Resource-Sharing

How do all the hosts use the network at the same time? How do they use the same links at the same time?

multiplexing is when a system resource is shared among multiple users
- synchronous time division multiplexing (STDM) divides time up into equal $n$ intervals and sequentially switches the $n$ host connections, one after the other, sending any data, if requested.
- frequency-division multiplexing (FDM) transmits data along the link at $n$ different frequencies
- both of these are really amateur! they waste a lot of idle time and they require knowing the max connections ahead of time
statistical multiplexing is the winner; it's like STDM but the data is sent on demand; it's split into packets and if only one connection is in use, all the packets are sent consecutively. If multiple sources are sending packages, the switch decides on a packet-by-packet basis which one to forward. The decision could be
- FIFO
- Round robin
quality of service (QoS) is when a network tries to ensure that each connection receives a particular share of the link's bandwidth
if a switch receives packets faster than it can send them, and runs out of in memory buffer space, then some packets have to be dropped. In this case the switch is said to be congested.

Resource Sharing