Switching to the future with D-Link

In a LAN environment, the switch provides each network transmission with an independent path though the network, free of collisions with other network transmissions.

Many networks are experiencing bandwidth shortages because of an increase in traffic due to the sheer numbers of networked users, the amount of data transported between client/server applications, and the inefficient traffic patterns of some networks.

Switching establishes a direct line of communication between two ports and maintains multiple simultaneous links between various ports. It sends information directly from the port of origin to only its destination port and proficiently manages network traffic by reducing media sharing.

This technology enables some key benefits over traditional Ethernet bridged and routed networks. Firstly, a 10 Mbps or 100 Mbps shared media can be changed to 10 Mbps or 100 Mbps of dedicated bandwidth. Switches enable you to connect either a shared segment (a workgroup) or a dedicated one (a power user or server) to each port. Secondly, this is accomplished without modifying any software or hardware already running on the workstations. Finally, a switch installation is less complex than a bridge/router configuration.

Traditional Ethernet LANs run at 10 Mbps over a common bus-type design. Stations physically attach to this bus through a hub, repeater or concentrator, creating a broadcast domain. Every station is capable of receiving all transmissions from all stations, but only in a half-duplex mode. This means stations cannot send and receive data simultaneously.

Nodes on an Ethernet network transmit information following a simple rule: they listen before speaking. Only one node on the segment is allowed to transmit at any time due to the CSMA/CD protocol (Carrier Sense Multiple Access/Collision Detection).

Bridges and routers have similar bus-based architectures that, by design, function on shared media. Multiple segment contention is necessary for access to the bus whereas a switch eliminates the bus architecture. Bridges and routers have latencies that are significantly higher than switches (1-2 ms to store-and-forward a 1518 byte Ethernet packet compared to .020 ms for a switch). Bus-based designs are not very scalable due to propagation delay encountered when a bus length increases.

Ethernet switched segment a LAN into many parallel-dedicated lines that can enable a contentionless, scalable architecture.

When a single LAN station is connected to a switched port it may operate in full-duplex mode. Full-duplex does not require collision detection; there is a suspension of MAC protocols. A single device resides on that port, and therefore no collisions will be encountered. Full-duplex switching enables traffic to be sent and received simultaneously.

Switches change 10 Mbps shared segments into a group of dedicated 10 Mbps connections. 10/100 Ethernet switching transfers packets from a 10 Mbps shared segment to a LAN segmented workstation running at 100 Mbps. This enables multiple end stations or workgroups running at 10 Mbps to connect to a server or servers running a 100 Mbps.

Two types of architectures determine switching applications and performance: cut-through and store-and-forward.

Cut-through switching starts sending packets as soon as they enter a switch and their destination address is read (within the first 20-30 bytes of the frame). The entire frame is not received before a switch begins forwarding it to the destination port. This reduces transmission latency between ports, but it can propagate bad packets and broadcast storms to the destination port.

Store-and-forward switching, a function traditionally performed by bridges and routers, buffers incoming packets in memory until they are fully received and a cyclic redundancy check (CRC) is run. Buffered memory adds latency to the processing time and increases in proportion to the frame size. This latency reduces bad packets and collisions that can adversely effect the overall performance of the segment.

It is important to realise that just plugging everything into a switch may not be the most intelligent way to design a network. Resources particular to a department should remain on the department segment. It makes little sense to add the traffic these resources generate to an entire network.

Switching architectures should be designed so that local traffic to and from segment-specific resources remains local and enterprise-wide resources are accessible from multiple segments on a network.

By supporting parallel links and being able to change them instantly, switches provide incomparable speed and flexibility.

Switching controls traffic much more efficiently and facilitates migration to the speeds and bandwidths that will be indispensable. Changes to existing hardware and software will not be necessary. Switches will keep costs down and is much cheaper price-to-performance devices than bridges and routers.