What is a Protocol?
A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer.
See the Topology and Cabling sections of this tutorial for more information.
The most common protocols are:
· Ethernet
· FDDI
· ATM
The Ethernet protocol is by far the most widely used. Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system where each computer listens to the cable before sending anything through the network. If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computer will wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same instant. When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit. With this access method, it is normal to have collisions. However, the delay caused by collisions and retransmitting is very small and does not normally effect the speed of transmission on the network.
The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted over wireless access points, twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps up to 1000 Mbps.
To allow for an increased speed of transmission, the Ethernet protocol has developed a new standard that supports 100 Mbps. This is commonly called Fast Ethernet. Fast Ethernet requires the use of different, more expensive network concentrators/hubs and network interface cards. In addition, category 5 twisted pair or fiber optic cable is necessary. Fast Ethernet is becoming common in schools that have been recently wired.
The most recent development in the Ethernet standard is a protocol that has a transmission speed of 1 Gbps. Gigabit Ethernet is primarily used for backbones on a network at this time. In the future, it will probably be used for workstation and server connections also. It can be used with both fiber optic cabling and copper. The 1000BaseTX, the copper cable used for Gigabit Ethernet, is expected to become the formal standard in 1999.
LocalTalk is a network protocol that was developed by Apple Computer, Inc. for Macintosh computers. The method used by LocalTalk is called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). It is similar to CSMA/CD except that a computer signals its intent to transmit before it actually does so. LocalTalk adapters and special twisted pair cable can be used to connect a series of computers through the serial port. The Macintosh operating system allows the establishment of a peer-to-peer network without the need for additional software. With the addition of the server version of AppleShare software, a client/server network can be established.
The LocalTalk protocol allows for linear bus, star, or tree topologies using twisted pair cable. A primary disadvantage of LocalTalk is speed. Its speed of transmission is only 230 Kbps.
The Token Ring protocol was developed by IBM in the mid-1980s. The access method used involves token-passing. In Token Ring, the computers are connected so that the signal travels around the network from one computer to another in a logical ring. A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant. At this point, the data is captured by the receiving computer. The Token Ring protocol requires a star-wired ring using twisted pair or fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to the increasing popularity of Ethernet, the use of Token Ring in school environments has decreased.
Fiber Distributed Data Interface (FDDI) is a network protocol that is used primarily to interconnect two or more local area networks, often over large distances. The access method used by FDDI involves token-passing. FDDI uses a dual ring physical topology. Transmission normally occurs on one of the rings; however, if a break occurs, the system keeps information moving by automatically using portions of the second ring to create a new complete ring. A major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps.
Asynchronous Transfer Mode (ATM) is a network protocol that transmits data at a speed of 155 Mbps and higher. ATM works by transmitting all data in small packets of a fixed size; whereas, other protocols transfer variable length packets. ATM supports a variety of media such as video, CD-quality audio, and imaging. ATM employs a star topology, which can work with fiber optic as well as twisted pair cable.
ATM is most often used to interconnect two or more local area networks. It is also frequently used by Internet Service Providers to utilize high-speed access to the Internet for their clients. As ATM technology becomes more cost-effective, it will provide another solution for constructing faster local area networks.
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What is a Network Operating System?
Unlike operating systems, such as DOS and Windows, that are designed for single users to control one computer, network operating systems (NOS) coordinate the activities of multiple computers across a network. The network operating system acts as a director to keep the network running smoothly.
The two major types of network operating systems are:
Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source (See fig. 1). In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Peer-to-peer networks are designed primarily for small to medium local area networks. AppleShare and Windows for Workgroups are examples of programs that can function as peer-to-peer network operating systems.
Fig. 1. Peer-to-peer network
Advantages of a peer-to-peer network:
· Less initial expense - No need for a dedicated server.
· Setup - An operating system (such as Windows XP) already in place may only need to be reconfigured for peer-to-peer operations.
Disadvantages of a peer-to-peer network:
· Decentralized - No central repository for files and applications.
· Security - Does not provide the security available on a client/server network.
Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers (See fig. 2). The file servers become the heart of the system, providing access to resources and providing security. Individual workstations (clients) have access to the resources available on the file servers. The network operating system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location. Novell Netware and Windows 2000 Server are examples of client/server network operating systems.
Fig. 2. Client/server network
Advantages of a client/server network:
· Centralized - Resources and data security are controlled through the server.
· Scalability - Any or all elements can be replaced individually as needs increase.
· Flexibility - New technology can be easily integrated into system.
· Interoperability - All components (client/network/server) work together.
· Accessibility - Server can be accessed remotely and across multiple platforms.
Disadvantages of a client/server network:
· Expense - Requires initial investment in dedicated server.
· Maintenance - Large networks will require a staff to ensure efficient operation.
· Dependence - When server goes down, operations will cease across the network.
Examples of network operating systems
The following list includes some of the more popular peer-to-peer and client/server network operating systems.
· Apple Computer Inc.
(408) 996-1010
· Program Highlights:
· AppleShare is Apple Computer's networking solution. It includes both server and workstation software. Since it supports the multitasking features of System 7, services and applications can run concurrently.
· Back
· Microsoft Corporation
(800) 426-9400
fax (206) 936-7329
· Program Highlights:
· An enhanced version of Windows 2000 that provides a powerful client/server network operating system. It contains all of the features of Windows 2000 including capabilities as an application server and multitasking.
· Back
· Novell, Inc.
122 East 1700
Provo
(800) 453-1267
fax (801) 429-3098
· Program Highlights:
· Most popular client/server network operating program available on the market at this time. Has file by file compression which allows system files to hold more online data by compressing files that are infrequently accessed or used. Disk Duplexing and Disk Mirroring are features that protect data from failures in the hardware by writing the information in two different drives on the network. Technical support is good. Netware can handle almost any size network.
Computer Network Installation
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By Adrian Griffiths
Computer network installation has become an essential prerequisite for any efficient modern-day business as it allows employees to truly work as a team by sharing information, accessing the same database and staying in touch constantly. For a computer network to give the best results, a lot of detailed planning and foresight is required before installation.
Firstly, an organisation needs to clearly define its requirements – how many people would use the network, how many would use it locally (within the office) and how many might require remote access (from a different location), how many computers and other devices (servers, printers, scanners) would be connected to the network, what are the needs of the various departments and who would be in charge of running/managing the network. It also helps if one can anticipate the direction the company would take in the near future so potential growth can be factored in during computer network installation.
The technology issues should also be ironed out in advance – hardware, software, servers, switches, back-up devices, cables and network operating systems. Make sure you have the required licenses to run the software on all your machines before installing a computer network. Alongside computer network installation should proceed the building of a dedicated technical support staff, either within your own organisation or outside consultants. Delegate responsibility clearly for network management. Before installing the network, you also need to choose the security mechanism to protect corporate data and keep viruses at bay.
The transition to a new or upgraded computer network can bring some teething problems. To minimise chances of confusion, the company might need to train its staff to make them familiar with the new system. Careful planning will to a large extent prevent crises like system downtime and network crashes.
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