A+ Core 1 study notes on networking

A+ Certification : 220-1001

Memory  |  Display Adapters & Monitors   |  Floppy,CD-ROM & Hard Disk  |  CPU  |  Keyboard & Power Supply  |  Printers & Cables

Networking  |  Operating System  |  Computers  |  Motherboard  |  Security  |  Miscellaneous


Most commonly used network devices are hubs, switches (or bridges), and routers.

Router: A router for Internet sharing is normally configured using web browser. High-end routers may provide option for terminal connectivity, wherein you can connect a terminal, and issue commands for configuring the router.

Hub: A hub is basically a multi-port repeater. When it receives a packet, it repeats that packet out each port. This means that all computers that are connected to the hub receive the packet whether it is intended for them or not. It's then up to the computer to ignore the packet if it's not addressed to it. This might not seem like a big deal, but imagine transferring a 50 MB file across a hub. Every computer connected to the hub gets sent that entire file (in essence) and has to ignore it.

Bridge: A bridge is a kind of repeater, but it has some intelligence. It learns the layer 2 (MAC) addresses of devices connected to it. This means that the bridge is smart enough to know when to forward packets across to the segments that it connects. Bridges can be used to reduce the size of a collision domain or to connect networks of differing media/topologies, such as connecting an Ethernet network to a Token Ring network.

Switch: A switch is essentially a multi-port bridge. The switch learns the MAC addresses of each computer connected to each of its ports. So, when a switch receives a packet, it only forwards the packet out the port that is connected to the destination MAC address. Remember that a hub sends the packet out every port, and you can see how much more efficient this it.


Token Ring supports 4 Mbps and 16 Mbps speeds.

IRQs, and IRQ/ IO conflicts

IRQ Standard Device Assignment I/O Port Address
0 System timer 40Hex
Keyboard 60Hex
1 Cascade to IRQ9. Can't be used.
2 COM ports 2 and 4 COM4: 2E8-2EF
COM2: 2F8-2FF
3 COM ports 1 and 3 COM3: 3E8-3EF
COM1: 3F8-3FF
4 Parallel Port LPT2. Very often used for sound cards. LPT2: 278-27F
5 Floppy drive controller 3F0-3F7
6 Parallel Port, LPT1 LPT1: 378-37F
7 Real time clock 70Hex
8 Unassigned (Also redirected from IRQ2)
9 Available
10 Available. SCSI adapter will normally use this IRQ.
11 Available
12 Math co-processor. F0Hex
13 Primary hard-drive IDE controller Primary Hard Drive Controller: 1F0-1FF
14 Secondary hard-drive IDE controller. Secondary Hard Drive Controller: 0170-0177
15 Monochrome Graphic Adapter 3B0-3BF
16 Color Graphic Adapter 3D0-3DF

To determine the COM port assignments, or which COM ports are being used for what, you can use any of the following commands:

AT Computer interrupt controllers: An AT computer will have two interrupt controllers. The second interrupt controller need to deliver the interrupts through the primary interrupt controller. IRQ2 had been identified for this purpose on the primary and IRQ9 on the secondary interrupt controllers. In other words, IRQ2 and IRQ9 are cascaded.

Serial Interfaces: COM1, COM2 on a computer uses serial cable. The pin assignments are shown below. The computer acts as a DTE (Data Terminal Equipment) and the Modem acts as DCE (Data Communication Equipment).



DB9 Pin


Received Data



Transmitted Data



Data Terminal Ready






Data Set Ready



Request to Send



Clear to send


Normally, a DTE device connects to a DCE device. If you want to connect two DTR devices, as you would do to hook up two computers via the serial line to exchange files, the cable itself must have cross connections. Such a cable is called null modem cable.

Most commonly used modem commands:

On a Vista computer, when you connect for the first time to a network, you need to choose a network location. There are two network locations: Home/Work, and Public place. If the computer is shared within home office or small work place, Home/Work option is recommended. If your computer is in a public place or a large network, Public option is recommended.

If your computer is part of a domain, you won't be able to change the network location type because it is controlled by your network administrator.

Network location may be changed as below:

DNS stands for Domain Name System Server. DNS Server is the one responsible for converting the Domain names to IP addresses.

NIC, Network Interface Card is the one that interfaces your PC to the LAN. NIC sits in your PC on one of the slot available on the motherboard.

Attenuation: When signals are transmitted over long distance, there will be ohmic losses, which result in loosing the strength of the signals. This is known as attenuation. Amplification is opposite of attenuation.

Asynchronous serial communication uses Start bit/Data bits/Stop bit. A modem connecting to the Internet is a typical asynchronous device. Synchronous communication uses clock signals to transfer information. Does not use start/stop bits. Synchronous communication is normally used for high speed data transfers.

TCP/IP is the medium of transport when your are accessing the Internet.

ISDN:ISDN BRI (Basic Rate Interface) will have two B channels, each can carry data up to 64Kbps, aggregating to 128 Kbps.

Peer-to-peer model is best suited when you need to share files and folders among others in your office. If the number of networked computers becomes very large or if the security of data is very important, Client-Server model is recommended.

The SPDF - Sony/Phillips Digital Interface is designed to transfer digital signals between devices without degrading the signal by converting it to analog. This preserves the quality of the signal delivered to digital recording and playback devices.

Wireless Networking

The generic standard that defines wireless LAN technologies is 802.11. Specifically, the following standards exist:

Bluetooth is widely used for communication between smart phones and other accessories or between PDAs and information kiosks. The typical coverage for Bluetooth devices is up to 30 feet. It can be used for personal area networking devices like keyboards and headphones

SSID, short for service set identifier, a unique identifier attached to the header of packets sent over a WLAN. The SSID differentiates one WLAN from another, so all access points and all devices attempting to connect to a specific WLAN must use the same SSID. WEP together with SSID, provides basic protection for the wireless network.

WPA, short for Wi-Fi Protected Access, is a Wi-Fi standard that was designed to improve upon the security features of WEP (Wired Equivalent Privacy). The technology is designed to work with existing Wi-Fi products that have been enabled with WEP.

WEP, short for Wireless Equivalent Protection, is a security protocol designed to provide protection equivalent to wired LANs. WPA is an improved security protocol compared to WEP.

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