The basic units of data in layer 2 are frames. Bits are organized in to bytes and bytes into fields and fields into frames. A frame typically has fields such as start, address, length, typeof, userdata and checksum. Layer 2 devices are concerned with reliable error free transmission and reception of frames. They have a MAC address which is either built-in to the hardware or configured. Frames carry source and destination MAC addresses. Examples of Layer 2 devices are Bridges, Switches and Wireless Access Points
They are intelligent devices which keeps a table of MAC addresses connected to each of its ports. They build this table by examining the source address of incoming frames. When a frame arrives in one of its ports it examines the destination MAC address, consults the table and forwards it in the appropriate port. If the destination address is not known, then the frame is flooded in all the outgoing ports. If destination address corresponds to the same port as it arrived, then the frame is discarded.
These are similar to bridges and also forwards frames on appropriate ports by consulting the table of MAC addresses. The main differences being, they have more ports, they do the switching in hardware (Bridges in software), and offer more variance to speed in its ports.
These are used to connect wireless devices to a wired network. The most common wireless LAN technology today is WiFi (IEEE 802.11 a/b/g/n). Each wireless device makes a WiFi connection to the access point. When operating in this mode the wireless devices are said to be infrastructure mode because they are connecting to an existing wired infrastructure behind the access point. The access point is either a standalone device which connects to a router through a wire or it is a part of the router itself. A router that has a wireless access point integrated into it is called a wireless router.
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