1. Networks & telecommunications
November 11, 2015

2. LEARNING GOALS
Discuss networks communication models and principles of operation
Identify the major hardware and software components used networks.
Identify and explain the various types of computer networks.
Identify the various types of transmission media
Discuss LAN topology and operation 2

3. Networks communication models and operation
Define how the processing takes place on the network
Define the roles of each participating computer
Two primary models:
Client-server
Peer-to-peer (P2P) 3

4. Client-server model Computers are either clients or servers
Clients use services
Servers provide services
File service
service
Printing service
Database service
Etc.
Client software on client node cooperates with server software on server node
The WWW is the largest client/server network 4

5. Client-server model
Collaboration between Client and Server program 5

6. Client-server model Division of Labor
Client program handles lighter work, such as user interface chores and light processing chores
Server program handles heavy work, such as database retrieval
Server
Program
Client Program
Client Machine 6
Server

7. Peer-to-Peer network No dedicated server Computer are equal (peers)
Computers can all receive and provide service
Multiple P2P models over the years
Pure P2P
P2P Viral network
P2P with index server 7

8. Pure P2P network
Each computer must have the appropriate type of protocol & software for interaction with others
Each computer must have a network connection to others
Each computer can connect to any participating computer to get service (e.g. download files)
What can be the major issues associated with P2P networks? 8

9. Note: Response to Init and Seach msg not shown
Pure P2P viral network
Init or search msg
Init or search msg
Init or search msg
Client 2
Client 3
Client 1
Init or search msg
Init or search msg
P2P File download
Note: Response to Init and Seach msg not shown
Client 5
Client 4
Client connects to another client, which connects to several others, and so forth
When client first connects, it sends initiation msg to introduce itself via viral networking
Searches sent by a client are also passed to others through viral networking
When file is found, actual file downloads are done using direct (not viral) communication
Companies offering P2P viral networking service, put in place super clients that are always on with permanent IP addresses 9

10. P2P using Index server
Most common type of P2P networking used in file sharing
Introduced by Napster (now an online music store after law suits)
Relies on an Index server 10

11. Advantages of Network vs. Stand-alone PCs?11

12. Why Networking ? Resource sharing High reliability
Sharing hardware (printers, processors, etc.)
Sharing software (programs, data files)
High reliability
Can easily set automatic backups of programs and data at different locations
Fault tolerance: can duplicate servers so that if one is down, others can provide service. Servers have RAID so that if a disk fails, data available on other disks)
Possible cost savings
Communication tool
Console messages and internal service
Remote Access service 12

13. Computer Network
Once connected to the network, the computer (or another device) becomes a network node
An interconnection of computers and computing equipment using either wires or wireless transmission media over small or large geographical distances.
DEF
GHI
“Connect to GHI”
ABC
JKL
MNO 13

14. Computer Network (cont.)
Based on the definition from the previous slide, what hardware elements are needed to implement a computer network? 14

15. Network scope
Local area network (LAN): computer network where the nodes are all in close proximity spanning a room, building, or campus
Metropolitan area network (MAN): network that serves an area of 3 to 30 miles - approximately the area of a typical city.
Wide area network (WAN): a large network that encompasses parts of states, multiple states, countries, and the world 15

16. Transmission Media Physical media
Wireless
Physical media
Transmission media used to physically connect nodes to the network
Transmits electrical or optical signals
Could be copper wire or fiber optic cable 16

17. Transmission Media (Continued)
Twisted Pair
Category
Use
Signal
Data rate
Distance
Problem
Category 1
Telephone
Analog/Digital
<100Kbps
3-4 miles
Security, noise
Category 2
T1, ISDN
Digital
<2 Mbps
Category 3
LANs
10 Mbps
100 m
Category 4
20 Mbps
Category 5
100 Mhz
Category 6
250 Mhz
Category 7
600 Mhz
Fiber optic
Thin glass fibers surrounded by coating
Uses laser or light for data transmission
Very fast (10+ Gbps, 100 miles without any repeater)
Very secure
Photo receptor
(LED or LD)
Photo diode
(LED or LD)
Destination
Source 17
Fiber optic cable

18. Wireless transmission media
Infrared light
Has many of the same characteristics as visible light
Travels in straight lines
Cannot penetrate solid objects
Radio waves
Travel in straight lines
Can penetrate through nonmetallic objects
Can travel long distances

19. Wireless Media issues
Use electromagnetic waves or electromagnetic radiation for data transmission
Propagation through space, and indirectly, through solid objects
Many problems:
Thick objects can block the direct path. So, Receiver will be in a Shadow zone where it cannot well receive.
Radio waves tend to bounce off objects. Receiver can receive 2 or more signals.
Electromagnetic
Interference (EMI) from
Other stations,
Microwave ovens, etc
Shadow
Zone
Insecure: Easier to “intercept” messages
Multipath
Interference
Laptop
Comm. Tower

