8/20/2019 Ccn Unit1 VTU Raghudathesh http://slidepdf.com/reader/full/ccn-unit1-vtu-raghudathesh 1/51 COMPUTER COMMUNICATION NETWORK (VTU) - 10EC71 UNIT - 1 Layered tasks, OSI Model, Layers in OSI model, TCP/IP Suite, Addressing, Telephone and cable networks for data transmission, Telephone networks, Dial up modem, DSL, Cable TV for data transmission. 7 Hours TEXT BOOKS: 1. Data Communication and Networking, B Forouzan, 4 th Ed, TMH 2006. 2. Computer Networks, James F. Kurose, Keith W. Ross: Pearson education, 2 nd Edition, 2003. 3. Introduction to Data communication and Networking, Wayne Tomasi: Pearson education 2007. Special Thanks To: Faculty (Chronological): Arun A Badiger (GMIT Davengere), Dr. Manjunath N (JNNCE Shimoga), Harisha G C (GMIT Davangere), Suresha V Sathegala (KVGCE Sullia) Students: BY: RAGHUDATHESH G P Asst Prof ECE Dept, GMIT Davangere 577004 Cell: +917411459249 Mail: [email protected]Quotes: Change is hard at first, messy in the middle and gorgeous at the last. Forget what hurt you, but never forget what it taught you. People change, love hurts, friends leave, things go wrong. But just remember that life goes on. Effort is important but where to make an effort makes all the difference. All my life I thought air was free, until I bought a bag of chips. People won’t remember days but they remember the moments with you. Unit 1 RAGHUDATHESH G P Asst Professor Department of ECE raghudathesh.weebly.com Page No - 1
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Scenario: let us consider two friends who communicate through postal mail. The figure below
shows the steps in this task.
Figure: Tasks involved in sending a letter
The process of sending a letter to a friend would be complex if there were no services
available from the post office.
The task includes a sender, a receiver, and a carrier that transports the letter.
There is a hierarchy of tasks:
1. Higher Layer
2. Middle Layer and
3. Lower Layer.
Activities that take place at each layer at each side is described below:
At the Sender Site:
H igher Layer: the sender writes the letter, inserts the letter in an envelope, writes
the sender and receiver addresses, finally drops the letter in a mailbox. Middle Layer: the letter is picked up by a letter carrier and delivered to the post
office.
Lower l ayer: the letter is sorted at the post office; a carrier transports the letter.
On the Way:
The letter is then on its way to the recipient.
On the way to the recipient’s local post office, the letter may actually go through a
central office.
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In addition, it may be transported by trunk, train, airplane, boat, and/or a
combination of these.
At the Receiver Site:
Lower L ayer: The carrier transports the letter to the post office.
Middle Layer: The letter is sorted and delivered to the recipient’s mailbox.
H igher Layer: the receiver picks up the letter, opens the envelope, and reads it. Each layer performs specific tasks and uses the services of the layer immediately
below it.
Layered networking model is advantageous because
1. Divides networking into less complex components
2. Enables programmers to specialize in a particular level
3. Allows upgrades to a specific layer without effecting other layers
4. Encourages interoperability
5. Allows for standardized interfaces
Definition:
Open System: It is a set of protocols that allows any two different systems to communicate
regardless of their underlying architecture.
The OSI Reference Models:
It was first introduced in the late 1970s.
It is expanded as Open Systems Interconnection model.
It was developed by International Standards Organization (ISO).
The Open Systems Interconnection (OSI) model is an ISO standard that covers all aspects
of network communications.
The purpose of the OSI model:
To show how to facilitate communication between different systems without
requiring changes to the logic of the underlying hardware and software.
The OSI model is not a protocol; it is a model for understanding and designing
a network architecture that is flexible, robust, and interoperable.
The OSI model is a layered framework for the design of network systems thatallows communication between all types of computer systems.
Advantages of Reference Models:
It divides the network communication process into smaller and simpler
components, thus aiding component development, design, and troubleshooting.
It allows multiple-vendor development through standardization of network
components.
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Figure below hop-to-hop (node-to-node) delivery by the data link layer
Figure: Hop-to-Hop deliveries
As the figure above shows, communication at the Data Link layer occurs between two
adjacent nodes. To send data from A to F, three partial deliveries are made. First, the DLL at A sends a frame to the DLL at B (a router). Second, the data link layer
at B sends a new frame to the data link layer at E. Finally, the DLL at E sends a new
frame to the DLL at F.
Here the frames that are exchanged between the three nodes have different values in the
headers. The frame from A to B has B as the destination address and A as the source
address. The frame from B to E has E as the destination address and B as the source
address. The frame from E to F has F as the destination address and E as the source
address.
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This layer is responsible for source to destination delivery of individual packet may be
across multiple networks/links.
Figure: Network layer
Other responsibilities of network layer include:
Logical addressing:
Physical address used in data link layer handles addressing locally i.e., within the
network.
If the packet moves out of the network then network layer adds the header to the
packet coming from upper layer which specifies the address of the sender and the
receiver which are present on the different network.
Routing:
Various independent networks/links are interconnected to form a large
network/internetwork; packets are delivered to the destination through differentnetwork using routers/switches. This is one of the basic functions of the network
layer.
