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Media and Topologies part 2

Media and Topologies Part 2

1.4 Recognize the following media connectors and describe their uses:

RJ-11

Standard telephone cable connectors, usually have 4-6 wires.

RJ-45

RJ-45 connectors are used with 10-100BaseT cables. These resemble telephone RJ-11 connectors, but are larger and house 8 wires while RJ-11 house 4 or 6 wires. They are connected to the cable by crimping.

For an in-depth look at how these are connected to cables go here.

AUI

A thicknet network connection uses a 15 pin attachment unit interface (AUI) to connect the 15 pin DB 15 connector on the back of the network adapter card to an external transceiver (shown left). The transceiver for thicknet Ethernet includes a vampire tap (shown on top of the transceiver) which pierces the thicknet cable to make the network connection. From the transceiver to the network card a drop cable is attached.

BNC

BNC connector for coaxial cables. These are either soldered, or crimped to the end of the cable. BNC T connector, which joins the network card to the network cable.
BNC barrel connector, used to connect two cables together. It is better to use one continuous length of cable, as these connectors weaken the signal strength.

ST / SC

Fiber network segments always require two fiber cables: one for transmitting data, and one for receiving. Each end of a fiber cable is fitted with a plug that can be inserted into a network adapter, hub, or switch. In the North America, most cables use a square SC connector that slides and locks into place when inserted into a node or connected to another fiber cable, Europeans use a round ST connector instead.

Both connectors offer the same features as far as distance and reliability, Connectors of different types can communicate with the use of adapters or couplers, but it is best to choose one type of connector and stick with it over your entire network.

Round ST connector used with fiber optic cabling.

Square SC connector, used with fiber optic cabling.

Twisted-pair

Twisted-pair cabling comes in two basic types shielded and unshielded. Unshielded twisted-pair cable (UTP) is the most widely used in medium size LAN's. UTP is easy to work with and inexpensive. Shielded twisted-pair (STP) cable protects signals from cross signaling that can result from other, nearby cables. STP offers higher data transmission speeds, and larger networks.

Networks that use twisted-pair cabling include Token Ring, Ethernet, and Fast Ethernet networks.

1.6 Describe the purpose, features, and functions of the following network components:

Hubs

Stackable hubs Small hub

A Hub is a component that provides a common connection point for computers, printers, and other network devices in a star topology network. Allowing them to be managed from a central location. Also, hubs allow you to connect and disconnect an individual computer/device without disrupting the network. Hubs operate at the physical layer of the OSI Model.

There are two basic types of hubs, passive and active.

Passive hubs simply provide a junction point, to send the data signal on to other devices on the network.

Active Hubs, regenerate and retransmit the data signal, because they repeat the signal they can, increase the diameter of the network. In an Ethernet hub the signal is regenerated to all devices at the same time, while a Token Ring hub will only regenerate the signal to the next to the next device in line. You can tell if a hub is active because it requires electricity.

Active hubs because they act like repeaters are sometimes called multiport repeaters.

Switches

Switches are a special type of hub that offers an additional layer of intelligence to basic, physical-layer, repeater hubs. A switch must be able to read the MAC address of each frame it receives. This information allows switches to repeat incoming data frames only to the computer or computers to which a frame is addressed. This speeds up the network and reduces congestion.

Switches operate at both the physical layer and the data link layer of the OSI Model.

Bridges

A bridge is used to join two network segments together, it allows computers on either segment to access resources on the other. They can also be used to divide large networks into smaller segments. Bridges have all the features of repeaters, but can have more nodes, and since the network is divided, there is fewer computers competing for resources on each segment thus improving network performance.

Bridges can also connect networks that run at different speeds, different topologies, or different protocols. But they cannot, join an Ethernet segment with a Token Ring segment, because these use different networking standards.

Bridges operate at both the Physical Layer and the MAC sublayer of the Data Link layer. Bridges read the MAC header of each frame to determine on which side of the bridge the destination device is located, the bridge then repeats the transmission to the segment where the device is located.

Routers

A device used to connect networks of different types, such as those using different topologies and protocols. They can operate at the first three layers of the OSI Model. This means they can switch and route packets across multiple networks. Routers determine the best path for sending data.

