To understand how wireless networking works, you first need to understand the basic elements of computer hardware, software, and networking. A quick review of the basics will help lay the foundation for the concepts in the later chapters. Let's start by examining the fundamental concepts of the computing and networking environment.

The chapter is divided into two sections:

• Computer architecture. The hardware/software elements that create a computer system.
• Network technology. The internetworking elements that enable computer systems to communicate with each other.

Computer Basics

The fundamental building blocks of a computer describe its architecture. These hardware and software elements combine to create the entire computing platform. A computer's architecture has four basic elements:

• The central processing unit (CPU) and its related processes
• Random access memory (RAM), read-only memory (ROM), and other types of memory
• Various input/output (I/O) devices
• The operating system and software

CPU

The basic functions of modern computers haven't really changed much since John von Neumann's "stored program concept" and Alan Turing's "universal machine" propositions of the 1930s. Although the technology functionality has improved exponentially, the process of binary computation (XOR, NAND, and so on) remain basically unchanged, as do the fundamental concepts of the architecture.

The CPU contains an arithmetic logic unit (ALU). The ALU performs arithmetic andlogical operations on the binary code of the computer. The CPU also contains other processing elements and functions, including program counters, control logic, accumulators, the instruction register, and other general-purpose registers.

Bus

The computer processing elements coordinate their activities by the means of a computer bus. A computer bus is a collection of electronic conductors running on a common plane and connecting these different computer functions.

In contrast to CPU speed, which has been steadily and dramatically increasing for years, it is only recently that bus speed, previously a major limiting factor in the computer's architecture, has been radically altered and improved. Computers may have a bus speed of 33 MHz, 66 MHz, 100 MHz, or higher.

Memory

The term "memory" often causes confusion because a computer's architecture uses many different types of memory for many different functions. Let's look at the main types of memory:

Random access memory (RAM). RAM is directly addressable and alterable memory. RAM is volatile, meaning that data will be lost if the power is removed from the system. RAM is used for primary (sometimes called "real") memory storage. This is the high-speed memory directly addressable by the CPU and used for storage of instructions and data associated with the program being executed.

Cache memory. Cache memory is a very small amount of high-speed RAM used to dynamically store the most recently used data and computer instructions. It improves the performance of the CPU by storing data that is most frequently accessed. Cache memory greatly improves the execution time of various processes.

Read-only memory (ROM). ROM provides the computer with nonvolatile storage, which means the data is (relatively) permanent. Nonvolatile storage retains its information even when the computer loses power. ROM is used to hold programs and data that is rarely changed, such as firmware. The contents of some ROM cannot be altered, whereas other ROM can be upgraded from the flash process, such as an EPROM.

Secondary memory. Secondary memory is a data storage area that, like ROM, is also nonvolatile. It is a larger, slower memory storage area, and consists of the familiar hard drives, floppy-disk drives, zip drives, and tapes. These are referred to as secondary memory.

Virtual memory. Virtual memory is a combination of primary and secondary memory that creates a large addressable memory space. This space allows the processor to access much larger amounts of memory than the RAM alone would be able to address. The Windows swap file is an example of virtual memory.

Operating Systems and Software

The primary program that controls the operations of the computer is called an operating system (OS). Windows NT, Windows 98, Windows 2000, Linux, and Unix are examples of operating systems. Operating systems manage various processes, such as memory and the file allocation tables.

The OS communicates with I/O systems through a controller, which is a device that interfaces with the peripherals and runs device drivers to communicate with the device. Examples of this type of controller are a disk controller, a network interface card (NIC), a modem, and a video controller.

Software

The CPU executes sets of instructions that tell the hardware what to do. These sets of instructions are grouped into various hierarchical levels of languages, which range from binary or mnemonic code (called assembly language) to high-level languages, like Java and BASIC.

High-level languages are converted into machine language through either interpreter or compiler programs. An interpreter operates on each high-level language source statement individually and executes the requested operation immediately, whereas a compiler first translates the entire software program into its corresponding machine language then executes them as a unit.

