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Networking Essentials
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Networking Essentials Study Guide

TechRepublic, THE site for IT professionals

    You should know everything on this page before even attempting this exam. This is not a hard exam if you know a good bit about hardware, and the basic theory behind networking. I recommend that you know the OSI Model backwards and forwards and the protocols associated with each level.

Topologies

    You should know all the topologies and the cables associated with each.

  1. Star Topology - Machines connect to a hub through cable segments.   Ethernet uses this topology.

  2. Ring Topology - All the computers are connected on a ring. Where the cable connects the first computer and the last computer together.

  3. Mesh Topology - Used mostly for Wan configurations. Every computer is connected to every other computer to provide for redundancy. Would be an absolute nightmare for an Admin.

  4. Bus - A single cable connects all the computers. Each end of the cable is terminated.

Ethernet uses CSMA/CD, which stands for Collision Detection. Each computer listens to the line for traffic before it attempts to send data.

AppleTalk uses CSMA/CA, which stands for Collision Avoidance. Each computer announces it's intent to send data.

Token Ring uses token passing. The first computer online issues a token that travels around the ring, if a computer needs to transmit data it has to wait until the token gets to it.

Media

    Cable is a big part of the Networking Essentials Exam. There are four main types thicknet, thinnet, UTP/STP, and Fiber Optic

Thicknet Coax is .5 inches thick and carries a signal approximately 500 meters before the signal needs to be regenerated. A vampire tap is used to connect to the cable.

Unshielded Twisted Pair(UTP) is a twisted pair line (allot like a phone line). It an carry a signal 100 meters before regeneration is needed. You can not use this in an industrial area where allot of high voltage machines run because of UTP's susceptibility to electromagnetic interference and crosstalk.

Shielded Twisted Pair (STP) just like UTP but has a foil jacket around the core to reduce electromagnetic interference and crosstalk.

UTP/STP

Category

Bandwidth

Cat 2

4 MBPS

Cat 3

10 MBPS

Cat 4

16 MBPS

Cat 5

100 MBPS

    I think Cat 5 is the way to go in most situations.

Thinnet is .25 inches thick and carries a signal 185 meters before needing regeneration. It has a 50 OHM resistance. There are allot of different types of Thinnet Coax that you should be familiar with.

Thinnet Types

RG-58 /U

Has a solid copper core

RG-58/AU

Has a stranded copper core

RG-58 /CU

Military Specification with stranded core

RG-59

Broadband Transmission

RG-62

Arcnet

Fiber Optic has a glass core which a light pulse travels through at speeds upto 2 GBps (theoretically)

Ethernet Specs

Type Cable Types Connection Type Maximum Length
10Base2 RG-58 Thinnet BNC-T Connectors 185 Meters
10Base5 Thicknet DIX /AUI Connectors 500 Meters
10BaseT Cat 3,4, or 5 RJ-45 100 Meters
100BaseT Cat 5 RJ-45 100 Meters

      Another good place to find Ethernet specs is Cavebear.com, it's kinda hard to read but there is an abundance of information that will help you in a real job not just your exams.

OSI Model

    The OSI Model is the standard method for networking used in the industry today. The ISO developed these standards in 1978 and then revised them in 1984. Since then the model has become the international standards for network communication. The OSI model is divided into seven layers and each layer handles a portion of the networking process. Without this process it would be impossible for the hardware and the software to communicate correctly.

    Layers

Validate Skills
  1. Application Layer - This is the layer that provides the interface for applications. It allows access to all the network services. It also controls the flow and provides some error recovery for applications when it can. Application Protocols include: AFP(Apple Talk File Protocol), FTP (File Transfer Protocol), NCP(NetWare Core Protocol), SMTP( Simple Mail Transport Protocol), and SNMP (Simple Network Protocol), SMB

  2. Presentation Layer - This layer changes the data format of the information into one that can be understood by the lower layers on outbound data or to a format that the applications can understand on the inbound data.The redirector operates at this level. The redirector is where the decision is made as to where the information requested resides either locally or on the network.

  3. Session Layer - This layer establishes and maintains the two way communication between the network devices. Checkpoints are placed in the packet at this level so that if communications fail then only the most recent data after the last checkpoint will have to be retransmitted. This is what the programs that allow you to resume a download use.

  4. Transport Layer -  This layer segments the data from longs strings into the maximum packet size. Error checking is done at this layer and an acknowledgement is sent from this layer that the data was received. TCP, SPX, ATP(Apple Talk) and NetBEUI protocols live at this layer.

  5. Network Layer - This layer handles the addressing of the packets headers are added to the packets here. This layer also decides the best route to the intended host. Routers and Brouters operate at this layer. The protocols at this layer are IP, IPX, DDP (Delivery Data Protocol) and NetBEUI.

