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A+™ Essentials  Technologies

8.Networking

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.

Ethernet:

- 10BaseT Ethernet complies to IEEE standard 802.3 and requires an RJ-45 connector to connect to the NIC. The maximum specified transmission speed for 10BaseT Ethernet is 10Mbps. For 100BaseT, it is 100Mbps.
- 802.11b operates at 2.4 GHz, while 802.11a operates at 5 GHz. Typical data rate for 802.11b is 11 Mbps where as it is 54mbps for 802.11a.
- 802.11b is compatible with 802.11g. 802.11a operates at 5 GHz, and is not compatible. Bluetooth is entirely a different protocol standard
- Ethernet is based on CSMA/CD, which stands for Carrier Sense Multiple Access / Collision Detect.
- CAT3, CAT4 or, CAT5 cabling is used with 10BaseT Ethernet. Thin coax is used with 10Base2 Ethernet. Thick coax is used with 10Base5 Ethernet. FDDI uses Optic Fiber as the medium.
- 10Base2 network, also known as Thin-net, uses BNC connector to connect to the NIC.
- A repeater can extend the distance over which the signal can travel without loosing out due to attenuation.
- The maximum length of the cable for 10BaseT Ethernet segment is 100 meters.
- Thin co-axial and thick co-axial cables have conductive grounding sheath surrounding the center conductor. Therefore, the electromagnetic interference (EMI) is significantly less.

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

1

Keyboard

60Hex

2

Cascade to IRQ9. Can't be used.

 

3

COM ports 2 and 4

COM4: 2E8-2EF
COM2: 2F8-2FF

4

COM ports 1 and 3

COM3: 3E8-3EF
COM1: 3F8-3FF

5

Parallel Port LPT2. Very often used for sound cards.

LPT2: 278-27F

6

Floppy drive controller

3F0-3F7

7

Parallel Port, LPT1

LPT1: 378-37F

8

Real time clock

70Hex

9

Unassigned (Also redirected from IRQ2)

 

10

Available

 

11

Available. SCSI adapter will normally use this IRQ.

 

12

Available

 

13

Math co-processor.

F0Hex

14

Primary hard-drive IDE controller

Primary Hard Drive Controller: 1F0-1FF

15

Secondary hard-drive IDE controller.

Secondary Hard Drive Controller: 0170-0177

 

Monochrome Graphic Adapter

3B0-3BF

 

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:
1. MODE command
2. DEBUG command
3. MSD
4. Corresponding device applet in the control panel

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).

Signal

Name

DB9 Pin

RX

Received Data

2

TX

Transmitted Data

3

DTR

Data Terminal Ready

4

GND

Ground

5

DSR

Data Set Ready

6

RTS

Request to Send

7

CTS

Clear to send

8

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:

· ATA- Answer the phone
· ATD-Dial the phone, ATDT for Tone dialing, ATDP for Pulse dialing
· ATH-Hang up
· ATZ-Reset
· AT&F-Reset modem parameters and settings to factory defaults
· AT&W- Write the current parameter values and settings

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:

1.Log on to the network.
2.Open Network and Sharing Center by clicking the Start button Picture of the Start button, clicking Control Panel, clicking Network and Internet, and then clicking Network and Sharing Center.
3.Click Customize, and then click either Public (for "Public place" networks) or Private (for "Home" or "Work" networks). Administrator permission required If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
4.Click Next and then click Close.

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:
a. 802.11: applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band.
b. 802.11a: an extension to 802.11 that applies to wireless LANs and provides up to 54 Mbps in the 5GHz band. 
c. 802.11b (initially referred to as 802.11 or Wi-Fi): an extension to 802.11 that applies to wireless LAN and provides up to 11 Mbps transmission in the 2.4 GHz band. 
d. 802.11g: applies to wireless LANs and provides 20+ Mbps in the 2.4 GHz band.

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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