Switch Network

An Ethernet switch is a type of of network hub used in star topologies, including Ethernet. The difference with HUB comes from the method of returning the data to the destination, a hub simply return the data to all connected devices, the switch keeps a internal table in memory address. It first decodes the message to send only the network port (computer) partner.

Another difference, a switch work in Full duplex. He can send and receive data over a single network port simultaneously, thus bidirectional, by doubling the transfer rate. The Switches includes Auto Negotiation. They automatically detect how full or half duplex depending on the equipment connected. Auto MDI / MDIX means the automatic detection of cable RJ45 patch / cross, it is the case of most current models. Otherwise, you must use a crossover cable or a dedicated port with two connectors including a reverse or a pushbutton that crosses the connection internally.

Operation of a switch.

With each new connection, it built a table of equivalence MAC address - port connection in its internal memory. A switch does not work with IP addresses, computers use an ARP table that contains the correspndance between IP address and MAC address and only send the MAC address on the network (TCP IP address she sent over IP). Depending on model and type, memory is more or less limited.

When a switch receives a destination address, it checks if the address is in memory (correspondence physical address / Ethernet). If the MAC address is known, it sends data to the network port associated. If we use several cascaded switches or if the address is not in the ARP table. Il will send a special message (a MAC address FF.FF.FF.FF.FF.FF called Broadcast) on all its ports to ask where this device is connected. By receiving this message, the second switch will check its own table if a match between the MAC address and its port. If known, it will send a message to the first switch that will update its mapping table (connection port switch to in the second) and send the message to the second switch).

Type of switch

The technology (mode) is related to the types of data exchanged at the network architecture but also levels of performance.

• Store and Forward (standard model) saves all frames in memory before passing on the port associated with the destination address. Before saving frames, it will analyze the level of detection errors (RUNT for example), updating the address table to the filtering devices for Level 3 Administrative OSI, Depending on model. This type of frames do not send incomplete and can mix Ethernet copper connections with fiber optics or even using many different connection speeds. The memory storage frames is 256 KB to 8 MB over the next pattern. Models of low-end desktop using the same memory by grouping ports, between them, the dedicate a larger buffer per port. Lantence time depends on the size of the frames, resulting in a slowdown during large file transfers, also limited by the MTU.
• Cut Through does not save the frames and does not decode the header as the destination MAC address. He does not read the message content. This solution is used for client / server applications.
• Cut Through Runt Free (called Fragment Free in models CISCO) follows from the previous. Collision on the Ethernet network, a RUNT less than 64 bytes is sent. Indeed, these switches analyze the first 64 bytes of each frame. It is sent only if the length is 64 bytes minimum and ignored otherwise. The advantage is low latency.
• Adaptive Cut Through includes mainly a correction of errors. These switches register ports with repetitive errors .. When a threshold is exceeded, the switch port Store and Forward, isolating some parts of the network (cabling). If the error rate becomes normal, the switch port returns to Cut Through.

Additional Features

• A Switch stackable allows connection of several switches between them (even model), the number is limited. All share the same mapping table by grouping them. The technology uses Meshing. The Port Trunking reserve a certain number of ports for connections between 2 LAN switches.
• A Managed Switch allows management of ports.
• The switches said level 4 does not support layer 4 of OSI model (it is a misnomer, by extension level 3). They can analyze applications originally transmitted data. This feature allows them to give priority to certain software in terms of bandwidth or even ban certain applications (peer to peer for example).

Related Definitions: LAN - Types of computer networks - router - Network Protocols - Bay 19 " - RJ 45 Wiring and fiber optics