IT Essentials I v. 3Module 10 Networking Fundamentals * 2004, Cisco Systems, Inc. All rights reserved.

Module 10 Networking Fundamentals 10.1 Introduction to PC Networking10.2 Types of Networks10.3 Adding a Network Interface Card (NIC)10.4 Physical Components of a Network10.5 LAN Architectures10.6 Networking Protocols and the OSI Model10.7 TCP/IP Utilities10.8 Connecting to the Internet

Introduction to PC Networking

Defining a Computer Network A computer network allows users to communicate with other users on the same network by transmitting data on the cables used to connect them. A computer network is defined as having two or more devices (such as workstations, printers, or servers) that are linked together for the purpose of sharing information, resources, or both.

Defining a Computer NetworkA network consists of many overlapping systems, such as cabling, addressing schemes, or applications. The layers work together to transmit and receive data. The Open Systems Interconnection (OSI) reference model, was created to define these multiple layers.

File, Print, and Application Services Computer networks offer file and print services.In networks, different computers take on specialized roles or functions. Once connected, one or more computers in the network can function as network file servers. The server is a repository for files that can be accessed and shared across the network by many users.

File, Print, and Application ServicesAll network operating systems offer file and print services. Sharing information, collaborating on projects, and providing access to input and output devices are common services of computer networks.

Mail Services E-mail services work like the postal system, with one computer taking on the function of post office. The user e-mail account operates like a post office box, where mail is held for the user until it is picked up over the network by an e-mail client program running in the user system.The e-mail is sent from the client computer to the server, which acts as the post office. The server sends it to the e-mail address.

Directory and Name Services To enable users and systems on the network to find the services they require, computer networks make use of directories and name services.

Directory and Name ServicesDirectory and name services make a network easier to use. After the initial setup of the directory or name service, this translation takes place transparently.In addition to their ease of use, they also make the network more flexible.

The Internet The Internet is a worldwide public network of networks, interconnecting thousands of smaller networks to form one large web of communication. The Internet functions like a highway to facilitate exchange between geographically separated users, organizations, and branches of companies.

The InternetThe phrase information superhighway describes the benefit of the Internet to business and private communication. The Internet breaks down barriers of time and space, enabling the sharing of information around the globe almost instantaneously.

Network Administration The ongoing task of network administration is to maintain and adapt the network to changing conditions. Network administrator responsibilities include: Setting up new user accounts and services Monitoring network performanceRepairing network failures

Simplex, Half-Duplex, and Full-Duplex Transmission Simplex transmission is a single one-way baseband transmission. It is also called unidirectional because the signal travels in only one direction. An example of simplex transmission is the signal sent from the cable TV station to the home television.

Simplex, Half-Duplex, and Full-Duplex TransmissionThis means that only one side can transmit at a time.Two-way radios, such as Citizens Band (CB) and police/emergency communications mobile radios, work with half-duplex transmissions.

Simplex, Half-Duplex, and Full-Duplex TransmissionTraffic can travel in both directions at the same time.A regular telephone conversation is an example of full-duplex communication. Both parties can talk at the same time, and the person talking on the other end can still be heard by the other party while they are talking.

Types of Networks

Overview By using local-area network (LAN) and wide-area network (WAN) technologies, many computers are interconnected to provide services to their users.

In providing services, networked computers take on different roles or functions in relation to each other.

Some types of applications require computers to function as equal partners. Other types of applications distribute work so that one computer functions to serve a number of others in an unequal relationship.

Peer-to-Peer Networks In a peer-to-peer network, the networked computers act as equal partners, or peers, to each other.

As peers, each computer can take on the client function or the server function alternately.

Client/Server Networks In a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients.

The server contains the file, print, application, security, and other services in a central computer that is continuously available to respond to client requests.

Local-Area Networks (LANs) A local-area network (LAN) can connect many computers in a relatively small geographical area such as a home, an office, or a campus.

It allows users to access high bandwidth media like the Internet and allows users to share devices such as printers.

Local-Area Networks (LANs)The general shape or layout of a LAN is called its topology.

Topology defines the structure of the network. This includes the physical topology which is the actual layout of the wire or media, and the logical topology which is how the media is accessed by the hosts.

Wide-Area Networks (WANs) A WAN, as the name implies, is designed to work over a larger area than a LAN.

A WAN uses point-to-point or point to multipoint, serial communications lines.

Point-to-point lines connect only two locations, one on each side of the line. Point-to-multipoint lines connect one location on one side of the line to multiple locations on the other side.

Wide-Area Networks (WANs)The following are some of the more common WAN technologies: ModemsIntegrated Services Digital Network (ISDN) Digital subscriber line (DSL) Frame RelayAsynchronous Transfer Mode (ATM) The T (US) and E (Europe) Carrier series (T1, E1, T3, E3, and so on) Synchronous Optical Network (SONET)

Wide-Area Networks (WANs)Connections across WAN lines may be temporary or permanent. Telephone or dialup lines, might make a temporary connection to a remote network from a computer in a home or small office.In both temporary and permanent cases, computers that connect over wide area circuits must use a modem or channel service unit/data service unit (CSU/DSU) at each end of the connection.

Wide-Area Networks (WANs)The public telephone system, sometimes referred to as plain old telephone service (POTS), is a circuit-switched communications network.When a telephone call is placed in this type of network, only one physical path is used between the telephones for the duration of that call. This pathway is maintained for the exclusive use of the call, until the connection is ended and the telephone is hung up.

Wide-Area Networks (WANs)In a packet-switched network, each individual packet of data can take a different route and no dedicated pathway or circuit is established.

Adding a Network Interface Card (NIC)

What is a NIC? A network interface card (NIC) is a device that plugs into a motherboard and provides ports for the network cable connections. It is the computer interface with the LAN. The NIC communicates with the network through serial connections and communicates with the computer through parallel connections.

