1. Data and Communication Systems
Lecture 1
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Engr. Ahmad Bilal
Assistant Professor
University of Lahore

2. What is Internet
Internet is a combination of millions of devices, connected together , and are enable to send or receive data . Simply Internet can be termed as “Networks of Network:” Internet is the best revolution and example of data communication .
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3. What is Network
A network is a mixture / collection of hardware , software, protocols and transmission media , which are able to connect to different devices.
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4. Networking
Computer networks have opened up an entire frontier in the world of computing called the client/server model

5. What are the responsibilities of network
Transmission system utilization need to make efficient use of transmission facilities typically shared among a number of communicating devices
A device must interface with the transmission system
once an interface is established, signal generation is required for communication
Most networks use distributed processing, in which a task is divided among multiple computers.
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6. What are the responsibilities of network
There must be synchronization between transmitter and receiver, to determine when a signal begins to arrive and when it ends
Error detection and correction are required in circumstances where errors cannot be tolerated
Flow control is required to assure that the source does not overwhelm the destination by sending data faster than they can be processed and absorbed
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7. What are the responsibilities of network
Addressing and routing, so a source system can indicate the identity of the intended destination, and can choose a specific route through this network
Message formatting has to do with an agreement between two parties as to the form of the data to be exchanged or transmitted
Frequently need to provide some measure of security in a data communications system
Network management capabilities are needed to configure the system, monitor its status, react to failures and overloads, and plan intelligently for future growth
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8. Examples of Networks
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9. Some Important Key Terms
Host An end device that normally initiates a connection Data Transfer rate The Speed at which date moves or is transmitted File server A computer dedicated to storing and managing files for network users Web server A computer dedicated to responding to requests made by host
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10. Type of Networks
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11. Classification by scale

12. Personal Area Network (PAN)
Very small scale network
Range is less than 2 meters
Cell phones, PDAs, MP3 players

13. Local Area Networks
Privately owned. Can be up to several kilometers long;
Ex. in a building
Size: Restricted so worst case transmission time can be contained.
Transmission technology: Single channel with multiple machines connected to it. Run at speeds of 10, 100, or more Mbps.
Topology: two popular broadcast networks:
Bus
Ring
A LAN is a communications network that interconnects a variety of devices and provides a means for information exchange among those devices. The scope of the LAN is small, typically a single building or a cluster of buildings. It is usually the case that the LAN is owned by the same organization that owns the attached devices. The internal data rates of LANs are typically much greater than those of WANs.
LANs come in a number of different configurations. The most common are switched LANs and wireless LANs. The most common switched LAN is a switched Ethernet LAN, others are ATM & Fibre Channel LANs. Wireless networks provide advantages in the areas of mobility and ease of installation and configuration.

14. Metropolitan Area Networks
Larger version of LAN ("city" wide).
Public or private / data or voice.
middle ground between LAN and WAN
high speed
large area
Ex. A metropolitan area network based on cable TV

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16. Wide Area Networks span a large geographical area
cross public rights of way
rely in part on common carrier circuits
alternative technologies used include:
circuit switching
packet switching
frame relay
Asynchronous Transfer Mode (ATM)
Wide area networks generally cover a large geographical area, require the crossing of public right-of-ways, and rely at least in part on circuits provided by a common carrier. Typically, a WAN consists of a number of interconnected switching nodes. Traditionally, WANs have been implemented using one of two technologies: circuit switching and packet switching. More recently, frame relay and ATM networks have assumed major roles.

17. Wide Area Networks
Ex. A stream of packets from sender to receiver.

18. Circuit Switching
uses a dedicated communications path established for duration of conversation
comprising a sequence of physical links
with a dedicated logical channel
eg. telephone network
In a circuit-switching network, a dedicated communications path is established between two stations through the nodes of the network. That path is a connected sequence of physical links between nodes, with a logical channel dedicated to the connection. Data generated by the source station are transmitted along the dedicated path as rapidly as possible. The most common example of circuit switching is the telephone network.

