Chapter 8: Local Area Network: Part 2

INTRODUCTION

Network operating systems and network support software are two of the most important. Network operating systems are essential if the network is going to allow multiple users to share resources. The network operating system provides users with password protection on their accounts and network administrators with services that help them control access to network resources as well as use and administer network


WIRELESS ETHERNET

• Wireless LAN or Wireless Ethernet: a LAN that is not based primarily on physical wiring but uses wireless transmissions between workstations
• Workstation can be anywhere as long as it is within transmitting distance to an access point
• The access point: is essentially the interface device between the wireless user device and the wired LAN
• Access point acts as a bridge between the wired and wireless networks and can perform basic routing functions
• Typically found in 3 basic configuration:
• Single-cell wireless LAN: at the center cell is the access point
• Multiple-cell layout: multiple cells are supported by multiple access points, as in cellular telephone work
• Ad hoc or peer to peer: the is no access point, each user device communicates directly with the other users devices

1. Wireless LAN Standards

• IEEE 802.11
• Original wireless standard, transmission rated for infrared wireless range from 1-2 Mbps
• IEEE 802.11b
• Second wireless standard, can transmit data at a theoretical rate of 11 Mbps using 2.4 GHz signals
• With directional antennae designed for point-to-point transmission (rare), 802.11b can transmit for more than 10 miles
• IEEE 802.11a
• Capable of supporting a theoretical transmitting rate at 54 Mbps  using the 5-GHz frequency range
•  IEEE 802.11g
• Capable of transmitting data at 54 Mbps (theoretical) but using the same frequencies as 802.11b (2.4-GHz)
• IEEE 802.11n (100 Mbps theoretical) is the latest standard to be approved
• 802.11n 
• has a theoretical maximum data rate of 600 mbps with actual rates of roughly 100-145 Mbps
• uses MIMO technology (multiple input multiple output)–Sender and receiver have multiple antennas for optimum reception
• 802.11ac uses advanced MIMO, wider channels in the 5 GHz band and advanced QAM techniques to achieve high data rates
• To provide security, most systems use either:
• Wired Equivalent Privacy (WEP): provides either 40- or 128-bit key protection (dated)
• WPA or WPA 2 (Wi-Fi Protected Access)
• WPA 2 uses the most advanced encryption techniques
• Wireless LANs may also be configured without an access point 
• These configurations are called “ad-hoc”

2. Wireless CSMA/CA

• Carrier sense multiple access with collision avoidance (CSMA/CD): supporting wireless LANs limits when workstation can transmit, in an attempt to reduce the number of collisions
• How does CSMA/CA do this?
• All devices, before they transmit, must wait an amount of time called an interframe space (IFS)
• Some applications have a short IFS, while others have a long IFS
• If two applications want to transmit at same time, the application with shorter IFS will go first

3. CSMA/CA Frame Format

• Frame format for wireless Ethernet CSMA/CA has four address fields

NETWORK OPERATING SYSTEM

• Operating system is the program initially loaded into computer memory when the computer is turned on; it manages all the other programs (applications) and resources
• Application programming interface (API): application makes use of the operating system by making service requests
• Multitasking operation system: allow multiple programs to run at the same time. The OS runs only one program at a time, but it jumps from one program to the next so fast that it appears as if multiple programs are running at the same time
• Network OS is large, complex program that manages the resources common on most local area network

NETWORK OPERATING SYSTEMS PAST AND PRESENT

1. Novell NetWare

• NetWare directory services (NDS): an intelligent system that authenticates users and includes a distributed database of information about every application, user, server, and resource on a network
• Version 3 
• User logs onto a particular server–Bindery maintains directory system that contains the usernames and passwords of network users and groups of users authorized to log in that server
• Version 4
• Bindery replaced by powerful NDS database–No longer supported by Novell (beginning of 2004)
• Novell NDS (NetWare Directory Services)
• A database that maintains information on, and access to, every resource on the network, including users, groups of users, printers, data sets and servers
• Network administrator creates a hierarchical tree structure that represents the layout of the organization
• Tree structure is composed of organizational units which are composed of further objects, and leaf objects which are usually entities such as users, peripherals, servers, printers, queues and other network sources

2. Microsoft Windows NT and Window Server

Windows NT Version 4

• User interface for single user personal computers
• NT had only Domain
• Container object that contained users, servers, and other resources that share account and security information
• Domains are not hierarchal and in many cases they increase the level of administration 