Figure below shows the source to destination delivery by the network layer.
Figure: Source-to-destination delivery
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The size and format of these addresses vary depending on the network.
Ex., Ethernet uses a 6-byte (48-bit) physical address that is imprinted on the network
interface card (NIC). LocalTalk (Apple), however, has a 1-byte dynamic address that
changes each time the station comes up.
Scenario: In Figure a node with physical address 10 sends a frame to a node with
physical address 87, The two nodes are connected by a link (bus topology LAN). At thedata link layer, this frame contains physical (link) addresses in the header. These are the
only addresses needed. The rest of the header contains other information needed at this
level. The trailer usually contains extra bits needed for error detection. As the figure
shows, the computer with physical address 10 is the sender, and the computer with
physical address 87 is the receiver. The data link layer at the sender receives data from an
upper layer. It encapsulates the data in a frame, adding a header and a trailer. The header,
among other pieces of information, carries the receiver and the sender physical (link)
addresses. Note that in most data link protocols, the destination address, 87 in this case,
comes before the source address (10 in this case).
Figure: Physical addresses
Most local-area networks use a 48-bit (6-byte) physical address written as 12hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown
below:
07:01:02:01:2C:4B
In order to find the physical/link/MAC address of your system go to command prompt
and type ipconfig/all, the following information will be displayed as shown below
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Scenario: Figure below shows a part of an internet with two routers connecting three
LANs.
Each device has a pair of addresses (logical and physical) for each connection. In this
case, each Computer is connected to only one link and therefore has only one pair of
addresses. Each router, however, is connected to three networks (only two are shown in
the figure). So each router has three pairs of addresses, one for each connection. The physical addresses will change from hop to hop, but the logical addresses usually remain
the same.
Figure: IP addresses
In order to find the logical/IP address of your system go to command prompt and type
ipconfig/all, the following information will be displayed as shown below
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Thus, for these above processes to receive data simultaneously, we need a method to
label the different processes. In other words, they need addresses.
In the TCP/IP architecture, the label assigned to a process is called a port address.
A port address in TCP/IP is 16 bits in length represented by one decimal number like
753.
Scenario: Figure below shows two computers communicating via the Internet. Thesending computer is running three processes at this time with port addresses A, B, and c.
The receiving computer is running two processes at this time with port addresses j and K.
Process A in the sending computer needs to communicate with process J in the receiving
computer.
Note: although physical addresses change from hop to hop, logical and port addresses
remain the same from the source to destination.
Figure: Port addresses
The port numbers are divided into three ranges:
1. Well-known ports.
2. Registered ports.
3. Dynamic/private ports.
In your machine Port number is seen as below
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The telephone network had its beginnings in the late 1800s.
Telephone networks were originally created to provide voice communication.
Telephone networks use circuit switching.
The entire network, which is referred to as the plain old telephone system(POTS), was originally an analog system using analog signals to transmit voice.
With the advent of the computer era, the network, in the 1980s, began to carry
data in addition to voice.
During the last decade, the telephone network has undergone many technical
changes. The network is now digital as well as analog.
Major Components:
The telephone network, as shown in figure below
Figure: Telephone system
The telephone network shown in figure above has made three major components:
Local Loops:
A twisted-pair cable that connects the subscriber telephone to the nearest end
office or local central office.
Its B.W is 4 kHz for voice communication.
The first three digits of a local telephone number define the office, and the
next four digits define the local loop number.
Trunks:
These are transmission media that handle the communication between offices.
Trunk normally handles hundreds or thousands of connections through
multiplexing.
Transmission is usually through optical fibers or satellite links.
Switching Offices:
To avoid having a permanent physical link between any two subscribers, the
telephone company has switches located in a switching office.
Switch connects several local loops or trunks and allows a connection
between different subscribers.
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A small state may have one single LATA; a large state may have several LATAs.
A LATA boundary may overlap the boundary of a state or part of a LATA can be in one
state, part in another state.
There are two types of LATAs Services like:1. Intra-LATA Services
2. Inter-LATA Services
Intra-LATA Services:
The services offered by the common carriers (telephone companies) inside a LATA are
called intra-LATA services.
The carrier that handles these services is called a local exchange carrier (LEC).
Before the Telecommunications Act of 1996 intra-LATA services were granted to one
single carrier. This was a monopoly.
After 1996, more than one carrier could provide services inside a LATA.
The carrier that provided services before 1996 owns the cabling system (local loops) and
is called the Incumbent Local Exchange Carrier (ILEC).The new carriers that can provide
services are called Competitive Local Exchange Carriers (CLECs).
CLECs would provide other services such as mobile telephone service, toll calls inside a
LATA, and so on. Communication inside a LATA is handled by end switches and
tandem switches.
A call that can be completed by using only end offices is considered toll-free. A call that has to go through a tandem office (intra-LATA toll office) is charged.
Figure: Switching offices in a LATA
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The network uses a combination of fiber-optic and coaxial cable.
The transmission medium from the cable TV office to a box, called the fiber node, is
optical fiber; from the fiber node through the neighborhood and into the house is stillcoaxial cable. Figure below shows a schematic diagram of an HFC network.
