SWITCHES
When a repeater hub is replaced with an Ethernet switch,
the single large collision domain used by the hub is split up into
smaller ones, reducing or eliminating the possibility and scope of
collisions and, as a result, increasing the potential throughput. Because
broadcasts are still being forwarded to all connected devices, the
newly formed network segment continues to be a broadcast domain.
An Ethernet switch operates at the data link layer (layer 2) of the OSI model to create a separate collision domain for each switch port. Each device connected to a switch port can transfer data to any of the other ones at a time, and the transmissions will not interfere – with the limitation that, in half duplex mode, each switch port can only either receive from or transmit to its connected device at a certain time. In full duplex mode, each switch port can simultaneously transmit and receive, assuming the connected device also supports full duplex mode.
In the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would also result in collisions, requiring retransmissions.
The network switch plays an integral role in most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a residential gateway to access small office/home broadband services such as DSL or cable Internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for Voice over IP (VoIP) protocol.
Segmentation involves the use of a bridge or a switch (or a router) to split a larger collision domain into smaller ones in order to reduce collision probability, and to improve overall network throughput. In the extreme case (i.e. microsegmentation), each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports. This allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has only one transmitter and one receiver per "collision domain", making collisions impossible.
In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of the layers mentioned. While the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing. Devices that interconnect at the layer 3 are traditionally called routers, so layer 3 switches can also be regarded as relatively primitive and specialized routers.
Where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall, network intrusion detection, and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.
In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systems and packet sniffers.
While switches may learn about topologies at many layers, and forward at one or more layers, they do tend to have common features. Other than for high-performance applications, modern commercial switches use primarily Ethernet interfaces.
At any layer, a modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as a VoIP phone or wireless access point, to have a separate power supply. Since switches can have redundant power circuits connected to uninterruptible power supplies, the connected device can continue operating even when regular office power fails.
A network hub, or a repeater, is a simple network device that does not manage any of the traffic coming through it. Any packet entering a port is flooded out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions affect the entire network, limiting its overall capacity.
A network switch creates the layer 1 end-to-end connection only virtually, while originally it was mandatory. The bridging function of a switch uses information taken from layer 2 to select for each packet the particular port(s) it has to be forwarded to, removing the requirement that every node is presented with all traffic. As a result, the connection lines are not "switched" literally, instead they only appear that way on the packet level.
A network bridge, operating at the data link layer, may interconnect a small number of devices in a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device.
While layer 2 switch remains more of a marketing term than a technical term, the products that were introduced as "switches" tended to use microsegmentation and full duplex to prevent collisions among devices connected to Ethernet. By using an internal forwarding plane much faster than any interface, they give the impression of simultaneous paths among multiple devices. 'Non-blocking' devices use a forwarding plane or equivalent method fast enough to allow full duplex traffic for each port simultaneously.
While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is not always the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth and uplinks into a higher bandwidth.
Within the confines of the Ethernet physical layer, a layer-3 switch can perform some or all of the functions normally performed by a router. The most common layer-3 capability is awareness of IP multicast through IGMP snooping. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group.
Unless port mirroring or other methods such as RMON, SMON or sFlow are implemented in a switch, it is difficult to monitor traffic that is bridged using a switch because only the sending and receiving ports can see the traffic. These monitoring features are rarely present on consumer-grade switches.
In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. In the traditional circuit-switched telephone network, one or more switches are used to set up a dedicated though temporary connection or circuit for an exchange between two or more parties. On an Ethernet local area network (LAN), a switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of. In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip to the intended destination.
In the Open Systems Interconnection (OSI) communications model, a switch performs the Layer 2 or Data-link layer function. That is, it simply looks at each packet or data unit and determines from a physical address (the "MAC address") which device a data unit is intended for and switches it out toward that device. However, in wide area networks such as the Internet, the destination address requires a look-up in a routing table by a device known as a router. Some newer switches also perform routing functions (Layer 3 or the Network layer functions in OSI) and are sometimes called IP switches.
In the simplest networks, a switch is not required for messages that are sent and received within the network. For example, a local area network may be organized in a token ring or bus arrangement in which each possible destination inspects each message and reads any message with its address.
Most data today is sent, using digital signals, over networks that use packet-switching. Using packet-switching, all network users can share the same paths at the same time and the particular route a data unit travels can be varied as conditions change. In packet-switching, a message is divided into packets, which are units of a certain number of bytes. The network addresses of the sender and of the destination are added to the packet. Each network point looks at the packet to see where to send it next. Packets in the same message may travel different routes and may not arrive in the same order that they were sent. At the destination, the packets in a message are collected and reassembled into the original message.
Advanced routing and switching considerations: Routing and switching, the core functions of any network, are becoming more intelligent, with even low-end products now including features once only available to enterprise data centers. Learn the routing and switching considerations that every solution provider should know before offering their services.
