IPT - Network Connection Devices

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Network Connection Device

NCD. Used to connect nodes to form a LAN and also to transfer data between networks.

Network Interface Card

NIC. Convert data between the computer into a form suitable for transmission across the network. Conversion uses the rules of the data link and physical link protocols in operation. It is the NIC that negotiates access to the network, including collision detection (or avoidance).

Repeaters

Any device that receives a signal, amplifies it and then transmits the amplified signal down another link. Used to increase the physical range of the transmission media.

Uses of repeaters

Dedicated repeaters used to extend the reach of fibre optic cable.
Most wireless points can be used as simple repeaters to extend the coverage rand of WLANs
Transponders used for ground-based and satellite microwave transmissions are also repeaters.

Hub

Also known as multipart repeaters. When a hub receives a packet of data it amplifies it before retransmitting it to all attached nodes. They make no attempt to identify the destination node of the message. Hubs connect nodes together into a single network segment.

Bridge

Splits a logical bus network into two collision domains. They determine the destination MAC address of each frame. If the destination node with the MAC address is on the other side of the bridge en the frame repeated onto that segment, otherwise the frame is dropped.

Switch

Sets up a direct connection between the sender and receiver. They determine the MAC address of the sender and intended receiver that precedes each message. The receiver's address is used to identify the destination nod and forward the message to that node only.Can be thought of as an intelligent hub or a multipoint bridge.

Gateway

Connects two networks together. Gateways can connect networks that use different lower level protocols, however they can also be used to filter traffic movements between two similar networks.

Uses of gateways

Connect a LAN to the Internet.
Connect to networks, i.e. ADSL and routers include gateway functionality to convert between the low level Ethernet protocols used by the LAN and the low level protocols used by ADSL and cable connections.

Wireless Access Point/Access Points

WAPs or AC. The central nodes on wireless LANs that broadcast to all wireless nodes within the coverage area.

Issues with WLANs

Any user within the coverage range can potentially access the network.

WLAN security types

Wired Equivalent Privacy (WEP) WiFi Protected Access (WPA)

WEP

Type of WLAN security which uses a single shared key encryption system. Not as secure as WPA.

WPA

Type of WLAN security which generates new encryption keys at regular intervals. More secure than WEP.

Modem

Modulation and demodulation are the primary processes performed by all modems.

Uses of Modems

Used to connect a computer up to a local Internet Service Provider which provides a high-speed ADSL or cable connection to the Internet.

ISP

Internet Service Provider

Connecting a modem to a computer

Via USB port or an Ethernet network connection. These interfaces are digital links, using electromagnetic wave but representing the data using different voltages. The electronic circuits within the computer can use these voltage changes directly.

Modulation

The process of encoding digital information onto an analog wave by changing its amplitude frequency or phase.

Demodulation

The process of decoding a modulated wave back into its original digital signal.

ADSL modems

Use existing copper telephone lines to transfer broadband signals. Digital strength deteriorates over long distances and can't be maintained at distances greater than 5400 metres.

ADSL

Asymmetrical Digital Subscriber Lines

Cable modems

Cable modems connect to the Internet via coaxial cables; usually the same cable that transmits cable TV stations. The bandwidth used in a cable system is significantly larger than that used for ADSL and achieve speeds similar to ADSL connections. Cable connections are shared by multiple users.

Router

Direct messages over the most efficient path to their destination.

Security measures in routers

Able to block messages based on the sender's IP address
Block access to specific websites
Restrict communication to certain high level protocols

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