Network Operating System

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 and Client/Server

The following list includes some of the more popular peer-to-peer and client/server network operating systems. Examples: Artisoft's LANtastic, AppleShare, Banyan VINES, Microsoft Windows for Workgroups, Microsoft Windows NT Server, Novell's NetWare, and Microsoft's LAN Manager are examples of network operating systems.
Peer-to-Peer
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. 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 and therefore are known as peers. 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.

Each computer functions as both a client and a server. There is no dedicated server. Peer-to-Peer networks are also called workgroups. The term workgroup describes a small group of individual, typically ten or fewer, who work together.

Peer to Peer networks are of good choices for environments where:
• There are fewer users.
• Users share resources.
• Security is not an issue.
• No centralized control needed.


Fig: 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 95) 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
In an environment with more users, a peer-to-peer network with computers acting as both server and client will probably not be adequate. Therefore a network must have dedicated server. A dedicated server is one that only functions as a server and it is not used as a client or workstation. Client Server networks has become the standard model for networking.
Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers. 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 allows multiple users to simultaneously share the same resources irrespective of physical location. Novell Netware and Windows NT Server are examples of client/server network operating systems.

Client/server computing is also a commonly used model on the Internet. Users typically have client software (called Web Browser) that provides an easily used interface for interacting with this giant WAN. Other types of processing, such as receiving, storing, sending e-mail message and serving information are carried out by remote computers (called Web Server) running the server part of the relevant software.


Fig: 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.


Novell Netware
It is a network operating system developed by Novell, Inc that initially used cooperative multitasking to run various services on a PC. NetWare evolved from a very simple concept: one or more dedicated servers were connected to the network, and disk space was shared in the form of volumes.

NetWare was based on the NetWare Core Protocol (NCP), which is a packet-based protocol that enables a client to send requests to and receive replies from a NetWare server.
The following are Different Versions of Novell Netware with their specific features:
• Netware 3.x: Netware Loadable Module (NLM)
• NetWare 4.x: Novell Directory Services
• Netware 5.x: Network Storage Services, Java Virtual Machine etc.
• Netware 6.x: SMP Support, Domain Controller etc.
• Novell Open Enterprise Server: A dual Kernel Product that ran on Linux Platform

Windows NT
Microsoft released Windows NT (New Technology), a 32-bit operating system for PCs, in 1993. It was originally designed as the successor to DOS but by the time it was ready for release, it has become too large to run on most of the PCs. As the result

Microsoft separated Windows NT into two products:
Windows NT Workstation
Windows NT Server.

1 Windows NT Workstation
• It can run on a broader range of CPUs.
• Typically used on individual, stand-alone PCs that may or may not be part of a network.
• It incorporates much greater security than Microsoft’s other OS like users must have an account; resources can be configured to limit access to specific user.
• Use new file system NT File System (NTFS), a high performance file system that replaces the older FAT file system introduced by MS-DOS.
• It is more fault-tolerant than other Microsoft’s OS
• Also integrates features that provide for disk mirroring.

2 Windows NT Server
• Incorporates all the features of Windows NT Workstation but also has other capabilities.
• Deigned as file and print servers
• Offers expanded security features for grouping and authenticating users and controlling their access to network resources.
• Support RAID (Redundant Array of Independent Disks) for disk duplexing, disk striping and disk mirroring.

Windows 2000
Windows 2000 combines the user-friendly interface and features of Windows 98 with the file system, networking, power and stability of Windows NT. Different versions of Windows 2000 are available:

• Windows 2000 Professional: This version is found primarily on office PCs. it includes support for symmetric multiprocessing (SMP) with up to two processors. SMP is a protocol that allows the OS and applications to run on multiple processors at the same time, improving performance on huge jobs.

• Windows 2000 Server: This version is for a network server for the average business, with SMP support for up to two processors.

• Windows 2000 Advanced Server: This version is a more powerful version of the server edition. It includes support for SMP with up to four processors, enhanced balancing of network and component loads, and support for more RAM. Another important feature is print server clustering. With clustering, Windows 2000 can group print server to provide alternate printers if one print server fails.

UNIX
• UNIX is older than all the other PC OS and in many ways it served as a model for them.
• UNIX is a multitasking and multi-user OS developed by Bell Lab in 1969.
• UNIX also supports multiprocessor systems.
• UNIX was designed for engineers and programmers and very strong and powerful OS for them. But for non-technical persons, it is an extremely difficult OS.
• It runs on mini, mainframe, super computers and notebook
• It is also used with powerful 32-bit microcomputers.
• Initially UNIX has command-line interface but developers have created windows-based GUIs for UNIX such as MOTIF and OpenLook.
• UNIX has cryptic instruction.

