1. 901325 Data Communications & Networking
Chapter 1
Introduction
الثاني 2014/2015

2. Data Communication & Networking
Sharing information.
Sharing can be local (face to face) or remote (over distance)
Tele communication
(telephone, television, telegraphy) means communication at a distance remote communication. (tele: far)
Data communication:
exchange of data between two devices via transmission medium (wire cable)
Communicating devices
made up of : H.W( physical equipments )and S.W

3. Why Study Data Communication & Networking?
Because Data Communication & Networking are changing the way we do business and the way we live
Require immediate access to accurate information
Database, online shopping
Enable long distance communication
Internet, IP phone
Access variable of information (text, voice and image)
, messenger, video conference

4. Networks
Network
is a collection of computers and devices (Nodes) connected by communications channels that facilitates communications among users and allows users to share resources with other users
A node can be a computer, printer, or any other device can capable of sending and/or receiving data generated by other nodes on the network.
Nodes attached to media through NIC (network interface card)
Distributed Processing
Most network uses distributed processing , in which a task is divided among multiple computers. Instead of a single machine responsible for all aspects of a process, separate

5. Network Components Software components Communication Protocols
Network Operating System- NOS
peer-to-peer (Windows Xp,Win7)
Client-server (Windows server 2003 وLinux)
Hardware components
Server
Workstations
Connecting Devices
Cabling system
Shared resource & peripherals

6. A Data Communication Model
Protocol
is a set of rules that governs data communications. It represents an agreement between the communicating devices.
Without a protocol two devices may be connected but not communicating

7. Key elements Protocols
Protocols are set of rules that govern data communication to define
What is communicated?
How it communicated?
When it is communicated?
Key elements
Syntax
Structure or format of the data, meaning the order in which they are presented
Example: A simple protocol might expect the first byte of data to be the address of the sender, the second byte to be the address of the receiver and the reset of the stream to be the message itself.
Semantics
Refers to the meaning of each section of bits.
Example: does an address identify the route to be taken or the final destination of the message
Timing
When data to should be sent?
How fast they can be sent?
If a sender produces data at 100Mpbs but the receiver can process data at only 1Mpbs, transmission will overload the receiver and data will be largely lost

8. Standards Organizations
provides a model for development
allows for interoperability
Types
De jure/Formal
legislated by an officially recognized body
De facto
Have been adopted as standers through widespread use
Established by manufacturers that define the functionality of a new product or technology
Standards Organizations
International Organization for Standardization (ISO)
International Telecommunication Union Telecommunication standard sector ( ITU-T)
American National Standards Institute (ANSI)
Institute of Electrical and Electronics Engineers (IEEE)
Electronic Industries Association (EIA)

9. Data Representation represented as a bit pattern; codes often used
Text
represented as a bit pattern; codes often used
ASCII: 7-bit pattern (128 different symbols)
Extended ASCII: 8-bit pattern (with an extra 0 at left from to
Unicode:32 bits pattern (65,536,216) symbols, which is definitely enough to represent any symbol in the world
ISO
Numbers
represented by binary equivalent
Images
represented by matrix of pixels, small dot.
The size of pixel represent the resolution
One method to represent color images is RGB
Audio represent sound by continuous (analog) signal
Video

10. History of Internet
Experimental work was funded by the U.S. DoD Advanced Research Projects Agency (DARPA).
The goal was to connect the major universities together to share computing resources for improving the cooperation of scientists in joint projects & publications.
ARPA contracted with BBN Corp. (formerly Bolt, Beranek and Newman) to develop “ARPAnet”. This was the first ever network that was developed by DoD.
The first program was created in NSF created a CNET connecting the academic researchers together.
In 1985 the defense withdraw from the network and it became funded by US National Science Foundation. The network was called NSFNET with linked many of the universities, Research labs, Libraries to access their super computers thus establishing the communication. The network grew very rapidly.
It was turned over to private Internet Service Providers (ISP) in 1995.
In early 90’es a new information service, www was developed at CERN by Timothy Berners-Lee. With the graphical browser it changed the whole picture as multimedia capabilities became possible.
Finally giving rise to INTERNET connecting millions of computers together

11. Effectiveness of data communication depends on
Delivery
System must deliver data to correct destination. Data must be received by only intended device or user.
Accuracy
Data delivered accurately
Altered data which left uncorrected are unusable.
Timeliness
Data delivered in timely manner without delay (real-time)
Jitter
variation in packet arrival time, It is the uneven delay in the delivery of audio or video packets

12. Direction of Data Flow Simplex
communication is unidirectional. (one-way-street). Only one of the two devices on a link can transmit; the other can only receive, As Keyboard and monitors
Half-duplex
Each station can both transmit and receive , but not at the same time. When one device is sending the other can receive and vice versa. one-lane road with two direction)
Full-duplex
Both stations can transmit and receive simultaneously. ( telephone network)
Like two way street with traffic flowing in both directions at the same time
Signals going in either direction share the capacity of the link in two ways:
Either the link must contain two physically separate transmission paths one for sending and other for receiving.
Capacity of the channel is divided between signals traveling in both direction

13. Connecting devices
Divided into 5 different categories based on the layer in which they operate in a network
Below the physical layer: passive hub
At the physical layer: repeater or active hub
At the physical and data link layers: bridge or two-layer switch
At the physical, data link, network layers: router or three-layer switch
At all five layers: gateway

14. Passive Hub Passive hub is just a connector.
In a star-topology Ethernet LAN, it is just a point where signals coming from different stations collide.
The hub is the collision point.
This type of hub is part of the media
its location in the Internet model is below the physical layer.

