Results 1 to 12 of 12

Thread: Network Guide Part 1 - Network Fundamentals

  1. #1
    Join Date
    May 2004
    Posts
    124

    Post Network Guide Part 1 - Network Fundamentals

    By themselves, computers are powerful tools. When they are connected in a network, they become even more powerful because the functions and tools that each computer provides can be shared with other computers. Networks exist for one major reason: to share information and resources.

    Networks can be very simple, such as a small group of computers that share information, or they can be very complex, spanning large geographical areas. Regardless of the type of network, a certain amount of maintenance is always required. Because each network is different and probably utilizes many diverse technologies, it is important to understand the fundamentals of networking and how networking components interact.

  2. #2
    Join Date
    May 2004
    Posts
    124

    Post Network Elements

    Network Elements
    In the computer world, the term network describes two or more connected computers that can share resources such as data, a printer, an Internet connection, applications, or a combination of these. In this section, we’ll discuss each type of network and describe the situation that is most appropriate for its use.

    Local Area Network
    By definition, a local area network (LAN) is limited to a specific area, usually an office, and cannot extend beyond the boundaries of a single building. The first LANs were limited to a range (from a central point to the most distant computer) of 185 meters (about 600 feet) and no more than 30 computers. Today’s technology allows a larger LAN, but practical administration limitations require dividing it into small, logical areas called workgroups. A workgroup is a collection of individuals (a sales department, for example) who share the same files and databases over the LAN

    Wide Area Network
    Chances are, you are an experienced wide area network (WAN) user and didn’t know it. If you have ever connected to the Internet, you have used the largest WAN on the planet. A WAN is any network that crosses metropolitan, regional, or national boundaries. Most networking professionals define a WAN as any network that uses routers and public network links. The Internet fits both definitions.

    WANs differ from LANs in the following ways:
    • WANs cover greater distances.

      WAN speeds are slower.

      WANs can be connected on demand or permanently connected; LANs have permanent connections between stations.

      WANs can use public or private network transports; LANs primarily use private network transports.
    WANs can use either full- or half-duplex communications. LANs have typically used half-duplex communications, although most local area networks today use full-duplex communications (see the sidebar “Full-Duplex vs. Half-Duplex Communications”).


    The Internet is actually a specific type of WAN. The Internet is a collection of networks that are interconnected and, therefore, is technically an internetwork (Internet is short for the word internetwork ).

    A WAN can be centralized or distributed. A centralized WAN consists of a central computer (at a central site) to which other computers and dumb terminals connect. The Internet, on the other hand, consists of many interconnected computers in many locations. Thus, it is a distributed WAN

    Full-Duplex vs. Half-Duplex Communications


    All network communications (including LAN and WAN communications) can be categorized as half-duplex or full-duplex. With half-duplex, communications happen in both directions, but in only one direction at a time. When two computers communicate using half-duplex, one computer sends a signal and the other receives; then they switch sending and receiving roles. Chances are that you are familiar with half-duplex communications. If you ever use a CB radio, you are communicating via half-duplex: One person talks, and then the other person talks.

    Full-duplex, on the other hand, allows communication in both directions simultaneously. Both stations can send and receive signals at the same time. Full-duplex communications are similar to a telephone call, in which both people can talk simultaneously.


    Host, Workstation, and Server

    You need a good understanding of the three primary components of a network: workstations, servers, and hosts. Each one of these items can be found on most networks.


    Understanding Workstations
    [b]
    In the classic sense, a workstation is a powerful computer used for drafting or other math-intensive applications. The term is also applied to a computer that has multiple central processing units (CPUs) available to users. In the network environment, the term workstation normally refers to any computer connected to the network that is used by an individual to do work. Workstation can also refer to software, as in Windows NT Workstation. It is important to distinguish between workstations and clients. A client is any network entity that can request resources from the network; a workstation is a computer that can request resources. Workstations can be clients, but not all clients are workstations. For example, a printer can request resources from the network, but it is a client, not a workstation.

    Understanding Servers

    In the truest sense, a server does exactly what the name implies: It provides resources to the clients on the network (“serves” them, in other words). Servers are typically powerful computers that run the software that controls and maintains the network. This software is known as the network operating system

    Servers are often specialized for a single purpose. This is not to say that a single server can’t do many jobs, but, more often than not, you’ll get better performance if you dedicate a server to a single task. Here are some examples of servers that are dedicated to a single task:

    File Server Holds and distributes files.

    Print Server Controls and manages one or more printers for the network.

    Proxy Server Performs a function on behalf of other computers (proxy means “on behalf of”).

    Application Server Hosts a network application.

    Web Server Holds and delivers web pages and other web content using the Hypertext Transfer Protocol (HTTP).

    Mail Server Hosts and delivers e-mail. It’s the electronic equivalent of a post office.

    Fax Server Sends and receives faxes (via a special fax board) for the entire network without the need for paper.

    Remote Access Server Hosts modems for inbound requests to connect to the network. Remote access servers provide remote users (working at home or on the road) with a connection to the network.

    Telephony Server Functions as a “smart” answering machine for the network. It can also perform call center and call-routing functions.

