A high-level overview of network bridging, using the and terminologyA network bridge is a that creates a single aggregate network from multiple. This function is called network bridging. Bridging is distinct from. Routing allows multiple networks to communicate independently and yet remain separate, whereas bridging connects two separate networks as if they were a single network. In the, bridging is performed in the (layer 2).

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2. Wireless Bridge

If one or more segments of the bridged network are, the device is known as a wireless bridge.The main types of network bridging technologies are simple bridging, multiport bridging, and learning or transparent bridging. Contents.Transparent bridging Transparent bridging uses a table called the to control the forwarding of frames between network segments. The table starts empty and entries are added as the bridge receives frames. If a destination address entry is not found in the table, the frame is flooded to all other ports of the bridge, flooding the frame to all segments except the one from which it was received. By means of these flooded frames, a on the destination network will respond and a forwarding database entry will be created. Both source and destination addresses are used in this process: source addresses are recorded in entries in the table, while destination addresses are looked up in the table and matched to the proper segment to send the frame to. (DEC) originally developed the technology in the 1980s.In the context of a two-port bridge, one can think of the forwarding information base as a filtering database.

A bridge reads a 's destination address and decides to either forward or filter. If the bridge determines that the destination host is on another segment on the network, it forwards the frame to that segment. If the destination address belongs to the same segment as the source address, the bridge filters the frame, preventing it from reaching the other network where it is not needed.Transparent bridging can also operate over devices with more than two ports. As an example, consider a bridge connected to three hosts, A, B, and C. The bridge has three ports. A is connected to bridge port 1, B is connected to bridge port 2, C is connected to bridge port 3.

A sends a frame addressed to B to the bridge. The bridge examines the source address of the frame and creates an address and port number entry for A in its forwarding table.

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The bridge examines the destination address of the frame and does not find it in its forwarding table so it floods it to all other ports: 2 and 3. The frame is received by hosts B and C. Host C examines the destination address and ignores the frame. Host B recognizes a destination address match and generates a response to A. On the return path, the bridge adds an address and port number entry for B to its forwarding table. The bridge already has A's address in its forwarding table so it forwards the response only to port 1.

Host C or any other hosts on port 3 are not burdened with the response. Two-way communication is now possible between A and B without any further flooding in network.Simple bridging A simple bridge connects two network segments, typically by operating transparently and deciding on a frame-by-frame basis whether or not to forward from one network to the other.

A technique is typically used so, as part of forwarding, the frame integrity is verified on the source network and delays are accommodated on the destination network. In contrast to repeaters which simply extend the maximum span of a segment, bridges only forward frames that are required to cross the bridge. Additionally, bridges reduce collisions by creating a separate on either side of the bridge.Multiport bridging A multiport bridge connects multiple networks and operates transparently to decide on a frame-by-frame basis whether to forward traffic. Additionally a multiport bridge must decide where to forward traffic. Like the simple bridge, a multiport bridge typically uses store and forward operation. The multiport bridge function serves as the basis for.Implementation The stored in (CAM) is initially empty. For each received ethernet frame the switch learns from the frame's source MAC address and adds this together with an ingress interface identifier to the forwarding information base.

The switch then forwards the frame to the interface found in the CAM based on the frame's destination MAC address. If the destination address is unknown the switch sends the frame out on all interfaces (except the ingress interface). This behaviour is called.Forwarding Once a bridge learns the addresses of its connected nodes, it forwards data link layer frames using a layer-2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth methods were performance-increasing methods when used on 'switch' products with the same input and output port bandwidths:.: the switch buffers and verifies each frame before forwarding it; a frame is received in its entirety before it is forwarded.: the switch starts forwarding after the frame's destination address is received.

There is no error checking with this method. When the outgoing port is busy at the time, the switch falls back to store-and-forward operation. Also, when the egress port is running at a faster data rate than the ingress port, store-and-forward is usually used.: a method that attempts to retain the benefits of both store and forward and cut through. Fragment free checks the first 64 of the, where information is stored. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frame transmissions that are aborted because of a collision will not be forwarded. Error checking of the actual data in the packet is left for the end device.: a method of automatically selecting between the other three modes.Shortest Path Bridging.

Wireless Bridge

September 14, 1999. Archived from (PDF) on May 31, 2013. Retrieved July 27, 2012. Retrieved July 27, 2012.

July 14, 1989. Retrieved October 19, 2013. Archived from (PPT) on May 13, 2014. Retrieved December 2, 2012. (PPT). Retrieved December 2, 2012.

Cisco Systems, Inc. Retrieved June 20, 2010. Dong, Jielin (2007). Javvin Technologies Inc. Retrieved June 25, 2016. IDG Network World Inc.

July 1, 1996. Retrieved June 25, 2016. September 7, 2011. Retrieved September 11, 2011. Luo, Zhen; Suh, Changjin (March 3, 2011).

'An improved shortest path bridging protocol for Ethernet backbone network'. The International Conference on Information Networking 2011 (ICOIN2011).

Information Networking, International Conference on. Pp. 148–153. (PDF). September 2011. Retrieved December 25, 2011.

Shuang Yu. IEEE Standards Association. Retrieved June 19, 2012. Using the IEEE’s next-generation VLAN, called a Service Interface Identifier (I-SID), it is capable of supporting 16 million unique services compared to the VLAN limit of four thousand.Further reading.

August 1, 1999. Retrieved December 20, 2015.

