Del Mar College ITNW 1392-Beginning Router Configuration Intructor:Michael P. Harris
Sem2Les1

Semester 2, Lesson 1 Notes:

The OSI 7-Layer Internetworking Model

Six reasons why a layered network model is used in Internetworking...

A layered network model;

1. reduces complexity,
2. standardizes interfaces,
3. facilitates modular engineering,
4. ensures interoperable technology,
5. accelerates the evolution of networking technology, and
6. simplifies teaching and learning

The OSI 7 layers and brief descriptions of their function:

Layer 7 - Application - network processes for application

Layer 6 - Presentation - Data Representation

Layer 5 - Session - Interhost communication

Layer 4 - Transport - End-to-end connections

Layer 3 - Network - Addresses and best path

Layer 2 - Data Link - Access to media

Layer 1 - Physical - Binary transmission

OSI Model

----- Host layers: provide accurate data delivery between computers

         7. Application Layer(Network Services/processes to apps)

-Layer 7 of the OSI model. This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them) , synchronizes cooperating applications, and establishes agreement on proceedures for error recovery and control of data integrity.

         6. Presentation Layer (Data representation/code formatting{encription, ASCI, EBCDIC, JPEG, GIF, MIDI, MPEG, QuickTime})

-Layer 6 of the OSI reference model. This layer ensures that information sent by the application layer of one system will be readable by the application layer by another. The presentation layer is also concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer.

         5. Session Layer (Interhost communication/coordinates service requests and responses/synchronization of communication between applications {NSF, SQL, X-Windows})

-Layer 5 of the OSI reference model. This layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities.

---top 3 layers... 5, 6, & 7 (data)

         4. Transport Layer (End-to-end connection reliability, segmenting & flow control)

-Layer 4 of the OSI reference model. This layer is responsible for reliable network communication between end nodes. The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recover, and information flow control. Segmenting and reassembling data into a data stream. Uses application segmenting and port numbers.

---Layer 4 (segments)

---Media Layers: (layers 1, 2, & 3) controls physical delivery of the message over the network.

         3. Network Layer (Addresses and best path)

-Layer 3 of the OSI reference model. This layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs. Headers are added to the segments.

---Layer 3 (packets)

         2. Data Link Layer (Access to networking media)

-Layer 2 of the OSI reference model. This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: The LCC sublayer (refers upward to higher-layer software functions) and the MAC sublayer (refers downward to lower layer hardware functions). Sometimes simply called "link layer". Bridges and Switches operate at the data link level.

---Layer 2 (frames)

         1. Physical Layer (Binary transmission; wires, connections, voltages, and data rates)

-Layer 1 of the OSI reference model. The physical layer defines the electrical, mechanical, procedural, and funtional specifications for activating, maintaining, and deactivating the physical link between end systems. The function of the physical layer is the transmission of data. Typically such transmission is accomplished through the use of such things as wires, connectors, and voltages. Repeaters operate at the Physical layer.

--Layer 1 (bits)

-----The upper 5 layers are software only

-----Layer 2 is hardware and software

-----Layer 1 is hardware only

"Peer-to-Peer Communication" - Each layer in a source host system uses it's own layer protocol to communicate with it's peer layer in the destination host system. In other words, like layers talk to each other. Implied in peer-to-peer communication is that each layer "below" the current layer provides services to the layer above it.

The process of "data encapsulation": (data, segment, packet, frame, bits)

The application (layer 7), presentation (layer 6), and session (layer 5) layers present 'data' to the transport layer (layer 4), where it is converted inot 'segments'. These transport layer (layer 4) 'segments' are passed down to the network layer (layer 3), where they gain header information and become 'packets'. Thses network layer (layer 3), 'packets' are passed down to the data link layer (layer 2), where they gain additional information and become 'frames'. Finally, these data link (layer 2) 'frames' are passed to the physical layer (layer 1), where they are converted to 'bits' - voltage - or light pulses representing binary ones and zeros. This process is similar to preparing a package for mailing -- wrapping it, addressing it, & transporting it.

The information added during "data encapsulation" in the transport, network, and data link layers: The transport layer (layer 4) breaks up the 'data' into 'segments', which include "segment headers" for ensuring that hosts at both ends can reliably communicate.

The network layer (layer 3) adds a "network header", which includes source and destination logical addresses.

The data link layers (layer 2) adds "frame trailers and headers", including source and destination physical addresses and information to allow access and connection to the next directly connected device on the working network.

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    This page is maintained by:   Michael P. Harris

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	viking.delmar.edu Last updated April 4		mpharris@surf.delmar.edu Copyright © 1999