    Notice that each server type’s name consists of the type of service the server provides (remote access, for example) followed by the word “server,” which, as you remember, means to serve.

    Regardless of the specific role (or roles) these servers play, they should all have the following in common:
    • Hardware and/or software for data integrity (such as backup hardware and software)
    • The capability to support a large number of clients
    Physical resources, such as hard-drive space and memory, must be greater in a server than in a workstation because the server needs to provide services to many clients. Also, a server should be located in a physically secure area.

    Understanding Hosts
    The term host is most commonly used when discussing TCP/IP related services and functions. A host, in TCP/IP terms, is any network device that has a TCP/IP network address. Workstations, servers, and any other network device (as long as it has TCP/IP addresses) can all be considered hosts. In conversation, you may also hear the word “host” used to describe any minicomputer or server.

    Peer-to-Peer vs. Client/Server Architecture

    The purpose of networking is to share resources. How this is accomplished depends on the architecture of the network operating system software. The two most common network types are peer-to-peer and client/server.
    If you were to look at an illustration of a group of computers in a LAN, it would be impossible to determine if the network was a peer-to-peer or a client/server environment. Even a videotape of this same LAN during a typical workday would reveal few clues as to whether it is peer-to-peer or client/server. Yet, the differences are huge. Since you can’t see the differences, you might guess correctly that they are not physical but logical.

    Peer-to-Peer Network

    In peer-to-peer networks, the connected computers have no centralized authority. From an authority viewpoint, all of these computers are equal. In other words, they are peers. If a user of one computer wants access to a resource on another computer, the security check for access rights is the responsibility of the computer holding the resource.

    Each computer in a peer-to-peer network can be both a client that requests resources and a server that provides resources. This is a great arrangement, provided the following conditions are met:
    Each user is responsible for local backup.

    Security considerations are minimal.

    A limited number of computers are involved.

    Networks that run Windows 95/98 as their network operating system or networks using Windows NT in a workgroup are considered peer-topeer networks. Peer-to-peer networks present some challenges. For example, backing up company data becomes an iffy proposition. Also, it can be difficult to remember where you stored a file. Finally, because security is not centralized, users and passwords must be maintained separately on each machine, Passwords may be different for the same users on different machines.

    Client/Server Network

    In contrast to a peer-to-peer network, a client/server network uses a network operating system designed to manage the entire network from a centralized point, which is the server. Clients make requests of the server, and the server responds with the information or access to a resource.

    Client/server networks have some definite advantages over peer-to-peer networks. For one thing, the network is much more organized. It is easier to find files and resources because they are stored on the server. Also, client/server networks generally have much tighter security. All usernames and passwords are stored in the same database (on the server), and individual users can’t use the server as a workstation. Finally, client/server networks have better performance and can scale almost infinitely. It is not uncommon to see client/server networks with tens of thousands of workstations. Note that the server now holds the database of user accounts, passwords, and access rights.

    Network Attached Storage

    The most common type of server found on networks is the file server. File servers are typically the most accessed servers as well, storing files for all the users on the network. Traditionally, these servers are just computers, running a special network operating system that allows files and programs to be shared. Additionally, these servers cost several thousand dollars.
    In the last few years, however, it has become very attractive to network administrators to replace these file servers with a new breed of device known as network attached storage. Network attached storage, such as the Quantum Æ SNAP! Server, is basically a small network device, or “black box,” with a network card and a large hard disk. The network attached storage device usually runs a special proprietary operating system that allows the box to function as a file server.

    The major reason these devices are so attractive to network administrators is that they are very inexpensive compared to traditional file servers. For example, a typical Pentium II Server with 256MB of RAM might cost a few thousand dollars. On the other hand, a 20GB network attached storage device might cost only a few hundred dollars.

    Another advantage to these devices is that they are very easy to administrate. Usually, security and access are set up by connecting to the device with a web browser and making changes using a web interface.

    The final advantage to these devices is their ease and speed of setup. It would take most network technicians about three hours to add another server to a network. Quantum, however, expresses setup times for its network attached storage devices in minutes and seconds. Basically, all an administrator has to do is plug in the power, plug in the network cable, turn the device on, and set up security and access, and the device will be ready to use.
    Last edited by mindreader; 21-07-2004 at 07:51 PM.

  3. #3
    Join Date
    May 2004
    Posts
    124

    Post Physical Topologies

    Physical Topologies
    A topology is basically a map of a network. The physical topology of a network describes the layout of the cables and workstations and the location of all network components. Often, physical topologies are compared to logical topologies, which define how the information or data flows within the network. The topologies are usually similar. It is important to note, however, that a network can have one type of physical topology and a completely different logical topology. You'll learn more about this later in this chapter.

    The cables or connections in a physical topology are often referred to as network media (or physical media). Choosing how computers will be connected in a company's network is critical. A wrong decision in the physical topology makes the media difficult to correct, because it is costly and disruptive to change an entire installation once it is in place. The typical organization changes the physical layout and physical media of a network only once about every 10 years, so it is important to choose a configuration that you can live with and that allows for growth.

