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Ethernet Tutorial - Part I: Networking Basics

Computer networking has become an integral part of business today. Individuals, professionals and academics have also learned to rely on computer networks for capabilities such as electronic mail and access to remote databases for research and communication purposes. Networking has thus become an increasingly pervasive, worldwide reality because it is fast, efficient, reliable and effective. Just how all this information is transmitted, stored, categorized and accessed remains a mystery to the average computer user.
This tutorial will explain the basics of some of the most popular technologies used in networking, and will include the following:

• Types of Networks - including LANs, WANs and WLANs
• The Internet and Beyond - The Internet and its contributions to intranets and extranets
• Types of LAN Technology - including Ethernet, Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet,
  ATM, PoE and Token Ring
• Networking and Ethernet Basics - including standard code, media, topographies, collisions and CSMA/CD
• Ethernet Products - including transceivers, network interface cards, hubs and repeaters

Types of Networks

In describing the basics of networking technology, it will be helpful to explain the different types of networks in use.

Local Area Networks (LANs)

A network is any collection of independent computers that exchange information with each other over a shared communication medium. Local Area Networks or LANs are usually confined to a limited geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but can often link hundreds of computers used by thousands of people. The development of standard networking protocols and media has resulted in worldwide proliferation of LANs throughout business and educational organizations.

Wide Area Networks (WANs)

Often elements of a network are widely separated physically. Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the several LANs with dedicated leased lines such as a T1 or a T3, by dial-up phone lines (both synchronous and asynchronous), by satellite links and by data packet carrier services. WANs can be as simple as a modem and a remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked. Special routing protocols and filters minimize the expense of sending data over vast distances.

Wireless Local Area Networks (WLANs)

Wireless LANs, or WLANs, use radio frequency (RF) technology to transmit and receive data over the air. This minimizes the need for wired connections. WLANs give users mobility as they allow connection to a local area network without having to be physically connected by a cable. This freedom means users can access shared resources without looking for a place to plug in cables, provided that their terminals are mobile and within the designated network coverage area. With mobility, WLANs give flexibility and increased productivity, appealing to both entrepreneurs and to home users. WLANs may also enable network administrators to connect devices that may be physically difficult to reach with a cable.
The Institute for Electrical and Electronic Engineers (IEEE) developed the 802.11 specification for wireless LAN technology. 802.11 specifies over-the-air interface between a wireless client and a base station, or between two wireless clients. WLAN 802.11 standards also have security protocols that were developed to provide the same level of security as that of a wired LAN.
The first of these protocols is Wired Equivalent Privacy (WEP). WEP provides security by encrypting data sent over radio waves from end point to end point.
The second WLAN security protocol is Wi-Fi Protected Access (WPA). WPA was developed as an upgrade to the security features of WEP. It works with existing products that are WEP-enabled but provides two key improvements: improved data encryption through the temporal key integrity protocol (TKIP) which scrambles the keys using a hashing algorithm. It has means for integrity-checking to ensure that keys have not been tampered with. WPA also provides user authentication with the extensible authentication protocol (EAP).

Wireless Protocols

Specification	Data Rate	Modulation Scheme	Security
802.11	1 or 2 Mbps in the 2.4 GHz band	FHSS, DSSS	WEP and WPA
802.11a	54 Mbps in the 5 GHz band	OFDM	WEP and WPA
802.11b/High Rate/Wi-Fi	11 Mbps (with a fallback to 5.5, 2, and 1 Mbps) in the 2.4 GHz band	DSSS with CCK	WEP and WPA
802.11g/Wi-Fi	54 Mbps in the 2.4 GHz band	OFDM when above 20Mbps, DSSS with CCK when below 20Mbps	WEP and WPA

The Internet and Beyond

More than just a technology, the Internet has become a way of life for many people, and it has spurred a revolution of sorts for both public and private sharing of information. The most popular source of information about almost anything, the Internet is used daily by technical and non-technical users alike.

The Internet:  The Largest Network of All

With the meteoric rise in demand for connectivity, the Internet has become a major communications highway for millions of users. It is a decentralized system of linked networks that are worldwide in scope. It facilitates data communication services such as remote log-in, file transfer, electronic mail, the World Wide Web and newsgroups. It consists of independent hosts of computers that can designate which Internet services to use and which of their local services to make available to the global community.
Initially restricted to military and academic institutions, the Internet now operates on a three-level hierarchy composed of backbone networks, mid-level networks and stub networks. It is a full-fledged conduit for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to virtually any point on the planet.

Intranet:  A Secure Internet-like Network for Organizations

With advancements in browser-based software for the Internet, many private organizations have implemented intranets. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides easy access to corporate information for designated employees.

Extranet:  A Secure Means for Sharing Information with Partners

While an intranet is used to disseminate confidential information within a corporation, an extranet is commonly used by companies to share data in a secure fashion with their business partners. Internet-type tools are used by content providers to update the extranet. Encryption and user authentication means are provided to protect the information, and to ensure that designated people with the proper access privileges are allowed to view it.

Types of LAN Technology

Ethernet

Ethernet is the most popular physical layer LAN technology in use today. It defines the number of conductors that are required for a connection, the performance thresholds that can be expected, and provides the framework for data transmission. A standard Ethernet network can transmit data at a rate up to 10 Megabits per second (10 Mbps). Other LAN types include Token Ring, Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet, Fiber Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM) and LocalTalk.
Ethernet is popular because it strikes a good balance between speed, cost and ease of installation. These benefits, combined with wide acceptance in the computer marketplace and the ability to support virtually all popular network protocols, make Ethernet an ideal networking technology for most computer users today.
The Institute for Electrical and Electronic Engineers developed an Ethernet standard known as IEEE Standard 802.3. This standard defines rules for configuring an Ethernet network and also specifies how the elements in an Ethernet network interact with one another. By adhering to the IEEE standard, network equipment and network protocols can communicate efficiently.

