Network Hardware

The following set of notes corresponds to the Network Basics module of the Internet Design course, providing students an outline of the information they are expected to understand. The corresponding reading for this module is chapter one of i-Net+ Study Guide by David Groth, et. al., pages 2-34.

Network Topologies

• A LAN (Local Area Network) is a collection of computers sharing resources in a confined area.
• LANs can be configured in a bus topology (all computers connected along a single line), a star topology (each device connected to a central hub), ring topology (each computer connected to two others in a circular layout), or a mesh topology (each computer physically connected to every other computer). Of these, the star topology is the most common.
• A LAN may be broken up into smaller workgroups, each connected via to the main backbone or hub
• LANs use either an ethernet or token ring method for transmitting data.
• In an ethernet network, each computer takes turns sending data along the network lines using a technology called Carrier Sense Mulitiple Access with Collision Detection (CSMA/CD). A computer waits until the line is free, then sends its data. If the data collides with another set of data being sent simultaneously, the computer stops, waits a random period of time, and then tries to send again.
• In a token ring network, all computers are connected to a multi-station access unit (MSAU) or controlled- access unit (CAU). Within the unit, a token is passed sequentially from one computer to another. A computer wishing to send data must wait for the token, then attach data to the token, which will in turn be passed around the ring of computers, being repeated by each computer and changed slightly by the client for whom the token was intended, until it returns back to the computer that sent it.
• A WAN (Wide Area Network) can cover an unlimited geographical range, typically runs slower than a LAN, and will likely use routers and public network links.
• A centralized WAN connects to a central computer, while a distributed WAN connects numerous computers.

Hardware Components

• On a network, a workstation is a computer connected to the network, while a client is any component that requests resources from the network (such as a printer).
• A server is a computer that provides resources to the network. These can include files (file server), print management (print server), applications (application server), web pages (web server), e-mail hosting and delivery (mail server), fax services (fax server), functions on behalf of other computer (proxy server), remote connections to the network (remote access server), or even telephone related services (telephony server).
• A NIC (Network Interface Card) is the physical component on the computer that allows the workstation to connect to the network. The NIC must be compatible with both your computer and the network interface being used.
• Thin-net coaxial cabling has a range limit of 185 meters and must have a special terminating device at the ends of the cable. It uses a BNC connection.
• Thick-net coaxial cabling has a range of 500 meters but is more combursome and expensive.
• Twisted pair cabling comes in either sheilded (STP) or unsheilded (UTP) varities. The most common is Category 5 (Cat 5) UTP, which contains four twisted pairs, is rated for 100 Mbps, has a range of 100 meters, and is the standard cable used in a majority of LANs.
• Cat5 UTP cabling is connected to the NIC with an RJ-45 connector that looks a lot like a phone plug.
• Fiber-optic cabling is the fastest cabling available, is immune to electro-magnetic interference (EMI) and radio-frequency interference (RFI), and has a range of up to 4 kilometers, but it is the most expensive of the cabling options.
• A hub is a box to which network clients connect. The hub serves as a central connection port, taking the signal from one port and sending it out over all the other ports.
• An active hub is a powered hub that amplifies and cleans the signal it receives before broadcasting it to the connected ports.
• A passive hub is not powered and serves only as a physical connection point. Cables connected to a passive hub may have reduced range.
• A switch (or switching hub) improves upon the design of the hub by sending out data only to the designated receiver instead of broadcasting the signal down all connections.
• A bridge connects two segments of a LAN, allowing people on each side of the LAN to communicate with a specific client on the other side. Bridges also help reduce traffic flow by keeping local traffic from crossing over to the other portion of the LAN.
• A router "intelligently" connects LANs by reading the address of the data being sent and selecting the best route to send that data based on the information stored in the router's memory.
• A firewall is any device (computer or specialized firewall device) residing between your LAN and the Internet that prevents unauthorized users from accessing your private network. Firewalls may offer protection through packet filtering (accepting or rejecting each packet based on your rules), application gateways (applies security measures to specific applications only), circuit level gateways (applies security measures when a connection is first made, then allows all packets to pass freely), proxy servers (intercepts all messages and hides the true network address), or some combination of these technologies.
• A modem (MODulator / DEModulator) converts digital data into analog signals, thus allowing a computer to communicate over telephone lines, cable lines, or other analog communication networks.
• A gateway is a combination of hardware and software that allows two different types of networks to communicate.

Network Operating Systems

• A network operating system (NOS) is in charge of running the server computer as well as managing services provided over the network.
• The three most popular network operating systems are Microsoft Windows NT / 2000, Novell NetWare, and various flavors of Unix / Linux.

Boxed Solutions

• An Internet-in-a-box component provides Internet access to a workgroup or very small LAN without the need for a true server computer. The box is connected to a LAN cable and also to a modem, DSL, or other type of Internet connection (depending on the type of box), thereby sharing a single Internet connection with a small workgroup.
• Internet-in-a-box solutions vary in the features they provide, but may serve as DHCP servers, firewalls, web caches, search engines, or variety of other features.
• A cache-in-a-box device stores portions of commonly accessed web pages, then delivers those portions from within the local LAN instead of the Interenet in order to speed up data delivery.
• Internet-in-a-box (Ibox) and cache-in-a-box devices are types of firmware, hardware with hard-wired software.