Network Technologies

In this book, the term network technologies refers to those hardware and software elements that allow computers to communicate with each other, whether to send email, surf the Web, or share a printer or documents. Since this book is about wireless networking, you should have some background in:

• Local area networks (LANs)
• Wide area networks (WANs)
• Virtual private networks (VPNs)
• Firewalls
• Protocols

Analog versus Digital

There are several differences between analog and digital signals. If you access the Internet via a dial-up connection at home, you probably are using a modem to create an analog circuit-switched connection. But analog technologies are more prone to interference; and they are less secure and run at slower speeds than digital technologies.

Digital has other advantages over analog as well. Long circuit-switched session setup and teardown times make analog networks unsuitable for high-speed networking, including wireless LANs. Also, digital communications can be managed by software, making it possible to build sophisticated communications switching products.

Local Area Networking

A data network consists of two or more computers connected for the purpose of sharing files, printers, exchanging data, email, and so on. To communicate via the network, every workstation must have a network interface card (NIC); a transmission medium such as copper, fiber, or wireless; and a network operating system (NOS). The networked computer usually connects to a network device of some sort (hub, bridge, router, or switch).

A local area network (LAN) is designed to operate in a specific limited geographic area. LANs connect workstations with file servers so they can share network resources like printers, email, and files. LAN devices are linked using a type of connection medium (copper wire, fiber optics) and use various LAN protocols and access methods to communicate through LAN devices (bridges, routers, wireless access points). LANs may be connected to a public switched network.

LAN Topology

Common LAN topologies are bus, ring, and star. In a bus topology, all network node transmissions travel the full length of cable and are received by all other stations. Ethernet uses primarily this topology.

In a ring topology, the network nodes are connected by unidirectional transmission links to form a closed loop. Token ring and Fiber-Distributed Data Interface (FDDI) both use this topology.

In a star topology, the nodes of the network are connected directly to a central LAN device.

The two most common LAN transmission protocol forms are carrier-sense multiple access with collision detection (CSMA/CD) used by Ethernet, and token passing, used in token ring and FDDI networks. Ethernet, ARCnet, token ring, and FDDI, the most common LAN types, use these transmission protocols.

Institute of Electrical and Electronic Engineers Standards

The Institute of Electrical and Electronic Engineers (IEEE) is a U. S. organization that participates in the development of standards for data transmission systems. IEEE has made significant progress in the establishment of standards for LANs by creating the IEEE 802 series of standards, which govern all LAN transmission methods and media access technology.

The LAN types are defined as follows:

Ethernet. Ethernet is a LAN media access method that uses CSMA/CD. Ethernet was originally designed to serve networks with sporadic, occasionally heavy traffic. Ethernet comes in three cabling types: thinnet coax, thicknet coax, and unshielded twisted pair (UTP). UTP is the most common of the three types, and 10BaseT/100BaseT cables and equipment are the most common. Cable types are described later in this chapter.

ARCnet. ARCnet is one of the earliest LAN technologies. It provides predictable but slow network performance.

Token ring. IBM originally developed token ring in the 1970s. Although it was originally the primary LAN network type, it was eventually surpassed in popularity by Ethernet. The term "token ring" can refer to either IBM's Token Ring network (in which case, it is capitalized to indicate it is a trademarked name) or any IEEE 802.5 network. In a token ring network, all end stations are attached to a device called a multistation access unit (MSAU).

Fiber Distributed Data Interface (FDDI). Similar to token ring, FDDI is a token-passing media access topology. It consists of dual rings operating at 100 Mbps, commonly over fiber optic cabling, although a version using category 5 copper cable exists, called Copper Distributed Data Interface (CDDI). FDDI employs a token-passing media access with dual counter-rotating rings, with only one ring active at any given time. If a break or outage occurs, the ring will wrap back in the other direction, keeping the ring intact.

