In our minds, switches are network devices that connect LAN nodes. In fact, they also exist in wide area networks (WANs) and are widely used, especially in telecommunications operations. Examples include ATM switches and current Fibre Channel switches, though they are often less commonly seen. This article, however, mainly introduces the various interfaces and connection methods of commonly used LAN switches. How is an Ethernet switch connected to a router, and what are its uses?
1. Ethernet switch connection method
In a switched Ethernet network, the switch's MAC address determines which port a data frame should be sent to based on the received data frame. Because frame transmissions between ports are mutually shielded, nodes do not worry about whether frames sent through the switch will conflict with frames sent by other nodes.
2. Ethernet Switch Functions
• Reduce collisions: Switches isolate collisions on each port (each port is a collision zone) to prevent the propagation of collisions.
• Increase bandwidth: Each node on the access switch can use the bandwidth instead of sharing it.
• Learning: Ethernet switches know the MAC address of connected devices and the port corresponding to each port mapping address, and store them in the MAC address table in the switch cache.
Forwarding/Filtering: When the destination address of a data frame is in the data frame, and there is a mapping in the address table, the MAC will forward it to the port connected to the destination node, instead of all ports (if the data frame is a broadcast/multicast frame, it will be forwarded to all ports).
• Circuit Elimination: When a switch contains redundant circuits, the Ethernet switch avoids circuits through the Spanning Tree Protocol, allowing for backup paths.
3. Switch working principle:
The switch establishes a mapping between the address and the switch port based on the source MAC address in the received data frame and writes it into the MAC address table.
• The switch establishes a MAC comparison address table for the target switch MAC address in the data frame to determine which port to forward the data to.
If the destination MAC address in a data frame is not in the MAC address table, it will be forwarded to all ports. This process is called flooding.
Broadcast frames and multicast frames are forwarded to all ports.
4. Switch operating characteristics:
• The network segment connected to each port of the switch is an independent collision domain.
• Devices connected to the switch are still in the same broadcast field, meaning the switch does not isolate broadcast environments (the only exception is VLANs equipped with broadcast).
Switches forward data based on frame header information; therefore, switches are network devices that operate at the data link layer.
5. Switch Classification:
Based on the different operating modes of the exchanged processing frames, it can be divided into two categories.
Store and forward: The switch must receive the entire frame and check for errors before forwarding it, then send the frame to the destination address. The frame forwarding delay varies with the frame length.
Cut-through: As soon as the switch checks the destination address in the frame header, it forwards the frame immediately without waiting to receive all frames or verify errors. Because the length of the Ethernet frame header is always fixed, the forwarding delay of the frame through the switch remains constant.
Ethernet switches? Ethernet's advantages include good compatibility with older systems and relatively low price. Gigabit Ethernet is identical within the same system. ATM's main competitive advantage lies in its ability to keep up with demand.
