Chapter 7: Network Reference Models and Standards

Presentation layer

At Layer 6 of the OSI model, data can be encrypted and/or compressed to facilitate delivery. Platform-specific application formats are translated into generic data formats for transmission or from generic data formats into platform- specific application formats for delivery to the Application layer.

Open Systems Interconnection (OSI) reference model

ISO Standard 7498 defines a frame of reference for understanding networks by dividing the process of network communication into seven layers. Each layer is defined in terms of the services and data it handles on behalf of the layer above it and the services and data it needs from the layer below it.

Physical layer

Layer 1, the bottom layer of the OSI model, transmits and receives signals and specifies the physical details of cables, NICs, connectors, and hardware behavior.

Data Link layer

Layer 2 in the OSI model is responsible for managing access to the network medium and delivery of data frames from the sender to the receiver or from sender to an intermediate device, such as a router.

Network layer

Layer 3 of the OSI model handles logical addressing and routing of PDUs across internetworks.

Transport layer

Layer 4 of the OSI model is responsible for reliable delivery of data streams across a network. Layer 4 protocols break large streams of data into smaller chunks and use sequence numbers and acknowledgements to provide communication and flow control.

Session layer

Layer 5 of the OSI model responsible for setting up, maintaining, and ending communication sequences (called sessions) across a network.

Application layer

Layer 7 in the OSI model provides interfaces that enable applications to request and receive network services.

protocol data unit (PDU)

a unit of information passed as a self-contained data structure from one layer to another on its way up or down the network protocol stack.

access control

in the context of the Network layer and routing, the process by which a router consults a list of rules before forwarding an incoming packet. The rules determine whether a packet meeting certain criteria (such a source and destination address) should be permitted to reach the intended destination.

peer communication

in the layered approach, each layer on one computer behaves as though it were communicating with its counterpart on the other computer. This means each layer on the receiving computer sees network data in the same format its counterpart on the sending computer did.

encoding

representing 0s and 1s as a physical signal, such as electrical voltage or a light pulse.

International Organization for Standardization (ISO)

the international stands-setting body based in Geneva, Switzerland, that sets worldwide technology standards.

Media Access Control (MAC) sublayer

the lower sublayer of the IEEE Project 802 model for teh OSI model's Data Link layer. It handles accessing network media and mapping between logical and physical network addresses for NICs.

maximum transmission unit (MTU)

the maximum frame size allowed to be transmitted across a network medium

deenacapsulation

the process of stripping the header from a PDU as it makes its way up the communication layers before being passed to the next higher layer.

Logical Link Control (LLC) sublayer

the upper sublayer of the IEEE Project 802 model for the OSI model's Data Link layer. It handles error-free delivery and controls the flow of frames between sender and receiver across a network.