1.
What is the application of computer networkers? Applications
of computer networks are: information exchange, military, music and video on
demand, etc.
globally organized companies need computer network for providing
communication between employees, email, video conferencing, instant messaging, streaming stored video clips, etc.
globally organized companies need computer network for providing
communication between employees, email, video conferencing, instant messaging, streaming stored video clips, etc.
2.
What is OSI model? Explain the function and
protocol and services of each layer? What is OSI model is Open
Systems Interconnection model (OSI) served by the layer below it.
For example, a layer that provides error-free communications across a network
provides the path needed by applications above it, while it calls the next
lower layer to send and receive packets that make up the contents of that path.
Two instances at one layer The Open Systems Interconnection model (OSI)
is a conceptual model that characterizes and standardizes the internal functions
of a communication system by partitioning it into abstraction layers.
The model is a product of the Open
Systems Interconnection project
at the International
Organization for Standardization
(ISO), maintained by the identification ISO/IEC 7498-1.
The model groups communication functions
into seven logical layers. A layer serves the layer above it and are connected
by a horizontal connection on that layer.
The Open Systems Interconnect (OSI) model
has seven layers. This article describes and explains them, beginning with the
'lowest' in the hierarchy (the physical) and proceeding to the 'highest' (the
application). The layers are stacked this way:
Application
- Presentation
- Session
- Transport
- Network
- Data Link
- Physical
PHYSICAL LAYER
The physical layer, the lowest layer of the
OSI model, is concerned with the transmission and reception of the unstructured
raw bit stream over a physical medium. It describes the electrical/optical,
mechanical, and functional interfaces to the physical medium, and carries the
signals for all of the higher layers. It provides:
- Data
encoding: modifies the simple digital signal pattern (1s and 0s) used by
the PC to better accommodate the characteristics of the physical medium,
and to aid in bit and frame synchronization. It determines:
- What
signal state represents a binary 1
- How
the receiving station knows when a "bit-time" starts
- How
the receiving station delimits a frame
- Physical
medium attachment, accommodating various possibilities in the medium:
- Will
an external transceiver (MAU) be used to connect to the medium?
- How
many pins do the connectors have and what is each pin used for?
- Transmission
technique: determines whether the encoded bits will be transmitted by
baseband (digital) or broadband (analog) signaling.
- Physical
medium transmission: transmits bits as electrical or optical signals
appropriate for the physical medium, and determines:
- What
physical medium options can be used
- How
many volts/db should be used to represent a given signal state, using a
given physical medium
DATA LINK LAYER
The data link layer provides error-free
transfer of data frames from one node to another over the physical layer,
allowing layers above it to assume virtually error-free transmission over the
link. To do this, the data link layer provides:
- Link
establishment and termination: establishes and terminates the logical link
between two nodes.
- Frame
traffic control: tells the transmitting node to "back-off" when
no frame buffers are available.
- Frame
sequencing: transmits/receives frames sequentially.
- Frame
acknowledgment: provides/expects frame acknowledgments. Detects and
recovers from errors that occur in the physical layer by retransmitting
non-acknowledged frames and handling duplicate frame receipt.
- Frame
delimiting: creates and recognizes frame boundaries.
- Frame
error checking: checks received frames for integrity.
- Media
access management: determines when the node "has the right" to
use the physical medium.
NETWORK LAYER
The network layer controls the operation of
the subnet, deciding which physical path the data should take based on network
conditions, priority of service, and other factors. It provides:
- Routing:
routes frames among networks.
- Subnet
traffic control: routers (network layer intermediate systems) can instruct
a sending station to "throttle back" its frame transmission when
the router's buffer fills up.
- Frame
fragmentation: if it determines that a downstream router's maximum
transmission unit (MTU) size is less than the frame size, a router can
fragment a frame for transmission and re-assembly at the destination
station.
- Logical-physical
address mapping: translates logical addresses, or names, into physical
addresses.
- Subnet
usage accounting: has accounting functions to keep track of frames
forwarded by subnet intermediate systems, to produce billing information.
