switch buffering

An Ethernet switch uses a memory buffering technique to store frames before forwarding to the destination. The switch uses Buffering when the destination port is busy due to congestion. As a result, frames must be buffered until transmitted. So without an effective memory buffering scheme, frames are more likely to be dropped anytime traffic oversubscription or congestion occurs.

During congestion at the port, the switch stores the frame until it is transmitted. The memory buffer is the area where the switch stores the data. There are two methods of buffering:-

Port-based Memory Buffering

In this type, all frames have stored common memory buffers and queues linked to specific incoming ports. Switches utilizing port-buffered memory in this type of buffering. In the port buffering switch, each Ethernet port has a certain amount of high-speed memory to buffer frames until transmitted.  A disadvantage of port-buffered memory is the dropping of frames when a port runs out of buffers. It is also possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. This delay occurs even if the other frames could be transmitted to open destination ports.

Shared Memory Buffering

Some of the earliest Cisco switches use a shared memory design for port buffering. Shared buffering deposits all frames into a common memory buffer that all the ports on the switch share. The amount of buffer memory required by a port is dynamically allocated. The frames in the buffer are dynamically connected to the destination port. This allows the packet to be received on one port and transmitted to another port without moving it to a different queue.