LAN Cabling

LAN cabling comes in three common varieties: coaxial (called coax), unshielded twisted pair (called UTP), and fiber optic. Let's briefly look at each type.

Unshielded twisted pair (UTP). UTP wiring consists of four wire pairs (eight connectors) individually insulated and twisted together. UTP comes in several categories based on how tightly the insulated copper strands are twisted together. The tighter the twist, the higher the rating and its resistance against interference and attenuation.

Coaxial cable. Coaxial cable (commonly called coax) consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor. Coax comes in two common types: thinnet (RG58), and thicknet (RG8 or RG11). Because the shielding reduces the amount of electrical noise interference, coax can extend to much greater lengths than twisted pair wiring.

Fiber optic. Fiber optic cable is a physical medium capable of conducting modulated light transmission, thereby creating higher transmission speeds and greater distances. It is the most resistant to electromagnetic interference. Fiber optic cable is a very reliable cable type but is very expensive to install and terminate.

LAN Network Devices

LANs are connected by communication devices, such as hubs, bridges, routers, switches, or gateways. Let's take a look at these.

Hubs. Hubs amplify the data signals to extend the length of the network segment and help compensate for signal deterioration due to attenuation. They don't add any intelligence to the process; that is, they don't filter packets, examine addressing, or alter anything in the data packet. Hubs are used to connect LAN devices into a concentrator.

Bridges and switches. Bridges are like hubs, but they add some intelligence. A bridge forwards the data to all other network segments if the media access control (MAC) or hardware address of the destination computer isn't on the local network segment. If the destination computer is on the local network segment, it doesn't forward the data. A switch is similar to a bridge or a hub, except that a switch will send the data packet only to the specific port where the destination MAC address is located, rather than to all ports attached to the hub or bridge. This improves performance.

Routers. Routers add even more intelligence to the process of forwarding data packets. A router opens up the data packet and reads either the hardware or network address (IP address) before forwarding it, then forwards the packet only to the network to which the packet was destined. This prevents unnecessary network traffic from being sent over the network by blocking broadcast information and blocking traffic to unknown addresses.

Gateways. Gateways are primarily software products that can be run on computers or other network devices. They can be multi-protocol (link different protocols) and can examine the entire packet.

Wireless Access Protocol (WAP) gateway. A gateway device, called a WAP gateway, is used to serve HTML-style content to WAP-enabled devices, such as Internet-enabled cell phones. WAP gateways are discussed in more detail in Chapter 3.

Wireless access points (APs). An AP functions like a bridge or router, but is made for wireless, 802.11 communications. The most common APs on the market today are 802.11b Ethernet-compatible, but a new Ethernet format with a faster transmission speed, 802.11a, is becoming available for the home and office market. However, 802.11b will continue to dominate the market for some time. A more complete description of wireless access points is given in Chapter 2. Some APs made for use in the home or small office/home office (SOHO) often have several additional functions, for example:

• Broadband routing, to allow sharing of a single high-speed cable modem or DSL Internet line.
• Dynamic Host Configuration Protocol (DHCP) service, which provides the workstation with a usable IP address, and provides network address translation (NAT).
• Printer sharing through a printer server.
• Redundant dial-up access, in case of failure of the broadband line.

The GigaFast USB 802.11b network interface adapter is designed to operate with the Gigafast access point shown earlier, but like most 802.11b USB adapters, can operate with any WLAN-compliant network.

An 802.11b AP manufactured by SMC Networks 2 has these additional routing features. Features of this kind were unheard of in the home or SOHO environment just a couple of years ago. SMC's most recent product introduction, the Barricade Plus Cable/DSL Broadband Router, offers integrated stateful packet inspection (SPI) and a VPN tunneling feature, which supports up to five VPN tunnels.

Another recent vendor with an entry into the 802.11b home or SOHO market is Belkin Components 3, more well known as a maker of cables and PC accessories. Like Gigafast and SMC, they offer several WLAN products, including a wireless Cable/DSL gateway router, and a wireless USB network adapter.