Communications
Subnet
The network layer software must build
headers so that the network layer software residing in the subnet intermediate
systems can recognize them and use them to route data to the destination
address.
This layer relieves the upper layers of the need to know anything about the data transmission and intermediate switching technologies used to connect systems. It establishes, maintains and terminates connections across the intervening communications facility (one or several intermediate systems in the communication subnet).
In the network layer and the layers below, peer protocols exist between a node and its immediate neighbor, but the neighbor may be a node through which data is routed, not the destination station. The source and destination stations may be separated by many intermediate systems.
This layer relieves the upper layers of the need to know anything about the data transmission and intermediate switching technologies used to connect systems. It establishes, maintains and terminates connections across the intervening communications facility (one or several intermediate systems in the communication subnet).
In the network layer and the layers below, peer protocols exist between a node and its immediate neighbor, but the neighbor may be a node through which data is routed, not the destination station. The source and destination stations may be separated by many intermediate systems.
TRANSPORT
LAYER
The transport layer ensures that messages are
delivered error-free, in sequence, and with no losses or duplications. It
relieves the higher layer protocols from any concern with the transfer of data
between them and their peers.
The size and complexity of a transport protocol depends on the type of service it can get from the network layer. For a reliable network layer with virtual circuit capability, a minimal transport layer is required. If the network layer is unreliable and/or only supports datagrams, the transport protocol should include extensive error detection and recovery.
The transport layer provides:
The size and complexity of a transport protocol depends on the type of service it can get from the network layer. For a reliable network layer with virtual circuit capability, a minimal transport layer is required. If the network layer is unreliable and/or only supports datagrams, the transport protocol should include extensive error detection and recovery.
The transport layer provides:
- Message
segmentation: accepts a message from the (session) layer above it, splits
the message into smaller units (if not already small enough), and passes
the smaller units down to the network layer. The transport layer at the
destination station reassembles the message.
- Message
acknowledgment: provides reliable end-to-end message delivery with
acknowledgments.
- Message
traffic control: tells the transmitting station to "back-off"
when no message buffers are available.
- Session
multiplexing: multiplexes several message streams, or sessions onto one
logical link and keeps track of which messages belong to which sessions
(see session layer).
Typically, the transport layer can accept
relatively large messages, but there are strict message size limits imposed by
the network (or lower) layer. Consequently, the transport layer must break up
the messages into smaller units, or frames, prepending a header to each frame.
The transport layer header information must then include control information, such as message start and message end flags, to enable the transport layer on the other end to recognize message boundaries. In addition, if the lower layers do not maintain sequence, the transport header must contain sequence information to enable the transport layer on the receiving end to get the pieces back together in the right order before handing the received message up to the layer above.
The transport layer header information must then include control information, such as message start and message end flags, to enable the transport layer on the other end to recognize message boundaries. In addition, if the lower layers do not maintain sequence, the transport header must contain sequence information to enable the transport layer on the receiving end to get the pieces back together in the right order before handing the received message up to the layer above.
End-to-end
layers
Unlike the lower "subnet" layers
whose protocol is between immediately adjacent nodes, the transport layer and
the layers above are true "source to destination" or end-to-end
layers, and are not concerned with the details of the underlying communications
facility. Transport layer software (and software above it) on the source
station carries on a conversation with similar software on the destination
station by using message headers and control messages.
SESSION
LAYER
The session layer allows session
establishment between processes running on different stations. It provides:
- Session
establishment, maintenance and termination: allows two application
processes on different machines to establish, use and terminate a
connection, called a session.
- Session
support: performs the functions that allow these processes to communicate
over the network, performing security, name recognition, logging, and so
on.
PRESENTATION
LAYER
The presentation layer formats the data to be
presented to the application layer. It can be viewed as the translator for the
network. This layer may translate data from a format used by the application
layer into a common format at the sending station, then translate the common
format to a format known to the application layer at the receiving station.
The presentation layer provides:
The presentation layer provides:
- Character
code translation: for example, ASCII to EBCDIC.
- Data
conversion: bit order, CR-CR/LF, integer-floating point, and so on.
