1. Networking Standards and the OSI Model
Chapter Two
Networking Standards
and the OSI Model

2. Standards
Documented agreements containing technical specifications or other precise criteria that stipulate how a particular product or service should be designed or performed
Many different industries use standards to ensure that products, processes, and services suit their purpose

3. Networking Standards Organizations
American National Standards Institute (ANSI)
Comprised of industry and government representatives
Determine standards for electronics industry in addition to other fields
Electronic Industries Alliance (EIA)
Trade organization composed of representatives from electronics manufacturing firms across United States
Sets standards for members, helps write ANSI standards, and lobbies for legislation favorable to the industry

4. Networking Standards Organizations
Institute of Electrical and Electronic Engineers (IEEE)
International society of engineering professionals
Promotes development and education in electrical engineering and computer science fields
International Organization for Standardization (ISO – Greek for equal)
Collection of standards organizations (130 countries)
Goal is to establish international technological standards to facilitate global exchange of information and barrier-free trade
ISO-9000/QS-9000

5. Networking Standards Organizations
International Telecommunication Union (ITU)
Formerly called Consultative Committee on International Telegraph and Telephony (CCITT)
United Nations agency that regulates international telecommunications
Founded in Paris in 1865
Assists developing countries

6. The OSI Model Open Systems Interconnection (OSI) Model
Model for understanding and developing computer-to-computer communication
Developed in the 1980s by ISO
Divides network architecture into seven layers

7. The OSI Model Figure 2-1: The OSI Model
Phil Donahue Never Televises Sick People Anymore!

8. Physical Layer Data Link Layer
First layer of OSI Model
Contains physical networking media
NIC, cabling, connectors, hubs, and repeaters
Sets data transmission rate and monitors data error rates
Data Link layer
Second layer of OSI Model
Primary function is to divide data it receives from Network layer into distinct frames that can be transmitted by Physical layer

9. Figure 2-2: A simplified data frame
Frames
Structured package for moving data
Includes raw data (or payload) along with sender’s and receiver’s:
Network addresses
Error-checking and control information
Figure 2-2: A simplified data frame

10. Network Layer Third layer of OSI Model
Translates network addresses into their physical counterparts
Decides how to route data from sender to receiver

11. Network Layer
Because Network layer handles routing, routers belong in Network layer
To route means to direct data based on addressing, usage patterns, and availability

12. Transport Layer Transport layer protocols also accomplish:
Fourth layer of OSI Model
Ensures that data are transferred between points reliably and without errors
Handles flow control
Method of gauging appropriate rate of data transmission
Transport layer protocols also accomplish:
Segmentation – decreasing the size of the data units (and sequencing)
Reassembly – reconstructing the segmented data units
Protocols TCP & IPX operate here

13. Transport Layer Acknowledgement (ACK)
Response generated in Transport layer
Confirms to sender that its frame was received correctly

14. Session Layer Session Fifth layer of OSI Model
Establishes and maintains communication between two nodes on the network
Session
Refers to a connection for data exchange between two parties
Term session is most often used in context of terminal and mainframe communications

15. Presentation Layer Application Layer
Sixth layer of OSI Model
Translates between application and network
Manages data encryption/decryption
Application layer
Seventh, or top, layer of OSI Model
Provides interface to software enabling programs to use network devices, or API
API (Application Programming Interface) - Routine that allows a program to interact with the operating system

16. Table 2-1: Functions of the OSI layer
Applying the OSI Model
Table 2-1: Functions of the OSI layer

17. Communication Between Two Systems
Figure 2-3: Data transfer between two systems
Formulates a request from remote node
Determines format or encryption
Assigns data token (approval)
Break down into manageable chunks
Adds addressing information
Data blocks packaged into individual frames
Deliver the data to the cabling

18. Communication Between Two Systems
Figure 2-4: Data transformed through the OSI Model

19. Communication Between Two Systems - Terms
Token
Special control frame indicating to rest of network that a particular node has right to transmit data
Frame Check Sequence (FCS)
Field in a frame responsible for ensuring that data carried by frame arrives intact

20. Frame Specifications Ethernet
Networking technology originally developed in 1970s by Xerox
Four types of Ethernet technology are used on LANs today
Each type is governed by a set of IEEE standards

21. Frame Specifications Token Ring
Networking technology developed by IBM in the 1980s
Relies upon direct links between nodes and a ring topology, using tokens to allow nodes to transmit data

22. A Typical Ethernet Frame
802.3 standard (p. 49)
IEEE standard for Ethernet networking devices and data handling
Figure 2-5: Ethernet frame as specified by the IEEE standard

23. Components of the Ethernet 802.3 Frame
Preamble
Marks beginning of entire frame
Start of Frame Delimiter (SFD)
Indicates beginning of addressing frame
Destination Address
Contains destination node address

24. Components of the Ethernet 802.3 Frame
Source Address
Contains address of originating node
Length (LEN)
Indicates length of packet
Data
Contains data, or segmented part of data, transmitted from originating node

25. Components of the Ethernet 802.3 Frame
Pad
Used to increase size of the frame to its minimum size requirement of 46 bytes
Frame Check Sequence (FCS)
Provides an algorithm to determine whether data were correctly received
Most commonly used algorithm is Cyclic Redundancy Check (CRC)

26. Typical Token Ring Frame
802.5 Standard
IEEE standard for Token Ring networking devices and data handling
Figure 2-6: Typical Token Ring frame

27. Components of Token Ring Frame
Start Delimiter (SD)
Signifies beginning of packet
Access Control (AC)
Contains information about priority of the frame
Frame Control (FC)
Defines type of frame

28. Components of Token Ring Frame
Destination Address
Contains destination node address
Source Address
Contains address of originating node
Data
Contains data transmitted from originating node

29. Components of Token Ring Frame
Frame Check Sequence (FCS)
Used to check integrity of the frame
End Delimiter (ED)
Indicates end of the frame
Frame Status (FS)
Indicates whether destination node recognized and correctly copied the frame

30. Addressing Through the Layers
Data Link layer address
Also called MAC address, after Media Access Control (MAC) sublayer
Number uniquely defining a network node
Composed of Block ID and Device ID
Manufacturer-hard codes the address on the NIC
3COM Ethernet – 00608C
Intel Ethernet – 00AA00

31. Addressing Through the Layers
Network layer address
Resides at Network level of OSI Model
Follows hierarchical addressing scheme
Can be assigned through operating system software
More useful to internetworking devices, such as routers, since data is sorted more logically
IP address (similar to long distance phone)
Ex. WINIPCFG or IPCONFIG /all

32. IEEE Networking Specifications
Table 2-2: IEEE 802 standards

33. IEEE Networking Specifications
To accommodate shared access for multiple network nodes, IEEE expanded OSI Model by separating Data Link layer into two sublayers:
Logical Link Control (LLC) sublayer
Media Access Control (MAC) sublayer

34. Data Link Layer Sublayers
LLC
Upper sublayer
Provides common interface
Supplies reliability and flow control services
MAC
Lower sublayer
Appends physical address of destination computer onto the frame

35. Subdivided Data Link Layer
Figure 2-7: LLC and MAC sublayers