PACE-IT: Basic Network Concepts (part 1)

Basic network concepts I.

Instructor, PACE-IT Program – Edmonds Community College

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M.B.A., IT Management, Western Governor’s University

B.S., IT Security, Western Governor’s University

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Brian K. Ferrill, M.B.A.


– Encapsulation.

– Modulation.

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Encapsulation.Basic network concepts I.

Encapsulation.

The OSI (Open Systems Interconnection) reference model uses a layered approach to enable disparate devices to be able to communicate effectively.

During communication between two devices or nodes, each layer is only responsible for being understood by the corresponding layer on the other device.

As data flows down from the application layer through to the physical layer, it is encapsulated—layer information is wrapped around the data—at each layer with information to help the corresponding layer at the other end of the communication line understand what is happening.

As the data is received at the other end, it is de-encapsulated—unwrapped—as it moves up the OSI stack.


Encapsulation.

– Encapsulation at work.» The application layer begins the process by sending

data that is encapsulated, or wrapped, with application layer control information to the presentation layer.

• The encapsulated data is called a PDU (protocol data unit).

» The application layer PDUs are segmented by the presentation layer, with each segment being encapsulated by presentation layer control information. They are now presentation layer PDUs.

• The process of segmenting and encapsulating continues down through the OSI stack until it is transmitted as bits by the physical layer.

» The receiving physical layer passes the bits to the receiving data link layer, which reads the data link layer PDU information and then de-encapsulates and de-segments it, sending the new packets to the network layer as network layer PDUs.

• The process of de-encapsulating and de-segmenting continues up the OSI stack until it is received by the application layer, where it is finally fully de-encapsulated and fully reassembled.


Modulation.Basic network concepts I.

Modulation.

The physical layer of the OSI stack is responsible for transmitting bits (literal zeros and ones) of data across some form of media (e.g., a cable).

The question arises, how does the physical layer transmit the data across the media?

The bits of data are modulated (or encoded) by the physical layer and placed on the carrier signal (which can also be called a carrier channel) of the media, which carries the modulated data on to its next destination.

Once the bits are received, they are de-modulated (un-encoded) by the receiving physical layer.


Modulation.

– Carrier signal defined.» A carrier signal is a standard waveform, usually in the

form of a sine wave, that is used as the base carrier of another input signal.

• A sine wave is a mathematical curve that is represented by a smooth repeating oscillation.

– Modulation defined.» Modulation is the process of varying one or more

properties of a carrier signal with an input signal—usually for the purpose of conveying information.

• Modulation can be used to encode digital network traffic onto media that uses a digital carrier signal (e.g., using an ISDN connection between two networks).

• Modulation can be used to encode a digital signal onto a media that uses an analog carrier signal—digital network traffic traveling over the public switched telephone network (PSTN).

• Multiplexing can be used to increase the number of modulated signals that can be placed onto a carrier signal.


Modulation.

– Multiplexing explained.» The type of carrier signal will determine if multiplexing

can occur.• A baseband carrier signal cannot have multiplexing

occur, as the modulated signal will consume all of the available frequency (or channel width).

• Multiplexing can be utilized on a broadband carrier channel, as each modulated input is assigned a portion of the channel width of the carrier signal.

» Multiplexing can use one of two methods to weave streams of modulated signal into the carrier signal.

• Frequency division multiplexing is the process of mathematically dividing the carrier channel frequency into multiple segments and assigning the results to modulated input signals.

• Time division multiplexing is the process of mathematically dividing the carrier channel width into multiple time segments and assigning the time slots to different modulated signal input streams.


Modulation.

– Baseband.» A stream of data that is sent over a carrier channel as a

digital modulated signal.• The digital signal will take all of the carrier signal’s

available frequency (or time).• While the modulated input does take all of the carrier

channel’s available frequency, the communication is bidirectional (it can flow back and forth).

– Broadband.» A stream of data that is sent over a carrier channel as

an analog modulated signal.• The analog signal will be assigned a portion of either

the carrier channel’s available frequency or time.• While the modulated input doesn’t take all of the

carrier channel’s available frequency, the communication is not bidirectional. For two way communication to take place, multiplexed channels must be created (a channel for each direction).


What was covered.Basic network concepts I.

The OSI network model relies upon a layered approach to ensure communication can occur between disparate systems. The OSI model uses encapsulation to help the layers understand the communication. When sending, each layer segments and encapsulates the data that it receives from the layer above it. When receiving the data, each layer unwraps its layer’s control information and hands it up to the next layer.

Topic

Encapsulation.

Summary

The physical layer is responsible for modulating the data stream and placing it on the network’s carrier signal. A carrier signal is a waveform that can be represented as a sine wave. Modulation is the process of changing one or more properties of the carrier channel, as a means of encoding data into the signal. In some situations, multiplexing—either through frequency or time division—can be used to place multiple data streams onto a carrier signal at the same time. Baseband is when a digital modulated signal occupies all of the carrier channel. Broadband is when an analog modulated signal occupies only a portion of a carrier channel, allowing multiplexing to take place.

Modulation.

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PACE-IT: Basic Network Concepts (part 1)

Education

Transcript of PACE-IT: Basic Network Concepts (part 1)