    In this section, we'll look at the five most common topologies:
    • Bus

      Ring

      Star

      Mesh

      Wireless


    Bus
    In a bus topology, all computers are attached to a single continuous cable that is terminated at both ends, which is the simplest way to create a physical network. Originally, computers were attached to the cable with wire taps. This did not prove practical, so drop cables are now used to attach computers to the main cable.
    When communicating on a network that uses a bus topology, all computers see the data on the wire. This does not create chaos, though, because the only computer that actually accepts the data is the one to which it is addressed. You can think of a bus network as a small party. David is already there, along with 10 other people. David would like to tell Joe something. David yells out, 'Joe! Will you grab me a cup of coffee, please?' Everyone in the party can hear David, but only Joe will respond. A star network with a hub, which you'll read about later in this section, also operates in this manner.

    Real World Scenario: A bus sounds good, but . . .
    Despite the simplicity of the bus topology, there are some inherent disadvantages to this design. For example, what happens if the wire breaks or is disconnected? Neither side can communicate with the other, and signal bounce occurs on both sides. The result is that the entire network is down. For this reason, bus topologies are considered to have very little fault tolerance.

    Sometimes, because a cable is inside a wall, you cannot physically see a break. To determine if a break has occurred, you can use a tool known as a Time Domain Reflectometer, or TDR (also called a cable tester). This device sends out a signal and measures how much time it takes to return. Programmed with the specifications of the cable being tested, it determines where the fault lies with a high degree of accuracy. We'll discuss cable testers in Chapter 6, 'Network Installation and Upgrades.'

    As with most things, there are pros and cons to a bus topology. On the pro side, a bus topology:

    Is simple to install
    Is relatively inexpensive
    Uses less cable than other topologies

    On the con side, a bus topology:

    Is difficult to move and change
    Has little fault tolerance (a single fault can bring down the entire network)
    Is difficult to troubleshoot

    Star
    Unlike those in a bus topology, each computer in a star topology is connected to a central point by a separate cable. The central point is a device known as a hub. Although this setup uses more cable than a bus, a star topology is much more fault tolerant than a bus topology. This means that if a failure occurs along one of the cables connecting to the hub, only that portion of the network is affected, not the entire network. It also means that you can add new stations just by running a single new cable

    The design of a star topology resembles an old wagon wheel with the wooden spokes extending from the center point. The center point of the wagon wheel would be considered the hub. Like the wagon wheel, the network's most vulnerable point is the hub. If it fails, the whole system collapses. Fortunately, hub failures are extremely rare.

    As with the bus topology, the star topology has advantages and disadvantages. The increasing popularity of the star topology is mainly due to the large number of advantages, which include the following:
    New stations can be added easily and quickly.
    A single cable failure won't bring down the entire network.
    It is relatively easy to troubleshoot.

    The disadvantages of a star topology include the following:
    Total installation cost can be higher because of the larger number of cables, but prices are constantly becoming more and more competitive.
    It has a single point of failure, the hub.

    Ring
    In the ring topology, each computer is connected directly to two other computers in the network. Data moves down a one-way path from one computer to another The good news about laying out cable in a ring is that the cable design is simple. The bad news is that, as with bus topology, any break, such as adding or removing a computer, disrupts the entire network. Also, because you have to 'break' the ring in order to add another station, it is very difficult to reconfigure without bringing down the whole network. For this reason, the physical ring topology is seldom used.

    Note Although its name suggests a relationship, Token Ring does not use a physical ring topology. It instead uses a physical star, logical ring topology

    A few pros and many cons are associated with a ring topology. On the pro side, the ring topology is relatively easy to troubleshoot. A station will know when a cable fault has occurred because it will stop receiving data from its upstream neighbor.

    On the con side, a ring topology is:
    Expensive, because multiple cables are needed for each workstation.
    Difficult to reconfigure.
    Not fault tolerant. A single cable fault can bring down the entire network.

    Mesh
    A path exists from each station to every other station in the network. While not usually seen in LANs, a variation on this type of topology-the hybrid mesh-is used on the Internet and other WANs in a limited fashion. Hybrid mesh topology networks can have multiple connections between some locations, but this is done only for redundancy. Also, it is not a true mesh because there is not a connection between each and every node, just a few for backup purposes

    a mesh topology can become quite complex as wiring and connections increase exponentially. For every n stations, you will have n(n -1)/2 connections. For example, in a network of 4 computers, you will have 4(4-1)/2 connections, or 6 connections. If your network grows to only 10 computers, you will have 45 connections to manage! Given this impossible overhead, only small systems can be connected this way. The payoff for all this work is a more fail-safe, or fault-tolerant, network, at least as far as cabling is concerned.

    Today, the mesh topology is rarely used, and then only in a WAN environment and only because the mesh topology is fault tolerant. Computers or network devices can switch between these multiple, redundant connections if the need arises. On the con side, the mesh topology is expensive and, as you have seen, quickly becomes too complex.

    Wireless
    Radio frequency (RF) systems are being used all over corporate America. The RF networking hardware that is available today makes it easy for people to connect wirelessly to their corporate network as well as to the Internet.

