network link that connects two router is limited by how much data it can transfer per unit of time, commonly reffered as bandwidth or capacity of a link. which is represented by data rate such as 1.54 megabits per second. a network carries traffic on its links and through its routers to the eventual destination; traffic in a network refers to packets generated by different applications such as web/mail.
if traffic suddenly increase, for ex, many users trying to download from the same website, then packets generated can possibly queued at routers or even dropped.
Router actually mantains finite amount of space = buffer. to store backlogged packets temporarily, it is possible to reach the buffer limit.
for efficient delivery of packets there are several key factors to consider :
1. Router with a reasonable amount of buffer space
2. links with adequate bandwidth
3. actual transmission with mininal error
4. Router effeciency in swithing a packet to the appropriate outgoing link