An example of a Wi-Fi networkA wireless LAN ( WLAN) is a that links two or more devices using to form a (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users the ability to move around within the area and remain connected to the network. Through a, a WLAN can also provide a connection to the wider.Most modern WLANs are based on standards and are marketed under the brand name.Wireless LANs have become popular for use in the home, due to their ease of installation and use. They are also popular in that offer wireless access to their employees and customers.

54 Mbit/s WLAN PCI Card (802.11g)Wireless LAN hardware initially cost so much that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards, primarily the various versions of IEEE 802.11 (in products using the brand name). Beginning in 1991, a European alternative known as HiperLAN/1 was pursued by the (ETSI) with a first version approved in 1996. This was followed by a HiperLAN/2 functional specification with influences accomplished February 2000.

Neither European standard achieved the commercial success of 802.11, although much of the work on HiperLAN/2 has survived in the physical specification for IEEE, which is nearly identical to the PHY of HiperLAN/2.In 2009 was added to 802.11. It operates in both the 2.4 GHz and 5 GHz bands at a maximum data transfer rate of 600 Mbit/s. Most newer routers are able to utilise both wireless bands, known as dualband. This allows data communications to avoid the crowded 2.4 GHz band, which is also shared with devices. The 5 GHz band is also wider than the 2.4 GHz band, with more channels, which permits a greater number of devices to share the space.A group formed in 1997 to promote a technology aimed for residential use, but it disbanded at the end of 2002.

Architecture Stations All components that can connect into a wireless medium in a are referred to as stations (STA).All stations are equipped with (WNICs).Wireless stations fall into two categories:, and clients.Access points (APs), normally, are base stations for the wireless network. Peer-to-Peer or ad hoc wireless LANAn (not the same as a ) is a network where stations communicate only peer to peer (P2P). There is no base and no one gives permission to talk.This is accomplished using the Independent Basic Service Set (IBSS).A is another type of network where stations communicate peer to peer.In a Wi-Fi P2P group, the group owner operates as an access point and all other devices are clients. There are two main methods to establish a group owner in the Wi-Fi Direct group. In one approach, the user sets up a P2P group owner manually. This method is also known as Autonomous Group Owner (autonomous GO).

In the second method, also called negotiation-based group creation, two devices compete based on the group owner intent value. The device with higher intent value becomes a group owner and the second device becomes a client. Group owner intent value can depend on whether the wireless device performs a cross-connection between an infrastructure WLAN service and a P2P group, remaining power in the wireless device, whether the wireless device is already a group owner in another group and/or a received signal strength of the first wireless device.A network allows wireless devices to directly communicate with each other. Wireless devices within range of each other can discover and communicate directly without involving central access points. This method is typically used by two computers so that they can connect to each other to form a network. This can basically occur in devices within a closed range.If a signal strength meter is used in this situation, it may not read the strength accurately and can be misleading, because it registers the strength of the strongest signal, which may be the closest computer.

: Devices A and C are both communicating with B, but are unaware of each otherdefines the physical layer (PHY) and MAC (Media Access Control) layers based on (Carrier Sense Multiple Access with Collision Avoidance). This is in contrast to Ethernet which uses CSMA-CD (Carrier Sense Multiple Access with Collision Detection). The 802.11 specification includes provisions designed to minimize collisions, because two mobile units may both be in range of a common access point, but out of range of each other.Bridge A bridge can be used to connect networks, typically of different types.

A wireless bridge allows the connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the Wireless LAN.Wireless distribution system A (WDS) enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of a WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points.An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet.

A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Connections between clients are made using MAC addresses rather than by specifying IP assignments.All base stations in a WDS must be configured to use the same radio channel, and share WEP keys or WPA keys if they are used. They can be configured to different service set identifiers. WDS also requires that every base station be configured to forward to others in the system as mentioned above.WDS capability may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging).

Throughput in this method is halved for all clients connected wirelessly.When it is difficult to connect all of the access points in a network by wires, it is also possible to put up access points as repeaters.Roaming. Roaming among Wireless Local Area NetworksThere are two definitions for wireless LAN roaming:. Internal roaming: The Mobile Station (MS) moves from one access point (AP) to another AP within a home network if the signal strength is too weak. An authentication server (RADIUS) performs the re-authentication of MS via 802.1x (e.g. The billing of QoS is in the home network.

A Mobile Station roaming from one access point to another often interrupts the flow of data among the Mobile Station and an application connected to the network. The Mobile Station, for instance, periodically monitors the presence of alternative access points (ones that will provide a better connection). At some point, based on proprietary mechanisms, the Mobile Station decides to re-associate with an access point having a stronger wireless signal. The Mobile Station, however, may lose a connection with an access point before associating with another access point. In order to provide reliable connections with applications, the Mobile Station must generally include software that provides session persistence.

External roaming: The MS (client) moves into a WLAN of another Wireless Internet Service Provider (WISP) and takes their services (Hotspot). The user can use a foreign network independently from their home network, provided that the foreign network allows visiting users on their network. There must be special authentication and billing systems for mobile services in a foreign network. Applications Wireless LANs have a great deal of applications. Modern implementations of WLANs range from small in-home networks to large, campus-sized ones to completely mobile networks on airplanes and trains.Users can access the Internet from WLAN hotspots in restaurants, hotels, and now with portable devices that connect to 3G or 4G networks. Oftentimes these types of public access points require no registration or password to join the network. Others can be accessed once registration has occurred and/or a fee is paid.Existing Wireless LAN infrastructures can also be used to work as with no modification to the existing hardware.See also.References.