    The most popular example of an RF network today is what is known as an ad hoc RF network. These networks are created when two or more entities with RF transceivers that support ad hoc networking are brought within range of each other. The two entities will send out radio waves to each other, and they will both recognize that there is another RF device close by that they can communicate with. These ad hoc networks allow people with laptops or handheld devices to create their own networks on the fly and transfer data

    The other example of an RF network is a multipoint RF network. This type of RF network has many stations, each with an RF transmitter and receiver, and each station communicates with a central device known as a wireless bridge. A wireless bridge (known as a wireless access point, or WAP, in RF systems) is a device that provides a transparent connection to the host LAN via an Ethernet or Token Ring connection and uses some wireless method (e.g., infrared, RF, or microwave) to connect to the individual nodes. This type of network is mainly used for two applications: office 'cubicle farms' and metropolitan-area wireless Internet access. Each of these applications requires that the wireless bridge be installed at some central point and the stations that are going to access the network be within the operating range of the bridge device

    Note that the workstations at the top of the figure can communicate wirelessly to the server and printer connected to the same network as the bridge device.

    There are many different brands, makes, and models of RF LAN equipment. This used to be a source of difficulty with LAN installers. In the infancy of RF wireless networking, every company used different frequencies, different encoding schemes, different antennas, and different wireless protocols. The marketplace was screaming for a standard to be proposed. For this reason, the IEEE 802.11 standard was developed. 802.11 is a networking standard that specifies various protocols for wireless networking. It does in fact specify that either infrared or RF can be used for the wireless network, but most RF systems are the only ones advertising IEEE 802.11 compliance.

    Backbones and Segments
    With complex networks, we must have a way of intelligently identifying which part of the network we are discussing. For this reason, we commonly break networks into backbones and segments

    Understanding the Backbone
    A backbone is the part of the network to which all segments and servers connect. A backbone provides the structure for a network and is considered the main part of any network. It usually uses a high-speed communications technology of some kind, such as FDDI (Fiber Distributed Data Interface) or 100-Megabit Ethernet (Fast Ethernet). All servers and all network segments typically connect directly to the backbone so that any segment is only one segment away from any server on that backbone. Because all segments are close to the servers, the network is more efficient.

    Understanding Segments
    Segment is a general term for any short section of the network that is not part of the backbone. Just as servers connect to the backbone, workstations connect to segments. Segments are connected to the backbone to allow the workstations on them access to the rest of the network.

    Selecting the Right Topology
    • Ease of installation
    • Ease of maintenance
    • Cable fault tolerance

  4. #4
    Join Date
    May 2004
    Posts
    124

    Physical Media

    Physical Media
    Although it is possible to use several forms of wireless networking, such as radio and infrared, most networks communicate via some sort of cable. In this section, we'll look at three types of cables:

    Coaxial

    Twisted-pair Fiber-optic

    Coaxial Cable

    Coaxial cable (or coax) contains a center conductor, made of copper, surrounded by a plastic jacket, with a braided shield over the jacket. A plastic such as PVC or Teflon covers this metal shield. The Teflon-type covering is frequently referred to as a plenum-rated coating. That simply means that the coating does not produce toxic gas when burned (as PVC does) and is rated for use in air plenums that carry breathable air. This type of cable is more expensive but may be mandated by electrical code whenever cable is hidden in walls or ceilings. Plenum rating applies to all types of cabling.

    Coaxial cable is available in different specifications that are rated according to the RG Type system. Different cables have different specifications and, therefore, different RG grading designations (according to the U.S. military specification MIL-C-17). Distance and cost are also considerations when selecting coax cable. The thicker the copper, the farther a signal can travel- and with that comes higher costs and a less flexible cable.

    Using Thick Ethernet
    The original Ethernet cable is known as Thick Ethernet cable, or Thicknet. It is also called 10Base5 and is graded as RG-8. To the folks who installed the cable, it was more commonly called a 'frozen garden hose' because of its ½" diameter.

    With Thick Ethernet, a station attaches to the main cable via a vampire tap, which clamps onto the cable. A vampire tap is so named because a metal tooth sinks into the cable, thus making the connection with the inner conductor. The tap is connected to an external transceiver that, in turn, has a 15-pin AUI connector (also called DIX or DB-15 connector) to which you attach a cable that connects to the station DIX got its name from the companies that worked on this format-Digital, Intel, and Xerox.


    Using Thin Ethernet

    Thin Ethernet, also referred to as Thinnet or 10Base2, is a thin coaxial cable. It is basically the same as thick coaxial cable except that the diameter of the cable is smaller (about 1/4" in diameter). Thin Ethernet coaxial cable is RG-58
    With Thinnet cable, you use BNC connectors to attach stations to the network. It is beyond my province to settle the long-standing argument over the meaning of the abbreviation BNC. BNC could mean BayoNet Connector, Bayonet Nut Connector, or British Navel Connector. What is relevant is that the BNC connector locks securely with a quartertwist motion.