Setting the IP Address In a (TCP/IP)-based LAN, PCs use an IP address to identify each other. These addresses allow computers that are attached to the network to locate each other.IP addresses for hosts on a LAN can be assigned in two ways: Manually assigned by the network administrator Assigned by a Dynamic Host Configuration Protocol (DHCP) server

DHCP Servers The most common and efficient way for computers on a large network to obtain an IP address is through a Dynamic Host Configuration Protocol (DHCP) server. DHCP is a software utility that runs on a computer and is designed to assign IP addresses to PCs. When the DHCP server receives a request from a host, it selects IP address information from a set of predefined addresses that are stored in its database.

Default Gateway A computer located on one network segment that is trying to talk to another computer on a different segment sends the data through a default gateway. The default gateway is the near side interface of the router, the interface on the router to which the network segment or wire of the local computer is attached.

Domain Name System Most hosts are identified on the Internet by friendly computer names known as domain names. The Domain Name System (DNS) is used to translate computer names such as cisco.com to their corresponding unique IP address. The DNS server keeps records that map computer (host) names and their corresponding IP address. These record types are all combined in the DNS table.

Physical Components of a Network

Network Topologies The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions. Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

Network TopologiesThe star topology is the most commonly used architecture in Ethernet LANs. When installed, the star topology resembles spokes in a bicycle wheel.Larger networks use the extended star topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host.

Network TopologiesA frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame. The frame then continues around the ring until it finds the destination node, which takes the data out of the frame. Single ring All the devices on the network share a single cable Dual ring The dual ring topology allows data to be sent in both directions although only one ring is used at a time.

Network TopologiesThe mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by governments. Implementing the mesh topology is expensive and difficult.

Physical versus Logical Topology Networks have both a physical and logical topology: Physical topology the layout of the devices and media. Logical topology the paths that signals travel from one point on the network to another. The way in which data accesses media and transmits packets across it.

Networking Media Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means). Coaxial cable is a copper-cored cable surrounded by a heavy shielding and is used to connect computers in a network. There are several types of coaxial cable, including thicknet, thinnet, RG-59 (standard cable for cable TV), and RG-6 (used in video distribution).

Networking MediaTwisted-pair is a type of cabling that is used for telephone communications and most modern Ethernet networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs. There are two basic types, shielded twisted-pair (STP) and unshielded twisted-pair (UTP).

Networking MediaUTP comes in several categories that are based on the number of wires and number of twists in those wires.

Category 3 is the wiring used primarily for telephone connections.

Category 5 and Category 5e are currently the most common Ethernet cables used.

Networking MediaFiber-optic cable is a networking medium capable of conducting modulated light transmissions. Fiber-optic refers to cabling that has a core of strands of glass or plastic (instead of copper), through which light pulses carry signals.Signals that represent data are converted into beams of light.

Networking MediaIf the cost of running cables is too high or computers need to be movable without being tethered to cables, wireless is an alternative method of connecting a LAN. Wireless networks use radio frequency (RF), laser, infrared (IR), and satellite/microwaves to carry signals from one computer to another without a permanent cable connection.

Common Networking Devices A hub is a device that is used to extend an Ethernet wire to allow more devices to communicate with each other. Hubs are most commonly used in Ethernet 10BASE-T or 100BASE-T networks, although there are other network architectures that use them.

Common Networking DevicesBridges connect network segments. The basic functionality of the bridge resides in its ability to make intelligent decisions about whether to pass signals on to the next segment of a network. A switch is a more sophisticated device than a bridge, although the basic function of the switch is deceptively simple. Ethernet switches are becoming popular connectivity solutions because they increase network performance.

Common Networking DevicesRouters are slower than bridges and switches, but make smart decisions on how to route (or send) packets received on one port to a network on another port. Routers contain tables of network addresses along with optimal destination routes to other networks.

Server Components Server components are those components that are used exclusively with the network server. End users depend on the server to provide the services required. To keep the server running at it is optimal performance, a higher level of preventive maintenance must be maintained.

LAN Architectures

EthernetThe Ethernet architecture is based on the IEEE 802.3 standard. The IEEE 802.3 standard specifies that a network implements the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access control method. Standard transfer rates are 10 Mbps or 100 Mbps, but new standards provide for gigabit Ethernet, which are capable of attaining speeds up to 1 Gbps over fiber-optic cable or other high-speed media.

Ethernet10BASE-T uses a star topology. The 10 stands for the common transmission speed of 10 MBps, the "BASE" stands for baseband mode, and the "T" stands for twisted pair cabling.

Ethernet100BASE-X comes in several different varieties. It can be implemented over 4-pair Category 3, 4, or 5 UTP (100BASE-T). It can also be implemented over 4-pair Category 5 UTP or Shielded Twisted Pair (STP) (100BASE-TX), or as Ethernet over 2-strand fiber-optic cable (100BASE-FX).

Ethernet1000BASE-T is Gigabit Ethernet.

This architecture supports data transfer rates of 1 Gbps.

Token RingThe Token Ring standards are defined in IEEE 802.5.A Token Ring network uses a token (that is, a special signal) to control access to the cable. A token is initially generated when the first computer on the network comes online. When a computer wants to transmit, it waits for and then takes control of the token when it comes its way. The token can travel in either direction around the ring, but only in one direction at a time.

Fiber Distributed Data Interface (FDDI)FDDI is a type of Token Ring network.It runs on fiber-optic cable, and thus combines high-speed performance with the advantages of the token-passing ring topology.It runs at 100 Mbps, and its topology is a dual ring. The outer ring is called the primary ring and the inner ring is called the secondary ring.

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