Fast Ethernet

The Fast Ethernet standard (IEEE 802.3u) has been established for Ethernet networks that need higher transmission speeds. This standard raises the Ethernet speed limit from 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure. Fast Ethernet provides faster throughput for video, multimedia, graphics, Internet surfing and stronger error detection and correction.
There are three types of Fast Ethernet: 100BASE-TX for use with level 5 UTP cable; 100BASE-FX for use with fiber-optic cable; and 100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable. The 100BASE-TX standard has become the most popular due to its close compatibility with the 10BASE-T Ethernet standard.
Network managers who want to incorporate Fast Ethernet into an existing configuration are required to make many decisions. The number of users in each site on the network that need the higher throughput must be determined; which segments of the backbone need to be reconfigured specifically for 100BASE-T; plus what hardware is necessary in order to connect the 100BASE-T segments with existing 10BASE-T segments. Gigabit Ethernet is a future technology that promises a migration path beyond Fast Ethernet so the next generation of networks will support even higher data transfer speeds.

Gigabit Ethernet

Gigabit Ethernet was developed to meet the need for faster communication networks with applications such as multimedia and Voice over IP (VoIP). Also known as "gigabit-Ethernet-over-copper" or 1000Base-T, GigE is a version of Ethernet that runs at speeds 10 times faster than 100Base-T. It is defined in the IEEE 802.3 standard and is currently used as an enterprise backbone. Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a Gigabit Ethernet backbone to interconnect high performance switches, routers and servers.
From the data link layer of the OSI model upward, the look and implementation of Gigabit Ethernet is identical to that of Ethernet. The most important differences between Gigabit Ethernet and Fast Ethernet include the additional support of full duplex operation in the MAC layer and the data rates.

10 Gigabit Ethernet

10 Gigabit Ethernet is the fastest and most recent of the Ethernet standards. IEEE 802.3ae defines a version of Ethernet with a nominal rate of 10Gbits/s that makes it 10 times faster than Gigabit Ethernet.
Unlike other Ethernet systems, 10 Gigabit Ethernet is based entirely on the use of optical fiber connections. This developing standard is moving away from a LAN design that broadcasts to all nodes, toward a system which includes some elements of wide area routing. As it is still very new, which of the standards will gain commercial acceptance has yet to be determined.

Asynchronous Transfer Mode (ATM)

ATM is a cell-based fast-packet communication technique that can support data-transfer rates from sub-T1 speeds to 10 Gbps. ATM achieves its high speeds in part by transmitting data in fixed-size cells and dispensing with error-correction protocols. It relies on the inherent integrity of digital lines to ensure data integrity.
ATM can be integrated into an existing network as needed without having to update the entire network. Its fixed-length cell-relay operation is the signaling technology of the future and offers more predictable performance than variable length frames. Networks are extremely versatile and an ATM network can connect points in a building, or across the country, and still be treated as a single network.

Power over Ethernet (PoE)

PoE is a solution in which an electrical current is run to networking hardware over the Ethernet Category 5 cable or higher. This solution does not require an extra AC power cord at the product location. This minimizes the amount of cable needed as well as eliminates the difficulties and cost of installing extra outlets.

LAN Technology Specifications

Name	IEEE Standard	Data Rate	Media Type	Maximum Distance
Ethernet	802.3	10 Mbps	10Base-T	100 meters
Fast Ethernet/ 100Base-T	802.3u	100 Mbps	100Base-TX 100Base-FX	100 meters 2000 meters
Gigabit Ethernet/ GigE	802.3z	1000 Mbps	1000Base-T 1000Base-SX 1000Base-LX	100 meters 275/550 meters 550/5000 meters
10 Gigabit Ethernet	IEEE 802.3ae	10 Gbps	10GBase-SR 10GBase-LX4 10GBase-LR/ER 10GBase-SW/LW/EW	300 meters 300m MMF/ 10km SMF 10km/40km 300m/10km/40km

Token Ring

Token Ring is another form of network configuration. It differs from Ethernet in that all messages are transferred in one direction along the ring at all times. Token Ring networks sequentially pass a “token” to each connected device. When the token arrives at a particular computer (or device), the recipient is allowed to transmit data onto the network. Since only one device may be transmitting at any given time, no data collisions occur. Access to the network is guaranteed, and time-sensitive applications can be supported. However, these benefits come at a price. Component costs are usually higher, and the networks themselves are considered to be more complex and difficult to implement. Various PC vendors have been proponents of Token Ring networks.

Networking and Ethernet Basics

Protocols

After a physical connection has been established, network protocols define the standards that allow computers to communicate. A protocol establishes the rules and encoding specifications for sending data. This defines how computers identify one another on a network, the form that the data should take in transit, and how this information is processed once it reaches its final destination. Protocols also define procedures for determining the type of error checking that will be used, the data compression method, if one is needed, how the sending device will indicate that it has finished sending a message, how the receiving device will indicate that it has received a message, and the handling of lost or damaged transmissions or "packets".
The main types of network protocols in use today are: TCP/IP (for UNIX, Windows NT, Windows 95 and other platforms); IPX (for Novell NetWare); DECnet (for networking Digital Equipment Corp. computers); AppleTalk (for Macintosh computers), and NetBIOS/NetBEUI (for LAN Manager and Windows NT networks).
Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence," which means that devices which are compatible at the physical and data link layers allow the user to run many different protocols over the same medium.

The Open System Interconnection Model

The Open System Interconnection (OSI) model specifies how dissimilar computing devices such as Network Interface Cards (NICs), bridges and routers exchange data over a network by offering a networking framework for implementing protocols in seven layers. Beginning at the application layer, control is passed from one layer to the next. The following describes the seven layers as defined by the OSI model, shown in the order they occur whenever a user transmits information.

Layer 7: Application

This layer supports the application and end-user processes. Within this layer, user privacy is considered and communication partners, service and constraints are all identified. File transfers, email, Telnet and FTP applications are all provided within this layer.

Layer 6: Presentation (Syntax)

Within this layer, information is translated back and forth between application and network formats.  This translation transforms the information into data the application layer and network recognize regardless of encryption and formatting.