    Tip
    The BNC connector can be attached to a cable in two ways. The first is with a crimper, which looks like funny pliers and has a die to hold the connector. Pressing the levers crimps the connector to the cable. Choice number two is a screw-on connector, which is very unreliable. If at all possible, avoid the screw-on connector!

    Signal Bounce
    With coaxial cable, the signal travels up and down the entire length of the wire. When the signal reaches the end of the wire, the electrical change from copper to air prevents the conversation from simply falling out the end. Instead, the signal bounces back down the wire it just traversed. This creates an echo, just as if you were yelling into a canyon. These additional signals on the wire make communication impossible. To prevent this, you place a terminator on each end of the wire to absorb the unwanted echo.

    Technically, proper termination also requires that one terminator be connected to a ground. Connecting both terminators to a ground can create a ground loop, which can produce all kinds of bizarre, ghostlike activity (for example, a network share that appears and disappears).

    If you are not sure where to find a good ground point, connect one terminator to a screw holding a power supply inside a computer. This ensures that you are using the same ground as the PC. This does assume, however, that the outlet into which the PC is plugged is properly grounded.

    Twisted-Pair Cable
    Twisted-pair cable consists of multiple, individually insulated wires that are twisted together in pairs. Sometimes a metallic shield is placed around the twisted pairs. Hence, the name shielded twisted-pair (STP). (You might see this type of cabling in Token Ring installations.) More commonly, you see cable without outer shielding; it's called unshielded twisted-pair (UTP). UTP is commonly used in 10BaseT, star-wired networks.

    Let's take a look at why the wires in this cable type are twisted. When electromagnetic signals are conducted on copper wires that are in close proximity (such as inside a cable), some electromagnetic interference occurs. In this scenario, this interference is called crosstalk. Twisting two wires together as a pair minimizes such interference and also provides some protection against interference from outside sources. This cable type is the most common today. It is popular for several reasons:

    It's cheaper than other types of cabling.

    It's easy to work with.

    It permits transmission rates considered impossible 10 years ago.

    UTP cable is rated in the following categories:

    Category 1 Two twisted-pair (four wires). Voice grade (not rated for data communications). The oldest UTP. Frequently referred to as POTS, or plain old telephone service. Before 1983, this was the standard cable used throughout the North American telephone system. POTS cable still exists in parts of the Public Switched Telephone Network (PSTN).

    Category 2 Four twisted-pair (eight wires). Suitable for up to 4Mbps.

    Category 3 Four twisted-pair (eight wires), with three twists per foot. Acceptable for 10Mbps. A popular cable choice since the mid-80s.

    Category 4 Four twisted-pair (eight wires) and rated for 16Mbps.

    Category 5 Four twisted-pair (eight wires) and rated for 100Mbps.

    Category 6 Four twisted-pair (eight wires) and rated for 1000Mbps. Became a standard in December 1998.

    Note Frequently, you will hear Category shortened to Cat. Today, any cable that you install should be a minimum of Cat 5. This is a minimum because some cable is now certified to carry a bandwidth signal of 350MHz or beyond. This allows unshielded twisted-pair cables to reach a speed of 1Gbps, which is fast enough to carry broadcast-quality video over a network. A common saying is that there are three ways to do things: the Right way, the Wrong way, and the IBM way. IBM uses types instead of categories when referring to TP (twisted-pair) cabling specifications. Even though a cabling type may seem to correspond to a cabling category (such as Type 1 and Category 1), the two are not the same; IBM defines its own specifications.

    Category 5 Cabling Tips
    If you expect data rates faster than 10Mbps over UTP, you should ensure that all components are rated to the category you want to achieve and be very careful when handling all components. For example, pulling too hard on Cat 5 cable will stretch the number of twists inside the jacket, rendering the Cat 5 label on the outside of the cable invalid. Also, be certain to connect and test all four pairs of wire. Although today's wiring usually uses only two pairs, or four wires, at the time of this writing the proposed standard for Gigabit Ethernet over UTP requires that all four pairs, or eight wires, be in good condition.

    You should also be aware that a true Cat 5 cabling system uses rated components from end to end, patch cables from workstation to wall panel, cable from wall panel to patch panel, and patch cables from patch panel to hub. If any components are missing or if the lengths do not match the Category 5 specification, you don't have a Category 5 cabling installation. Also, installers should certify that the entire installation is Category 5 compliant.

    Connecting UTP
    Clearly, a BNC connector won't fit easily on UTP cable, so you need to use an RJ (Registered Jack) connector. You are probably familiar with RJ connectors. Most telephones connect with an RJ-11 connector.

    The connector used with UTP cable is called RJ-45. The RJ-11 has four wires, or two pairs, and the network connector RJ-45 has four pairs, or eight wires
    In almost every case, UTP uses RJ connectors. Even the now-extinct ARCnet used RJ connectors. You use a crimper to attach an RJ connector to a cable, just as you use a crimper with the BNC connector. The only difference is that the die that holds the connector is a different shape. Higherquality crimping tools have interchangeable dies for both types of cables.

    Signaling Methods
    The amount of a cable's available bandwidth (overall capacity, such as 10Mbps) that is used by each signal depends on whether the signaling method is baseband or broadband. Baseband uses the entire bandwidth of the cable for each signal (using one channel). It is typically used with digital signaling.