19. Timing in Circuit Switching
Information
Host 1
Host 2
Switch 1
Switch 2
Transmission delay
propagation delay
between Host 1
and Switch1
Circuit Establishment
propagation delay
between Host 1
and Host 2
Transfer
time
Circuit Teardown

20. Circuit Switching With Human Operator

21. Advantages
1. The dedicated path/circuit established between sender and receiver provides a guaranteed data rate. 2. Once the circuit is established, data is transmitted without any delay as there is no waiting time at each switch. 3. Since a dedicated continuous transmission path is established, the method is suitable for long continuous transmission.
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22. Disadvantages
The various disadvantages of circuit switching are: 1. As the connection is dedicated it cannot be used to transmit any other data even if the channel is free. 2. It is inefficient in terms of utilization of system resources. As resources are allocated for the entire duration of connection, these are not available to other connections. 3. Dedicated channels require more bandwidth. 4. Prior to actual data transfer, the time required to establish a physical link between the two stations is too long.
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23. Packet Switching data sent out of sequence
small chunks (packets) of data at a time
packets passed from node to node between source and destination
used for terminal to computer and computer to computer communications
A packet-switching network uses a quite different approach, without need to dedicate transmission capacity along a path through the network. Rather, data is sent in a sequence of small chunks, called packets. Each packet is passed through the network from node to node along some path leading from source to destination. At each node, the entire packet is received, stored briefly, and then transmitted to the next node. Packet-switching networks are commonly used for terminal-to-computer and computer-to-computer communications.

24. Connection-Oriented and Connectionless Services (1)
Connection oriented service:
Like the phone system. The system establishes a connection, uses it, and closes it. Acts like a tube. Data comes out the other end in the same order as it goes in.
Connection Setup
Data Transfer
Connection Termination
Connectionless service:
Like the post office. Each message has the entire address on it. Each message may follow a different route to its destination. Ordering not maintained.

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26. The Internet Internet evolved from ARPANET
first operational packet network
applied to tactical radio & satellite nets also
had a need for interoperability
led to standardized TCP/IP protocols
The Internet evolved from the ARPANET, developed in 1969 by the Advanced Research Projects Agency (ARPA) of the U.S. Department of Defense. It was the first operational packet-switching network. The network was so successful that ARPA applied the same packet-switching technology to tactical radio communication (packet radio) and to satellite communication (SATNET). The need for interworking between these led to Vint Cerf and Bob Kahn of ARPA developing methods and protocols for such internetworking, which led eventually to the development of TCP/IP.

27. Internet Elements
Stallings DCC8e Figure 1.4 illustrates the key elements that comprise the Internet, whose purpose is to interconnect end systems, called hosts; including PCs, workstations, servers, mainframes, and so on. Most hosts that use the Internet are connected to a network, such as a local area network (LAN) or a wide area network (WAN). These networks are in turn connected by routers.

28. Internet Architecture
The Internet today is made up of thousands of overlapping hierarchical networks, an overview of the common, general characteristics can be made. Stallings DCC8e Figure 1.5 illustrates this. See hosts grouped into LANs, linked to an an Internet service provider (ISP) through a point of presence (POP). The connection is made in a series of steps starting with the customer premises equipment (CPE). ISPs can be classified as regional or backbone, with peering links between.

29. Example Configuration
Stallings DCC8e Figure 1.6 illustrates some of the typical communications and network elements in use today. In the upper-left-hand portion of the figure, we see an individual residential user connected to an Internet service provider (ISP) through some sort of subscriber connection. The Internet consists of a number of interconnected routers that span the globe. The routers forward packets of data from source to destination through the Internet. The lower portion shows a LAN implemented using a single Ethernet switch. This is a common configuration at a small business or other small organization.