Layer 5: Session

Within this layer, connections between applications are made, managed and terminated as needed to allow for data exchanges between applications at each end of a dialogue.

Layer 4: Transport

Complete data transfer is ensured as information is transferred transparently between systems in this layer. The transport layer also assures appropriate flow control and end-to-end error recovery.

Layer 3: Network

Using switching and routing technologies, this layer is responsible for creating virtual circuits to transmit information from node to node. Other functions include routing, forwarding, addressing, internetworking, error and congestion control, and packet sequencing.

Layer 2: Data Link

Information in data packets are encoded and decoded into bits within this layer. Errors from the physical layer flow control and frame synchronization are corrected here utilizing transmission protocol knowledge and management. This layer consists of two sub layers: the Media Access Control (MAC) layer, which controls the way networked computers gain access to data and transmit it, and the Logical Link Control (LLC) layer, which controls frame synchronization, flow control and error checking.

Layer 1: Physical

This layer enables hardware to send and receive data over a carrier such as cabling, a card or other physical means. It conveys the bitstream through the network at the electrical and mechanical level. Fast Ethernet, RS232, and ATM are all protocols with physical layer components.

This order is then reversed as information is received, so that the physical layer is the first and application layer is the final layer that information passes through.

Standard Ethernet Code

In order to understand standard Ethernet code, one must understand what each digit means. Following is a guide:

Guide to Ethernet Coding

10	at the beginning means the network operates at 10Mbps.
BASE	means the type of signaling used is baseband.
2 or 5	at the end indicates the maximum cable length in meters.
T	the end stands for twisted-pair cable.
X	at the end stands for full duplex-capable cable.
FL	at the end stands for fiber optic cable.

For example: 100BASE-TX indicates a Fast Ethernet connection (100 Mbps) that uses a
twisted pair cable capable of full-duplex transmissions.

Media

An important part of designing and installing an Ethernet is selecting the appropriate Ethernet medium. There are four major types of media in use today: Thickwire for 10BASE5 networks; thin coax for 10BASE2 networks; unshielded twisted pair (UTP) for 10BASE-T networks; and fiber optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL) networks. This wide variety of media reflects the evolution of Ethernet and also points to the technology's flexibility. Thickwire was one of the first cabling systems used in Ethernet, but it was expensive and difficult to use. This evolved to thin coax, which is easier to work with and less expensive. It is important to note that each type of Ethernet, Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet, has its own preferred media types.
The most popular wiring schemes are 10BASE-T and 100BASE-TX, which use unshielded twisted pair (UTP) cable. This is similar to telephone cable and comes in a variety of grades, with each higher grade offering better performance. Level 5 cable is the highest, most expensive grade, offering support for transmission rates of up to 100 Mbps. Level 4 and level 3 cable are less expensive, but cannot support the same data throughput speeds; level 4 cable can support speeds of up to 20 Mbps; level 3 up to 16 Mbps. The 100BASE-T4 standard allows for support of 100 Mbps Ethernet over level 3 cables, but at the expense of adding another pair of wires (4 pair instead of the 2 pair used for 10BASE-T). For most users, this is an awkward scheme and therefore 100BASE-T4 has seen little popularity. Level 2 and level 1 cables are not used in the design of 10BASE-T networks.
For specialized applications, fiber-optic, or 10BASE-FL, Ethernet segments are popular. Fiber-optic cable is more expensive, but it is invaluable in situations where electronic emissions and environmental hazards are a concern. Fiber-optic cable is often used in inter-building applications to insulate networking equipment from electrical damage caused by lightning. Because it does not conduct electricity, fiber-optic cable can also be useful in areas where heavy electromagnetic interference is present, such as on a factory floor. The Ethernet standard allows for fiber-optic cable segments up to two kilometers long, making fiber-optic Ethernet perfect for connecting nodes and buildings that are otherwise not reachable with copper media.

Cable Grade Capabilities

Cable Name	Makeup	Frequency Support	Data Rate	Network Compatibility
Cat-5	4 twisted pairs of copper wire -- terminated by RJ45 connectors	100 MHz	Up to 1000Mbps	ATM, Token Ring,1000Base-T, 100Base-TX, 10Base-T
Cat-5e	4 twisted pairs of copper wire -- terminated by RJ45 connectors	100 MHz	Up to 1000Mbps	10Base-T, 100Base-TX, 1000Base-T
Cat-6	4 twisted pairs of copper wire -- terminated by RJ45 connectors	250 MHz	1000Mbps	10Base-T, 100Base-TX, 1000Base-T

Topologies

Network topology is the geometric arrangement of nodes and cable links in a LAN. Two general configurations are used, bus and star. These two topologies define how nodes are connected to one another in a communication network. A node is an active device connected to the network, such as a computer or a printer. A node can also be a piece of networking equipment such as a hub, switch or a router.
A bus topology consists of nodes linked together in a series with each node connected to a long cable or bus. Many nodes can tap into the bus and begin communication with all other nodes on that cable segment. A break anywhere in the cable will usually cause the entire segment to be inoperable until the break is repaired. Examples of bus topology include 10BASE2 and 10BASE5.

General Topology Configurations

10BASE-T Ethernet and Fast Ethernet use a star topology where access is controlled by a central computer. Generally a computer is located at one end of the segment, and the other end is terminated in central location with a hub or a switch. Because UTP is often run in conjunction with telephone cabling, this central location can be a telephone closet or other area where it is convenient to connect the UTP segment to a backbone. The primary advantage of this type of network is reliability, for if one of these 'point-to-point' segments has a break; it will only affect the two nodes on that link. Other computer users on the network continue to operate as if that segment were non-existent.

Collisions

Ethernet is a shared medium, so there are rules for sending packets of data to avoid conflicts and to protect data integrity. Nodes determine when the network is available for sending packets. It is possible that two or more nodes at different locations will attempt to send data at the same time. When this happens, a packet collision occurs.
Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users on the network. This leads to competition for network bandwidth and can slow the performance of the network from the user's point of view. Segmenting the network is one way of reducing an overcrowded network, i.e., by dividing it into different pieces logically joined together with a bridge or switch.