    In broadband, multiple signals can be transmitted on the same cable simultaneously by means of frequency division multiplexing (FDM). Multiplexing is dividing a single medium into multiple channels. With FDM, the cable's bandwidth is divided into separate channels (or frequencies), and multiple signals can traverse the cable on these frequencies simultaneously.

    FDM is typically used for analog transmissions. Another method, time division multiplexing (TDM), can also be used to further divide each individual FDM frequency into individual time slots. Additionally, TDM can be used on baseband systems.

    Ethernet Cable Descriptions
    Ethernet cable types are described using a code that follows this format: N<Signal>X. Generally speaking, N is the signaling rate in megabits per second, and <Signal> is the signaling type, which is either base or broad (baseband or broadband). X is a unique identifier for that specific Ethernet cabling scheme.

    Let's use a generic example: 10BaseX. The two-digit number 10 indicates that the transmission speed is 10Mb, or 10 megabits. The value X can have different meanings. For example, the 5 in 10Base5 indicates the maximum distance that the signal can travel-500 meters. The 2 in 10Base2 is used the same way, but fudges the truth. The real limitation is 185 meters. Only the IEEE committee knows for sure what this was about. We can only guess that it's because 10Base2 seems easier to say than 10Base1.85.

    Another 10Base standard is 10BaseT. The T is short for twisted-pair. This is the standard for running 10-Megabit Ethernet over two pairs (four wires) of Category 3, 4, or 5 UTP. The fourth, and currently final, 10Base is 10BaseF. The F is short for Fiber. 10BaseF is the standard for running 10-Megabit Ethernet over fiber-optic cable.

    100BaseT
    As network applications increased in complexity, so did their bandwidth requirements. Ten-megabit technologies were too slow. Businesses were clamoring for a higher speed standard so that their data could be transmitted at an acceptable rate of speed. A 100-megabit standard was needed. Thus the 100BaseT standards were developed.

    The 100BaseT standard is a general category of standards for Ethernet transmissions at a data rate of 100Mbps. This Ethernet standard is also known as Fast Ethernet. There are two major standards for 100BaseT:

    100BaseTX The implementation of 100BaseT that is simply a faster version of 10BaseT. It uses two UTP pairs (four wires) in a Category 5 UTP cable (or Type 1 STP).

    100BaseT4 The implementation of 100BaseT that runs over four pairs (eight wires) of Category 3, 4, or 5 UTP cable.

    100BaseVG
    This 100-Megabit Ethernet replacement came from HP, and in the popularity race, it lost. Even the name wasn't settled upon, so you may find it referred to as VG LAN, VGAnyLAN, or AnyLAN. Although it used UTP cable, it didn't follow the popular Ethernet standard. It attempted to improve on Ethernet by using collision avoidance as a method of controlling network traffic.

    You will see details on Ethernet and several methods of handling traffic in chapters throughout this book. The point here is that the 100BaseVG standard was not compatible with 10BaseX and Ethernet. The combination of its incompatibility and its actually less than 100Mbps throughput (due to its media access method, which is discussed elsewhere in this book) ultimately spelled its demise. However, it was basically 100Mb, and it was out the door early in the game. Because some companies implemented this standard, you need to know about it.

    Fiber-Optic Cable
    Because fiber-optic cable transmits digital signals using light pulses rather than electricity, it is immune to EMI and RFI but you should know at this point that both could affect network performance. Anyone who has seen UTP cable for a network run down an elevator shaft would, without doubt, appreciate this feature of fiber. Light is carried on either a glass or a plastic core. Glass can carry the signal a greater distance, but plastic costs less. Regardless of which core is used, there is a shield wrapped around it, and it is surrounded by cladding, which is more glass that refracts the light back into the core. This is then wrapped in an armor coating, typically Kevlar, and then sheathed in PVC or Plenum.

    Fiber-optic cables can use a myriad of different connectors, but the two most popular and recognizable are the straight tip (ST) and subscriber connector (SC) connectors. The ST fiber-optic connector, developed by AT&T, is probably the most widely used fiber-optic connector. It uses a BNC attachment mechanism similar to the Thinnet connection mechanism, which makes connections and disconnections fairly easy. Its ease of use is one of the attributes that makes this connector so popular.

    The SC connector (sometimes known also as a square connector) is another type of fiber-optic connector. SC connectors are latched connectors. This makes it impossible for the connector to be pulled out without releasing the connector's latch (usually by pressing some kind of button or release).

    SC connectors work with either single-mode or multimode optical fibers, and they will last for around 1,000 matings. They are seeing increased use, but aren't as popular as ST connectors for LAN connections.

    Note If data runs are measured in kilometers, fiber-optic is your cable of choice, because copper cannot reach more than 500 meters (about 1500 feet) without electronics regenerating the signal. You may also want to opt for fiber-optic cable if an installation requires high security, because it does not create a readable magnetic field. Although fiber-optic technology was initially very expensive and difficult to work with, it is now being used in some interesting places, such as Gigabit Internet backbones. Also, some companies plan to bring fiber-optic speeds to the desktop. Ethernet running at 10Mbps over fiber-optic cable is normally designated 10BaseF; the 100Mbps version of this implementation is 100BaseFX.


