Chapter 5: Networking Components
Chapter Outline
1. On the Test
a. 1.6 Identify the purpose, features, and functions of the following network components: hubs;
switches; bridges; routers; gateways; CSU/DSU; network interface cards/ISDN adapters/system area
network cards; wireless access points; modems.
b. 3.3: Identify the main characteristics of VLANs.
2. Hubs
a. Hubs are the most basic form of multistation access unit.
b. They are used to connect devices, such as computers and printers, in a network.
c. Hubs may also be used to connect different network segments together.
3. Passive Hubs
a. A passive hub takes the signal (data) that it receives from a device, copies it, and sends it out the other
ports in the hub to all of the other networked devices.
b. It does not manipulate or view the data and it does nothing to amplify, clean up, or change the data
signal.
c. Passive hubs extend only the length of the cable that is being used on the network.
4. Active Hubs
a. Active hubs have the ability to repair weak signals.
b. They do this by regenerating or amplifying the data signal. This regeneration consists of intercepting a
weak signal and raising it back up to the original voltage.
c. Once the signal is regenerated, it is sent back out of the hub to all of the other devices.
d. An active hub can be used to add additional computers to a network or to allow for increased distances
between workstations and servers.
e. An active hub is commonly called a repeater.
5. Managed or Intelligent Hubs
a. A managed or intelligent hub allows you to configure and monitor each individual port.
b. Ports can be enabled or disabled through a hub management utility that is normally provided by the
manufacturer.
c. Hub management will also allow you to gather network parameters such as the number or types of
packets that have been transmitted, how many errors have occurred, and the number of collisions taking
place on the network.
6. Switches
a. Instead of just copying and sending data out to every device on the network, a switch has the ability to
learn the physical addresses of all of the devices on the network.
b. Once it has that address, it will send the data only to the port to which the destination device is
connected.
c. By sending data only to its intended recipient, network traffic is dramatically reduced, providing more
available bandwidth.
d. Also, it helps cut down on the number of data collisions that take place on Ethernet networks.
e. Most switches have the ability to auto-sense network transmission speeds
7. Layer 3 Switches: incorporate features of both routers and switches.
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8. Virtual Local Area Network (VLAN)
a. A VLAN is a group of network devices (workstations, servers, printers, etc) that can be grouped into a
logical network, without regard for physical location.
b. All of the devices act as though they are connected to a single network segment, even though they may
be physically located in different buildings or even different states.
c. There are three basic VLAN models. These models are based on how the VLAN is established.
i.
Port-based: A network administrator assigns each port of a switch to a VLAN.
ii. MAC address-based: Membership in the VLAN is based on source and destination MAC
addresses of the devices that are attached to the switch.
iii. Protocol-based: Protocol-based VLANs, also known as Layer 3 VLANs, are based on the
protocols being used (IP, IPX, etc.) and their respective Layer 3 (OSI Model Network layer) addresses.
9. Bridges
a. The primary purpose of a bridge is to allow devices that are attached to separate LANs or LAN
segments to communicate as if they are all located on the same LAN.
b. Bridges are also able to contain or limit network traffic to the section of the network to which it belongs.
c. The bridge can be configured to deny or reject traffic on one segment from being transmitted to another
segment.
d. Bridges decide which packets to pass between networks through the use of a routing table.
e. Bridges are typically classified as either local or remote.
i.
Local bridges exist when there is a direct connection between several LAN segments.
ii. Remote bridges use WAN connections, generally leased telephone lines, to connect LAN
segments.
f. There are four basic types of bridging algorithms: transparent, source-route, translational, and sourceroute transparent.
10. Transparent Bridges
a. The transparent bridge has the capability of automatically identifying all of the devices that are
connected to each segment of the network.
b. The transparent bridge listens to the traffic traveling on the network and learns the addresses of devices
that are located on the segments.
c. This information is then stored in a table within the bridge.
d. Whenever the bridge receives a packet, it can check its internal table to determine exactly where the
destination device is located.
11. Source-Route Bridges
a. Source-route bridging is commonly found in Token Ring networks.
b. When a networked device wishes to communicate in a source-route network, it first sends a broadcast
across the network.
c. When the destination device hears the broadcast, it replies back to sender. This reply includes the route
that the broadcast packet took to get to the destination device.
d. The sender then uses that route to communicate with the destination device.
12. Translational Bridges
a. Translational bridges are used to connect dissimilar networks together.
b. For example, a bridge could be used to connect an Ethernet network segment to a Token Ring network
segment.
c. The conversion of the frames from one type to another is typically done through encapsulation.
13. Source-Route Transparent Bridges: combine aspects of both source-route and translational bridges in order
to enable network communication in networks with a mix of Ethernet and Token Ring technologies.
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14. Routers
a. A router is a device that connects multiple network segments together to form a larger network, or large
networks together to form an internetwork.
b. Routers are the devices used to connect local area networks (LANs), making a wide area network
(WAN).
c. Routers join networks together by ensuring that traffic generated by a host on one network finds its way
to a host on another network.
d. Routers have the ability to use redundant paths.
e. Routers are small microcomputers containing their own processors, memory, and operating system.
f. Routing is the technique used to help data find its way from one computer to another, or one network to
another.
g. Routing tables may be either static or dynamic.
i.
Static tables are built manually by an administrator.
ii. Dynamic tables are built automatically by the router.
h. In order for routers to build a routing table dynamically, routers must have the ability to talk with each
other and exchange information. To do this, they use one of two types of algorithm, distance vector and
link state.