CSMA/CD

In order to manage collisions Ethernet uses a protocol called Carrier Sense Multiple Access/Collision Detection (CSMA/CD). CSMA/CD is a type of contention protocol that defines how to respond when a collision is detected, or when two devices attempt to transmit packages simultaneously. Ethernet allows each device to send messages at any time without having to wait for network permission; thus, there is a high possibility that devices may try to send messages at the same time.
After detecting a collision, each device that was transmitting a packet delays a random amount of time before re-transmitting the packet. If another collision occurs, the device waits twice as long before trying to re-transmit.

Ethernet Products

The standards and technology just discussed will help define the specific products that network managers use to build Ethernet networks. The following presents the key products needed to build an Ethernet LAN.

Transceivers

Transceivers are also referred to as Medium Access Units (MAUs). They are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BASE-T or 10BASE2 transceiver which allows them to be connected directly to Ethernet without the need for an external transceiver.
Many Ethernet devices provide an attachment unit interface (AUI) connector to allow the user to connect to any type of medium via an external transceiver. The AUI connector consists of a 15-pin D-shell type connector, female on the computer side, male on the transceiver side.
For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices.

Network Interface Cards

Network Interface Cards, commonly referred to as NICs, are used to connect a PC to a network. The NIC provides a physical connection between the networking cable and the computer's internal bus. Different computers have different bus architectures. PCI bus slots are most commonly found on 486/Pentium PCs and ISA expansion slots are commonly found on 386 and older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number of bits that can be transferred to the NIC, the faster the NIC can transfer data to the network cable. Most NICs are designed for a particular type of network, protocol, and medium, though some can serve multiple networks.
Many NIC adapters comply with plug-and-play specifications. On these systems, NICs are automatically configured without user intervention, while on non-plug-and-play systems, configuration is done manually through a set-up program and/or DIP switches.
Cards are available to support almost all networking standards. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Gigabit Ethernet NICs are 10/100/1000 capable with auto negotiation depending on the user’s Ethernet speed. Full duplex networking is another option where a dedicated connection to a switch allows a NIC to operate at twice the speed.

Hubs/Repeaters

Hubs/repeaters are used to connect together two or more Ethernet segments of any type of medium. In larger designs, signal quality begins to deteriorate as segments exceed their maximum length. Hubs provide the signal amplification required to allow a segment to be extended a greater distance. A hub repeats any incoming signal to all ports.
Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later.
A very important fact to note about hubs is that they only allow users to share Ethernet. A network of hubs/repeaters is termed a "shared Ethernet," meaning that all members of the network are contending for transmission of data onto a single network (collision domain). A hub/repeater propagates all electrical signals including the invalid ones. Therefore, if a collision or electrical interference occurs on one segment, repeaters make it appear on all others as well. This means that individual members of a shared network will only get a percentage of the available network bandwidth.
Basically, the number and type of hubs in any one collision domain for 10Mbps Ethernet is limited by the following rules:

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Cisco IOS Command Line Interface Tutorial

Cisco IOS Command Line Interface Tutorial

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Abstract

The focus of this document is to introduce a new Cisco Internetworking Operating System (IOS) user to the IOS command line interface (CLI). After reading this document, a new user will understand how to use the IOS CLI to configure and manage an IOS router. For easier reference, Table 1 displays a collection of important terms and acronyms that are used throughout the document.

Table 1 - Glossary Of Important Terms And Acronyms Used In This Tutorial

Cisco IOS	- Cisco Internetworking Operating System
CLI	- Command Line Interface
EXEC	- Command line session to the router (could be console, modem, or telnet)
Flash	- Non-Volatile Memory used to store IOS software image
NVRAM	- Non-Volatile RAM used to store router configuration
RAM	- Random Access Memory

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CLI Architecture

A Cisco IOS router command line interface can be accessed through either a console connection, modem connection, or a telnet session. Regardless of which connection method is used, access to the IOS command line interface is generally referred to as an EXEC session.
As a security feature, Cisco IOS separates EXEC sessions into two different access levels - user EXEC level and privileged EXEC level. User EXEC level allows a person to access only a limited amount of basic monitoring commands. Privileged EXEC level allows a person to access all router commands (e.g. configuration and management) and can be password protected to allow only authorized users the ability to configure or maintain the router.
For example, when an EXEC session is started, the router will display a "Router>" prompt. The right arrow (>) in the prompt indicates that the router is at the user EXEC level. The user EXEC level does not contain any commands that might control (e.g. reload or configure) the operation of the router. To list the commands available at the user EXEC level, type a question mark (?) at the Router> prompt. (This feature is referred to as context sensitive help.)
Critical commands (e.g. configuration and management) require that the user be at the privileged EXEC level. To change to the privileged EXEC level, type "enable" at the Router> prompt. If an enable password is configured, the router will then prompt for that password. When the correct enable password is entered, the router prompt will change to "Router#" indicating that the user is now at the privileged EXEC level. To switch back to user EXEC level, type "disable" at the Router# prompt. Typing a question mark (?) at the privileged EXEC level will now reveal many more command options than those available at the user EXEC level. The text below illustrates the process of changing EXEC levels.

Router> enable
Password: [enable password]
Router# disable
Router>

Note: For security reasons, the router will not echo the password that is entered. Also, be advised that if configuring a router via telnet, the password is sent in clear text. Telnet does not offer a method to secure packets.
Once an EXEC session is established, commands within Cisco IOS are hierarchically structured. In order to successfully configure the router, it is important to understand this hierarchy. To illustrate this hierarchy, Figure 1 provides a simple high-level schematic diagram of some IOS commands.