LAN Manager
The LAN Manager was a Network Operating System (NOS) from Microsoft, developed in cooperation with 3Com. LAN Manager is based on the OS/2 and NBF protocol. There was also LAN Manager/X (LMX) for UNIX based systems. In 1990, Microsoft announced LAN Manager 2.0 with a lot of improvements. The latest version, LAN Manager 2.2, which included an MS-OS/2 1.31 base operating system, remained Microsoft's strategic server system until the release of Windows NT Advanced Server in 1993.

LANtastic
LANtastic is a peer-to-peer local area network operating system for DOS, Microsoft Windows, Novell NetWare and OS/2. LANtastic supports Ethernet, ARCNET and Token Ring adapters. Its multi-platform support allows a LANtastic client station to access any combination of Windows or DOS operating systems, and its interconnectivity allows sharing of files, printers, CD-ROMs and applications throughout an enterprise.

LANtastic was especially popular before Windows 95 arrived with built-in networking and was nearly as popular as the market leader at the time, Novell. LANtastic was originally developed by Artisoft Inc. in Tucson, Arizona. Following the release of TeleVantage, Lantastic and Artisoft's other legacy products were acquired by SpartaCom Technologies in 2000. SpartaCom is now known as Converging Technologies.

The current version is LANtastic 8.01. It can connect PCs running DOS 5.0 with Windows 3.x or higher o.s. including Windows XP.

The Internet
The Internet is an interconnected network of thousands of networks and millions of computers linking businesses, education institutions, government agencies and individuals together. The Internet provides around 400 millions people around the world and is increasing at a rapid rate. No one controls the Internet or how it functions, nor it is owned by anybody, yet it has provided the infrastructure for a transformation in commerce, scientific research, and culture.

Intranet and Extranet
Before the advent of the World Wide Web, most corporate networks basically supported file sharing and e-mail. However, corporate and academic networks are being configured more frequently to resemble the Internet. Two common types of “corporate spin-offs” of the web are called intranets and extranets. These systems are designed to support data sharing, scheduling and workgroup activities within an organization.

An intranet is a Local area Network or wide area network that uses TCP/IP protocol but belongs exclusively to a corporation, school, or organization. An intranet is a private network that uses internet protocols, network connectivity, and possibly the public telecommunication system to securely share part of an organization's information or operations with its employees. The intranet is accessible only to the organization’s workers. If the intranet is connected the Internet, then it is secured by a firewall to prevent unauthorized users from gaining access to it.

An extranet is an intranet that can be accessed by outside users over the Internet. To gain entrance to the extranet’s resource, an external user (such as a business partner) typically must log on to the networks by providing a valid user ID and password.


Some Definitions
• 10Base2 - Ethernet specification for thin coaxial cable. It transmits signals at 10 Mbps (megabits per second) with a distance limit of 185 meters per segment.
• 10Base5 - Ethernet specification for thick coaxial cable. It transmits signals at 10 Mbps (megabits per second) with a distance limit of 500 meters per segment.
• 10BaseF - Ethernet specification for fiber optic cable. It transmits signals at 10 Mbps (megabits per second) with a distance limit of 2000 meters per segment.
• 10BaseT - Ethernet specification for unshielded twisted pair cable (category 3, 4, or 5), transmits signals at 10 Mbps (megabits per second) with a distance limit of 100 meters per segment.
• 100BaseT - Ethernet specification for unshielded twisted pair cabling that is used to transmit data at 100 Mbps (megabits per second) with a distance limit of 100 meters per segment.
• 100BaseTX -Ethernet specification for unshielded twisted pair cabling that is used to transmit data at 1 Gbps (gigabits per second) with a distance limitation of 220 meters per segment.
• Token - A special packet that contains data and acts as a messenger or carrier between each computer and device on a ring topology. Each computer must wait for the messenger to stop at its node before it can send data over the network.
• Terminator - A device that provides electrical resistance at the end of a transmission line. Its function is to absorb signals on the line, thereby keeping them from bouncing back and being received again by the network.
• Protocol -A formal description of a set of rules and conventions that govern how devices on a network exchange information.
• PCMCIA - An expansion slot found in many laptop computers.
• Node - End point of a network connection. Nodes include any device attached to a network such as file servers, printers, PCs, Laptops, or workstations.
• Multiplexer - A device that allows multiple logical signals to be transmitted simultaneously across a single physical channel.
• File Server - A computer connected to the network that contains primary files/applications and shares them as requested with the other computers on the network. If the file server is dedicated for that purpose only, it is connected to a client/server network. An example of a client/server network is Novell Netware. All the computers connected to a peer-to-peer network are capable of being the file server. Two examples of peer-to-peer networks are LANtastic and Windows for Workgroups.
• Expansion Slot - Area in a computer that accepts additional input/output boards to increase the capability of the computer.
• CSMA/CD - Carrier Sense Multiple Access Collision Detection is a network access method in which devices that are ready to transmit data first check the channel for a carrier. If no carrier is sensed, a device can transmit. If two devices transmit at once, a collision occurs and each computer backs off and waits a random amount of time before attempting to retransmit. This is the access method used by Ethernet.