- Data
compression: reduces the number of bits that need to be transmitted on the
network.
- Data
encryption: encrypt data for security purposes. For example, password
encryption.
APPLICATION
LAYER
The application layer serves as the window for users and application processes to access network services. This layer contains a variety of commonly needed functions:
- Resource
sharing and device redirection
- Remote
file access
- Remote
printer access
- Inter-process
communication
- Network
management
Directory services
3.Explzin the following
a)
LAN
b)
MAN
c)
WAN
d)
ARPANET
Computer networks are bunch of interconnected
PC or computers that facilitate the exchange of data or some other purposeful
work. The first computer network to be designed was the "Advanced Research
Projects Agency Network" (ARPANET) for the United States Department of
Defense in the late 1960s and early 1970s. From then on, numerous new network
technologies have been developed.
Computer networks can be classified into different types based on their scale of operation. They include:
Computer networks can be classified into different types based on their scale of operation. They include:
- LAN:
Local Area Networks cover a small physical area, like a home, office, or a
small group of buildings, such as a school or airport.
- WLAN:
Wireless Local Area Networks enable users to move around within a larger
coverage area, but still be wirelessly connected to the network.
WAN: Wide Area Ne
- MAN:
Metropolitan Area Networks are very large networks that cover an entire
city.
tworks cover a broad area, like
communication links that cross metropolitan, regional, or na tional boundaries.
The Internet is the best example of a WAN.
4.what is IP addressing? How it is classified? How is subnet
addressing is performed? TCP/IP
(Transmission Control Protocol/Internet Protocol) is the basic communication
language or protocol of the Internet. It can also be used as a communications
protocol in a private network (either an intranet
or an extranet).
When you are set up with direct access to the Internet, your computer is
provided with a copy of the TCP/IP program just as every other computer that you
may send messages to or get information from also has a copy of TCP/IP.
Application Layer Functionality and
Protocols
Objectives
Upon completion of this chapter, you
will be able to answer the following questions:
■
How do the functions of the three upper
OSI
model layers provide network
services to
end-user applications?
■
How do the TCP/IP application layer
protocols
provide the services specified by
the upper
layers of the OSI model?
■
How do people use the application
layer to
communicate across the information
network?
■
What are the functions of well-known
TCP/IP
applications, such as the World Wide
Web and
e-mail, and their related services
(HTTP, DNS,
DHCP, STMP/POP, and Telnet)?
■
What are the file-sharing processes
that use
peer-to-peer applications and the
Gnutella
protocol?
■
How do protocols ensure that
services running
on one kind of device can send to
and receive
from many different network devices?
■
How can you use network analysis
tools to
examine and explain how common user application
work?
A Comparison of Network Models
There are two network models that describe how networks 'work'. The OSI
Model, the older model, was designed for the OSI protocol stack.
While different organizations were battling over standards, Vint Cerf and Bob
Khan worked out the TCP/IP software from which the TCP/IP
Model was co-designed. The diagram below shows how the two
networking models compare, and how the logical and physical networking
protocols relate to the layers in each of the two models.
- See more at:
http://www.inetdaemon.com/tutorials/basic_concepts/network_models/comparison.shtml#sthash.L18JNdt6.dpuf
Quiz 6
IP address is short for Internet
Protocol
(IP)
address.
An IP address is an identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination.
The Format of an IP Address
The format of an IP address is a 32-bit numeric address written as four
numbers separated by periods. Each number can be zero to 255. For example,
1.160.10.240 could be an IP address.
IP Address Classification, IPv4
IP, Short for Internet Protocol, is an
address of a computer or other network device on a network using IP or TCP/IP
( Transmission Control Protocol / Internet Protocol ). For Example, the
number "166.70.10.23" is an example of such an address. These
addresses are similar to addresses used on houses and help data reach its
appropriate destination on a network. There are five classes of available IP ranges: Class A, Class B, Class C, Class D and Class E, while only A, B and C are commonly used. Each class allows for a range of valid IP addresses. Below is a listing of these addresses. |
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What is IPv4 and IPv6 ?