Figure 1 - IOS CLI hierarchy

Command options and applications vary depending on position within this hierarchy. Referring to the diagram in figure 1, configuration command options will not be available until the user has navigated to the configuration branch of the IOS CLI structure. Once in the configuration branch, a user may enter system level configuration commands that apply to the entire router at the global configuration level. Interface specific configuration commands are available once the user has switched to the particular interface configuration level. More detailed information and examples on how to navigate through the IOS CLI hierarchy are offered in the Router Configuration section.
To assist users in navigation through IOS CLI, the command prompt will change to reflect the position of a user within the command hierarchy. This allows users to easily identify where within the command structure they are at any given moment. Table 2 is a summary of command prompts and the corresponding location within the command structure.
Table 2 - IOS Command Prompt Summary

Router>	- User EXEC mode
Router#	- Privileged EXEC mode
Router(config)#	- Configuration mode (notice the # sign indicates this is only accessible at privileged EXEC mode.)
Router(config-if)#	- Interface level within configuration mode.
Router(config-router)#	- Routing engine level within configuration mode.
Router(config-line)#	- Line level (vty, tty, async) within configuration mode.

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CLI Editor Features

Context Sensitive Help
Cisco IOS CLI offers context sensitive help. This is a useful tool for a new user because at any time during an EXEC session, a user can type a question mark (?) to get help. Two types of context sensitive help are available - word help and command syntax help.
Word help can be used to obtain a list of commands that begin with a particular character sequence. To use word help, type in the characters in question followed immediately by the question mark (?). Do not include a space before the question mark. The router will then display a list of commands that start with the characters that were entered. The following is an example of word help:

Router# co?

configure connect copy

Command syntax help can be used to obtain a list of command, keyword, or argument options that are available based on the syntax the user has already entered. To use command syntax help, enter a question mark (?) in the place of a keyword or argument. Include a space before the question mark. The router will then display a list of available command options with <cr> standing for carriage return. The following is an example of command syntax help:

Router# configure ?

memory Configure from NV memory network Configure from a TFTP network host overwrite-network Overwrite NV memory from TFTP network host=20 terminal Configure from the terminal <cr>

Command Syntax Check
If a command is entered improperly (e.g. typo or invalid command option), the router will inform the user and indicate where the error has occurred. A caret symbol (^) will appear underneath the incorrect command, keyword, or argument. The following example displays what happens if the keyword "ethernet" is spelled incorrectly.

Router(config)#interface ethernat
                               ^
% Invalid input detected at '^' marker.

Command Abbreviation
Commands and keywords can be abbreviated to the minimum number of characters that identifies a unique selection. For example, you can abbreviate the "configure" command to "conf" because "configure" is the only command that begins with "conf". You could not abbreviate the command to "con" because more than one command could fit this criteria. The router will issue the following error message if you do not supply enough characters.

cisco(config)#i
% Ambiguous command:  "i"

Hot Keys
For many editing functions, the IOS CLI editor provides hot keys. The following table lists some editing shortcuts that are available.
Table 3 - Summary Of Hot Keys

Delete	- Removes one character to the right of the cursor.
Backspace	- Removes one character to the left of the cursor.
TAB	- Finishes a partial command.
Ctrl-A	- Moves the cursor to the beginning of the current line.
Ctrl-R	- Redisplays a line.
Ctrl-U	- Erases a line.
Ctrl-W	- Erases a word.
Ctrl-Z	- Ends configuration mode and returns to the EXEC.
Up Arrow	- Allows user to scroll forward through former commands.
Down Arrow	- Allows user to scroll backward through former commands.

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Router Configuration

Entering Configurations
Perhaps the best way to illustrate IOS CLI navigation is by walking through a simple router configuration. The comments in the example do not attempt to explain the meaning of each individual command, but rather intend to display where configuration commands are entered within the IOS command structure. Pay particular attention to how the command prompt changes as the user navigates through the IOS CLI hierarchy. Also notice that global parameters are configured at the global configuration level (indicated by the "Router(config)#" prompt) whereas interface specific commands are entered after switching to the particular interface (indicated by the "Router(config-if)#" prompt). Global parameters and interface parameters are discussed further in the Displaying Configurations section under Router Management.

Router> enable	- switches to privileged EXEC level
Router# configure terminal	- switches to global configuration level
Router(config)# enable secret cisco	- configures router with an enable secret (global)
Router(config)# ip route 0.0.0.0 0.0.0.0 20.2.2.3	- configures a static IP route (global)
Router(config)# interface ethernet0	- switches to configure the ethernet0 interface
Router(config-if)# ip address 10.1.1.1 255.0.0.0	- configures an IP address on ethernet0 (interface)
Router(config-if)# no shutdown	- activates ethernet0 (interface)
Router(config-if)# exit	- exits back to global configuration level
Router(config)# interface serial0	- switches to configure the serial0 interface
Router(config-if)# ip address 20.2.2.2 255.0.0.0	- configures an IP address on serial0 (interface)
Router(config-if)# no shutdown	- activates serial0 (interface)
Router(config-if)# exit	- exits back to global configuration level
Router(config)# router rip	- switches to configure RIP routing engine
Router(config-router)# network 10.0.0.0	- adds network 10.0.0.0 to RIP engine (routing engine)
Router(config-router)# network 20.0.0.0	- adds network 20.0.0.0 to RIP engine (routing engine)
Router(config-router)# exit	- exits back to global configuration level
Router(config)# exit	- exits out of configuration level
Router# copy running-config startup-config	- saves configuration into NVRAM
Router# disable	- disables privileged EXEC level
Router>	- indicates user is back to user EXEC level

In the above example, notice how the exit command is used to back up a level within the IOS hierarchy. For example, if in the interface configuration level (i.e. Router (config-if)# prompt), typing exit will put the user back in the global configuration level (i.e. Router (config)# prompt).
Taking Interfaces Out Of Shutdown
Routers ship from the factory with all interfaces deactivated. Deactivated interfaces are referred to as being in a shutdown state. Before an interface can be used, it must be taken out of the shutdown state. To take an interface out of shutdown, type "no shutdown" at the appropriate interface configuration level. The example above includes these commands for both the ethernet and serial interfaces.
Removing Commands / Resetting Default Values
IOS provides an easy way to remove commands from a configuration. To remove a command from the configuration, simply navigate to the proper location and type "no" followed by the command to be removed. The following example displays how to remove an IP address from the ethernet0 interface.

