Network Operating Systems
By Stephen Bucaro
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.
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.
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 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:
• The OSI Session Layer
• Session Border Controllers - More Than Just a Voice Firewall
• Evolution of the Microsoft NOS (Active Directory)
• Neighbor Discovery Protocol (NDP)
• What Are Private IP Addresses?
• Classless IP Addressing
• Internet Protocol versions IPv4, IPv5 and IPv6
• Routing Datagrams
• TCP Windowing
• Video - The Upper Layers 5 Through 7 of the OSI Networking Model