11/7/2013Associate Level Material
Appendix C

OSI Model Key Terms Table

Use the following table to define the key terms related to the OSI model. Describe the functions of any hardware connectivity devices and tools listed.

|TTerm |Definition |Function |
| | |(if applicable) |
|Physical layer |Responsible for the transmission of bits |Converts data to physical signals that |
| |across the network’s physical medium. |represent o’s and 1’s and then transmits |
| | |the physical signals to its destination. |
|Data link layer |Responsible for error free data |Divides data received from the network |
| |transmission and establishing local |layer into frames the physical layer can |
| |connections between two computers. |transmit. |
|Network layer |Responsible for addressing and routing |Establishes, maintains and terminates |
| |processes that permit data to be moved from|network connects between different |
| |one network to another. |networks. Also makes routs data from one |
| | |network o another. |
|Transport layer |Responsible for error free delivery from |Handles error corrections, dividing data |
| |one ends to another. |into smaller packets that arrive out of |
| | |order. |
|Session layer |Responsible for administrating tasks and |This allows users to establish control and |
| |handles security. |terminate a connection. |
|Presentation layer |Responsible for changing data from the |This ensures applications on separate ends |
| |application layer to common syntax and |of a network connection can communicate. |
| |semantics. | |
|Application layer |Responsible for the end user application |Initiates communication requests and |
| |process. |provides an interface to access file |
| | |transfer services, printer access and |
| | |email. |
|Signaling |Signaling is the method for using |Electrical signals are probably the most |
| |electrical, light, energy, or radio waves |common available technology in signaling. |
| |to communicate data among all network |They can interpret data through the current|
| |computers. |state method or the transition method. |
|Synchronous | |Uses a clock signal to organize |
| | |communications between devices. |
|Asynchronous |Intermittent and do not depend on a clock. |These signals use a start signal, the |
| | |payload of the datagram or frame and a stop|
| | |signal to communicate their data. |
|Bandwidth |The amount of data that can be carried on a| |
| |given transmission medium. | |
|Point-to-point topology |When two nodes on a network are connected |This type of connection is used when the |
| |together directly. |devices are intended to monopolize the |
| | |transmission medium between them. |
|Multipoint connection |Three or more devices that are connected |This requires each individual device to |
| |through a single transmission medium. |have a way to identify itself and the |
| | |target machine to which it wishes to |
| | |communicate. |
|MAC |Media Access Control, Ensures routing |The MAC address is unique to each device on|
| |devices on a network send information to |a network. |
| |the intended location. | |
|LLC |Logical Link Control, controls data linked |The LLC sub-layer is a sub-layer of the |
| |between two or more computers on the same |data link layer. |
| |subnet. | |
|SAP |Service Access Point that is used on a |SAP’s allow the LLC to identify which |
| |multi-protocol LAN. |protocol is being used. |
|Access method |This is the set of rules that defines how a|Sometimes called arbitration, this process |
| |computer inserts data onto a network cable |reduces data collisions that cause |
| |and how it acquires data from the same |corrupted data packets. |
| |cable. | |
|CSMA/CD |Carrier Sense Multiple Access with |Used in Ethernet this form of contention |
| |Collision Detection |analyzes network traffic to notice |
| | |collisions and start retransmissions. |
|Gateway |Software or Hardware that connects two |This can be used at any layer of the OSI |
| |different types of networks by converting |model, but are usually identified with |
| |data from one operating system to another. |upper layers since they must communicate |
| | |what an application, establish and manage |
| | |sessions, translate encoded data, and |
| | |interpret addressing data. |
|Hubs |Multiport connection point used to connect |Found in a star topology, this device sends|
| |network devices via a cable segment. |data packets or duplicates them to each of |
| | |the ports. That way all the network devices|
| | |can see them. Not very efficient on |
| | |networks with heavy traffic. |
|Bridges |Link two LANS and makes them appear as one.|Can connect a ring network to a bust |
| |They can also be used to link two segments |network (or other dissimilar network types)|
| |on the same LAN. |as long as the bridge operates |
|Token passing |Method of arbitration that uses a special |Only the device possessing the “token” may |
| |data packet passed around a network. |transmit data over the network’s |
| | |transmission. |
|Polling |Method of arbitration that has a single |The channel access administrator gives |
| |device acting as a channel access |permission to devices to transmit data over|
| |administrator. |the communication channel. |