Router> enable	- switches to privileged EXEC level
Router# configure terminal	- switches to global configuration level
Router(config)# interface ethernet0	- switches to configure the ethernet0 interface
Router(config-if)# no ip address	- removes IP address
Router(config-if)# exit	- exits back to global configuration level
Router(config)# exit	- exits out of configuration level
Router# disable	- disables privileged EXEC level
Router>	- prompt indicates user is back to user EXEC level

Some configuration commands in IOS are enabled by default and assigned a certain default value. When left at the default value, these commands will not be displayed when the configuration is listed. If the value is altered from the default setting, issuing a "no" form of the command will restore the value to the default setting.
Saving Configurations
A Cisco IOS router stores configurations in two locations - RAM and NVRAM. The running configuration is stored in RAM and is used by the router during operation. Any configuration changes to the router are made to the running-configuration and take effect immediately after the command is entered. The startup-configuration is saved in NVRAM and is loaded into the router's running-configuration when the router boots up. If a router loses power or is reloaded, changes to the running configuration will be lost unless they are saved to the startup-configuration. To save the running-configuration to the startup configuration, type the following from privileged EXEC mode (i.e. at the "Router#" prompt.)

Router# copy running-config startup-config

Note: Prior to 11.x software, the command to save the running-configuration to the startup-configuration was different. Use the following command if your IOS version is prior to 11.x:

Router#write memory

IMPORTANT: When editing a configuration, SAVE the configuration often!

---

Router Management

IOS supports many different types of show commands. This section covers a few of the common show commands used to both manage and troubleshoot a router. The scope of this document is not to instruct how to use these commands to troubleshoot a router, but to make the user aware that these management options exist. For specific information about troubleshooting a network using these commands, refer to the appropriate troubleshooting document.
Displaying Configurations
To display the running-configuration, type the following command in privileged EXEC mode:

Router#show running-config

To display the startup-configuration that is stored in NVRAM, type the following command in privileged EXEC mode:

Router#show startup-config

The following is the show running-config output from the example used in the Router Configuration section.

Current configuration:
!
version 11.2
!
hostname cisco
!
enable password cisco
!
interface Ethernet0
 ip address 10.1.1.1 255.0.0.0
!
interface Serial0
 ip address 20.2.2.2 255.0.0.0
!
router rip
 network 10.0.0.0
 network 20.0.0.0
!
ip route 0.0.0.0 0.0.0.0 20.2.2.3
!
line vty 0 4
 password telnet
 login
!
end

When displaying a configuration, the exclamation marks (!) function as line separators to make reading easier. Referring to the above example, notice how commands entered at the interface configuration level appear indented underneath the respective interface (e.g. interface Ethernet0). Likewise, commands entered underneath the routing engine configuration level appear indented underneath the routing engine (e.g. router rip). Global level commands are not indented. This type of display allows a user to easily identify which configuration parameters are set at the global configuration level and which are set at the various configuration sub-levels.
Note: If an interface was in a shutdown state, the word 'shutdown' would appear indented under the particular interface in shutdown state. Also, commands that are enabled by default are not displayed in the configuration listing.
Displaying Software Version And More
The show version command provides a lot of information in addition to the version of software that is running on the router. The following information can be collected with the show version command:

Software Version	- IOS software version (stored in flash)
Bootstrap Version	- Bootstrap version (stored in Boot ROM)
System up-time	- Time since last reboot
System restart info	- Method of restart (e.g. power cycle, crash)
Software image name	- IOS filename stored in flash
Router Type and Processor type	- Model number and processor type
Memory type and allocation (Shared/Main)	- Main Processor RAM - Shared Packet I/O buffering
Software Features	- Supported protocols / feature sets
Hardware Interfaces	- Interfaces available on router
Configuration Register	- Bootup specifications, console speed setting, etc.

The following is a sample output of a show version command.

Router# show version
Cisco Internetwork Operating System Software
IOS (tm) 3600 Software (C3640-J-M), Version 11.2(6)P, SHARED PLATFORM,
RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1997 by cisco Systems, Inc.
Compiled Mon 12-May-97 15:07 by tej
Image text-base: 0x600088A0, data-base: 0x6075C000

ROM: System Bootstrap, Version 11.1(7)AX [kuong (7)AX], EARLY DEPLOYMENT
RELEASE SOFTWARE (fc2)

Router uptime is 1 week, 1 day, 38 minutes
System restarted by power-on
System image file is "flash:c3640-j-mz_112-6_P.bin", booted
via flash
Host configuration file is "3600_4-confg", booted via tftp
from 171.69.83.194

cisco 3640 (R4700) processor (revision 0x00) with 107520K/23552K bytes
of memory.
Processor board ID 03084730
R4700 processor, Implementation 33, Revision 1.0
Bridging software.
SuperLAT software copyright 1990 by Meridian Technology Corp).
X.25 software, Version 2.0, NET2, BFE and GOSIP compliant.
TN3270 Emulation software.
Primary Rate ISDN software, Version 1.0.
2 Ethernet/IEEE 802.3 interface(s)
97 Serial network interface(s)
4 Channelized T1/PRI port(s)
DRAM configuration is 64 bits wide with parity disabled.
125K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102

Displaying Interface States
To view information about a particular interface, use the show interface command. The show interface command provides the following list of important information:

Interface State (e.g. UP, DOWN, LOOPED)

Protocol addresses

Bandwidth

Reliability and Load

Encapsulation type

Packet Rates

Error Rates

Signaling Status (i.e. DCD,DSR,DTR,RTS,CTS)

The following is an example of a "show interface serial0" output:

