Auto-negotiation and traffic flow between different speed ports

Gigabit is gigabit--any time data is moving over it it is moving at the gigabit rate. If the devices attached to the switch cannot accept data at the rate that it is coming into the switch, the switch may generate pause frames or may just drop frames for which it does not have room in its buffer--both modes of operation are consistent with the Ethernet standards. Usually any throttling takes place at a level above that of Ethernet--TCP/IP detects that frames are being dropped and adjusts its behavior accordingly.

You'll find a bit of information on this at .

It isn't even close to true.

All moderns switches use a "store and forward" architecture. They receive a packet at whatever speed (e.g., 10 mbit) and store the entire packet, and then release the packet into the internal bus. The internal bus transmits at the maximum internal speeds supported by the various internal hops in the architecture, until the packet logically reaches the destination port in the same switch (or switch "cluster"). The internal hardware then waits until the destination port is available, and when it is, transmits at whatever speed the destination port supports.

In your example, switch 1 would receive the printer packet at 10 Mbit/s, shuffle it internally, and queue it up for the 1 gigabit uplink that is the destination as far as switch 1 is concerned. The packet would go over the uplink at 1 gigabit as soon as there is an opportunity, where it would be received at switch 2 at 1 gigabit. Switch 2 would then shuffle the packet internally, and queue it up for the port for the PC, transmitting it at 100 Mbit/s as soon as there is an opportunity on that port.

One switch port has absolutely no effect on another. Each port will independently set it's speed to match what's on the other end of the cable.

Thank you all for your knowledge.

Tom