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Network+ Study Guide (N10-003)

                                                                                               Index            

Wireless Technologies

The table below shows some of the various wireless networking technologies.
 

Standard	Frequency	Description	Maximum Length	Speed
802.11b - WiFi	2.4 Ghz	Wireless networking commonly used in homes and SOHO environments. Being replaced by the faster 802.11g standard. Uses a wireless access point (WAP) to connect to other wireless computers.	150+ feet	11 mbps
802.11g - WiFi	2.4 Ghz	Wireless networking commonly used in homes and SOHO environments. Uses a wireless access point (WAP) to connect to other wireless computers. Backward compatible with 802.11b	150+ feet	54 mbps
Infrared - IrDA	Uses light, not radio frequencies	Uses line of sight connections making it useful for sharing data between personal devices.	150+ feet	Usually 16mbps - high powered beams can reach 10Gbps
Bluetooth	2.4 Ghz	See below	Up to 30 feet	721 kbps

Infrared - IrDA
Infrared is typically a short-range line of sight technology which means that there cannot be obstructions between 2 devices that are trying to communicate. It is often used for file sharing between portable devices and can communicate at speeds up to 16Mbps. In certain situations, high power infrared beams transfer high-speed data from 45Mbps to 10Gbps and are installed between buildings within a few miles of each other.

Bluetooth
Bluetooth (IEEE 802.15.1), originally developed by Ericsson and later formalized by the Bluetooth Special Interest Group (SIG), is a specification for wireless personal area networks that facilitates the exchange of data between electronic devices, such as mobile phones, PDAs, laptops, personal computers, printers and digital cameras. The devices, containing a low-cost transceiver, connect to each other using a short range radio frequency (2.45 gHz) of up to 328 feet. Each Bluetooth enabled device is assigned a unique 48-bit address and a 24-bit class identifier. The class identifier provides information as to the nature of the device (phone, PC, etc.) and is transmitted to other devices performing an inquiry.

Bluetooth was developed out of a demand to create networks that were easy to install, configure and use without using the standard cabling. There have been three major versions of Bluetooth released: 1.1, 1.2 and 2.0. Each release increased the transmission speed and the 2.0 release also decreased the power consumption.

Bluetooth is not without security vulnerabilities. In 2004, a proof-of-concept virus that spread via Bluetooth enabled devices appeared, though it never propagated outside of the test environment. Active Bluetooth devices can be detected using directional antennas, allowing unattended devices to be located and stolen. Experiments to reverse engineer the device PIN have also been successful.
 

Bluetooth is competing against two other major methods of wireless networking: IrDA and WiFi. However, WiFi is most useful as a replacement for LANs and IrDa is limited by its need for an unobstructed line-of-sight between connecting devices.

Network Hardware
Below are some of the common hardware devices found on a network. NOTE: The higher the network device is in the OSI layer the more intelligent the device is.
 

 

• Network Interface Card: - A Network Interface Card, often abbreviated as NIC, is an expansion board you insert into a computer so the computer can be connected to a network. Most NICs are designed for a particular type of network, protocol and media, although some can serve multiple networks.
• Hub: - A hub is used to connect computers on an ethernet network.
• Repeater: - Boosts signals in order to allow a signal to travel farther and prevent attenuation. Attentuation is the degradation of a signal as it travels farther from its origination. Repeaters do not filter packets and will forward broadcasts. Both segments must use the same access method, which means that you can't connect a token ring segment to an Ethernet segment. Repeaters can connect different cable types.
• Bridge - Functions the same as a repeater, but can also divide a network in order to reduce traffic problems. A bridge can also connect unlike network segments (ie. token ring and ethernet). Bridges create routing tables based on the source address. If the bridge can't find the source address it will forward the packets to all segments. Bridging methods:

 

• Transparent - Only one bridge is used.
• Source-Route - Bridging address tables are stored on each PC on the network
• Spanning Tree - Prevents looping where there exists more than one path between segments

 

• Switch - A switch prevents traffic jams by ensuring that data goes straight from its origin to its proper destination, with no wandering in between. Switches remember the address of every node on the network, and anticipate where data needs to go. It only operates with the computers on the same LAN. It isn't smart enough to send data out to the internet, or across a WAN. These functions require a router.
• Router - A router is similar to a switch, but it can also connect different logical networks or subnets and enable traffic that is destined for the networks on the other side of the router to pass through. Routers can connect networks that use disimilar protocols. Routers also typically provide improved security functions over a switch. Unroutable protocols can't be fowarded.
• Gateway - Often used as a connection to a mainframe or the internet. Gateways enable communications between different protocols, data types and environments. This is achieved via protocol conversion, whereby the gateway strips the protocol stack off of the packet and adds the appropriate stack for the other side.
• Modem - The modem is a device that converts digital information to analog by MODulating it on the sending end and DEModulating the analog information into digital information at the receiving end. Most modern modems are internal, however, they can be internal or external. External modems are connected to the back of the system board via a RS-232 serial connection. Internal modems are installed in one of the motherboard's PCI or ISA expansion slots depending on the modem. The modem contains an RJ-11 connection that is used to plug in the telephone line. Modems have different transmission modes as follows:
  • Simplex - Signals can be passed in one direction only.
  • Half Duplex - Half duplex means that signals can be passed in either direction, but not in both simultaneously. Half-duplex modems can work in full-duplex mode.
  • Full Duplex - Full duplex means that signals can be passed in either direction simultaneously.

 

• Modems can also be classified by their speed which is measured by the BAUD rate. One baud is one electronic state change per second. Since a single state change can involve more than a single bit of data, the Bits Per Second(BPS) unit of measurement has replaced it as a better expression of data transmission speed. Common modem speeds are V.34 at 28.8 kbps, V.34+ at 33.6 kbps and V.90 at 56 Kbps.
• ISDN Adapter - ISDN service is an older, but still viable technology offered by phone companies in some parts of the U.S. ISDN requires an ISDN adapter instead of a modem, and a phone line with a special connection that allows it to send and receive digital signals.
• CSU/DSU - A CSU/DSU (Channel Service Unit / Data Service Unit) is a piece of equipment that connects a leased line from the telephone company to the customer's equipment (such as a router). Although CSU/DSU's look similar to modems, they are not modems, and they don't modulate or demodulate between analog and digital. All they really do is interface between a 56K, T1, or T3 line and serial interface (typically a V.35 connector) that connects to the router. Many newer routers have 56K or T1 CSU/DSUs build into them.
• Wireless Access Point - A Wireless Access Point is a radio frequency transceiver which allows your wireless devices to connect to a network. A wireless access point will support up to 32 wireless devices. There are currently 2 mainstream wireless standards: 802.11b operates at 11mbps and 802.11g works at a speed of 54mbps.
• Proxy - A proxy server acts as a middle-man between clients and the Internet providing security, administrative control, and caching services. When a user makes a request for an internet service and it passes filtering requirements, the proxy server looks in its local cache of previously downloaded web pages. If the item is found in cache, the proxy server forwards it to the client. This reduces bandwidth through the gateway. If the page is not in the cache, the proxy server uses Network Address Translation (NAT) to use one of its own IP addresses to request the page from the appropriate server.
• Firewall - Either a hardware or software entity that protects a network by stopping network traffic from passing through it. In most cases, a firewall is placed on the network to allow all internal traffic to leave the network (emails to the outside world, web access, etc.), but stop unwanted traffic from the outside world from entering the internal network.