Router#show interface serial 0
Serial0 is up, line protocol is down
Hardware is QUICC Serial
Internet address is 10.1.1.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec)
LMI enq sent 207603, LMI stat recvd 113715, LMI upd recvd 0, DTE LMI
down
LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0
LMI DLCI 1023 LMI type is CISCO frame relay DTE
Broadcast queue 0/64, broadcasts sent/dropped 0/0, interface broadcasts
62856
Last input 1w, output 00:00:08, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/64/0 (size/threshold/drops)
Conversations 0/1 (active/max active)
Reserved Conversations 0/0 (allocated/max allocated)
5 minute input rate 1000 bits/sec, 1 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
1012272 packets input, 91255488 bytes, 0 no buffer
Received 916 broadcasts, 0 runts, 0 giants
18519 input errors, 0 CRC, 17796 frame, 0 overrun, 0 ignored, 723 abort
283132 packets output, 13712011 bytes, 0 underruns
0 output errors, 0 collisions, 31317 interface resets
0 output buffer failures, 0 output buffers swapped out
3 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up

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Wireless Router Tutorial

I wanted to start off the month of March with a feature of the “how to’s” of Wireless Routers. I am still amazed at how many people are not taking advantage of the wireless router, for making your entire home or business a working/playing zone. So, let’s get at it.
Wireless routers with Internet connection sharing, networking and firewall features are an alternative to Wired routers or Networking Software. Wireless routers are actually wired routers with wireless access points built in so you can have wired and/or wireless at the same time. Another choice is a wireless router with a built-in DSL or cable modem. Finally, you can consider a hardware and software security combo box to connect and protect your home network, see our Broadband Gateways page for more information.
 Security – Wireless routers are not as secure as hard wired. If you want wireless and security, read the security articles on this page and be prepared to spend some time setting up the security features of your wireless network. To make this easier, look at getting started and wireless utility software. A big deal here, though, is the ability to set keywords to block unwanted content from your router, especially if you have kids at home.
Testing – We recommend that you test the firewall features of a wireless router after installation and setup using an online service like Security Space.  This can help you figure out the vulnerabilities of your system pretty quick.

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Types of Internet Protocols

There's more to the Internet than the World Wide Web

When we think of the Internet we often think only of the World Wide Web. The Web is one of several ways to retrieve information from the Internet. These different types of Internet connections are known as protocols. You could use separate software applications to access the Internet with each of these protocols, though you probably wouldn't need to. Many Internet Web browsers allow users to access files using most of the protocols. Following are three categories of Internet services and examples of types of services in each category.
File retrieval protocols
This type of service was one of the earliest ways of retrieving information from computers connected to the Internet. You could view the names of the files stored on the serving computer, but you didn't have any type of graphics and sometimes no description of a file's content. You would need to have advanced knowledge of which files contained the information you sought.
FTP (File Transfer Protocol)
This was one of the first Internet services developed and it allows users to move files from one computer to another. Using the FTP program, a user can logon to a remote computer, browse through its files, and either download or upload files (if the remote computer allows). These can be any type of file, but the user is only allowed to see the file name; no description of the file content is included. You might encounter the FTP protocol if you try to download any software applications from the World Wide Web. Many sites that offer downloadable applications use the FTP protocol.
An example of a FTP Protocol Window:

Gopher
Gopher offers downloadable files with some content description to make it easier to find the file you need. The files are arranged on the remote computer in a hierarchical manner, much like the files on your computer's hard drive are arranged. This protocol isn't widely used anymore, but you can still find some operational gopher sites.
An example of a Gopher Window:

Telnet
You can connect to and use a remote computer program by using the telnet protocol. Generally you would telnet into a specific application housed on a serving computer that would allow you to use that application as if it were on your own computer. Again, using this protocol requires special software.
The following are external links and will open in pop-up windows:

FTP
Example of FTP Protocol: TUCOWS. Software, music, themes and games download sites.

Gopher
Example of Gopher Protocol: University of Minnesota

telnet
Hytelnet — Archive of Telnet sites

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How to crimp ethernet cable

How to crimp ethernet cable | How to crimp cross over cable or straight through cable with color code

Tag: how to crimb ethernet cable, how to crimb crossover cable or straight through cable with color code, straight through cable color code, crossover cable color code, cross over cable color code

Full detail to crimp Ethernet cable OR How to crimp cross over cable or straight through cable with color code. It is very easy to crimp straight through cable or cross over cable with these steps.

What we need to crimp a crossover or straight through cable:

• CAT 5 Cable - bulk Category 5, 5e or 6 cable
• RJ45 Ends
• Crimper for RJ45
• Wire Cutters - to cut and strip the cable if necessary

Recommend:

• Wire Stripper
• Cable Tester

About the Cable:
You can get the cables on any computer stores near you.
You want UTP (Unshielded Twisted Pair) Category 5 cable for basic 10/100 functionality.
You need CAT 5e for gigabit (1000BaseT) operation and CAT 6 gives you a measure of future proofing.
There are basically 2 categories, solid and braided cable. Braided cable tends to work better in "patch" applications for desktop use. It is more flexible and resiliant than solid cable and easier to work with, but really meant for shorter lengths. Solid cable is meant for longer runs in a fixed position. Plenum rated cable should/must be used whenever the cable travels through an air circulation space. For example, above a false celing or below a raised floor. You're likely going to want braided type cable but it may be difficult or impossible to tell from the box.

Here is what the internals of the cable look like:

Internal Cable Structure and Color Coding

Inside the cable, there are 8 color coded wires. These wires are twisted into 4 pairs of wires, each pair has a common color theme. One wire in the pair being a solid or primarily solid colored wire and the other being a primarily white wire with a colored stripe.
Note:- (Sometimes cable doesn't have any color on the striped cable, the only way to tell is to check which other wire it is twisted around).
About the RJ45 Ends:

The RJ45 end is a 8-position modular connector that looks like a large phone plug. There are a couple variations available. The primary variation you need to pay attention to is whether the connector is intended for braided or solid wire. For braided/stranded wires, the connector has contacts that actually pierce the wire. For solid wires, the connector has fingers which pierce the insulation and make contact with the wire by grasping it from both sides. The connector is the weak point in an Ethernet cable, choosing the wrong one will often cause grief later. If you just walk into a computer store, it's nearly impossible to tell what type of connector it is. Here is a diagram and pin out:



Ethernet Cable Pinouts:

There are basically two crimping types.

