Transmitting and Receiving
1. The school network is geographically shaped like a star topology in that there is a “central computer” of sorts which the whole network relies on to function (the server room), and that each node is linked to. If one device or cable is broken, most of the network can still operate, as is the norm in star topologies.
However, the network itself is a bus topology in that all the devices are connected to a bus line that travels around the entire network, rather than each device having their own bus line. Also, devices in the school network rely on the functioning of other devices to connect to the network, a common characteristic of bus topologies.
2. Exercise 3.3:
1. Simplex mode allows transmissions in one direction only from the sender to the receiver; half-duplex mode allows transmission in both direction but not at the same time; and full-duplex mode allows transmission in both directions at the same time.
2. Protocols define how a link is established, how data is transmitted and how errors are detected and corrected.
3. ZModem seeks to rectify the limitations associated with YModem, with new features like variable block size and CRC support. It provides for high-speed packet and network communication environments.
4. The X.25 protocol is the standard packet switching protocol. It is used for low-speed applications, such as credit card verifications and automatic teller machine transactions.
5. LANs connect computers within a single building or site, covering only a small geographical area. WANs, on the other hand, connect computers over hundreds or thousands of kilometers and consist of a host computer with a number of terminals.
6. A privately leased line offers higher transmission speeds and more accurate transfer of data than those available through the public switched telephone network.
7. Packet switching is a technique that divides messages into small data packets, transmits the packets and later joins the packets to form the original message. The data packets may be sent along different paths and thus may arrive at different times.
8. A bus topology is an arrangement where all the devices are attached to a bus which has a beginning and an end. Devices check the bus and retrieve the messages intended for them (recognized by their signals). A ring topology, on the other hand, is shaped like a ring and thus has no beginning or end. Data flow is in one direction only, moving from device to device until it reaches its destination.
9. Messages are transmitted simultaneously to all nodes on the network in both directions. Addressing information allows each node to recognize and receive individual data packets intended for it. Collisions occasionally occur.
With token ring, special data packets called tokens are continually passed between nodes on the network. Workstations with data to send capture a free token and attach data along with addressing information. A busy token with data cannot be used by other nodes. When the data arrives at the destination, the data is replaced with an acknowledgement and sent back to the original sending node.
10. When a node wishes to transmit, it “listens” to the bus for signals. When there are no signals on the bus, it transmits. However, collisions between packets do occur and when a collision is detected each device stops transmitting and the retransmits at another time.
11. There are 4 main types of servers:
- A file server is a controlling computer in a network that stores the programs and data shared by users. The files stored on this server can be retrieved by any node provided it has access rights.
- A print server is a computer in a network that controls one or more printers and stores data to be printed. A print server can be used with or without a file server.
- A mail server is a computer in a network that provides e-mail facilities. It stores incoming mail for distribution to users and forwards outgoing mail to appropriate devices.
- A Web server is a computer in a network that provides a connection to the Internet. All the Internet traffic is directed through this server.
12. A router maintains a table of available routes that a data packet can take and their conditions. It uses this table together with distance and cost algorithms to determine the best route for a given data packet.
13. A bridge is a combination of hardware and software to link two similar networks. It often connected LANs that use the same protocol. A gateway, on the other hand, is a combination of hardware and software to link two different types of networks. Unlike bridges, this usually involves converting different protocols.
14. A hub is a central connecting device in a network. Data arrives at the hub from one or more devices and is forwarded out using just one cable. It can also include a router.
15. There are 3 methods of wire transmission:
- Twisted-pair cable consists of two thin insulated copper wires, twisting to form a spiral. The twisting reduces the amount of interference from other cabling. It is the slowest medium, with a bandwidth of up to 60 Kbps.
- Coaxial cable consists of a single copper wire surrounded by an insulator, grounded shielding, and an outer insulator. The shielding allows data to be transmitted with little distortion. It is commonly used over distances of less than a few kilometers. The bandwidth for a coaxial cable is 10 Mbps.
- Fibre-optic cable uses a laser of light to carry data in small glass fibres about the diameter of a human hair. It is free from electromagnetic and radio interference and can transmit data at high speeds without errors. The bandwidth for fibreoptic cables is in excess of 400 Mbps. A single strand of optical fibre can carry thousands of telephone conversations.
16. Baseband networks use the entire capacity of the cable to transmit only one signal at a time, whereas broadband networks divide the cable so that several signals can be transmitted at the same time.
17. A microwave is a high-frequency radio signal sent through space in a straight line from one antenna to another. Microwaves have been used for several decades to transmit both voice and data. Microwave transmission is faster than telephone lines or coaxial cables. Even though it is reasonably error-free, weather conditions or such objects as trees and buildings can obstruct the signal and affect the transmission.
18. The responsibilities of a network administrator include network security, installing new applications, distributing software upgrades, monitoring daily activity, enforcing licensing agreements, developing a storage system and providing routine backups. These responsibilities are completed using the network operating system.
19. The tasks performed by a network operating system include:
- Administration- adds, removes and organizes users; installs hardware devices and software applications; and carries out maintenance operations, such as backup.
- File management- gives users access to the remote hard disks on the server and provides a file system and the ability to manage a network directory.
- Applications- handles requests from users to share data and applications.
- Resource management- allows network devices, such as printers and modems, to be shared; assigns users to printers; and orders print jobs.
- Security- monitors and restricts access to network resources.
20. Logon is the procedure used to get access to the network. The user is identified by means of a user ID and a password. The logon procedure usually allows two or three attempts to enter the correct name and password, accounting for errors in typing. After logging on, the user is given access to only those features authorized by the network administrator.
21. The main purpose of an intranet is to share information and computing resources among the employees of an organisation. This information may be staff news, product information, telephone directories, policies, employee manuals or calendars.