Please Accept My Topologies






Please Accept My Topologies

Imagine an aerial view of a network. Picture the network’s general shape. The pattern of connections that ties the workstations to the network is its topology. You may encounter the following topologies on the A+ exams:

  • Ethernet: Sometimes referred to as bus topology, Ethernet uses a full range of network media (using copper or fiber optics) and operates at 10 Mbps, 100 Mbps, or 1000 Mbps (1 Gbps). The 100-Mbps Ethernet is called Fast Ethernet and 1000 Mbps Ethernet is called Gigabit Ethernet. An Ethernet network (LAN) can support about 500 nodes. This is the most commonly installed type of network, probably because it is the cheapest and simplest. Ethernet devices connect to either a hub or a switch that is in turn connected to the network backbone.

  • FDDI: (I’ve heard this pronounced as fiddy, but it’s usually just spelled out.) FDDI stands for Fiber Distributed Data Interface. An FDDI NIC contains a laser or diode transceiver that converts its digital data into light to be transmitted on a fiber-optic network or back to a digital signal from incoming light impulses for use by the PC. FDDI is a standard of ANSI and the International Standards Organization (ISO) for data networks that use ring topology with dual and redundant rings and data speeds of 100 Mbps.

  • Token Ring: Sometimes referred to as ring topology, Token Ring also uses copper and fiber-optic cabling, operates at 4 Mbps to 16 Mbps, and supports about 260 nodes. A Token Ring network operates reliably but can be difficult to troubleshoot. Because IBM is involved with the exams now, look for at least one Token Ring question.

Connecting a workstation to the network

Each network topology is associated with a network technology or protocol. Ethernet networking is the most common on a bus topology, and Token Ring is the most common on a ring structure.

The network technology in use is important because when you connect a PC to the network for the first time, you need to know the network identity requirements for a new workstation.

Addressing the network

The three addressing elements that are used on a network are as follows:

  • MAC (Media Access Control) address: Every NIC or network adapter is assigned a unique ID (called the MAC address) by its manufacturer when it is made. This address is burned into the NIC’s firmware and cannot be changed. The MAC address is the basis for all network addressing, and all other address types are cross-referenced to it. A MAC address is a 48-bit address that is expressed as 12 hexadecimal digits (a hex digit is comprised of 4 bits). To display the MAC address (adapter address) of the NIC or NICs installed in a PC, you can use either the WINIPCFG command on Windows 9x and Me systems or the IPCONFIG command on Windows NT, 2000, and XP systems.

  •  Remember  IP (Internet Protocol) address: Many internal and all external networks use IP addresses to identify nodes on both LANs and WANs. An IP address for a network workstation combines the address of the network and the node into a 32-bit address that is expressed in four 8-bit octets (which means sets of eight). Figure shows the results of the IPCONFIG command, which displays the IP addressing information for a workstation. To run this command, open a command prompt and enter IPCONFIG on the command line.

    Click To expand
    Figure: The IPCONFIG command is used to display the IP address configuration of a PC.

    The IPCONFIG command displays the IP address that is assigned to the workstation (in this case, 192.168.1.100), the workstation’s subnet mask (which is used to differentiate between the network and host portion of an IP address), and the default gateway of the node.

  • Network names: The most common form of a network name are computer names, which are also called network names. A network name is the name assigned to a workstation or other networked device and used to identify that node by other network users. For example, it is much easier to find a printer with a network name or MAIN_LASER than trying to remember the printer’s MAC or IP address.

    Commonly, network names are NetBIOS (Network Basis Input/Output System) names. NetBIOS uses unique 15-character names that are periodically broadcast over the network so the names can be cataloged by the Network Neighborhood function. NetBIOS names are the names that show up in Windows Network Neighborhood.

Addressing protocols and services

Many protocols and services can be used on a network to aid in the correlation and translation of one address form to another. The ones that you need to know for the A+ exams are as follows:

  • DHCP (Dynamic Host Configuration Protocol): This protocol is used to automatically configure a network workstation with its IP address data. Each time that the workstation is logged on to the network, the DHCP server software, running on a network server or router, assigns or renews the IP configuration of the workstation. Typically, the address that is assigned is from blocks of IP addresses that have been set aside for use by internal networks. Depending on the network operating system, the IPCONFIG or WINIPCFG command can be used to view, renew, or release DHCP data.

  • DNS (Domain Name System): DNS is used to resolve (translate) Internet names to their IP address equivalents. For example, when you request www.wiley.com from your browser’s location line, a nearby DNS server (typically at your ISP) converts it to an IP address, such as 12.168.1.100, which is then used to request the data across the Internet.

  • WINS (Windows Internet Naming Service): WINS is Microsoft’s network name resolution software that converts NetBIOS names to IP addresses. Windows machines are assigned NetBIOS names (see the section, “Addressing the network,” earlier in this chapter), which are converted into IP addresses for use on a network using TCP/IP (Transmission Control Protocol/Internet Protocol), the foundation protocol suite of the Internet. The use of a WINS server allows nodes on one LAN segment to find nodes on other LAN segments by name.

Connecting to an Ethernet network

When a new workstation is added to an Ethernet network, the workstation identifies itself using its MAC address and computer name to the rest of the network. Those devices that need to hold this addressing information, such as a switch or bridge, store the information in their MAC address tables. When requests come in for a particular IP address, the MAC address of the node is looked up and the message is sent to that workstation. Before you bury me in e-mails, please understand that this description is highly simplified, but it represents the essence of what happens.

