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Each year 1.5 million shelter animals are euthanized (670,000 dogs and 860,000 cats). Source: ASPCA. The solution is not to shelter unwanted pets, but to SHUT DOWN THE PET MILLS. Anyone who wants a pet will just have to adapt a great pet from a shelter.

Network Operating Systems

The purpose of a network is to permit users share resources located on other computers and to share peripheral devices such as printers. A network operating system (NOS) is specialized systems software designed to provide networking functionality. Most network operating systems provide the following functions;

1. Permitting connection and access to network resources such as application software, data files, and peripherals.

2. Control access to the network's resources by allowing access to a resource only to users authorized to use the resource.

3. Provide means to configure the networks resources for efficiency and ability to monitor and troubleshoot the network.

The main network operating systems in use today are:

Various versions of Unix.
Various versions of Windows.
Novel Netware.

Novel NetWare

NetWare 3.x used the IPX/SPX protocol suite and lacks a centralized security database. Each NetWare 3.x server maintains its own security database called the "bindery". When a user logs in, the server locates the user's name and password in the binary and reads the account information to determine which resources it will share with the user. To access resources on three different servers, a user needs three separate user accounts.

NetWare 4.x organized user and resource information into a centralized security database called the Novel Directory Service (NDS). Users log into the NDS and are able to access resources anywhere on the network. TCP/IP is supported by "encapsulating" IPX/SPX packets inside TCP/IP packets. This made system performance less efficient by adding an additional layer of protocol.

NetWare 5.x removed the need for encapsulating IPX/SPX by using TCP/IP as its native protocol.

Unix

Bell Laboratories invented the Unix operating system. Bell Labs allowed Universities to modify the operating system for their own use. This resulted in many non-compatible varieties of Unix, including Sun Microsystems Solaris, and IBM's AIX. This fragmentation of the Unix operating system allowed Microsoft's Windows operating system to get a foothold in the network operating system market.

The Unix Network File System (NFS) enables a Unix system to treat files in directories on another Unix computer as though they were local files. The remote directory is "mounted" into the local file system, allowing the files to be shared transparently.

Linux is a variety of Unix developed by Linux Torvalds. Anyone who receives a copy of Linux also receives the full source code. Access to the source code allows programmers to modify the operating system. Torvalds license agreement requires that those who modify the source code must share the source code for those modifications.

The Linux operating system and some Linux applications are available for free download from the Internet. Red Hat and Caldera are companies that charge for providing a user's guide along with a copy of Linux. Because of the low cost, Linux is becoming the operating system of choice for Web servers.

Windows NT

Windows NT is Microsoft's business strength network operating system. It supports the TCP/IP protocol suite. Servers can be joined in a group called a "domain". One server acts as the Primary Domain Controller (PDC) by storing the Security Access Manager (SAM) database. When a user logs in, the SAM copies an "access token" to the user's computer. The access token permits the user to access resources in the domain. The domain may also contain one or more Backup Domain Controllers (BDC) which store duplicate copies of the SAM database.

Multiple Windows NT domains may communicate by configuring "trust" relationships between them.

More Networking Protocols and Standards:
• Remote Control Protocols
• How to Set Up FTP (File Transfer Protocol)
• SYN-ACK Handshake to Establish a TCP Connection
• Network Gateways
• Wireless Network Standards - 80211a, 80211b, 80211g, 80211n, 80216
• The OSI Reference Model
• Free eBook: IPv6 Addressing
• The OSI Presentation Layer
• What Are Private IP Addresses?
• Routing Datagrams

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