1. Introduction to Computer Science
Networks
Welcome to the component Introduction to Computer Science: Networks. This is Lecture b.
The component, Introduction Computer Science, provides a basic overview of computer architecture; data organization, representation, and structure; the structure of programming languages; and networking and data communication. It also includes some basic terminology from the world of computing.
Lecture b
This material (Comp 4 Unit 6) was developed by Oregon Health & Science University, funded by the Department of Health and Human Services, Office of the National Coordinator for Health Information Technology under Award Number 90WT0001.
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2. Learning Objectives - 1
Define what a communication network is (Lecture a)
Explain the purposes and benefits of a communication network (Lecture a)
Explain the Internet and the World Wide Web (WWW), their histories, and their structures (Lecture a)
Describe different ways of connecting to Internet (Lecture a)
The objectives for this unit on Networks are to:
Define what a communication network is
Explain the purposes and benefits of a communication network.
Explain the Internet and the World Wide Web, their histories, and their structures.
Describe different ways of connecting to the Internet.

3. Learning Objectives - 2 Explain the basics of network addressing
Internet Protocol (IP) addresses
Domain names
Lease vs. purchase from an Internet service provider (Lecture b)
Introduce network classification by the coverage size (Lecture b)
Explain the basics of network addressing: Internet Protocol, or IP, addresses and domain names, and how they can be leased or purchased from an Internet service provider.
Introduce network classification by the coverage size.

4. Learning Objectives - 3
Describe different network topologies (Lecture c)
Outline different standards and protocols that govern wired and wireless communications (Lecture c)
Describe different network topologies.
Outline different standards and protocols that govern wired and wireless communications.

5. Learning Objectives - 4
Describe the benefits and disadvantages of wireless communication (Lecture d)
Describe a typical wireless network setup (Lecture d)
Describe network hardware (Lecture d)
Introduce networking logical models and discuss Open Systems Interconnection (OSI) model (Lecture e)
Describe the benefits and disadvantages of wireless communication
Describe a typical wireless network setup.
Describe network hardware.
And, finally, to introduce networking logical models and discuss the Open Systems Interconnection, or OSI, model.

6. IP Addressing Basics
All Internet communication uses Internet Protocol (IP) addressing
The Internet expects each communicating device (host) to possess an Internet Protocol (IP) address
Two IP versions in today’s networks
We start this lecture with a discussion of the Internet Protocol, or IP. All Internet communication uses IP addressing. The Internet expects each communicating device, known as a host, to possess an IP address. An example of a communicating device is a computer that sends information to the Internet when the user sends an . On the other hand, a computer receives information from the Internet when the user receives an .
Currently, two versions of IP exist.

7. IP Version 4 (IPv4)
Defines an IP address as a 32-bit number, therefore provides 232 (~4.3×109) addresses
First version: ARPANET, 1983
We will run out of IPv4 addresses soon
Typical IPv4 looks like this:
IP version 4, or IPv4, defines an IP address as a 32-bit number, and therefore establishes a theoretical limit on the number of available addresses at 232 or approximately 4.3×109 addresses.
The first version of IPv4 was deployed for production in the Advanced Research Projects Agency Network, or ARPANET, in 1983.
We know we will run out of 32-bit addresses soon, however IPv4 is still in use.
An example of an IPv4 address would be:

8. IP Version 6 (IPv6) - 1
Defines address as a 128-bit number, allowing for 2128 (~3.4×1038) addresses
Was commercially deployed in 2006
Expected to replace IPv4
IP version 6, or IPv6, was designed to address the limitations of IPv4. Its addresses are 128-bit, which means that, theoretically, it can provide 2128 or approximately 3.4×1038 addresses.
IPv6 was commercially deployed in 2006 and many institutions have migrated to it. It is expected to eventually replace all IPv4 addresses.
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9. IP Version 6 (IPv6) - 2
Unlike IPv4 that uses decimal numbers, IPv6 uses hexadecimal numbers
The hexadecimal numeral system (also known as hex) uses 16 characters: 0-9 and A-F (to represent numbers from 10 to 15)
A typical IPv6 address looks like this: fe80:0cd0:2414:dc09:e6f5:23b1:528f:7fe2
Unlike IPv4, which uses decimal numbers, IPv6 uses hexadecimal numbers. The hexadecimal numeral system, also known as hex, uses 16 characters: 0 through 9 and A through F. “A” through “F” represent the numbers 10 through 15. “A” corresponds to 10, “B” corresponds to 11, “C” corresponds to 12, and so on through the letter “F”. The slide shows a typical IPv6 address.
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10. Public and Private IP Addresses
Public IP address is assigned to every computer that connects to the Internet
There cannot be two computers with the same public IP address
Private IP address are used for computers within a private network, such as an Intranet or Local Area Network (LAN)
An IP address can be public or private. A public IP address is assigned to every computer that connects to the Internet. Every computer connected to the Internet has to have a unique IP address so there cannot exist two computers with the same public IP address in the entire Internet.
A public IP address is assigned to the computer by the Internet Service Provider as soon as the computer is connected to the Internet gateway. ISPs purchase public IP addresses from regional organizations responsible for managing public IP addresses. Then, companies or households lease public IP addresses from the ISPs.
Private IP addresses are used for computers within a private network, including home, school, or business LAN or an Intranet.

