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Embed code for: 03.4 Switches
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9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/3/pages/4 1/3 Switches Section 3: Introducing LANs Like a multiport bridge, a LAN switch creates a collision domain on each port. LAN switches also build MAC address forwarding tables; this is where the similarity to classical Ethernet connectivity ends. Instead of Ethernet stations connecting to shared media, stations connect directly to a port on the LAN switch, providing two features that are unavailable in shared Ethernet LANs: Dedicated bandwidth: Because there is only one station connected to a LAN switch port, the station does not compete for access to the media with other Ethernet stations and receives the full bandwidth that is configured on the port. Fullduplex operation: In classical shared Ethernet, a station can either transmit or receive at a given time, which is referred to as halfduplex operation. Because the Ethernet station now directly connects its transmit and receive wires to the switch port, it can simultaneously transmit and receive; this is termed full duplex. Half duplex mode is available for legacy 10BASET NICs that do not support fullduplex operation. 9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/3/pages/4 2/3 The following are some important features of switches: High port density: Switches have high port densities; 24 and 48port switches operate at speeds of 100 Mb/s, 1 Gb/s, and 10 Gb/s. Large enterprise switches may support hundreds of ports. Large frame buffers: The ability to store more received frames before having to start dropping them is useful, particularly when there may be congested ports to servers or other parts of the network. Port speed: Depending on the switch (or switch port module in a modular switch), it may be possible to support a mixture of speeds. Ports of 10 Mb/s are occasionally required to support legacy equipment, but switches offering ports supporting 100 Mb/s and 1 Gb/s are most common. 10Gb/s Ethernet ports are becoming common in data center environments. 9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/3/pages/4 3/3 Fast internal switching: Having fast internal switching allows speeds of 100 Mb/s, 1 Gb/s, and 10 Gb/s. The method that is used may be a fast internal bus or shared memory, which affects the overall performance of the switch. Low perport cost: Switches provide high port density at a low cost. For this reason, LAN switches can accommodate network designs featuring fewer users per segment, therefore increasing the average available bandwidth per user. Up Next: LAN Components