IPv4 and IPv6 refer to versions of Internet
Protocol Addressing schemes. IPv4 was adopted in the fall of 1989. as mentioned above it consists of 4 numbers in the range of ( 0 thru 255 ) separated by the "." period character. IPv4 stands for Internet Protocol ( IP ) version 4. IPv4 superceded version 3, IPv3. IPv3 consisted of 3 numbers in the range of ( 0 thru 255 ). IPv3 supported 16,777,216 addresses ( 256 x 256 x 256, 256 ^ 3 ). We quickly ran out of addresses even before the "internet" and "world wide web" were common household names. So in the fall of 1989, IPv4 came along, and supports 4,294,967,296 (256 x 256 x 256 x 256, 256 ^ 4) addresses. We have used some smart tricks to use these efficiently, like DHCP and NAT, but we still ran out of addresses. June 8, 2011. IPv6, version 6. Yes, we skipped version 5. This version is a different beast entirely. IPv6 consists of 8 numbers in the range of ( 0 thru 65535 ), separated by a ":" colon character, and written using the Hexadecimal format or numbering system. IPv6 supports 65536 ^ 8, or 3.4×10^38 addresses. Here is an example of a full IPv6 address. FE80:0000:0000:0000:0202:B3FF:FE1E:8329 This can also be written in a compressed form as: FE80::0202:B3FF:FE1E:8329. How many is 3.4 x 10 ^ 38 ? it's pronounced 340 Undecillion , 340 x 10 ^ 36, or 3.4 x 10 ^ 38. So, when the earth reaches 7 Billion people (7,000,000,000), as we are at 6.9 billion in July 2011, then each of the 30 trillon red blood cells (30,000,000,000,000) per person, could have 1.6 quadrillion (1,619,047,620,000,000) ip addresses for itself. It's the first time in the history of mankind, that someone could request a trillion of something, with the exception of germs, and actually get it. |
Subnetting
Subnetting enables the network administrator to further divide the host part
of the address into two or more subnets. In this case, a part of the host
address is reserved to identify the particular subnet. This is easier to see if
we show the IP address in binary format.
5.what is TCP/IP model? Explain the function and protocols
and services of each layer compare it with OSI model? In this
tutorial we will discuss the concept of Ports and how they work with IP
addresses. If you have not read our article on IP addresses and need a brush
up, you can find the article here. If you
understand the concepts of IP addresses, then lets move on to TCP and UDP ports
and how they work.
The devices and comptuers connected
to the Internet use a protocol called TCP/IP to communicate with each other.
When a computer in New York wants to send a piece of data to a computer in
England, it must know the destination IP address that it woud like to send the information
to. That information is sent most often via two methods, UDP and TCP.
The two Internet workhorses: UDP and
TCP
UDP? TCP? I know you are getting
confused, but I promise I will explain this in very basic terms so that you can
understand this concept.
TCP stands for Transmission Control
Protocol. Using this method, the computer sending the data connects directly to
the computer it is sending the data it to, and stays connected for the duration
of the transfer. With this method, the two computers can guarantee that the
data has arrived safely and correctly, and then they disconnect the connection.
This method of transferring data tends to be quicker and more reliable, but
puts a higher load on the computer as it has to monitor the connection and the data
going across it. A real life comparison to this method would be to pick up the
phone and call a friend. You have a conversation and when it is over, you both
hang up, releasing the connection.
UDP stands for User Datagram
Protocol. Using this method, the computer sending the data packages the
information into a nice little package and releases it into the network with
the hopes that it will get to the right place. What this means is that UDP does
not connect directly to the receiving computer like TCP does, but rather sends
the data out and relies on the devices in between the sending computer and the
receiving computer to get the data where it is supposed to go properly. This
method of transmission does not provide any guarantee that the data you send will
ever reach its destination. On the other hand, this method of transmission has
a very low overhead and is therefore very popular to use for services that are
not that important to work on the first try. A comparison you can use for this
method is the plain old US Postal Service. You place your mail in the mailbox
and hope the Postal Service will get it to the proper location. Most of the
time they do, but sometimes it gets lost along the way.
