1. Understanding Networks

2. Objectives Compare client and network operating systems Learn about local area network technologies, including Ethernet, Token Ring, FDDI, and wireless Use the OSI model to understand networking Learn how network computers and servers are addressed

3. Understanding the OSI Model In an effort to identify and standardize all the levels of communication needed in networking, ISO developed a networking model called the Open Systems Interconnection (OSI) reference model. The OSI reference model provides a universally accepted reference illustrating how data is transmitted on a network or between two or more networked devices.

4. OSI Reference Model Foundation that brings continuity to LAN and WAN communications Product of two standards organizations: –ISO –ANSI Developed in 1974 Set of communication guidelines for hardware and software design

5. OSI Guidelines Specify… Methods to ensure that network transmissions are received correctly How network devices maintain a consistent rate of data flow How electronic data is represented on network media

6. OSI Layers

7. Understanding the OSI Model (Continued) Application Layer The Application layer of the OSI model is responsible for interfacing with application software, such as Web browsers or Web servers. Presentation Layer The Presentation layer receives requests for files from the Application layer, and presents the requests to the Session layer. The Presentation layer reformats, compresses, or encrypts data as necessary.

8. Understanding the OSI Model (Continued) Session Layer The Session layer is responsible for establishing and maintaining a session between two networked stations or hosts. A host is any computer or other device on a network that has been assigned an IP address.

9. Understanding the OSI Model (Continued) Transport Layer The Transport layer is responsible for error checking and requests retransmission of data if it detects errors. The Transport layer might or might not guarantee successful delivery of data. Network Layer The Network layer is responsible for dividing a block of data into segments that are small enough to travel over a network.

10. Understanding the OSI Model (Continued) Network Layer (Continued) Segments of data are called packets, data packets, or datagrams and contain data, along with special identifying information in headers and trailers at the beginning and end of the packet. Data Link Layer The Data Link layer is responsible for receiving packets of data from the Network layer and presenting them to the Physical layer for transport.

11. Understanding the OSI Model (Continued) Physical Layer The OSI Physical layer is responsible for passing data packets on to the cabling or wireless media (whether the media be cabling or wireless). When software is permanently embedded on a hardware device, it is called firmware.

12. Communicating Between Stacks OSI model provides standards for: –Communicating on a LAN –Communicating between LANs –Internetworking between LANs and WANs and between WANs and WANs

14. Peer Protocols

15. Applying the OSI Model

16. The OSI Model Applied to a TCP/IP Network On a TCP/IP network, TCP/IP is managed by the operating system and covers the first five layers of the OSI model. When a browser wants to access a Web server, it uses the address and port of the Web server to make a request to the operating system. This request takes the form of an Application Program Interface (API).

17. The OSI Model Applied to a TCP/IP Network (Continued) In a TCP/IP network, the API call for a Web page from a Web server causes the operating system to generate an HTTP request. HTTP does not operate in the lower layers of the network model. Instead, it hands data over to TCP, which resides in the Transport layer.

18. The OSI Model Applied to a TCP/IP Network (Continued) A frame provides information at the beginning of the data, called a header, and information at the end of the data, called a trailer. A checksum is a calculated value that can be compared to the value calculated by the receiving Data Link layer. This technique of calculating and comparing values is called a cyclical redundancy check (CRC).