GTU-MCA-SEM IV - Fundamentals of Networking

1. Chapter 4

55. WI-FI WiMAX Indoor - deals with mobility- 802.11 was designed to be mobile Ethernet Outdoor -provides service to buildings, and buildings are not mobile. They do not migrate from cell to cell often- so 802.16 was designed to be wireless, but stationary building distances involved can be several meters distances involved can be several kilometers LAN – more secure MAN - open communication over a city means that security and privacy are essential and mandatory 802.11 can use half-duplex communication , (single radio –which switch back & forth between Tx & Rx mode)something avoids to keep the cost of the radios low & that's why we have CSMA/CA & not CD. Uses spread spectrum 802.16 can use full-duplex communication - Traditional narrow-band radio is used with conventional modulation schemes QAM, QPSK etc. Indoor technology-Less users-required less bandwidth-use 2.4 and 5 GHz ISM range – less error prone Outdoor technology - Supports more users – need more bandwidth-uses 10-66 GHz ISM range- millimetre waves – use line of sight –absorb by rain – more error prone-need completely diff Tx-Rx tech-so completely diff physical layer- 802.11 is Omni directional Millimetre waves can be focused into directional beams , so multipath propagation is major issue. QoS- quality of service - 802.11 provides some support for real-time traffic (using PCF mode), it was not really designed for telephony and heavy-duty multimedia usage 802.16 is expected to support these applications completely because it is intended for residential as well as business use.

67. bps = baud per second x the number of bit per baud The number of bit per baud is determined by the modulation technique. Here are two examples: When FSK ("Frequency Shift Keying", a transmission technique) is used, each baud transmits one bit; only one change in state is required to send a bit. Thus, the modem's bps rate is equal to the baud rate: When we use a baud rate of 2400, you use a modulation technique called phase modulation that transmits four bits per baud. So: 2400 baud x 4 bits per baud = 9600 bps Such modems are capable of 9600 bps operation.

72. Chipping code

86. Diffracted Signal Reflected Signal Transmitter Receiver Direct Signal Building Scattered Signal

89. Hidden Terminal Problem Exposed Terminal Problem Hidden Terminal problem: - Z can’t sense X; Tx to Y and collision with X Exposed terminal problem: - W senses Y but can’t send to X X Y Z X Y Z W

113. ISM: Industry, Science, Medicine unlicensed frequency spectrum: 900Mhz, 2.4Ghz, 5.1Ghz, 5.7Ghz

114. and 802.11b/g 802.11a

116. IEEE 802.11 variants DSSS: direct sequence spread spectrum FHSS: frequency hopping spread spectrum OFDM: orthogonal frequency division multiplexing 802.11a 802.11b 802.11g 802.11 Standard approved Sep. 1999 Sep. 1999 June 2003 July 1997 Available bandwidth 300 MHZ 83.5 MHZ 83.5 MHZ 83.5 MHZ freq. of operation 5.15-5.35G 5.725-5.825G 2.4-2.4835G 2.4-2.4835G 2.4-2.4835G No. of non-overlapping Ch. 4 3 3 3 Rate per channel (Mbps) 6,12,24,36,48,54 1, 2, 5.5, 11 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, 54 1, 2 Range ~150 feet (indoor) 225 (outdoor) ~225 feet ~225 feet ?? Modulation OFDM DSSS/CCK DSSS/CCK; DSSS/OFDM DSSS, FHSS

148. WI-FI WiMAX Indoor - deals with mobility- 802.11 was designed to be mobile Ethernet Outdoor -provides service to buildings, and buildings are not mobile. They do not migrate from cell to cell often- so 802.16 was designed to be wireless, but stationary building distances involved can be several meters distances involved can be several kilometers LAN – more secure MAN - open communication over a city means that security and privacy are essential and mandatory 802.11 can use half-duplex communication , (single radio –which switch back & forth in Tx & Rx mode)something avoids to keep the cost of the radios low & that's why we have CSMA/CA & not CD. 802.16 can use full-duplex communication Indoor tech-Less users-less bandwidth-use 2.4 and 5 GHz ISM range – less error prone Outdoor tech - Supports more users – need more bandwidth-uses 10-66 GHz ISM range- millimetre waves – use line of sight –absorb by rain – more error prone-need completely diff Tx-Rx tech-so completely diff physical layer 802.11 is omnidirectional Millimeter waves can be focused into directional beams , so multipath propagation is major issue. QoS- quality of service - 802.11 provides some support for real-time traffic (using PCF mode), it was not really designed for telephony and heavy-duty multimedia usage 802.16 is expected to support these applications completely because it is intended for residential as well as business use.

158. 802.16a ~5.0 bps/Hz ~2.7 bps/Hz 54 Mbps 20 MHz 63 Mbps* 10, 20 MHz; 1.75, 3.5, 7, 14 MHz; 3, 6 MHz 802.11a Channel Bandwidth Maximum bps/Hz Maximum Data Rate * Assuming a 14 MHz channel 802.16a is designed for metropolitan performance

166. 802.11 and 802.16 both gain broader industry acceptance through conformance and interoperability by multiple vendors 802.16 complements 802.11 by creating a complete MAN-LAN solution 802.11 is optimized for license-exempt LAN operation 802.16 is optimized for license-exempt and licensed MAN operation.