Now that you understand what TCP and
UDP are, we can start discussing TCP and UDP ports in detail. Lets move on to
the next section where we can describe the concept of ports better.
TCP and UDP Ports
As you know every computer or device
on the Internet must have a unique number assigned to it called the IP address.
This IP address is used to recognize your particular computer out of the
millions of other computers connected to the Internet. When information is sent
over the Internet to your computer how does your computer accept that
information? It accepts that information by using TCP or UDP ports.
An easy way to understand ports is
to imagine your IP address is a cable box and the ports are the different
channels on that cable box. The cable company knows how to send cable to your
cable box based upon a unique serial number associated with that box (IP
Address), and then you receive the individual shows on different channels
(Ports).
Ports work the same way. You have an
IP address, and then many ports on that IP address. When I say many, I mean
many. You can have a total of 65,535 TCP Ports and another 65,535 UDP ports.
When a program on your computer sends or receives data over the Internet it
sends that data to an ip address and a specific port on the remote computer,
and receives the data on a usually random port on its own computer. If it uses
the TCP protocol to send and receive the data then it will connect and bind
itself to a TCP port. If it uses the UDP protocol to send and receive data, it
will use a UDP port. Figure 1, below, is a represenation of an IP address split
into its many TCP and UDP ports. Note that once an application binds itself to
a particular port, that port can not be used by any other application. It is
first come, first served.
6.Difine computer network ? Is the
combination of two or more computer which hare a common resources like folder,
file ,software and etc.
l
Discus the
various types of networks topologies in a computer network? A topology is
a way of “laying out” the network. Topologies can be either physical or
logical. The following are types of computer network topology Bus
l
A bus is the
simplest physical topology. It consists of a single cable that runs to every
workstation
l
This topology
uses the least amount of cabling, but also covers the shortest amount of
distance.
l
Each computer
shares the same data and address path. With a logical bus topology, messages
pass through the trunk, and each workstation checks to see if the message is
addressed to itself. If the address of the message matches the workstation’s
address, the network adapter copies the message to the card’s on-board memory.
Star Topology
l
A physical star
topology branches each network device off a central device called a hub,
making it very easy to add a new workstation.
l
Also, if any
workstation goes down it does not affect the entire network. (But, as you might
expect, if the central device goes down, the entire network goes down.)
l
Some types of
Ethernet and ARCNet use a physical star topology. Figure 8.7 gives an example
of the organization of the star network.
Ring
l
Each computer
connects to two other computers, joining them in a circle creating a
unidirectional path where messages move workstation to workstation.
l
Each entity
participating in the ring reads a message, then regenerates it and hands it to
its neighbor on a different network cable.
Mesh
l
The mesh
topology is the simplest logical topology in terms of data flow, but it is
the most complex in terms of physical design.
l
In this physical
topology, each device is connected to every other device
l
This topology is
rarely found in LANs, mainly because of the complexity of the cabling.
l
If there are x
computers, there will be (x × (x–1)) ÷ 2 cables in the
network. For example, if you have five computers in a mesh network, it will use
5 × (5 – 1) ÷ 2, which equals 10 cables. This complexity is compounded when you
add another workstation.
l
For example, your
five-computer, 10-cable network will jump to 15 cables just by adding one more
computer. Imagine how the person doing the cabling would feel if you told them
you had to cable 50 computers in a mesh network—they’d have to come up with 50
× (50 – 1) ÷ 2 = 1225 cables!. The following table shows the advantages and
disadvantage of topologies
|
Topology
|
Advantages
|
Disadvantages
|
|
Bus
|
Cheap. Easy to install.
|
Difficult to reconfigure.
Break in bus disables
entire network.
|
|
Star
|
Cheap. Easy to install.
Easy to reconfigure.
Fault tolerant.
|
More expensive than bus.
|
|
Ring
|
Efficient. Easy to install.
|
Reconfiguration difficult.
Very expensive.
|
|
Mesh
|
Simplest. Most fault tolerant.
|
Reconfiguration extremely difficult.
Extremely expensive.
Very complex.
|
(h)
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