Network Adapters And The Theoretical Network

Network Adapter:

• Network adapters perform all the functions required to communicate on a network.

• They convert data from the form stored in the computer to the form transmitted or received on the cable and provide a physical connection to the network.
• Fiber-optic Ethernet adapters convert the data from 8, 16 or 32 bit words to serial pulses of light.
• Microwave network interfaces convert the computer data to serial radio waves.
• Network adapters receive the data to be transmitted from the motherboard of your computer into a small amount of RAM called a buffer.
• The data in the buffer is moved into a chip that calculates a checksum value for the chunk and add address information, which includes the address of the destination card and its own address.
• Ethernet adapter addresses are permanently assigned when the adapter is made at the factory.
• The network adapter must still convert the serial bits of data to the appropriate media in use on the network.
• Some cards have more than one type of transceiver built in so you can use them with your choice of media.
• While adapters transmit, they listen to the wire to make sure the data on the line matches the data being transmitted.
• If another adapter has interrupted, the data being heard by the transmitting network adapter will not match the data being transmitted.
• If then happens, the adapter ceases transmitting and transmits a solid on state instead, which indicates to all computers that it has detected a collision and that they should discard the current frame because has been corrupted.
• The network adapter waits a random amount of time and then again attempts to transmit the frame.

You have remember some condition for selecting an Adapter:

• What type of network are you attaching to?
• What type of media are you using?
• What type of bus does your computer have?

The Open System Interconnection Model attempts to define rules that apply to the following issues:

• How network devices contact each other and if they have different languages, how they communicate with each other.
• Methods by which a device on a network transmissions are received correctly and by the right recipient.
• Methods to ensure that network transmissions are received correctly and by the right recipient.
• How the physical transmission media are arranged and connected.
• How to ensure that network devices maintain a proper rate of data flow.
• How bits are represented on the network media.
• The OSI model is nothing tangible; if is simply a conceptual framework.
• The OSI model does not perform any functions in the communication process.
• The OSI model simply defines which tasks need to be done and which protocols will handle those tasks, at each of the seven layers of the model.

Signals Transmission In Network Communication

Signal Transmission:

Signaling is the way data is transmitted across the medium. It uses electrical energy to communicate.

Two types of signaling:

• Digital signaling 
• Analog signaling

Digital Signaling:
Most computer networks use digital signaling.

Encoding data in a digital signal is called encoding schemes.

• Current-state encoding
• State-transition encoding

Current-state encoding:

• In current-state encoding strategies, data is encoded by the presence or absence of a signal characteristics or state.
• The signal is monitored periodically by network
• State-transition encoding method use transitions in the signal to represent data.
• Presence of transition represents a 1 and the absence of transition indicate a 0.

State-transition encoding schemes:

• Bipolar-Alternative Mark Inversion (AMI)
• Non-Return-to-Zero (NRZ)Manchester
• Differential Manchester
• Biphase Space (FM-0)
• Comparing Signaling Methods

Advantages of digital signaling:

• Fewer errors from noise and interference
• Uses less expensive equipment

Disadvantages of digital signaling:

• Suffer from attenuation

Advantages of Analog signaling:

• Less attenuation than digital signal
• Can be multiplexed to increase bandwidth

Disadvantages of analog signaling:

• More prone to errors from noise and interference

Bit Synchronization:

The coordination of signal measurement timing is called bit synchronization.

Two major method of bit synchronization:

• Asynchronous bit synchronization
• Synchronous bit synchronization
  
  

Asynchronous bit synchronization:

Asynchronous bit synchronization

Asynchronous communication requires that messages begin with a start bit so that the receiving device can synchronize its internal clock with the timing of the message.

It is normally short and the end of the message is signaled by a stop bit.

Synchronous bit synchronization:

Synchronous communication requires that some kind of clocking mechanism be put into place to keep the clocks of the sender and receiver synchronized.

Methods used for synchronous timing coordination:

• Guaranteed state change
• Separate clock signal
• Oversampling

Baseband and broadband Transmission

Baseband: use the entire media bandwidth for a single channel. Commonly used for digital signaling. Most LANs use baseband signaling.

Broadband: Provide the entire media bandwidth into multiple channels. Since each channel can carry a different analog signal, broadband networks support multiple simultaneous conversations over a single transmission medium.

Broadband: Provide the entire media bandwidth into multiple channels. Since each channel can carry a different analog signal, broadband networks support multiple simultaneous conversations over a single transmission medium.