You can use routers, to segment a large network, and to connect local area segments to a single network backbone that uses a different physical layer and data link layer standard. They can also be used to connect LAN's to a WAN's.

Brouters are a combination bridge, and router in one device. Brouters are more cost effective as both the bridge and router are combined together

Gateways

A gateway is a device used to connect networks using different protocols. Gateways operate at the network layer of the OSI model.

In order to communicate with a host on another network, an IP host must be configured with a route to the destination network. If a configuration route is not found, the host uses the gateway (default IP router) to transmit the traffic to the destination host. The default t gateway is where the IP sends packets that are destined for remote networks. If no default gateway is specified, communication is limited to the local network.

Gateways receive data from a network using one type of protocol stack, removes that protocol stack and repackages it with the protocol stack that the other network can use.

CSU/DSUís

A CSU/DSU is a device that combines the functionality of a channel service unit (CSU) and a data service unit (DSU). These devices are used to connect a LAN to a WAN, and they take care of all the translation required to convert a data stream between these two methods of communication.

A DSU provides all the handshaking and error correction required to maintain a connection across a wide area link, similar to a modem. The DSU will accept a serial data stream from a device on the LAN and translate this into a useable data stream for the digital WAN network. It will also take care of converting any inbound data streams from the WAN back to a serial communication.

A CSU is similar to a DSU except it does not have the ability to provide handshaking or error correction. It is strictly an interface between the LAN and the WAN and relies on some other device to provide handshaking and error correction.

Network interface cards/ISDN adapters/system area network cards

Network Interface Card, or NIC is a hardware card installed in a computer so it can communicate on a network. The network adapter provides one or more ports for the network cable to connect to, and it transmits and receives data onto the network cable.

Every networked computer must also have a network adapter driver, which controls the network adapter. Each network adapter driver is configured to run with a certain type of network adapter.

A networked computer must also have one or more protocol drivers (sometimes called a transport protocol or just a protocol). The protocol driver works between the upper-level network software and the network adapter to package data to be sent on the network.

In most cases, for two computers to communicate on a network, they must use identical protocols. Sometimes, a computer is configured to use multiple protocols. In this case, two computers need only one protocol in common to communicate. For example, a computer running File and Printer Sharing for Microsoft Networks that uses both NetBEUI and TCP/IP can communicate with computers using only NetBEUI or only TCP/IP.

ISDN

Integrated Services Digital Network adapters can be used to send voice, data, audio, or video over standard telephone cabling. ISDN adapters must be connected directly to a digital telephone network. ISDN adapters are not actually modems, since they neither modulate nor demodulate the digital ISDN signal.

Like standard modems, ISDN adapters are available both as internal devices that connect directly to a computer's expansion bus and as external devices that connect to one of a computer's serial or parallel ports. ISDN can provide data throughput rates from 56 Kbps to 1.544 Mbps (using a T1 carrier service).

ISDN hardware requires a NT (network termination) device, which converts network data signals into the signaling protocols used by ISDN. Some times, the NT interface is included, or integrated, with ISDN adapters and ISDN-compatible routers. In other cases, an NT device separate from the adapter or router must be implemented.

ISDN works at the physical, data link, network, and transport layers of the OSI Model.

Wireless access points

A wireless network adapter card with a transceiver sometimes called an access point, broadcasts and receives signals to and from the surrounding computers and passes back and forth between the wireless computers and the cabled network.

Access points act as wireless hubs to link multiple wireless NICs into a single subnet. Access points also have at least one fixed Ethernet port to allow the wireless network to be bridged to a traditional wired Ethernet network..

Modems

A modem is a device that makes it possible for computers to communicate over telephone lines. The word modem comes from Modulate and Demodulate. Because standard telephone lines use analog signals, and computers digital signals, a sending modem must modulate its digital signals into analog signals. The computers modem on the receiving end must then demodulate the analog signals into digital signals.

Modems can be external, connected to the computers serial port by an RS-232 cable or internal in one of the computers expansion slots. Modems connect to the phone line using standard telephone RJ-11 connectors.

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