1. A straight through cable, which is used to connect different devices. Example, a hub and switch, Router and computer, hub and computer.
2. A cross over cable, which is used to operate in a peer-to-peer fashion without a hub/switch. Some interfaces can cross and un-cross a cable automatically as needed.

Straight-Through Crimping Color Codes ( Both Ends are Same )

1. White/Green
2. Green
3. White/Orange
4. Blue
5. White/Blue
6. Orange
7. White/Brown
8. Brown

Above is the Straight-Through Cable Pinout for T568A

Crossover Cable Crimping Color Codes ( Both Ends are Opposite )

First End Color Code:

1. Orange/White
2. Orange
3. Green/White
4. Blue
5. Blue/White
6. Green
7. Brown/White
8. Brown

Second End Color Codes

1. Green/White
2. Green
3. Orange/White
4. Brown/White
5. Brown
6. Orange
7. Blue
8. Blue/White

Note: The cross over cable layout is suitable for 1000Base-T operation, all 4 pairs are crossed.

How to wire Ethernet Cables:

1. Strip off about 2 inches of the cable sheath.
2. Untwist the pairs - don't untwist them beyond what you have exposed, the more untwisted cable you have the worse the problems you can run into.
3. Align the colored wires according to the diagrams above.
4. Trim all the wires to the same length, about 1/2" to 3/4" left exposed from the sheath.
5. Insert the wires into the RJ45 end - make sure each wire is fully inserted to the front of the RJ45 end and in the correct order. The sheath of the cable should extend into the RJ45 end by about 1/2" and will be held in place by the crimp.
6. Crimp the RJ45 end with the crimper tool Verify the wires ended up the right order and that the wires extend to the front of the RJ45 end and make good contact with the metal contacts in the RJ45 end.
7. Cut the cable to length - make sure it is more than long enough for your needs. Remember, an end to end connection should not extend more than 100m (~328ft). Try to keep cables short, the longer the cable becomes the more it may affect performance, usually noticable as a gradual decrease in speed and increase in latency.
8. Repeat the above steps for the second RJ45 end.
9. If a cable tester is available, use it to verify the proper connectivity of the cable.

That it! If your cable not worked, look closely at each end and see if you can find the problem. Usually a wire ended up in the wrong place or more commonly, one of the wires didn't extend to the front of the RJ45 connector and is making no, or poor contact. If you see a mistake or problem, cut the end off and start again.

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types of network cables

Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.
The following sections discuss the types of cables used in networks and other related topics.

• Unshielded Twisted Pair (UTP) Cable
• Shielded Twisted Pair (STP) Cable
• Coaxial Cable
• Fiber Optic Cable
• Wireless LANs
• Installing Cable - Some Guidelines

Unshielded Twisted Pair (UTP) Cable

Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1).

Fig.1. Unshielded twisted pair

The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.

Categories of Unshielded Twisted Pair

Type	Use
Category 1	Voice Only (Telephone Wire)
Category 2	Data to 4 Mbps (LocalTalk)
Category 3	Data to 10 Mbps (Ethernet)
Category 4	Data to 20 Mbps (16 Mbps Token Ring)
Category 5	Data to 100 Mbps (Fast Ethernet)

One difference between the different categories of UTP is the tightness of the twisting of the copper pairs. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. Buy the best cable you can afford; most schools purchase Category 3 or Category 5. Category 5 cable is highly recommended.
If you are designing a 10 Mbps Ethernet network and are considering the cost savings of buying Category 3 wire instead of Category 5, remember that the Category 5 cable will provide more "room to grow" as transmission technologies increase. Both category 3 and category 5 UTP have a maximum segment length of 100 meters. In Florida, Category 5 cable is required for retrofit grants. 10BaseT refers to the specifications for unshielded twisted pair cable (category 3, 4, or 5) carrying Ethernet signals.

Unshielded Twisted Pair Connector

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

Fig.2. RJ-45 connector

Shielded Twisted Pair (STP) Cable

A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology.

Coaxial Cable

Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

Fig.3. Coaxial cable

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are: thick coaxial and thin coaxial.
Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable is popular in school networks, especially linear bus networks.
Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

Coaxial Cable Connectors

The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather than screw, onto the cable.

Fig.4. BNC connector

Fiber Optic Cable

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals, eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.
Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.

Fig.5. Fiber optic cable

Facts about fiber optic cables:

• Outer insulating jacket is made of Teflon or PVC.
• Kevlar fiber helps to strengthen the cable and prevent breakage.
• A plastic coating is used to cushion the fiber center.
• Center (core) is made of glass or plastic fibers.

Fiber Optic Connector

The most common connector used with fiber optic cable is an ST connector. It is barrel shaped, similar to a BNC connector. A newer connector, the SC, is becoming more popular. It has a squared face and is easier to connect in a confined space.

Ethernet Cable Summary

Specification	Cable Type	Maximum length
10BaseT	Unshielded Twisted Pair	100 meters
10Base2	Thin Coaxial	185 meters
10Base5	Thick Coaxial	500 meters
10BaseF	Fiber Optic	2000 meters

Wireless LANs

Not all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals or infrared light beams to communicate between the workstations and the file server. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology or by satellite.
Wireless networks are great for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.
Wireless LANs also have some disadvantages. They are very expensive, provide poor security, and are susceptible to electrical interference from lights and radios. They are also slower than LANs using cabling.

Installing Cable - Some Guidelines

When running cable, it is best to follow a few simple rules:

• Always use more cable than you need. Leave plenty of slack.
• Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.
• Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.
• If it is necessary to run cable across the floor, cover the cable with cable protectors.
• Label both ends of each cable.
• Use cable ties (not tape) to keep cables in the same location together.

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