The Open Systems Interconnection Specifications

Inter-networking Models

Conceptual blueprints for effective communication and layered architecture

Layered Approach

Dividing communication processes into logical groupings called layers

Binding

Focusing on specific layer's functions when developing a protocol

Advantages of Reference Models

Hierarchical model for smooth interoperability and aiding component development

OSI Reference Model

Assists in data transfer between disparate hosts and provides a framework for networking standards

Upper Layers

Rules for applications' communication within host machines and with end users

Application (Layer 7)

Provides user interface and services like file, print, and database

Presentation (Layer 6)

Handles data processing such as encryption and compression

Session (Layer 5)

Keeps applications' data separate and manages sessions between entities

Lower Layers

Define how data is transmitted and include transport and network layers

Transport (Layer 4)

Provides reliable delivery, error correction, and flow control

Connection-Oriented Communication

Establishing a virtual circuit and synchronizing connection parameters

Windowing

Controlling the amount of unacknowledged data segments

Acknowledgements

Positive acknowledgment with retransmission for reliable data delivery

Network (Layer 3)

Provides logical addressing and routing services for internetwork

Routing

Determining the next-hop router for packet forwarding

Data Link (Layer 2)

Combines packets into frames, provides access to media using MAC address

Framing

Formatting messages into data frames with destination and source addresses

Physical (Layer 1)

Moves bits between devices, specifies cables' voltage and speed

Encapsulation

Wrapping data with protocol information at each layer of the OSI model

Protocol Data Units (PDUs)

Units used by each layer to communicate and exchange information

Modulation

Varying properties of a carrier signal with information to be transmitted

Modulator

Device that performs modulation of a signal

Demodulator

Device that performs demodulation, the inverse of modulation

Frequency-Division Multiplexing (FDM)

Transferring multiple low-pass signals over shared physical network

Time-Division Multiplexing (TDM)

Transmitting many independent signals over a common signal path

What layers make up the Upper layers of the OSI model?

Application, presentation, and session

What layers make up the Lower layers of the OSI model?

Transport, network, data link, and physical

Connection-Oriented Communication

When the sender's TCP process contacts the destination's TCP process to establish a connection

Data Packets

Used to transport user data through the internetwork

Route-Update Packets

Used to update neighboring routers about the networks connected to all routers within the internetwork

Media Access Control Data Link Sublayer

Defines how packets are placed on the media; contention media access is "first come, first served" access, where everyone shares the same bandwidth

Logical Link Control Data Link Sublayer

Responsible for identifying Network layer protocols and then encapsulating them, an LLC header tells the Data Link layer what to do with a packet once a frame is received

What is the first layer of the OSI model?

Physical Layer

What is the second layer of the OSI model?

Data Link Layer

What is the third layer of the OSI model?

Network Layer

What is the fourth layer of the OSI model?

Transport Layer

What is the fifth layer of the OSI model?

Session Layer

What is the sixth layer of the OSI model?

Presentation Layer

What is the seventh layer of the OSI model?

Application Layer