11. Leasing an IP Address ISPs lease IP addresses to subscribers
Your private (home or business) network usually uses private IP addressing
ISPs typically leases one public IP address per location
ISP’s equipment is provided with a public IP address to connect to the ISPs public network
ISP’s equipment is also provided with a private IP address to connect to your private network
ISPs lease IP addresses to subscribers. Homes or business networks usually use private IP addressing.
The ISP typically leases one public IP address for each location. The ISP's equipment is provided with a public IP address to connect to the ISP's public network. The ISP also provides equipment with a private IP address so that it can connect to the home or business network.

12. Dynamic IP Address Temporary, change from time to time Provided by ISP
More cost effective
Makes it trickier to remotely access your computer
There are dynamic and static IP addresses.
A dynamic IP address is temporary and changes periodically. For example, when you reboot an ISP’s equipment, such as a cable modem router, it will probably boot back up with a different IP address than it had previously.
ISPs generally provide customers with a dynamic IP address because dynamic IP addresses are more cost effective.
And, having a dynamic IP address makes it trickier to remotely access your computer.

13. Static IP Address
Devices having a static IP address always have the same IP address
Static IP address also can be leased from an ISP
ISPs charge more for a static IP address Monthly charge ranges from $5 to $100
Most Web sites use static IP addresses to map their domain name reliably to one IP address
A static IP address does not change. Devices assigned a static IP address always have the same IP address.
A static IP address can be leased from an ISP. It costs more than leasing a dynamic IP address, with monthly charges ranging from approximately five dollars to a hundred dollars.
Most Web sites use static IP addresses so that their domain name will be reliably mapped to one IP address. Imagine if the domain name of the White House, had a dynamic IP address. The IP address would constantly change. This would mean that the world’s domain name system, or DNS, servers would have to keep track of those changes. That would be pretty tough to do. Another example of a user needing an IP address that does not change is the network administrator who is working from home.

14. Domain Names - 1
Since people remember names better than numbers, the Domain Naming System (DNS) was created
According to Wikipedia:
“A domain name is an identification label that defines a realm of administrative autonomy, authority, or control on the Internet, based on the Domain Name System (DNS).”
No discussion of network communication is complete without adding some thought to domain names and their use. Networks and the Internet support the use of domain names. Imagine trying to navigate the Internet using IP addresses rather than names. is an example of a domain name.
Because people remember names more easily than numbers, network engineers devised the domain naming system, or DNS to allow people to use names in conjunction with IP addressing.
According to Wikipedia, a domain name is an identification label that defines a realm of administrative autonomy, authority, or control of the Internet, based on the domain name system or DNS. Therefore, in the example of a domain name, it appears that this domain name tells us that the White House is responsible for the administration of this Web site.

15. Domain Names - 2
People and organizations can purchase a domain name from the Internet Corporation for Assigned Names and Numbers (ICANN)
Domain names such as have three parts:
WWW = World Wide Web
Whitehouse = purchased domain name
gov = government entity
People and organizations can purchase a domain name from the Internet Corporation for Assigned Names and Numbers, or ICANN.
Domain names are comprised of three distinct pieces. The “www” portion of the domain name indicates this is a name associated with the World Wide Web. The domain name, whitehouse, indicates a purchased domain name of White House. The suffix “gov” indicates a government entity type.