This product overview focuses on the Cisco Nexus 9500 family of switches, which is designed for enterprises and highly virtualized data centers. Then get more info about the models, features and pricing of the Cisco Nexus 7700 switch series.
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers. You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy.
An Ethernet switch operates at the data link layer (layer 2) of the OSI model to create a separate collision domain for each switch port. Each device connected to a switch port can transfer data to any of the other ones at a time, and the transmissions will not interfere – with the limitation that, in half duplex mode, each switch port can only either receive from or transmit to its connected device at a certain time. In full duplex mode, each switch port can simultaneously transmit and receive, assuming the connected device also supports full duplex mode.
In the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would also result in collisions, requiring retransmissions.
The network switch plays an integral role in most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a residential gateway to access small office/home broadband services such as DSL or cable Internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for Voice over IP (VoIP) protocol.
Segmentation involves the use of a bridge or a switch (or a router) to split a larger collision domain into smaller ones in order to reduce collision probability, and to improve overall network throughput. In the extreme case (i.e. microsegmentation), each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports. This allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has only one transmitter and one receiver per "collision domain", making collisions impossible.
In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of the layers mentioned. While the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing. Devices that interconnect at the layer 3 are traditionally called routers, so layer 3 switches can also be regarded as relatively primitive and specialized routers.
Where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall, network intrusion detection, and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.
In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systems and packet sniffers.
While switches may learn about topologies at many layers, and forward at one or more layers, they do tend to have common features. Other than for high-performance applications, modern commercial switches use primarily Ethernet interfaces.
At any layer, a modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as a VoIP phone or wireless access point, to have a separate power supply. Since switches can have redundant power circuits connected to uninterruptible power supplies, the connected device can continue operating even when regular office power fails.
A network hub, or a repeater, is a simple network device that does not manage any of the traffic coming through it. Any packet entering a port is flooded out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions affect the entire network, limiting its overall capacity.
A network switch creates the layer 1 end-to-end connection only virtually, while originally it was mandatory. The bridging function of a switch uses information taken from layer 2 to select for each packet the particular port(s) it has to be forwarded to, removing the requirement that every node is presented with all traffic. As a result, the connection lines are not "switched" literally, instead they only appear that way on the packet level.
A network bridge, operating at the data link layer, may interconnect a small number of devices in a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device.
While layer 2 switch remains more of a marketing term than a technical term, the products that were introduced as "switches" tended to use microsegmentation and full duplex to prevent collisions among devices connected to Ethernet. By using an internal forwarding plane much faster than any interface, they give the impression of simultaneous paths among multiple devices. 'Non-blocking' devices use a forwarding plane or equivalent method fast enough to allow full duplex traffic for each port simultaneously.
While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is not always the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth and uplinks into a higher bandwidth.
Within the confines of the Ethernet physical layer, a layer-3 switch can perform some or all of the functions normally performed by a router. The most common layer-3 capability is awareness of IP multicast through IGMP snooping. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group.
Unless port mirroring or other methods such as RMON, SMON or sFlow are implemented in a switch, it is difficult to monitor traffic that is bridged using a switch because only the sending and receiving ports can see the traffic. These monitoring features are rarely present on consumer-grade switches.
In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. In the traditional circuit-switched telephone network, one or more switches are used to set up a dedicated though temporary connection or circuit for an exchange between two or more parties. On an Ethernet local area network (LAN), a switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of. In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip to the intended destination.
In the Open Systems Interconnection (OSI) communications model, a switch performs the Layer 2 or Data-link layer function. That is, it simply looks at each packet or data unit and determines from a physical address (the "MAC address") which device a data unit is intended for and switches it out toward that device. However, in wide area networks such as the Internet, the destination address requires a look-up in a routing table by a device known as a router. Some newer switches also perform routing functions (Layer 3 or the Network layer functions in OSI) and are sometimes called IP switches.
In the simplest networks, a switch is not required for messages that are sent and received within the network. For example, a local area network may be organized in a token ring or bus arrangement in which each possible destination inspects each message and reads any message with its address.
Most data today is sent, using digital signals, over networks that use packet-switching. Using packet-switching, all network users can share the same paths at the same time and the particular route a data unit travels can be varied as conditions change. In packet-switching, a message is divided into packets, which are units of a certain number of bytes. The network addresses of the sender and of the destination are added to the packet. Each network point looks at the packet to see where to send it next. Packets in the same message may travel different routes and may not arrive in the same order that they were sent. At the destination, the packets in a message are collected and reassembled into the original message.
Advanced routing and switching considerations: Routing and switching, the core functions of any network, are becoming more intelligent, with even low-end products now including features once only available to enterprise data centers. Learn the routing and switching considerations that every solution provider should know before offering their services.
This product overview focuses on the Cisco Nexus 9500 family of switches, which is designed for enterprises and highly virtualized data centers. Then get more info about the models, features and pricing of the Cisco Nexus 7700 switch series.
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers. You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy.
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