15. Repeaters Operates only in the physical layers
Can extend the physical length of a LAN
Receive the signal before it becomes too weak or corrupted and regenerates the original bit pattern
Do not actually connect two LANs
connects two segments of the same LAN
Segments connected are still part of one single LAN
A repeater cannot connect two LANs of different protocols

16. Repeaters Operates only in the physical layers
Can extend the physical length of a LAN
Receive the signal before it becomes too weak or corrupted and regenerates the original bit pattern
While, Amplifiers, Cannot discriminate between the intended signal and noise. It amplifies equally everything fed into I
Do not actually connect two LANs
connects two segments of the same LAN
Segments connected are still part of one single LAN
A repeater cannot connect two LANs of different protocols

17. Example repeater can overcome 10Base5 Ethernet length restriction
the length of the cable is limited to 500 m
divide the cable into (500 m) sections and connect them with repeaters
The whole network is still considered one LAN
Portions of the network separated by repeaters are called segments
Repeaters acts as two-port node and has no filtering capability

18. Active Hubs Actually a multiport repeater
Used to create connections between stations in a physical star topology
Can also be used to create tree topology to removes the length limitation of 10Base -T (100 m)

19. Example repeater can overcome 10Base5 Ethernet length restriction
the length of the cable is limited to 500 m
divide the cable into (500 m) sections and connect them with repeaters
The whole network is still considered one LAN
Portions of the network separated by repeaters are called segments
Repeaters acts as two-port node and has no filtering capability

20. Bridge
device that connects two LAN segments together, which may be similar or dissimilar, such as Ethernet and Token Ring. A bridge is inserted in the network to keep traffic contained within the segments to improve performance
Operates in both the physical and the data link layer
Physical layer : regenerates the signal
Data link layer : check the physical (MAC) addresses (source & destination) contained in the frame
Bridge has filtering capability, but repeaters has not.
Checks the MAC (physical) address of the destination when receives a frame, and decide if the frame should be forwarded or dropped
forwards the new copy only to the segment (specific port) to which the address belongs
Bridge has a table that maps addresses to the port.

21. Bridge Bridge has a table to Maps address to ports.
Used in filtering decisions

22. Transparent Bridges
Bridges in which the stations are completely unaware of the bridge’s existence. the stations does not reconfigured when a bridge is added or deleted
A system equipped with transparent bridges must meet three criteria:
Frame must be forwarded correctly one station to another.
The forwarding table is automatically made by learning frame movements in the network.
Loops in the system must be prevented.
Learning:
early bridges had static forwarding table
Administrated manually enter each table entry
simple, but not practical
better solution
dynamic table management that maps addresses to ports automatically
bridge gradually learns from the frame movement

23. Transparent Bridges
Destination physical address: used for the forwarding decision (table lookup).
Source physical address: used for adding entries to the table and for updating purposes.
A sends frame to D:flooding
E sends a frame to A: Forwarding
B sends a frame to C :flooding

24. Transparent Bridges Loop problem
bridges are normally installed redundantly to make the system more reliable
Two LANs may be connected by more than one bridge
they may create a loop packet may be going round and round

25. Bridges: Spanning Tree
Is graph in which there is no loop
Create a topology in which each LAN can be reached from any other LAN through one path only (no loop)
Create a logical topology that overlays physical topology which can not be changed
To find the spanning tree we need to Assign a cost (metric) to each LAN
The interpretation of the cost is left up to network admin
It may be the path with :
Minimum hops, (shortest distance)
Minimum delay, or maximum bandwidth

26. Spanning Tree with Minimum hops
The hop count is normally 1 from a bridge to the LAN and 0 in the reverse direction

27. Connecting Devices Network Interface cards

28. Connecting Devices Wireless Bridge
device that connects two LAN segments together via infrared or microwave transmission. A wireless bridge is often used to span buildings and provides a more economical method than laying cable or leasing a private line

29. Network Criteria Performance – depends on Reliability – measured by
Number of user
Type of transmission media,
Capabilities of connected H.W and the efficiency of software
Reliability – measured by
Frequency of failure
The time it takes to recover from failure
Network’s robustness in a catastrophe
Security
Protection from unauthorized access and Viruses

