leaked is (N – 1)T – τ, which because the leak is one unit per second, took exactly (N – 1)T – τ seconds to leak. Thus the shortest time in which all N packets can arrive and conform is (N – 1)T – τ seconds, which is exactly τ less than the time it would have taken if the packets had been arriving at exactly the emission interval. However, packets can only arrive with intervals less than T where the bucket is not filled by the previous packet. If it is, then the bucket must have drained by the full amount T before the next packet conforms. So once this tolerance has been used up by packets arriving at less than T, subsequent frames must arrive at intervals no less than T. They may, however, arrive at greater intervals, when the bucket will not be filled by them. When this has happened, packets may, again, arrive with intervals less than T until the tolerance is again used up. However, since the bucket stops leaking when it is empty, there is always a limit (τ) to how much tolerance can be accrued by these intervals greater than T, however, much greater than T they may be or, however, many of them there are. Since the limit value τ defines how much earlier a packet can arrive than would be expected, it is the limit on the difference between the maximum and minimum delays from the source to the point where the conformance test is being made (assuming the packets are generated with no jitter). Hence, the use of the term Cell Delay Variation tolerance (CDVt) for this parameter in ATM. As an example, a possible source of delay variation is where a number of connections (streams of packets) are multiplexed together at the output of a switch. Assuming that the sum of the bandwidths of these connections is less than that of the output, all of the packets that arrive can be transmitted, eventually. However, if their arrivals are independent, e.g. because they arrive at different inputs of the switch, then several may arrive at or nearly at the same time. Since the output can only transmit one packet at a time, the others must be queued in a buffer until it is their turn to be transmitted. This buffer then introduces an additional delay between a packet arriving at