type. The other sub layer level in the DLC layer is the Logical Link Control sub

Q6. If a binary signal is send over a 4 kHz channel whose S/N ratio is 30db, what is
the maximum achievable data rate?

Maximum data rate = H Log2 (1+S/N)
H= Maximum number of channels available
Max Data Rate = 4000 * Log2 (1+ 30)
                 = 37 kbps

Q7.      Explain ISDN?
Ans. Integrated Services Digital Network: It is a set of ITU-T standards for the transmisssion of
digital data primarily over standard       copper telephone line. This service      is quiet complex
but very flexible ISDN has two service levels: Basic Rate Interface         (BRI),    Primary rate
interface         (PRI).Thesew services use two types of channels: B Channels and D chennels.
The B channels provide 64kbps and are              used to transport either voice or data. In a basic
rate interface, there are two B channels and one D chennel, which is 16kbps. The D Chennel
is used to carry control and signalling information. In the PRI, there are 23 B chennels at 64kbps
         each, and one D chennel at 64 kbps.
                  In fact, there are several chennel types, including A,B,C,D, E and H but B and D
are by far the most commonly used in US. A BRI is used to carry one voice and one data circuit
into a small office or home, and a PRI is used to carry 23          channels of     voice or some
combination of 23 channels of voice and data. BRIs are usually used in a dial-up capacity
        where an ISDN modem only connects to the service provider, when there is data to
send. the PRI is usually a permanent connection.

Q8.      Explain Layer 2 and layer 3 Switch?
Ans.      Switchs and Bridges are the layer 2 devices.Once the number of users began to push
the limits of a single network segment, there was a need to create a new segment to link two
netw orks together a device called bridges        accomplished this. basically the bridges have 2
ports, one for each network, bridges actually inspect the data that passes        through
themand make decisions about whether to send it to the other network or not. This decision is
based on the MAC        address in ethernet networks and on the ring no. in Token Ring
Networks. Because of this behaviour( specifically that    bridges read and act on the data in the
Layer 2 headers of each frame), hence Bridges are layer 2 devices.
                 As networks become larger, and the amount of data transmitted by each
computer increaesed, segmenting                   networks became even more important. 2 port
bridges were no longer seffuicent then switch began as multiport bridges and are considered
layer two devices.Most switches have 12 to 24 ports but many are modular can have several
hundered ports.Switches can handle several conversations at same time each 100base -TX port
on a switch can send and recieve frames at the same time,so switches are Full Duplex and hubs
are Half-Duplex.

Router is a Layer 3 Device :- Routers are created to segregate brodcast domains.Roters act as
boundary between broadcast domains.Routers read and make decisions based on layer 3
headers,Like :- TCP/IP or IPX they become layer3 devices.A routers funcation is to
inspect incoming packet and determine whether it belongs to local network or to a Remote
if a local packet is determined then there is no need of routing and if a Remote packet is
determined then it will route that packet according to the routing table other wise the packet will
be discarded.

Q9. What is ip Address? Can a device have more then one ip address?Give reasons.
Ans.    It is a 32-bit address logical address. which is made up of the network ID, plus a unique
host ID. This address is typically represented with the decimal value of each octet separated by a
period (for example,            Every Host and router on the internet has an IP
Address.That can either be Static Or dynamic.In static address is to be given manually. But in
dynamic a DHCP server is to be configured to give ip address to the the Connected hosts
automatically. This address is used to uniquely identify each Network host over the network.Ip
address is divided into 5 categoery usually called classes. This allocation has come to be called
class full addresing.
Following are the classes of ip :-

        CLASSES                                RANGE

        Class A                 to

        Class B             to

        Class C             to

        Class D             to

        Class E             to
a Router has more than one IP address because router connects two or more different
networks.But A computer or host can only have one and a uniqe ip address. A routers funcation
is to inspect incoming packet and determine whether it belongs to local network or to a Remote
Network, if a local packet is determined then there is no need of routing and if a Remote packet is
determined then it will route that packet according to the routing table other wise the packet will
be discarded.

Q10.    How many amplitude levels are there for each of the following methods:
        NRZ-L, NRZI, Manchester and Differential Manchester?

Ans. NRZ-L (Nonreturn to zero level): this kind of encoding uses negative voltage to represent
       a binary 1 and positive voltage to represent a binary 0. As shown under: non return to
       zero is related with the voltage i.e voltage never returns to a value of zero and the value
       of the voltage during a bit time is known as level. bit time is related with the amount of
       time one bit of data occupies. the NRZ-L is used on very short connections, like the
       Connection between the computer and an external modem. its main problem is that , for
       long strings of 0's and 1's, the signal's voltage remain negative or positive for extended
       periods of time, this may lead to a situation called baseline wander, as this makes difficult
       to the receiver to properly decode the information. another problem with this is that in
       order for the sender and receiver to remain in synchronization, frequent changes in the
       signal are required. when there are long runs of high or low voltages, the sender        and
       receiver’s clocks may begin to wander so that the two devices are no longer in
       synchronization. To prevent this a separate clock is signal could be used on another
       channel but this takes up valuable data transmission space. To overcome this NRZI
       encoding is used.