20. Computing Equipment Network interface card (NIC): Device that
provides a computer with unique address
Converts data into signal for transmission
Hub / Switch: Central collection point for transmission media that interconnect computers
Modem
Converts digital data into analog signal and back again
Router
special hardware that determines optimal routing path for data packets
Usually used to connect a LAN to a WAN
Bridge
Forwards messages between LANs 20

21. Small Network illustrated
Wide Area Network
Hub or Switch
Media 21

22. (Except sending station)
Hub operation
(Except sending station)
Hubs split available bandwidth among computers, i.e. with a 100 Mbps hub, the network speed will be 100 Mbps / n (where n is the number of computers) Active hubs include repeater capabilities for regenerating signals. Passive hubs don't regenerate signals. Limited to a 30meter distance apart from computers.

23. Switch operation
Switching table
MAC Address Port
A1-44-D55-1F-AA-4C 1 (Station A)
B2-CD-13-5B-E (Station B)
C3-2D-55-3B-A9-4F 5 (Station C)
; ;
Switches send out a single port: destination port. Most switches can efficiently handle simultaneous transmissions Switches provide a full bandwidth to all connected computers.

24. Network Software Network operating system Workstation operating system
Used on servers
Used by network admins for managing network resources
Examples: Novell NetWare, Windows Server 2008
Workstation operating system
Used on client PCs
Used to manage local resources & access network resources
Network monitoring software
Packet sniffers – allow seeing data as it moves over network
Keystroke monitors – allow seeing what users are typing 24

25. Protocols
An agreed upon set of rules that govern communication in a network
All computers on a network must use same protocol for effective communication
Example of protocols:
Ethernet (for communication in a LAN)
Token Ring (for communication in a LAN)
TCP/IP suite (for communication in a LAN and the Internet)
Computer 1
Rules for Task 1
Rules for Task 2
Rules for Task 3
Rules for Task 4
Rules for Task 5
Computer 2

26. LAN network Topologies
The configurations of network components
How physically the network looks like
How logically data is transferred on the network
Types of network topologies:
Bus
Star
Ring 26

27. Bus topology Most simple network topology
All devices connected to a common central cable called a “bus”
Inexpensive
If cable fails, the entire network will shut down 27

28. Star topology Centered around central device called a hub or a switch
All network nodes connect to the hub/switch
Easy to install and update
If hub fails, network fails 28

29. Ring topology
Node connected to a logical ring in a central device called MAU
More reliable than bus or star
Only one node sends at a time (no collisions)
Expensive and limited speed 29

30. Summary Questions
Book
Notes
Name categories of computer networks based on their scope; i.e. their range of operation
2) Name one example of: (a) WAN, (b) LAN
3) Name physical and wireless media used in networking
What is the role of (a) a modem, (b) a router, (c) a bridge?
What is the difference between a Network operating system and a workstation operating system?
What is a network topology?
Distinguish between network topologies
Distinguish between Client-server and P2P networks 30

31. Summary Questions (cont.)
What category of network is illustrated here?

32. Summary Questions (cont.)
What category of network is illustrated here?

33. Problem
Four students share a dorm. They would like to set up a network in order to share programs and data files. Three of the students own PCs and the fourth student has a laptop computer.
Question: What computing equipments they need to buy in order to set up the network with a star topology? 33

34. Telecommunications

35. Voice vs. Data Communication
Originally, There was a Sharp Distinction:
Voice Communication
Data Communication, in which one or both parties is a computer
Database
Electronic mail
World Wide Web
Distinction is fading because voice communication is increasingly computer-based 35

36. Circuit Switching and Reserved Capacity
Circuit switching is traditionally used in telecommunications
Circuit capacity is reserved during duration of each call
At each switch
On each trunk line
Reserved
Capacity
Reserved
Capacity
Circuit 36

37. Pros and cons of Reserved Capacity
Nothing like the congestion on the Internet
Reserved Circuit Capacity is Expensive
Have to pay for it whether you use it or not
Good for voice, because conversations are fairly constant
Bad for data, because most data transmission is bursty; e.g., in World Wide Web, download, then stare at screen for a long time until next download 37

38. Packet-Switching Data Networks
Large messages are broken into small pieces called packets (or frames)
Packets are short (averaging a few hundred bytes) because networking devices handle short messages more efficiently
Message
Packets 38

39. Packet-Switching Data Networks
Multiplexing
Packets from many conversations are mixed (multiplexed) over each trunk line
Multiplexing on
Transmission Line
Packet Switching 39