30. LAN topologies Physical
Describes the geometric arrangement of components that make up the LAN

31. Bus LAN Transmission Logic
Listen to the bus for traffic
If no traffic is detected, then transmit
Otherwise, if the bus is busy with traffic, wait for a random period of time before attempting to transmit again
Repeated attempts will be made until the bus is found free

32. Bus topology
All networked nodes are interconnected, peer to peer, using a single, open-ended cable Both ends of the bus must be terminated with a terminating resistor to prevent signal bounce

33. Bus topology

34. Advantages of Bus LAN
Cabling is simple and easy to install in a local setup
Based on well established standards
IEEE 802.3
Also known as the Ethernet standard

35. Advantages of Bus topology
Easy to implement and extend
Well suited for temporary networks that must be set up in a hurry
Typically the least cheapest topology to implement
Failure of one station does not affect others

36. Collision of Data
Two workstations may find the bus free at the same time
Both would transmit at the same time
Collision of data occurs
Both workstations will now wait for a random period of time before attempting to transmit again

37. Disadvantages of Bus topology
Difficult to administer/troubleshoot
Limited cable length and number of stations
A cable break can disable the entire network; no redundancy
Maintenance costs may be higher in the long run
Performance degrades as additional computers are added

38. A Typical Installation
BNC Jack
Thin Coaxial Cable
T Connector
Terminator
Expansion
Slots

39. 10Base5 Feeder Connection
10Base 5 Feeder Line
10Base2
Clusters
Source: Black Box

40. MODULE
Topology: The Ring LAN

41. Ring topology
started out as a simple peer-to-peer LAN topology Each networked workstation had two connections: one to each of its nearest neighbors Data was transmitted unidirectionally around the ring Sending and receiving of data takes place by the help of TOKEN

42. Token Passing
Token contains a piece of information which along with data is sent by the source computer
This token then passes to next node, which checks if the signal is intended to it
If yes, it receives it and passes the empty to into the network
otherwise passes token along with the data to next node

43. Ring topology

44. Advantages of Ring topology
This type of network topology is very organized
Performance is better than that of Bus topology
No need for network server to control the connectivity between workstations
Additional components do not affect the performance of network
Each computer has equal access to resources

45. Disadvantages of Ring topology
Each packet of data must pass through all the computers between source and destination, slower than star topology
If one workstation or port goes down, the entire network gets affected
Network is highly dependent on the wire which connects different components

46. Ring LAN : Practical Implementation
Multi-Access Unit (MAU) Or Hub
Server WS
Physical Star/ Logical Ring

47. Ring LAN Advantages Orderly transmission of data
Guarantees an opportunity for each workstation to transmit
Performance deterioration is not as critical as in the case of the bus LAN
Data traffic congestion is minimized
Gradual decline in performance with increased load
A good topology for larger LANs
Used as a backbone in large enterprise networks

48. MODULE
Star Topolgy

49. Star topology
Have connections to networked devices that “radiate” out form a common point Each networked device in star topology can access the media independently Have become the dominant topology type in contemporary LANs Stars have made buses and rings obsolete in LAN topologies

50. Star topology

51. Advantages of star topology
Compared to Bus topology it gives far much better performance
Easy to connect new nodes or devices
Centralized management. It helps in monitoring the network
Failure of one node or link doesn’t affect the rest of network

52. Disadvantages of star topology
If central device fails whole network goes down
The use of hub, a router or a switch as central device increases the overall cost of the network
Performance and as well number of nodes which can be added in such topology is depended on capacity of central device

53. Daisy chains
Developed by serially interconnecting all the hubs of a network This simple approach uses ports on existing hubs for interconnecting the hubs Daisy chains are easily built and don’t require any special administrative skills Daisy chains were, historically, the interconnection method of choice for emerging, first-generation LANs

54. Daisy chains

55. Disadvantage of Daisy chain
Increases the number of connections, and therefore the number of devices, on a LAN. Too many devices competing for the same amount of bandwidth can create collisions and quickly incapacitate a LAN

56. Hierarchical rings

57. Hierarchical stars
Star topologies, can be implemented in hierarchical arrangements of multiple stars Hierarchical stars can be implemented as a single collision domain or segmented into multiple collision domains using switches, routers or bridges

58. Hierarchical stars

59. Hierarchical combinations
Overall network performance can be enhanced by not force-fitting all the functional requirements of the LAN into a single solution Today’s high-end switching hubs enable you to mix multiple technologies

60. Hierarchical combinations