    NRZI (Non Return to Zero Invert on 1):-
              It is related with the NRZ-L except the data encoded by either the presence or
      absence of voltage change at the beginning of the bit time. as shown under:         In this
      category of encoding when the signal changes from high to low voltage or from low to
      high voltage a binary 1 is encoded. When there is no change in the voltage at the
      beginning of the current bit time from the last bit time, a binary 0 is encoded. NRZI is also
      referred as non return to zero inverted.

    Manchester Encoding:
               In this encoding, the point at which the signal changes is used to represent data.
      as shown under, the locations at which the voltage changes from 0 to a positive value
      represents a binary 1 and when the voltage changes from positive to Zero, a binary 0 is
      represented. Manchester Encoding schemes use the edge triggered hardware and
      changes or transitions are known as rising or falling edges. When leading edge rises to a
      positive voltage, a binary 1 is encoded and when the leading edge falls to zero voltage, a
      binary 0 is encoded. due to this each bit period is divided into two equal intervals. Every
      bit period has a transition in the middle that makes it easier to the receiver to synchronize
      with the sender, Manchester Encoding uses a preamble to permit synchronization by the
      receiver, it will ensure that there is proper synchronization of the time slots used when
      sampling the signal by receiver. The preamble is composed of 64 alternating 1's and 0's,
      which is sent before the frame data. a pattern of alternating 1's and 0's produces a
      square wave from which the receiver can determine the value of the time slots. due to the
      preamble the need of external clock for synchronization is got eliminated.

    Differential Manchester Encoding:
                A variation on standard Manchester encoding is referred to as differential
        Manchester Encoding. In this a binary 1 is represented by the lack of a transition or
        voltage change the beginning of sampling interval. A binary 0 is encoded when a
       transition occurs at the beginning of the sampling interval. A binary 0 is encoded when a
       transition occurs at the beginning of sampling interval. Under this encoding more complex
       hardware is required., but it offers better immunity to influences from outside noises.
       differential Manchester encoding is used in token ring networks. The figure is showing the
       Differential Manchester encoding :

Q Expalin TCP/IP refrence Model

The TCP/IP Reference Model

Let us now turn from the OSI Reference model to the Reference model used in the
grandparent of all wide area computer networks, the ARPANET, and its successor, the
worldwide internet . the ARPANET was research network sponsored by the DOD ( U.S.
Department of Defense. When satellite and radio networks were added later, the existing
protocols had trouble interworking with them, so a new Reference architecture was
needed. Thus the ability to connect multiple networks in a seamless way was one of the
major design goals from the very beginning. This architecture later became known as the
TCO/IP Reference Model.
       It Has four layers Compare to Seven Layers Of OSI Reference Model




           Host To Network

               Tcp/IP Layers

The functions of Layers Are As Follow:-

Host To Network
       Below The Internet Layer is the host to network layer.In this Layer connectivity
through some medium to the network is defined. In this any specific protocol is not
defined. The protocol used varies from host to host.

The Internet Layer
        DoD wanted connections to remain intact as long as the source and destinaton
machines were functioning even if some of the machines or transmission line in between
were suddenly put out of operation, further more, a flexible architecture was needed since
applications with divergent requirements were envisioned, ranging transferring files to
real time speech transmission. All these requirements led to the choice of packet –
Switching network based on a connectionless inter works layer. This called the internet
layer is the linchpin that holds the whole architecture together. Its job is to permit hosts to
inject packets packer into any network and have them travel independently to the
destination (potentially on a different network). They may even arrive in a different order
than they were sent , in which case it is the job of higher layer to rearrange them if in
order delivery is desired
        The internet layer defines an official packet format and protocol called ip (internet
protocol). The job of the internet layer is to deliver IP packets where they are supposed to
go. Packet routing, is clearly the major issue here as is avoiding congestion. For these
reason, it is reasonable to say that the TCP/IP internet layer is similar in functionality to
the OSI network layer

The Transport Layer

       The layer above the internet layer in the TCP/IP model is know usually called the
Transport layer, it is designed to allow peer entities on the source and destination host to
carry on a conversation, just as in the OSI transport layer. Two end to end transport
protocol have been defined here.