30. TYPE OF CONNECTION Point to point Multipoint
A dedicated link is provided between two devices
Most of them uses an actual length of wire or cable to connect the two ends but other options ,such as microwave satellite are possible
Multipoint
More than two devices share a single line.
The capacity is shared either spatially or temporally.
Spatially: Several devices can use link simultaneously
Temporally: Users take turns , it is a timeshared
Point – to – point connection
Multipoint connection

31. Topology Physical topology Logical topology is how the signal travels.
Is how the wires are run
The way in which a network is laid out physically
Logical topology is how the signal travels.
A device can be wired to implement any logical topology.
LANs are logical busses or rings, depending on how the hub is wired
4 basic types: mesh, star, bus, ring
The most common physical topology is the star.
All the wires come back to a central point
May often see hybrid

32. Mesh Topology
Every device has a dedicated point-to-point link to every other devices in network
Mesh topology often used in MANs and WANs
A fully connected mesh network has n(n-1)/2 physical channels to link n devices, Every device on the network must have n-1 I/O ports
Advantage
Privacy or security(every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevents other user from gaining access the message
eliminating the traffic problems. The use of dedicated links guarantees that each connection can carry its own data load; that can occur when links must be shared by multiple devices.
A mesh is robust. If one link becomes unusable, it does not incapacitate the entire system.
Fault identification and fault isolation easy. This enables the network manager to discover the precise location of fault and aids in finding its cause and solution.
Disadvantage
Need more resource (cable & ports)
Expensive to implement

33. Easy to install and reconfigure and less expensive
Star Topology
Each device has a dedicated point-to-point link only to a central device (hub, switch, router)
No direct traffic and link between devices
Advantages of star topology
Easy to install and reconfigure and less expensive
Each device need only one link and I/O port to connect it to any other devices.)
Robustness, If one link fails, only that link affected and other links remain active.
Identification and fault isolation
Disadvantages of star topology
Failure of central device may cause network failure
Requires more cable than (Ring ,bus)

34. Tree topology Is a variation of star
Not every device plugs directly into the central hub. The majority of devices connect to secondary hub that in turn is connected to the central hub
The advantages and disadvantages of tree topology are generally the same as those of star.
The addition of secondary hubs bring more advantage:
Allow more devices to be attached to a single central hub, therefore increase the distance a signal can travel between devices.

35. Bus Topology A multipoint topology
Consists of cables connecting PCs or file servers
Terminator attached to each end of bus cable segment
to absorb signal and prevent signal reflection back on to covered path
Transmitting packet across bus
Detected by all nodes on segment
Given time limit to reach destination
Advantages of bus design
Requires less cable than other topologies
Easy to install and extend bus with a workstation
Disadvantages of bus topology
Not secured
Can become quickly congested with network traffic
A fault in bus cable stops all transmissions even between devices on the same side of the problem. The damaged area reflects signals back the direction of origin, creating noise in both directions
It can difficult to add new devices (adding more require modification of the backbone).

36. Ring Topology
Each device is dedicated point-to-point connection only with the two devices on either side of it
Signal is passed from device to device until it reaches destination
Each device functions as a repeater
Advantage
Relatively easy to install and reconfigure
Fault isolation is simplified
Disadvantage
Unidirectional traffic
A break in the ring can disable the entire network. This can be solved by use dual ring
Hybrid topology

37. Networks Categories
Network category is determined by its size, ownership, the distance it cover and its physical architecture

38. LAN
Privately owned and links the devices in a single office, building or campus
LANs designed to allow resources to be shared between PCs or workstations. The resources may be H.W or S.W or data.
In LANs one of the computers has a large capacity drive and becomes a server to other clients.
SW stored on server and used as needed by the whole group.
LAN size determined by licensing restrictions( No of users per copy of SW)
LAN use only one type of transmission medium.
The most common LAN topologies are bus, ring and star.
Today, LAN speed can be 100Mbps or 1000MBps(1G)

39. MAN
Owned by private company or it may be a service provided by public company ( such as local tel.-company)
Extended over an entire city.
May be single network such as a cable television network, or it may be connected number of LANs into a large network so that resources may be shared LAN-TO-LAN.
Examples:
Company can use MAN to connect the LANs in all its offices throughout the city.
A part of the telephone line network that can provide DSL line to the customer

40. WAN
Provides long distance transmission of data, voice , image and video information over large areas ( country or whole world)
In contrast to LAN, WAN may utilize public or private communication equipment's or combination

41. Switched and a Point-to-point WAN

42. Categories of Networks Based on Control
Peer-to-Peer Network
No single computer controls the network.
Each computer is the same (a peer) to all others
It is suitable for small offices.
Server-Based Network
The network is controlled by a special high-powered server.
The server is dedicated to running the network.
Print and file servers, application servers, communication servers, and directory service servers are common.

43. Interconnections of networks : internetwork
An internet (small i) is two or more networks that can
communicate with each other