15. Distance Vector Algorithm
a. Routers using distance vector protocols periodically broadcast the entire contents of their routing tables
to other routers.
b. The primary disadvantage to using distance vector protocols is the amount of network traffic they create.
c. Each router typically broadcasts the entire contents of their routing tables across the network every 30
seconds.
d. The most common distance vector protocol is Routing Information Protocol (RIP).
16. Routing Information Protocol (RIP)
a. Routers that use the Router Information Protocol (RIP) broadcast their entire routing table to
neighboring routers every 30 seconds.
b. When broadcasts are used, the broadcasted data is sent everywhere, which is a waste of bandwidth, as
every device sees the traffic when it only needs to be seen by other routers.
c. RIP is limited to 15 hops; therefore, any routers that are over 15 hops away are unreachable.
d. Routers using RIP have problems with slow convergence.
e. Convergence means that all routers have matching, up-to-date, and complete routing tables.
17. Link State Algorithm
a. Routers using a link state protocol are more efficient than routers using distance vector protocols.
b. Routers using link state protocols multicast their updates to other routers.
c. Multicast routers send only one copy of the routing table.
d. It addresses the packets containing the routing table information for the routers that should receive it.
e. Instead of sending the entire contents of the routing table, only updates are sent.
f. Updates are sent about every 5 minutes, instead of at 30-second intervals.
g. A commonly used link state protocol is Open Shortest Path First (OSPF).
18. Open Shortest Path First (OSPF)
a. Open Shortest Path First (OSPF) was designed to address some of the limitations imposed by RIP.
b. In OSPF, there is no limit on the number of hops between routers.
c. OSPF uses multicast to send routing table updates. This means an end to broadcasts and that only routers
running OSPF will receive updates.
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d. Updates are sent only when a routing table change actually occurs, instead of at predetermined intervals.
e. OSPF also converges faster, as routing changes are sent as soon as they occur.
19. Gateways
a. A gateway is used to connect dissimilar networks.
b. For example, a gateway could be used to connect a local area network to a mainframe network.
c. The gateway, which is generally a combination of hardware and software, converts or translates data or
protocols from one network to the other.
d. Gateways work with the top four layers of the OSI Model.
20. Channel Service Unit (CSU)/Data Service Unit (DSU)
a. The CSU is a piece of equipment containing an interface that is used to terminate a data line, such as a
T1 or T3 line.
b. Each CSU communicates with another CSU that is located at the other end of the data line.
c. The CSU has the ability to monitor the data line and provides some error correction for the data line.
d. A DSU provides a terminal connection to a digital line.
e. It operates essentially as a digital modem, converting the digital data frame that is used on the LAN into
a frame that can be transmitted over the WAN and vice versa.
21. Network Interface Cards
a. The network interface card (NIC) is the piece of hardware installed inside a computer that allows the
computer to be connected to the network.
b. The NIC is plugged into an expansion slot on the computer’s motherboard.
c. Once the NIC is physically installed, a network cable can be plugged into a port on the back of the NIC.
d. A piece of software known as a driver is then installed to allow the computer’s operating system to
interact with the NIC.
e. The NIC and the driver work together to support the Data Link layer protocol (Ethernet or Token Ring),
network access method (CSMA/CD or token passing), and other features.
22. Integrated Services Digital Network (ISDN) Adapters
a. Integrated Services Digital Network (ISDN) is a communications technology that allows digital signals
to pass through normal telephone lines, also referred to as Plain Old Telephone Systems (POTS) or
Public Switched Telephone Networks (PSTN).
b. ISDN allows you to combine one or more communications channels in order to provide high data
transfer speeds, generally in the area of 128Kbps.
c. An ISDN terminal adapter is used as the interface between the ISDN line and your computer.
d. The ISDN adapter will support one of two interfaces:
i.
U Interface: The U interface is used when transmitting the data signal over long distances, such
as from your home to a telephone switching station or the central telephone office.
ii. S/T Interface: The S/T interface is used when transmitting the data signal over short distances,
such as from a wall jack to your ISDN adapter.
iii. If your adapter has an S/T interface, you will need to purchase a Network Termination,
commonly referred to as NT-1.
23. Wireless Access Points (AP)
a. A wireless access point (AP) is the place with which a wireless network card communicates in order to
connect to the network.
b. A wireless network card acts like a hub in a wired network.
c. An access point can support a small group of users and generally has a range up to several hundred feet.
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24. Modems
a. A modem is a piece of hardware that transforms data from inside the computer into a form that can be
transmitted over some type of cable medium.
b. When using a modem for data communications, the modem “modulates,” which means it takes the
digital signal from your computer and changes it into an analog signal that can be transmitted over the
cable media.
c. When it receives data, it “demodulates,” meaning it takes the analog signal from the cable and changes it
into a digital signal that can be understood by the computer.
d. There are three basic categories of modems: traditional, Digital Subscriber Line, and cable.
25. Traditional: The traditional modem allows your computer to connect to a network using a dial-up telephone
line.
26. Digital Subscriber Line (DSL): Digital Subscriber Line (DSL) modems also support data transfer over
POTS or PSTN networks; however, DSL uses higher frequencies than traditional modems.
27. Cable: Cable modem service is another high-speed networking technology that uses the same coaxial cable
that powers cable television in most homes.
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