    1.      TCP (Transmission Control Protocol) a reliable connection oriented protocol.
    2.      UDP (User Datagram Protocol) a unreliable connectionless protocol.

TCP is used fro important type of applications where data is more important and it must
reach the destination.

UDP is used where fast delivery of data is more important then accurate delivery
(example:- Speech, Video).

The Application Layer :- Above the transport Layer is the application Layer. It contains
Protocols for
1. TELNET                              - For Virtual Terminal.
2. File Transfer Protocol(FTP)         - For File Transfer.
3. Simple Mail transfer Protocol(SMTP) - For Electronic Mail.
4. Domain Name system(DNS)              - For Converting address with the host names
                                          And vise-versa.

5.Hyper Text Transport Protocol(HTTP) - For World Wide Web.

Q. What is Cable modem?
Ans.     To access Internet Through a Cable TV Network requires a cable Modem. It has two
interfaces on it one for computer and other for Cable Network The Computer side interface is
usually is a USB Interface or 10Mbps Ethernet And The Cable Network is common cable wire
interface. This Modem makes a connection when it is turned on. Cable modems are always retain
the connection(unless they are switched off) because the cable operator does not charge for the
duration of connection.
                 When a cable Modem is switched on It scans the downstream channel looking for a
special packet periodically(special packet contains the modem configuration and sender of this is the
headend),After getting the packet, the new modem sends a packet on one of the upstream channel.
After getting a packet from a modem, headend sends a packet to the new modem assigning the
modem with downstream and upstream channels. The modem then determines its distance from
the headend by sending it a special packet and seeing how long it takes to get the response. This
process is called ranging. It is important for the modem to know its distance to accommodate the
way the upstream channels and to get the timing right. They are divided in time in minislots Each
upstream packet must fit in one or more consecutive minislots. The headend announces the start of
a new round of minislots periodically, but the starting gun is not heard at all modems
simultaneously due to the propagation time down the cable. By knowing how far it is from the
headend, each modem can compute how long ago the first minislot really started. Minislot length is
network dependent. A typical payload is 8 bytes
During   initialization the headend also assigns each modem to a minislot to use for requesting
upstream bandwidth. As rule, multiple modems will be assigned the same minislot, which leads to
contention. When a computer wants to send a packet, it transfer the packet to the modem, which
then requests the necessary number of minislots for it. If the request is accepted, the headend puts
an acknowledgement on the downstream channel telling the modem which minislots have been
reserved for its packet. The packet is then sent ., starting in the minislot allocated to it .Additional
packets can be requested using a field in the header.

Q. What is Telnet? What is its use?

         Telnet is a user command and an underlying TCP/IP protocol for accessing
remote computers. Through Telnet, an administrator or another user can access
someone else's computer remotely. With Telnet, you log on as a regular user with
whatever privileges you may have been granted to the specific application and data on
that computer. Telnet is most likely to be used by program developers and anyone who
has a need to use specific applications or data located at a particular host computer.
Telnet gives you access to the destination system's functions and files. The user name
you use to access the space determines the limits on what you can do -- restricted to
just using the menu to find information or permitted the liberty to execute programs.
Telnet has no graphical user interface (GUI). It's all ASCII and command line - set your
mouse aside.
         Telnet was one of the Internet's first tools, created to work across a broad range
of platforms, terminals and displays. Now that Windows has Telnet built-in (via the Run
dialog box or more lately, using the address box on the browser), it's easy to log into a
telnet account or site on the Internet once you have an Internet connection running on
both computers. If your own computer is the destination of the Telnet session, it must be
configured to let you run programs -- read your email, for example. And you need to
learn the menu commands of these programs. However, programs can be run on the
remote UNIX system to let you access email stored there using an email program like
Pine, Elm or Mail. Common editors are Pico, VI and EMACS. To open a Telnet session,
go to the UNIX command line or the Windows Run dialog box, and type telnet
[hostname] enter your user name and password, or the access information you know the
computer requires Command line interface is a different world of computing, but Telnet's
accessibility throughout the world -- most Internet cafés are running Windows - makes it
worth learning a few command lines.

Q. What is Internet:-
        A collection of interconnected networks is called a inter-network or Internet.many
networks exist in the world,often with different hardware and software.People connected
to one network often want to communicate with people attached to a diifrent one. The
fulfillment of this desire requires internet.
        The internet began in the 1960s as advanced research projects agency ( ARPA)
Project It first came on-line in 1969 with four nodes connected via 56kbps circuits. After
proving itself, similar networks were created by the military (MILNET). Universities and
various government agencies began connecting to the network and ARPANet was
created. In the mid-1980s, the national science Foundation created NSFNet, which had a
three-tier architecture that was far more robust than ARPANet. In 1988 56kbps speed

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