16. Domain Names - 3
A domain name is available when nobody currently owns it
Don’t assume domain name is an accurate indicator of business type
Many government entities own .com domain names
Keep in mind that anyone can buy any available domain name with any extension, if a person or organization is willing to pay for it and if the domain name is available. A domain name is available when another person or entity does not currently own it. When an entity's address ends with the .org or .gov, or other extension, this does not prove that the entity actually is that type of organization. Therefore, without doing further research, could it be truthfully said that the White House of the United States of America owns No, it would require more investigation to find out whether or not that was true. Finally, government entities own a number of domain names with the .com extension.

17. DNS & IP Work Well Together - 1
DNS maps an IP address to a domain name
When you visit your computer must first figure out this Web site’s IP address
One IP address for this site is This Web site is probably associated with many IP addresses.
It is important to point out that each time a user navigates to a Web site using a browser, the computer must first determine the Web site's IP address. Therefore, navigating to requires the browser to first resolve that name to an IP address and then, and only then, is the browser able to display the Web page.
One IP address for the White House appears on the slide. This Web site is probably associated with many IP addresses, one of which appears on the slide.

18. DNS & IP Work Well Together - 2
All domain names are mapped to an IP address and stored on global and privately-owned DNS servers
Global DNS servers are known as “root servers” and work together to map the globe’s names to their IP addresses
When your browser learns the destination site’s IP address from the DNS server, communication begins!
To summarize this section on IP addresses and DNS, a browser has to contact a DNS server to translate a domain name to the IP address. All domain names map to an IP address. This information is stored on globally and privately owned DNS servers.
Global DNS servers are root servers and work together to map the globe's domain names to specific IP addresses. Finally, when the browser learns the destination IP address from a DNS server, network communication finally begins.

19. Local Area Networks - LANs
Network with small geographical area of coverage
“Small” is arbitrary!
Usually one company with one site
Wireless LAN is called WLAN
LAN examples
Home
Office
Networks can be classified by their size. Networks with small geographical areas of coverage are referred to as local area networks or LANs.
Note that the term small is arbitrary.
However, a LAN is usually one company with one site. A home network could be referred to as a LAN.
Wireless LANs are called WLANs.
And, as mentioned previously, examples of LANs include a home and office space, one building, one floor in a building, or a small school with multiple buildings.
Entire building or single floor
Small school with multiple buildings

20. LANs Use IP and MAC
LAN communication uses IP and Media Access Control (MAC) addressing
MAC address stamped on each installed network interface controller (NIC)
MAC address used by switches for intranet communications; has no meaning outside of that local network
MAC addressing is used in all LAN communication
In a local area network such as a home network, a number of devices need to communicate with each other. These devices must be interconnected, most likely using cabling, a switch, and an ISP router. Or, these devices might be interconnected using wireless technologies, in which case a wireless access point or a WAP plugs into the switch. To understand how a local area network, or LAN, directs traffic, you need to know that the LAN uses more than IP addressing.
LAN communication uses IP addressing and media access control, or MAC, addressing. The MAC address is stamped on a sticker on each installed network interface controller, or NIC. Switches use MAC addresses for intranet communications. The MAC address on a NIC has no meaning outside of the local network.
All LAN communication uses MAC addressing. Switches consider IP addressing. If the destination address is an IP address unknown to the switch, then the switch will send that communication to the router. The router has to determine where that destination address is located using its routing tables.

21. MAC Address Example - 1
Open command prompt (search the internet for instructions specific to your operating system)
Now would be a good time to see an example of the MAC address of a NIC. Follow along on your own computer.
First, open a command prompt. If you don’t know how to do this, search the Internet for instructions based on your operating system.

22. MAC Address Example - 2
Open command prompt (search the internet for instructions specific to your operating system)
Use ipconfig command
MUST be a space after the command name
After the space, “/all”
Then press [Enter]
Second, we will be using the ipconfig command, but, before we do, you need to know a few things:
There must be a space after the ipconfig command.
After typing the space, you will type a slash, then the word all. The forward slash is known as a switch. The word “all” modifies the command to provide much more information than just executing the “ipconfig” command with no switch.
We will need to press Enter to run the command
The next slide will show you the entire command and have you type along with the instructions given.

23. MAC Address Example - 3
Open command prompt (search the internet for instructions specific to your operating system)
Use ipconfig command
Type ipconfig /all [Enter]
Type ipconfig, space, slash, a-l-l and press Enter to run the command.