    Although fiber-optic cable may sound like the solution to many problems, it has pros and cons, just as the other cable types. On the pro side, fiber-optic cable:

    Is completely immune to EMI or RFI

    Can transmit up to 4 kilometers (about 2 miles)

    On the con side, fiber-optic cable:

    Is difficult to install

    Requires a bigger investment in installation and materials

  5. #5
    Join Date
    May 2004
    Posts
    124

    Post Common Network Connectivity Devices

    Common Network Connectivity Devices
    Now that you are familiar with the various types of network media and connections, you should learn about some devices commonly found on today’s networks. Because these devices connect network entities, they are known as connectivity devices. These devices include:

    The network interface card (NIC)

    The hub

    The switch

    The bridge

    The router

    The gateway

    Other devices


    NIC
    The network interface card (NIC), as its name suggests, is the expansion card you install in your computer to connect, or interface, your computer to the network. This device provides the physical, electrical, and electronic connections to the network media. NICs are either an expansion card (the most popular implementation) or built in to the motherboard of the computer. In most cases, a NIC connects to the computer through expansion slots. An expansion slot connects expansion cards that are plugged in to a slot in the main computer assembly through a deceptively simple-looking connector, which is known as a bus. In some notebook computers, NIC adapters can be connected to the printer port or through a PC card slot.

    Hub
    As you learned earlier, in a star topology Ethernet network, a hub is the device that connects all the segments of that network together. Every device in the network connects directly to the hub through a single cable. Any transmission received on one port will be rebroadcast to all the other ports in the hub. So, if one station sends it, all the others receive it, but only the intended recipient listens to it.

    Switch
    Like a hub, a switch connects multiple segments of a network together, with one important difference. Whereas a hub rebroadcasts anything it receives on one port to all the others, a switch makes a direct link between the transmitting device and receiving device. Any party not involved in that communication will not receive the transmission. The benefit of a switch over a hub is that the switch increases performance because it doesn’t suffer from the wasted bandwidth of the extra transmissions.

    Bridge
    A bridge is a network device that connects two similar network segments together. The primary function of a bridge is to keep traffic separated on both sides of the bridge. Traffic is allowed to pass through the bridge only if the transmission is intended for a station on the opposite side. The main reason for putting a bridge in a network is to connect two segments together, or to divide a busy network into two segments.

    Router
    A router is a network device that connects multiple, often dissimilar, network segments into an internetwork. The router, once connected, can make intelligent decisions about how best to get network data to its destination based on network performance data that it gathers from the network itself.

    Gateways
    A gateway is any hardware and software combination that connects dissimilar network environments. Gateways are the most complex of network devices because they perform translations at multiple layers of the OSI model.

    For example, a gateway is the device that connects a LAN environment to a mainframe environment. The two environments are completely different. LAN environments use distributed processing, baseband communications, and the ASCII character set. Mainframe environments use centralized processing, broadband and baseband communications, and the EBCDIC character set. Each of the LAN protocols is translated to its mainframe counterpart by the gateway software.

    Another popular example is the e-mail gateway. Most LAN-based e-mail software, such as Novell’s GroupWise and Microsoft’s Exchange, can’t communicate directly with Internet mail servers without the use of a gateway. This gateway translates LAN-based mail messages into the SMTP format that Internet mail uses.

    Other Devices
    In addition to these network connectivity devices, there are several devices that, while maybe not directly connected to a network, participate in moving network data. Some of these devices include:

    Modems

    ISDN Terminal Adapters

    CSU/DSUs

    Modems
    A modem is a device that changes digital data into an analog form for transmission over an analog medium and then back to digital again at the receiving end. The term “modem” is actually an acronym that stands for MOdulator/DEModulator.

    When we hear the term modem, three different types should come to mind:

    Traditional (POTS)

    DSL

    Cable

    Traditional (POTS)
    Most modems you find in computers today fall into the category of traditional modems. These modems convert the signals from your computer into signals that travel over the plain old telephone service (POTS) lines. The majority of modems that exist today are POTS modems, mainly because PC manufacturers include one with a computer.

    DSL
    Digital subscriber line (DSL) is quickly replacing traditional modem access because it offers higher data rates for a reasonable cost. In addition, you can make regular phone calls while online. DSL uses higher frequencies (above 3200Hz) than regular voice phone calls use, which provides greater bandwidth (up to several megabits per second) than regular POTS modems. DSL “modems” are the devices that allow the network signals to pass over phone lines at these higher frequencies.

    Most often, when you sign up for DSL service, the company you sign up with will send you a DSL modem for free or for a very low cost. This modem is usually an external modem (although internal DSL modems are available), and it usually has both a phone line and an Ethernet connection. You must connect the phone line to the wall and the Ethernet connection to your computer (you must have an Ethernet NIC in your computer in order to connect to the DSL modem).

