Computer Network ,Network Hardware Components, Network Software Components, Transmission Technology of Network , Hardware types, Network software protocol
NETWORK HARDWARE :
Network hardware has 2 main dimensions :
- Transmission technology
- Scale
Transmission Technology
In transmission technology there are 2 types.
- broadcast links and
- point-to-point links.
- Point-to-point links connect individual pairs of machines. To go from the source to the destination on a network made up of point-to-point links, short messages, called packets is used.
- Point-to-point transmission with exactly one sender and exactly one receiver is sometimes called unicasting.
- On a broadcast network, the communication channel is shared by all the machines on the network; packets sent by any machine are received by all the others. An address field within each packet specifies the intended recipient. Upon receiving a packet, a machine checks the address field. If the packet is intended for the receiving machine, that machine processes the packet; if the packet is intended for some other machine, it is just ignored.
- A wireless network is a common example of a broadcast link, with communication shared over a coverage region that depends on the wireless channel and the transmitting machine.
- Broadcast systems usually also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting. Some broadcast systems also support transmission to a subset of the machines, which known as multicasting.
Scale:
- Distance is important as a classification metric because different technologies are used at different scales.
- At the top are the personal area networks, networks that are meant for one person. Beyond these come longer- range networks. These can be divided into local, metropolitan, and wide area networks, each with increasing scale.
NETWORK SOFTWARE :
Protocol hierarchies :
- To reduce the design complexity, most networks are organized as a stack of layers or levels, each one built upon the one below it. The number of layers, the name of each layer, the contents of each layer, and the function of each layer differ from network to network.
- The purpose of each layer is to offer certain services to the higher layers while shielding those layers from the details of how the offered services are actually implemented.
- A protocol is an agreement between the communicating parties on how communication is to proceed.
- The entities comprising the corresponding layers on different machines are called peers. The peers may be software processes, hardware devices, or even human beings. No data are directly transferred from layer n on one machine to layer n on another machine. It is transferred through the physical medium( actual communication occurs). Virtual communication is shown by dotted lines and physical communication by solid lines.
- Between each pair of adjacent layers is an interface. The interface defines which primitive operations and services the lower layer makes available to the upper one.
- A set of layers and protocols is called a network architecture. The specification of an architecture must contain enough information to allow an implementer to write the program or build the hardware for each layer so that it will correctly obey the appropriate protocol. A list of the protocols used by a certain system, one protocol per layer, is called a protocol stack.
- The above diagram is the example of providing communication to the top layer of 5 layer network.
- A message, M, is produced by an application process running in layer 5 and given to layer 4 for transmission.
- Layer 4 puts a header in front of the message to identify the message and passes the result to layer 3. The header includes control information, such as addresses, to allow layer 4 on the destination machine to deliver the message.
- Layer 3 decides which of the outgoing lines to use and passes the packets to layer 2. Layer 2 adds to each piece not only a header but also a trailer, and gives the resulting unit to layer 1 for physical transmission.
- At the receiving machine the message moves upward, from layer to layer, with headers being stripped off as it progresses.
Design Issues For the Layers :
Some of the design issues are
i) Reliability
ii) Evolution of the network
iii) Resource Allocation
iv) Security
Reliability :
- One mechanism for finding errors in received information uses codes for error detection. Information that is incorrectly received can then be retransmitted until it is received correctly. error correction, where the correct message is recovered from the possibly incorrect bits that were originally received.
- Another reliability issue is finding a working path through a network. The process of selecting a path for traffic in a network or between or across multiple networks is called routing.
Evolution of network :
- Since the networks grow larger and new designs emerge in the existing networks, key structuring mechanism used to support the change by dividing the overall problem called, protocol layering is implemented.
- Every layer needs a mechanism for identifying the senders and receivers that are involved in a particular message. This mechanism is called addressing or naming, in the low and high layers, respectively.
- The mechanism which involves in doing disassembling, transmitting, and then reassembling messages in overall network is called Internetwork. Designs that continue to work well when the network gets large are said to be scalable.
Resource Allocation :
- Networks provide a service to hosts from their underlying resources, such as the capacity of transmission lines(bandwidth).
Statistical Multiplexing :
- Sharing the resources based on the statistics of demand. It can be applied at low layers for a single link, or at high layers for a network or even applications that use the network.
Flow Control
- Flow control is a technique used to regulate data transfer between computers or other nodes in a network. Flow control ensures that the transmitting device does not send more data to the receiving device than it can handle.
Congestion
- When too many computers want to send the data and the network cannot handle it all. Thus overloading of computers are called congestion. This makes the end users’ network slow.
Quality of service(QoS)
- QoS is the use of mechanisms or technologies that work on a network to control traffic and ensure the performance of critical applications with limited network capacity.
Security :
Confidentiality:
- The data is only available to authorized parties. When information has been kept confidential, it means that it has not been compromised by other parties.
Authentication:
- Authentication is used by a client when the client need to know that the server is system it claims to be. In authentication, the user or computer has to prove its identity to the server or client.
Integrity:
- Integrity means guarding against improper information modification or destruction and includes ensuring information non repudiation and authencity.
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Computer network
