Unit7_WLAN_Framing_Retransmission

Unit7_WLAN_Framing_Retransmission - Unit 7 Wireless LAN...

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Unit 7 Wireless LAN, Framing, and Retransmission WLAN, Framing & Retransmission 7-1
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Unit 7: Outline 7.1 Wireless LAN 7.2 Introduction to Data Link Layer 7.3 Framing 7.4 Flow Control and Retransmission Protocols WLAN, Framing & Retransmission 7-2
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Unit 7.1 Wireless LAN WLAN, Framing & Retransmission 7-3
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IEEE 802.11: Different Versions 802.11 (1997) 2.4 GHz band up to 2 Mbps 802.11b (1999) 2.4 GHz band up to 11 Mbps 802.11a (1999) 5 GHz band up to 54 Mbps 802.11g (2003) 2.4 GHz band up to 54 Mbps 802.11n: (2009) 2.4 and 5 GHz bands up to 600 Mbps ° all use CSMA/CA as the MAC protocol ° all have base-station and ad-hoc network versions ° each has different PHY characteristics WLAN, Framing & Retransmission 7-4
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IEEE 802.11 PHY Standards 802.11 supports three different PHY layers: Infrared Simple and cheap requires line of sight, or ceiling for reflection Radio Frequency (RF) Uses 2.4 GHz band Two Options: Direct Sequence Spread Spectrum (DSSS) Frequency Hopping Spread Spectrum (FHSS) can cover a larger area (since RF signals can penetrate walls) WLAN, Framing & Retransmission 7-5
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IEEE 802.11 PHY Standards 802.11a Uses OFDM at 5 GHz band More easily absorbed by walls (obstructions) Less likely to experience interference 802.11n Uses both 2.4 and 5 GHz Uses multiple antennae at both transmitter and receiver. Also called Multiple- Input Multiple-Output (MIMO). Uses OFDM 802.11b and g Both use 2.4 GHz band Less easily absorbed by walls (obstructions) More likely to experience interference, since many other devices operate in the 2.4 GHz band (e.g. Bluetooth, microwave oven, cordless phones) 802.11b uses DSSS 802.11g uses DSSS or OFDM, backward compatible with 802.11b. WLAN, Framing & Retransmission 7-6
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IEEE 802.11 PHY Standards WLAN, Framing & Retransmission 7-7
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Data Rates of 802.11 LANs 802.11n can achieve 600 Mbps with four data streams. WLAN, Framing & Retransmission 7-8
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802.11 LAN architecture ° wireless host communicates with base station ± base station = access point (AP) ° Basic Service Set (BSS) (aka cell ) in infrastructure mode contains: ± wireless hosts ± access point (AP): base station ± ad hoc mode: hosts only BSS 1 BSS 2 Internet hub, switch or router WLAN, Framing & Retransmission 7-9
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Installing an Access Point (AP) When a network administrator installs AP(s), he/she assigns a Service Set Identifier (SSID) to the AP(s) The network administrator must also assign a channel number to each AP. 802.11b/g operates within 2.4 – 2.485 GHz. 11 partially overlapping channels (each with 22 MHz bandwidth) are defined. Two channels are non-overlapping iff they are separated by four or more channels. If two adjacent APs use the same channel, communication in the two BSAs are severely affected. If there are three adjacent APs, use channels 1, 6, and 11.
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  • Winter '13
  • Note, Transmission Control Protocol, IEEE 802.11, retransmission

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