Connecting to a Token Ring network

When you add a new node to a Token Ring network, the node must first establish that its address is unique. The workstation sends out test frames with its ID address, and the system responds with its own test frames that are sent to that address. If no other node responds (oops), the new ID address is accepted and established for the new ring node. If a duplication exists (it can happen), jumpers or DIP switches on the NIC can be used to alter the address.

Protocols and other niceties

In addition to the three network protocols (Ethernet, Token Ring, and FDDI) described earlier in this chapter, other protocols can be used to interconnect PCs to other PCs or networks. For the test, you need to know the names of these protocols, their acronyms, and the scope of what they interconnect. Figure lists other protocols that you may encounter on the A+ exams.

Figure: Networking and Communications Protocols

Protocol/Layer

Acronym

What It Does

Point-to-Point Protocol

PPP

Used to connect and manage network communications over a modem

Transmission Control Protocol/Internet Protocol

TCP/IP

The backbone protocol of the Internet

Internetwork Packet

IPX/SPX

The standard protocol of the Exchange/Sequenced Novell network operating system’s Packet Exchange

NetBIOS Extended User Interface

NetBEUI

A Microsoft protocol that is used only by Windows systems for LANs with no external connections; does not support routing (addressing through a router to other networks)

File Transfer Protocol

FTP

Used to send and receive files in client/ server mode to or from a remote host

Hypertext Transfer Protocol

HTTP

Used to send World Wide Web (WWW) documents, which are usually encoded in HTML, across a network

Network File Services

NFS

Allows the network node to access network drives as if they were local drives, files, and data; also performs the file-access and data-retrieval tasks that are requested of the network

Simple Mail Transfer Protocol

SMTP

Used to send electronic mail (e-mail) across a network

Telnet

Telnet

Used to connect and log in and manage a remote host

Discussing modems

Modems don’t hold the vaulted position on the A+ Hardware Technology exam that they have in the past, but expect to see questions on the exam about installing, configuring, and troubleshooting both internal and external modems.

Modem facts that you should know

A modem (which is an acronym for modulator/demodulator) converts the digital data signal of the PC into the analog data signal that is used on the plain old telephone system (POTS) — which is also called the public telephone switched network (PTSN). Modems can be installed inside the PC in an expansion slot, or they can be attached to the PC externally through a serial or USB port.

You may have heard of modems for other types of communications besides dialing into a network, such as an ISDN (Integrated Services Digital Network) modem or a DSL (Digital Subscriber Line) modem. You don’t need to know about these modem types for the A+ exams — and they’re not really modems.

Internal versus external modems

An internal modem is installed like any other expansion card — into a compatible expansion slot. Modern modems do not require physical configuration, but some modems have DIP switches or jumpers that need to be set. Fortunately, most of a modem’s configuration is performed automatically by the operating system.

AT commands

One modem topic that continues to be included on the A+ exams — although I’m not sure why in today’s world of software configuration tools and Plug and Play modems — is the AT command set. AT does not mean Advanced Technology, as it would with a motherboard or power supply. On a modem, AT refers to attention, which is used to precede each command that’s given to the modem from the AT command set.

 Instant Answer  The AT command set, which is officially known as the Hayes Standard AT Command Set, is used to drive and configure Hayes-compatible modems. For the A+ Hardware Technology exam, you should know the AT commands that are listed in Figure.

Figure: AT Modem Commands

Command

Action

ATDT xxx-xxxx

Dial the telephone number (indicated by the letters x) using touch-tone dialing

ATH

On hook (hang up)

ATL

Speaker loudness (volume)

ATZ

Reset the modem to default settings

Other commands can be used to control the modem during the dialing process. For example, if you are in an office or hotel where it is necessary to dial 9 to get an outside line, that digit can be entered into the string, along with appropriate pauses to wait for a second dial tone. For example, to dial out of an office, you could use the following command string:

ATDT 9,,15095551212

This string issues the following command sequence to the modem:

  1. Prepare to dial a phone number.

  2. Dial 9 to get an outside line, and pause 2 seconds (as indicated by the two commas) to wait for the outside dial tone.

  3. Dial the number 1-509-555-1212.

Troubleshooting a modem connection

If the internal modem will not begin the dialup process, the problem is prob-ably either a resource conflict or a device driver problem. Modems do not have a default IRQ assignment and must use an unassigned IRQ or share one with another device, such as a USB controller. An updated, newer version of a device driver can often solve a modem/operating system conflict.

An external modem uses the resources that are assigned to the COM port that it uses. Conflicts can arise when both an external modem and an internal device have both been assigned the same IRQ. To remedy this situation, move the external modem’s connector to a different COM port or reassign the internal device.

To check the resources and drivers that are assigned to a modem, use the System Information applet. Access this applet by choosing Start ® Programs ® Accessories ® System Tools ® System Information.

If the system has not detected the modem on startup after installing an internal modem, use the Add New Hardware icon in the Control Panel to start the Add New Hardware Wizard. Should that fail, open the system case, reseat the modem, or move the modem to another open slot and reboot the PC.

Connecting to a server

 Remember  Windows NT, Windows 2000, and Windows Server 2003 versions support Remote Access Services (RAS), which is the service that is used to manage and control incoming dialup connections. Not all dialup access is made to Internet providers. A remote user may need to dial up the RAS of a corporate server and log on to the corporate LAN and gain access to its WAN.



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