    Tip If you have DSL service on the same phone line you use to make voice calls, you must install DSL filters on all the phone jacks where you have a phone. Otherwise, you will hear a very annoying hissing noise (the DSL signals) on your voice calls.

    Cable
    Another high-speed Internet access technology that is seeing widespread use is cable modem access. Cable modems connect an individual PC or network to the Internet using your cable television cable. The cable TV companies use their existing cable infrastructure to deliver data services on unused frequency bands.

    The cable modem itself is a fairly simple device. It has a standard coax connector on the back as well as an Ethernet port. You can connect one PC to a cable modem (the PC will need to have an Ethernet NIC installed), or you can connect the modem to multiple PCs on a network (using a hub or switch).

    ISDN Terminal Adapters
    Integrated Service Digital Network (ISDN) is another form of high-speed Internet access. It delivers digital services (in 64Kbps channels) over standard telephone copper pairs. The device you must hook up to your computer to access ISDN services is properly known as an ISDN Terminal Adapter. It’s not a modem in the truest sense of the word because a modem changes from digital to analog for transmission, but an ISDN TA isn’t changing from digital to analog. It’s just changing between digital transmission formats.

    The box itself is about the size of a modem and looks similar to one. But, like DSL modems, there is a phone jack and an Ethernet jack. You connect a phone cord from the phone jack to the wall jack where your ISDN services are being delivered. Then, you connect an Ethernet cable from your PC to the ISDN TA’s Ethernet jack.

    CSU/DSUs
    The Channel Service Unit/Data Service Unit (CSU/DSU) is a common device found in equipment rooms when the network is connected via a T-series data connection (i.e., a T1). It is essentially two devices in one that are used to connect a digital carrier (the T-series or DDS line) to your network equipment (usually to a router). The Channel Service Unit (CSU) terminates the line at the customer’s premises. It also provides diagnostics and remote testing, if necessary. The Data Service Unit (DSU) does the actual transmission of the signal through the CSU. It can also provide buffering and data flow control.

    Both components are required if you are going to connect to a digital transmission medium, such as a T1 line. Sometimes, however, one or both of these components may be built into a router. If both components are built into a router, you only have to plug the T1 line directly into the router.

  6. #6
    Join Date
    May 2004
    Posts
    124

    ThumbsUp Summary - Network Guide Part 1 - Network Fundamentals

    You learned about the items that can be found on a typical network. You first learned what a network is and the various elements that make up a network, such as servers, workstations, and hosts. Then you learned about the different ways of laying out a network. You learned about bus, star, ring, mesh, hybrid, and wireless topologies.

    You also learned about the different types of physical media in use on networks today, including coaxial, twisted-pair, and fiber-optic media. Finally, you learned about some common network devices—including NICs, hubs, switches, bridges, routers, and gateways—seen on a typical network.

  7. #7
    Join Date
    Jan 2004
    Location
    /dev/null
    Posts
    85
    You wrote this?

    If you did then that awesome

  8. #8
    Join Date
    Jul 2004
    Posts
    4
    very gud article
    will see more from you soon.

    how can i take a print out of this article ?

  9. #9
    binaryman Guest
    Good Stuff man.........
    Makes me wonder what u r doing........
    i mean if u r studying,which course u r doing........coz all this is a part of S.Y.B.Sc(IT) subject Computer Networks.......
    Btw,great work.

  10. #10
    Join Date
    May 2004
    Posts
    124
    Quote Originally Posted by Anshul
    Good Stuff man.........
    Makes me wonder what u r doing........
    i mean if u r studying,which course u r doing........coz all this is a part of S.Y.B.Sc(IT) subject Computer Networks.......
    Btw,great work.
    hey Anshul,
    I used to study these things 10 years back i had all these materials since then.

    Working as a Systems Admin and Security Professional in Bangalore.
    was invited here from a friend

  11. #11
    Venkat Guest
    Fantastic!!! Basics but very useful stuff!

    And Anup use Thread tools,there u have an option to get a printable version.
    Last edited by Venkat; 26-07-2004 at 08:43 AM.

  12. #12
    Join Date
    Jul 2009
    Posts
    1

    Re: Network Guide Part 1 - Network Fundamentals

    thanks!!!! Love It

Similar Threads

  1. Network Guide Part 2 - Introducing the OSI Model
    By mindreader in forum Networking & Security
    Replies: 7
    Last Post: 06-02-2013, 01:57 AM
  2. Linux - Network Administrator's Guide
    By The#Danger in forum Guides & Tutorials
    Replies: 6
    Last Post: 22-12-2010, 07:39 AM
  3. Networking Guide 9 - Network Troubleshooting
    By mindreader in forum Networking & Security
    Replies: 29
    Last Post: 11-09-2009, 04:03 PM
  4. Network Guide Part 5 - Network Operating Systems
    By mindreader in forum Guides & Tutorials
    Replies: 8
    Last Post: 28-12-2004, 11:27 PM
  5. Networking Guide Part 3 - TCP/IP Fundamentals
    By mindreader in forum Networking & Security
    Replies: 26
    Last Post: 12-11-2004, 09:07 AM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Page generated in 1,711,695,010.19645 seconds with 17 queries