Explain the flow control mechanism. System for sending messages to other computer users based on e-mail addresses. SMTP provides mail exchange between users on the same. Post a comment. Where is the Menu? How to request Study Material?

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Types: 1. Local 2. Remote 1. Local: If the devices are restricted in a geographical area. Remote: If the devices are farther away without any geographical restriction. Fundamental Characteristics: 1. Delivery 2. Accuracy 3. Timeliness Components: Data communication systems are made up of five components. Message 2. Receiver 4. Medium 5. Protocol 1. Message: This is the information to be communicated. It can consist of text, numbers, pictures, sound or video or any combination of these. Sender: It is the device that sends the data message.

It may be a computer, workstation, telephone handset, video camera… 3. Receiver: It is the device that receives the message. It may be a computer, workstation, telephone handset, television… 4. Medium: It is the physical path which a message travels from sender to receiver. It may consist of twisted pair wire, coaxial cable, fiber optic cable, laser or radio waves.

Protocol: It is a set of rules that governs data communication. It is a agreement between the communication devices. Distributed processing: Here tasks are divided among multiple computers.

Each separate computer handles a subset. Advantages: 1. Distributed database 3. Faster problem solving 4. Security through redundancy 5. Network Criteria: A network must meet a number of criteria to be considered as effective and efficient.

Performance 2. Reliability 3. Security 1. Performance: The performance can be measured by two times are, I. Transit time II. Response time I. Transit time: It is the amount of time required for a message to travel from one device to another device. Response time: It is the elapsed time between an inquiry and a response. The performance can be measured by number factors are, i.

Number of user ii. Type of transition medium iii. Hardware iv. Software i. Number of user: Large number of concurrent users produces slow response time and heavy traffic loads. Type of transition medium: The medium defines the speed of data travel.

Hardware: The type of hardware can affect the speed and capacity of transmission. Software: The software can affect speed and reliability of a network link. Frequency of Failure: A network that fails often. Recovery time: How much time it takes to recover service after a failure has occurred? Catastrophe: Failures due to such reasons are fire, earthquake, theft… 3.

Security: It refers to protecting data from unauthorized access and viruses. Unauthorized Access: Sensitive data must be protected from unauthorized access. Protection can be done by user identification and passwords at the lowest level. At the highest level, encryption techniques may use. Viruses: A virus is an illicitly introduced code that damages the system. Local area network. Metropolitan area network. Wide area network. Local Area Network: They are usually privately owned and link the devices in a single office, building and campus.

Currently LAN size is limited to a few kilometers. The most common LAN topologies are bus, ring and star. They have data rates from 4 to 16 Mbps. Today the speed is on increasing and can reach mbps. Metropolitan Area Network: They are designed to extend over an entire city. It may be a single network or connecting a number of LANs into a large network. So the resources are shared between LANs.

Wide Area Network: It provides a long distance transmission of data, voice, image and video information over a large geographical are like country, continent or even the whole world. Point to point 2. Multi point. Point To Point: It provides a dedicated link between two devices of the channel. The entire capacity of the channel is reserved for transmission between those two devices. Multipoint: More than two devices can share a link by using this type of connection.

It also called as multidrop. The capacity channel is shared either temporary or spatially. It simultaneously use, it is spatially shared. If it takes turns, it is time shared line configuration. Two or more devices connect to a link; two or more links form a topology.

It is the geographical representation of the relationship of all the links and linking devices to each other. Mesh 2. Star 3. Tree 4. Bus 5. Mesh Topology: Here every device has a dedicated point to point link to every other device.

It must have n-1 IO ports. They use dedicated links so each link can only carry its own data load. So traffic problem can be avoided. It is robust. If any one link get damaged it cannot affect others 3. It gives privacy and security 4. Fault identification and fault isolation are easy. Disadvantages: 1. The amount of cabling and the number IO ports required are very large. Since every device is connected to each other devices through dedicated links. The sheer bulk of wiring is larger then the available space 3.

Hardware required to connect each device is highly expensive. Example: A mesh network has 8 devices. Calculate total number of cable links and IO ports needed. There is no direct traffic between devices. The transmission are occurred only through the central controller namely hub.









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