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WiFi Networks: ieee 802. 11b Wireless lans Carey Williamson
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səhifə | 1/4 | tarix | 27.09.2023 | ölçüsü | 0,75 Mb. | | #124006 |
| WiFi (1) WiFi Networks: IEEE 802.11b Wireless LANs Carey Williamson Department of Computer Science Background (1 of 2) - In many respects, the IEEE 802.11b wireless LAN (WLAN) standard is similar to that for classic IEEE 802.3 (Ethernet) LANs
- Similarities:
- LAN with limited geographic coverage
- multiple stations, with 48-bit MAC addresses
- shared transmission medium (broadcast technology)
- CSMA-based Medium Access Control protocol
- comparable data rates (11 Mbps vs 10 Mbps)
Background (2 of 2) - But there are also many distinct differences:
- wireless (air interface) versus wired (coax)
- wireless propagation environment (multipath)
- higher error rate due to interference, etc.
- successful frames are ACKed by receiver
- mobile stations versus fixed stations
- half-duplex versus full-duplex operation
- “hidden node” and “exposed node” problems
- potential asymmetries of links
- CSMA/CA versus CSMA/CD
- multiple data transmission rates (1, 2, 5.5, 11)
- Infrastructure mode vs “ad hoc” mode
- Access Point (AP) sends “beacon frames”
- Mobiles choose AP based on signal strength
- Multiple channel access protocols supported
- CSMA/CA (DCF); PCF; RTS/CTS
- MAC-layer can provide error control, retransmission, rate adaptation, etc.
- Direct Sequence Spread Spectrum (DSSS)
Where Does Wireless RF Live?
902-928 MHz
2400-2483.5 MHz
5725-5850 MHz
802.11/802.11b,g
802.11a
Bluetooth
Cordless Phones
Home RF
Baby Monitors
Microwave Ovens
Old Wireless
ISM (Industrial, Scientific, Medical) band
Telnet, FTP, Email, Web, etc.
IP, ICMP, IPX
TCP, UDP
Logical Link Control - 802.2
(Interface to the upper layer protocols)
MAC
802.3, 802.5, 802.11
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