802.11 Wireless LAN - IITK

802.11 Wireless LAN - IITK

LAN Technologies 802.11 Wireless LAN Network connectivity to the legacy wired LAN Desktop with PCI 802.11 LAN card Access Point Laptop with PCMCIA 802.11 LAN card Provides network connectivity over wireless media

An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network The AP is connected to wired network and is equipped with antennae to provide wireless connectivity LAN Technologies 802.11 Wireless LAN Range ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point To service larger areas, multiple APs may be installed with a 20-30% overlap A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off) Three flavors:

802.11b 802.11a 802.11g LAN Technologies Multiple Access with Collision Avoidance (MACA) other node in senders range sender RTS receiver other node in receivers range

CTS data ACK Before every data transmission Sender sends a Request to Send (RTS) frame containing the length of the transmission Receiver respond with a Clear to Send (CTS) frame Sender sends data Receiver sends an ACK; now another sender can send data When sender doesnt get a CTS back, it assumes collision LAN Technologies WLAN : 802.11b

The most popular 802.11 standard currently in deployment. Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band LAN Technologies WLAN : 802.11a Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band Incompatible with devices operating in 2.4GHz Supports Data rates up to 54 Mbps. LAN Technologies WLAN : 802.11g Supports data rates as high as 54 Mbps on the 2.4 GHz band

Provides backward equipment compatibility with 802.11b Repeater, HUB, Bridge & Switch REPEATER, HUB, BRIDGE AND SWITCH Repeater, Hub, Bridge & Switch Repeater A repeater receives a signal, regenerates it, and passes it

on. It can regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media. It operates at Physical Layer of OSI The Four Repeater Rule for 10-Mbps Ethernet should be used as a standard when extending LAN segments. This rule states that no more than four repeaters can be used between hosts on a LAN. This rule is used to limit latency added to frame travel by each repeater. Repeater, Hub, Bridge & Switch Hub Hubs are used to connect multiple nodes to a single physical device, which connects to the network.

Hubs are repeaters. actually multiport Using a hub changes the network topology from a linear bus, to a star. With hubs, data arriving over the cables to a hub port is electrically repeated on all the other ports connected to the same network segment, except for the port on which the data was sent.

Repeater, Hub, Bridge & Switch Bridge Bridges are used to logically separate network segments within the same network. They operate at the OSI data link layer (Layer 2) and are independent of higherlayer protocols. The function of the bridge is to make intelligent decisions about whether or not to pass signals on to the next segment of a network. When a bridge receives a frame on the network, the destination MAC address is looked up in the bridge table to determine whether to filter, flood, or copy the frame onto another segment Broadcast Packets are forwarded

Repeater, Hub, Bridge & Switch Switch Switches are Multiport Bridges. Switches provide a unique network segment on each port, thereby separating collision domains. Today, network designers are replacing hubs in their wiring closets with switches to increase their network performance and bandwidth while protecting their existing wiring investments. Like bridges, switches learn certain information about the data packets that are received from various computers on the network. Switches use this information to build forwarding tables to determine the destination of data being sent by one computer to another computer on the network.

Repeater, Hub, Bridge & Switch Switches: Dedicated Access Hosts have connection to switch direct Full Duplex: No collisions Switching: A-to-A and B-toB simultaneously, no collisions A C

B switch Switches can be cascaded to expand the network C B A

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