24. MAC Address Example - 4 Figure 1. Example of MAC Address
Compare what you see on your screen to what is shown in the slide.
Find your MAC address and IPv4 address.
The physical address is the MAC address associated with this specific NIC. Remember, the MAC address is used for local communication and the IP address is used for remote communication.
Leave the command prompt window open to complete an exercise on an upcoming slide.
Figure 1. Example of MAC Address

25. LAN Management Workgroups and Domains
There are two standard methods for network management: Workgroups and Domains

26. LAN Management – Workgroups
Typically 10 to 20 devices
Peer-to-peer network; each computer can communicate with any other without a server
No computer has control over another computer
To use any computer in the workgroup, user must have an account on that computer
The Workgroups method is used to manage small networks of say, ten to twenty devices.
A workgroup is defined as a peer-to-peer network in which computers can communicate and share data with each other.
This is a simple network solution, and does not require a server. 
No computer has control over another computer.
To use any computer in the workgroup, users have an account on that computer.

27. LAN Management – Domains
Unlimited number of devices
One or more domain controllers (DC), or servers
Servers control user accounts, security, domain rules, and much more
Implementing changes is easy: changes are automatically applied to all computers
User with an account on the domain can log on to any computer within the domain
Domain-based networks do not have any limit on the number of devices in the network. Domain-based networks have one or more computers serving as domain controllers, or DCs. Domain controllers are usually referred to as servers.
Network administrators use servers to control user accounts, security, domain rules, and much more. This makes it easy to implement changes because the changes are automatically applied to all computers.
Any user with an account on the domain can log on to any computer within the domain. User accounts on individual computers are not needed.

28. Wide Area Networks – WANs - 1
Network that covers large geographical area
Term “large” is arbitrary!
WAN usually made up of > 1 LAN
Same company, multiple sites
May or may not have Internet access
A network encompassing a large geographical area is called a Wide Area Network or a WAN. A WAN generally consists of one or more LANs. Remember that a LAN is a local area network, and has a small geographic area.
A WAN may exist within one company across multiple sites, for example. It may or may not have Internet access.

29. Wide Area Networks – WANs - 2
WAN examples
Offices in Chicago and London share servers
Five Portland offices (same city) share files
Intel, Dell, and Microsoft collaborate on new product launch
Some examples of WANs include:
A company with offices in Chicago and London, perhaps needing to share servers or printers and other devices.
Five offices in the city of Portland. In other words, the offices are in the same city but in different locations within the city.
Intel, Dell, and Microsoft joining their networks together, in a limited manner, to collaborate on the creation of a new product.
Why would companies join together to create a WAN? A WAN can facilitate intercompany communications, permitting the companies to share confidential documents.

30. Metropolitan Area Networks – MANs - 1
Large coverage area, but same city
Term “large” is arbitrary!
MAN usually made up of > 1 LAN
Same company, multiple physical sites
Office connected by fiber-optic links or other high-speed media
May or may not have Internet access
If a large network is comprised of five offices spread across the same city, the network is referred to as a metropolitan area network or a MAN. Again, the term large is arbitrary.
A MAN is like a WAN, usually consisting of at least one LAN. An example could be a company with multiple physical sites, with one of the sites connected to the main office by fiber-optic links or other high-speed media.
The MAN, just like the WAN, may or may not have Internet access for its devices.

31. Metropolitan Area Networks – MANs - 2
MAN examples
Company has many offices in same city
Large college campus
Examples of MANs include a company with many offices in the same city or a large college campus.

32. Networks Summary – Lecture b
Basics of network addressing
IP addresses and domain names
Public vs private IP addresses
Dynamic vs static IP addresses
Networks classification by the coverage size
Two methods of managing Local Area Networks (LANs): workgroups and domains
This concludes lecture b of Networks.
In summary, this lecture explained the basics of network addressing: IP addresses and domain names, different types of IP addresses, and how they can be leased or purchased.
And it described the classification of networks by the coverage size, and outlined two methods of Local Area Network management.

33. Networks References – Lecture b
Wikipedia. MAC Address. [Internet] Nov [cited 2011 Nov 07]. Retrieved Jan 2012 from:
References slide. No audio.

34. Introduction to Computer Science Networks Lecture b
This material was developed by Oregon Health & Science University, funded by the Department of Health and Human Services, Office of the National Coordinator for Health Information Technology under Award Number 90WT0001.
No audio.