Figure: Hybrid fiber-coaxial (HFC) network
The Regional Cable Head (RCH) normally serves up to 400,000 subscribers.
The RCHs feed the distribution hubs, each of which serves up to 40,000 subscribers.
Modulation and distribution of signals are done in the distribution hub; the signals are
then fed to the fiber nodes through fiber-optic cables.
The fiber node splits the analog signals so that the same signal is sent to each coaxial
cable. Each coaxial cable serves up to 1000 subscribers.
The use of fiber-optic cable reduces the need for amplifiers down to eight or less.
Communication in an HFC cable TV network can be bidirectional.
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Both upstream and downstream bands are shared by the subscribers.
Upstream Sharing:
The upstream data bandwidth is 37 MHz.
Only six 6-MHz channels available in the upstream direction.
A subscriber needs to use one channel to send data in the upstream direction. The question is, "How can six channels be shared in an area with 1000, 2000, or
even 100, 000 subscribers?" The solution is timesharing.
Downstream Sharing:
The downstream band has 33 channels of 6 MHz.
A cable provider probably has more than 33 subscribers; therefore, each channel
must be shared between a group of subscribers.
3. Cable Mode (CM) and Cable Mode Transmission System (CMTS):
To use a cable network for data transmission, need two key devices:i. Cable Modem (CM)
ii. Cable Modem Transmission System (CMTS).
1. Cable Mode (CM):
Cable modems transfer data across local cable TV lines, toggling between analog
and digital signals with data transfer rates comparable to DSL.
The cable modem connects a computer to the cable company network through the
same coaxial cabling that feeds cable TV (CATV) signals to a television set.
Uses Coaxial TV cable
1 to 10 Mbps download speeds
Up to 2 Mbps upload speeds
Cable connects from NIC to a cable modem, which has an RJ-45 port
Many users connect a router to the cable modem to provide access to several PC’s
or other network devices.
It is installed on the subscriber premises. It is similar to an ADSL modem, as
shown in figure below
Figure: Cable modem (CM)
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2. Which layers in the Internet model are the network support layers?
3. Which layer in the Internet model is the user support layer?
4. What is the difference between network layer delivery and transport layer delivery?5. What is a peer-to-peer process?
6. How does information get passed from one layer to the next in the Internet model?
7. What are headers and trailers, and how do they get added and removed?
8. What are the concerns of the physical layer in the Internet model?
9. What are the responsibilities of the data link layer in the Internet model?
10. What are the responsibilities of the network layer in the Internet model?
11. What are the responsibilities of the transport layer in the Internet model?
12. What is the difference between a port address, a logical address, and a physical address?
13. Name some services provided by the application layer in the Internet model.14. How do the layers of the Internet model correlate to the layers of the OSI model?
15. How are OSI and ISO related to each other?
16. Match the following to one or more layers of the OSI model:
17. What are the three major components of a telephone network?
18. Give some hierarchical switching levels of a telephone network.
19. What is LATA? What are intra-LATA and inter-LATA services?
20. Describe the SS7 service and its relation to the telephone network.
21. What are the two major services provided by telephone companies in the United States?
22. What is dial-up modem technology? List some of the common modem standards and
their data rates.
23. What is DSL technology? What are the services provided by the telephone companies
using DSL? Distinguish between a DSL modem and a DSLAM.
24. Compare and contrast a traditional cable network with a hybrid fiber-coaxial network.
25. How data transfer is achieved using CATV channels?
26. Distinguish between CM and CMTS.
27. Why circuit-switching was chosen for telephone networks?
28. Define end-to-end addressing in a telephone network when two parties communicate.
29. When we have an overseas telephone conversation, we sometimes experience a delay.
Give the reason?
30. Draw a bar chart to compare the different downloading data rates of common modems.
31. Draw a bar chart to compare the different downloading data rates of common DSL
technology implementations (use minimum data rates).
32. Calculate the minimum time required to download one million bytes of information using
each of the following technologies:
a. V32 modem
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e. Format and code conversion services (December 2011, 05 M)
15. What is DSL technology? What are the services provided by the telephone companies
using DSL? Distinguish between DSL and DSLAM (December 2011, 10 M)
16. Describe the ISO OSI reference model of a computer network. Discuss the function of
each layer. (December 2012, 10 M)17. Describe the SS7 service and its relation to the telephone network. (December 2012, 05
M)
18. Distinguish between a DSL modem and a DSLAM. (December 2012, 05 M)
19. Explain briefly with relevant examples, the 4 levels of address that are used in an internet
employing the TCP/IP Protocols. (July 2013, 10 M)
20. Briefly describe the function of physical layer and data link layer. (July 2013, 06 M)
21. Explain the operation of ADSL using Discrete Multitone Technique indicating the
different channels with diagram. (July 2013, 04 M)
22. How do the layers of TCP/IP model correlate to the OSI model?(January 2014, 08M)23. Explain about IxCs with a schematic. What are point of presence?( January 2014, 06M)
24. How ADSL could achieve higher data rate over existing local loops? Explain DSLAM. (