Window Server 2000

• Incorporated Active Directory: that stores information about all the objects and resources in a network and makes this information available to users, network administrators, and application program
• Active directory creates a hierarchical application structure of resources
• To construct an active directory hierarchy, a tree design is created
• Objects, such as users, groups of users, computers, applications, and network devices are the leaf items within the tree
• Leaf items are grouped in organizational units 

Window Server 2003

• Improvements to Active Directory, including new management tools
• Capability to interconnect up to 8 windows servers
• New and improved file and print support services
• Support for IPv6
• Better security features

Window Server 2008 and 2012

• The latest window of Window Network OS
• Expanded Active Directory, including new management tools
• New server core
• Self-healing server that can fix corrupted files and/or folders
• Increased processing speed
• Advancements in network security

3. Unix

• Well established and very popular multitasking OS capable of supporting network operations
• First OS written in the language C
• Very stable system capable of supporting very large operations

4. Linux

• OS based on the concept of Unix
• Many versions available for free or very small price
• Can receive the original source code along with the compiled code
• Very stable multitasking OS
• Is part of the growing family of open source software that is highly regarded within the business and educational industries

5. Mac OS X Server

• Apple created the Mac OS X server based on Unix concept, and shared some characteristics with both Unix and Linux operating systems such as fast, efficient, and stable code

SERVERS

• Server is the computer that stores software resources
• In order to support a network OS, you need one or more network servers
• Network servers are high-power workstations often with multiple processors, RAID, SCSI, and lots of memory and disk space–Various forms of servers include server appliances, and server blades
• Server virtualization allows you to create multiple servers in software all running on a single physical server
• To protect the server from catastrophic disk failure, disk drives on most network servers support one of the redundant array of independent disks (RAID) techniques
• RAID is a collection of techniques for interfacing multiple hard disk drives to a computer 
• Some of the more common RAID techniques include:
• RAID-0: Data is broken into pieces, and each piece is stored on different disk drives 
• This technique is known as striping–RAID-1
• Data is stored on at least two disk drives, in duplicate, to provide a level of redundancy (or fault tolerance), should one disk become corrupted
• This technique is known also as disk mirroring
• RAID-3: Data is redundantly stored across multiple disk drives (striping), and error-checking   information concerning the stored data is kept on a separate disk
• RAID-5
• Data is broken into pieces (stripes) and stored across three or more disks
• Parity information (error-checking code) is stored along with the striped data, not on a separate disk

2. Client/Server Networks versus Peer-to-Peer Networks

• A clear majority of LANs are client/server networks
• The client, or user workstation, requests something such as database from server. The server accepts the request, retrieves data and return a response
• Peer-to-peer networks also exist: may have servers, but the network relies less on the servers and more on the communications between workstations

NETWORK SUPPORT SOFTWARE

1. Utilities

• Utilities are software programs that operate int the background and support one or more functions to keep the network running at the optimal performance
• Some of the more common groups of network utility software:
• Antivirus software
• Anti-spam software
• Anti-spyware software
• Backup software
• Network-monitoring software
• Crash protection software
• Security software
• Remote software
• Uninstall software

2. Internet software

• the toolset to support internet-related services
• Web server software: the application or set of programs that stores web pages and allow users from anywhere in the world to access those web pages

SOFTWARE LICENSING AGREEMENTS

Licensing agreement: a legal contract and describes a number of conditions that must be upheld for proper use of the software package

Most licensing agreements specify conditions in the following areas:

• Software installation and use
• Network installation
• Backup copies
• Decompilation
• Rental Statement
• Upgrade availabilities
• Copyright restrictions
• Maintenance agreements

Most licensing agreements come in one of the following forms

• Single-user-single-station license: one station, one user at one time
• Single-user-multiple-station license: one user with multiple devices
• Interactive user license: operating system user licence and controlled number of concurrent users license
• Site license: allows software package to be installed on any and all workstations and servers at a given time
• Corporate License: allows software package to be install anywhere within a corporation, including multiple sites
• General public license: software that is free to share and change, however, the creator may still charge a fee

LAN SUPPORT DEVICES

Other devices necessary for the proper support of a LAN:

• Uninterruptible power supplies (UPS): a backup device that can maintain power to one or more pieces of equipment for short period of time
• Tape drives: backup device
• Printer
• Media converters: are necessary when connect one type of medium with another
• Workstation
• Thin client workstation: a computer with no disk drives of any kind, often with reduced memory and some kind of minimized operating system