  6. Data Link Layer - This layer is responsible for packaging the the   raw data into data frames for the network layer and preparing   the data for transmission onto the cables. This layer has two divisions the logical link layer and the media access control(MAC)

                1. Logical Link(802.2) - Provides for error correction and                      flow control

                2. Media Access Control(802.3, 802.4, 802.5, 802.12) - For                      access control, Mac address and the transceiver are at                      this layer. Communicate with the NIC    

     vii. Physical Layer - Consists of the hardware components and              converts bits into signals for transmission onto the cable media.

802 Specifications

802.1 Internetworking
802.2 LLC (logical Link Control)
802.3 Ethernet - CSMA/CD
802.4 Token Bus LAN
802.5 Token Ring LAN
802.6 Metropolitan Area Network (MAN)
802.7 Broadband Advisory Group
802.8 Fiber Optic Advisory Group
802.9 Integrated Voice and Data Networks
802.10 Network Security
802.11 Wireless Communications
802.12 100Base VG LAN

Network Components

  1. NIC (Network Interface Card) - The network adapter is the component that physically connects the computer to the network.

  2. Repeaters and Amplifiers regenerate the signal as it travels along the media. They operate at the physical layer of the OSI Model. Different topologies cannot be connected using a repeater. Repeaters reside on the physical layer.

  3. A Hub is a piece of hardware that acts as a central connecting device for a LAN. There are three types of hubs: intelligent, active and passive. Passive hubs don't require any power, they just pass data through them. Active hubs require power and can also act as a repeater. Intelligent hubs perform services such as packet switching and routing. Physical Layer

  4. Bridges operate at the Data Link Layer and  provides for connection of two different types of topologies. Bridges will pass broadcast storms from one segment to another. But the bridge will not pass along a packet that is meant for the same segment as the bridge it will discard those packets. It works with all protocols. Data Link Layer

  5. Router - The router's main function is to route packets across multiple networks. There are two types static and dynamic. The routing tables in the static routers have to be manually entered into the table, where a dynamic router can learn the routes it needs to send the packets. Unroutable protocols will not be passed. Network Layer

  6. Brouter - Combines the features of a router with a bridge. It routes the routable protocols and  still passes on the nonroutable protocols. Both the Network Layer and the Data Link Layer

  7. Gateway - connects different network operating systems. For example   NT and Main Frames. It repackages the packet into a protocol the receiving network can understand. Transport layer

  8. Multiplexer - Divides transmissions into multiple channels. Physical layer.

Protocols

    This is a list of most of the more prominent protocols this list is no where near exhaustive, but these are most of the ones you need for the test.

  1. NetBEUI- A network protocol designed by Microsoft for small LANs. It is a nonroutable protocol and is only compatible with Microsoft operating systems.

  2. IPX/SPX - Routable protocol used in Novell networks. Is the same thing as NWLink in Microsoft Products.

  3. TCP/IP - You should know this one well it is what this page was transmitted to you on. It is routable, probably the most used protocol used. To communicate with Unix you must have this.

  4. AppleTalk- Apple's Protocol, It is designed to operate on a small LAN also routable.

  5. Routing Information Protocol - This is the protocol used by routers to communicate with each other.

  6. Serial Line Internet Protocol (SLIP) - Used for dial up connection, does not provide error checking. A few ISP's still use this but not many.

  7. Point to Point Protocol (PPP) - Common dial up protocol, provides error checking and supports compression.

Troubleshooting

    Interrupt Requests

           

IRQ Common Device I/O Address
IRQ 0 System Timer N/A
IRQ 1 Keyboard N/A
IRQ 2 Video Adapter N/A
IRQ 3 Com2 or Com 4 2FO to 2FF
IRQ 4 Com1 or Com 3 3FO to 3FF
IRQ 5 Free (good place for NIC or LPT 2) N/A
IRQ 6 Floppy Disk Controller N/A
IRQ 7 LPT 1 N/A
IRQ 8 Real-time Clock N/A
IRQ 9 Maybe free or cascade from IRQ 2 370 to 37F
IRQ 10 Free( or primary SCSI) N/A
IRQ 11 Free( or secondary SCSI) N/A
IRQ 12 PS/2 Mouse N/A
IRQ 13 Math Coprocessor N/A
IRQ 14 Hard Disk Controller N/A
IRQ 15 Hard Disk Controller N/A

Network Diagnostic Tools

   

Tool Function
Digital Voltage meters Measures voltage in a cable
Time Domain Reflectors Sends a sonar pulse to detect a break or short in a cable. Can locate a break to within a few feet
Oscilloscope Measurement device that can measure signal voltage per unit of time.
Protocol analyzer Capture data packets and displays information about them. Usually called a sniffer
Power Monitor Logs fluctuations in power sources