Network Models

1. Network Models

2. Objectives • Learn how data logically travels between sending and receiving hosts • Explain common TCP and UDP ports, protocols, and their purpose

3. How Data is Transmitted on a Network?yt video 13:00 • Before data is transmitted on a network: • Data is broken up into segments and put into a packet • A packet contains the data and information that identifies the type of data, where it came from, and where its going

4. Network Models • A network model is designed to show how networks and their components should work • The ISO (International Standards Organization) developed the OSI (Open Systems Interconnection) Model • The OSI model helped manufacturers and vendors work toward interoperability standards and develop rules for data communication • When networks were first built no real standards existed • Manufacturers and vendors made equipment without regard to how they would work

5. OSI Reference Model • The OSI model is also used to break up the complexity of how one computer (host) sends data to another computer (host) • Like the layers of a cake, the OSI model has 7 layers stacked from bottom to top (network stack) • OSI Model • 7 Layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical • A mnemonic to memorize the OSI Model is, All People Seem To Need Data Processing

6. Encapsulation &De-encapsulation • On a sending computer data flows down the network stack and on a receiving computer data flows up the network stack • On the sending computer: • Each layer considers the data and adds a header and footer that contain addressing and error control information (encapsulation) • On the receiving computer: • Headers and footers are removed at each layer until the data reaches its destination • (de-encapsulation)

7. Network Models &network Protocols • Think of the OSI reference model as the map for a road; it tells you how the road should look • Computers and other network equipment must understand, accept, and use protocols to communicate • The map (model) will show you the location of a stop sign, but it doesn’t tell you to stoporlook both ways for traffic • Protocols are the rules that tell you how you must drive on the road • Examples of common protocols: TCP, UDP, SNMP, SMTP, IMAP, HTTP

8. TCP/IP Protocol Suite • When 2 devices communicate they use the same protocols • All networks today use a group or suite of protocols known as TCP/IP (Transmission Control Protocol/Internet Protocol) • The TCP/IP model was crafted directly from the TCP/IP protocol stack and is a more true representation of the functions and operations of network protocols

9. TCP/IP Application Protocols Network Protocols 8:00ports 11:25

10. USPS Analogy • If you send something through the USPS, it’s mixed in with everyone else's stuff, transferred to another Post Office, and sorted out again • An analogy that is used to describe packet switching and the HYBRID MODEL is the U.S. Postal Service • The Postal Service has no dedicated piece of network

11. Application Layer • When you send an email using a program such as Microsoft Outlook your computer and email program interacts with the Application Layer • Most applications have a specific protocol designed around their data types, functions, and features • Other Application Layer protocols include HTTP, FTP, DNS, POP3, IMAP, Telnet • At the Application Layer the data is like a letter written in a language the recipient will understand • However the data does not have an envelope that specifies an address in order to reach its destination • Hold up your blank envelope and look inside you’ll see data with no place to go • 

12. Transport Layer • The Transport Layer specifies which application layer protocol will be used to process data on the receiving computer 25 • Outlook sends the message to your email server using the SMTP protocol • Each application layer protocol is also assigned a unique port number, which is used to identify the protocol (SMTP port 25) John Doe (Transport Layer) • This destination port number is like putting a name on our envelope • Write down a class member’s name in the middle of your envelope as well as the words Transport Layer

13. Transport Layer • Just as there may be multiple people living at one address, multiple programs could be running on the destination computer • Each protocol has a unique port number so incoming data can find the correct program • The Transport Layer includes the destination port number in the data header that gets added to the data packet but also includes a source port number which would be like adding a return address name Chet (Transport Layer) John (Transport Layer) • Write your name in the upper left corner of your envelope and again write the words Transport Layer

14. Transport Layer • The Transport Layer has yet another important responsibility • When you send a letter you can add a stamp, drop it in the mailbox and assume it gets there (UDP) • Or you can request a return receipt to ensure letter has arrived- the transport layer offers a choice for this reliability (TCP) • UDP (User Datagram Protocol) is a fast, best effort delivery service and used for short, time sensitive data • With UDP the sending computer does not actually know if the receiving computer gets the data • TCP (Transmission Control Protocol) on the other hand is very robust offering error checking, recovery, and delivery notification • The Transport Layer determines if UDP or TCP will be used and then sends the data down to the Network Layer • I’ve already decided whether you are going to drop the mail in the mailbox and hope it gets there (UDP) or request a return receipt (TCP)

15. Network Layer • The Network Layer adds a source and destination IP address (we will discuss IP addressing a bit later) • Network Layer addressing is compared to adding your recipients street address (without the beginning numbers), and a return street address to the envelope Chet (Transport Layer) Maple (Network Layer) Sacramento, CA 49302 John (Transport Layer) • (1)Write down a (fake) mail to street name on the center of the envelope • (2) Write down your own (fake) street name on the top left corner of the envelope Walnut (Network Layer) Caledonia, MI 49316

16. Data Link Layer • The Data Link Layer adds a source and destination physical address (MAC address) • Layer 2 also converts data into ones and zeroes that the next layer, the Physical Layer, can understand • Whereas an IP address is like a street name, a MAC address is like a house number Chet (Transport Layer) Maple (Network Layer) Sacramento, CA 49302 123 John (Transport Layer) 321 Walnut (Network Layer) Caledonia, MI 49316 • Add a house number to both street names already provided

17. Physical Layer • The Physical Layer converts bits into electrical signals that get sent across the physical medium, such as telephone wires, fiber optic, or wireless • The Physical Layer is like the mail truck, airplane, or train that carries your letter from one post office to the next • If you have UDP raise your envelope in the air, if you have TCP patiently wait and hold your envelope (I will be the mail man delivering your envelopes - or the physical medium)