significantly earlier than it would if the cells were sent at the SCR: transmission duration = (MBS-1)/PCR rather than (MBS-1)/SCR. This bursting at the PCR puts a significantly higher load on shared resources, e.g. switch output buffers, than does transmission at the SCR, and is thus more likely to result in buffer overflows and network congestion. However, it puts a lesser load on these resources than would transmitting at the SCR with a limit value, τSCR, that allows MBS cells to be transmitted and arrive back-to-back at the line rate. If the limit value is large enough, then several packets can arrive in a burst and still conform: if the bucket starts from empty, the first packet to arrive will add T, but if, by the time the next packet arrives, the contents is below τ, this will also conform. Assuming that each packet takes δ to arrive, then if τ (expressed as the time it takes the bucket to empty from the limit value) is equal to or greater than the emission interval less the minimum interarrival time, T – δ, the second packet will conform even if it arrives as a burst with the first. Similarly, if τ is equal to or greater than (T – δ) × 2, then 3 packets can arrive in a burst, etc. The maximum size of this burst, M, can be calculated from the emission interval, T; the maximum jitter tolerance, τ; and the time taken to transmit/receive a packet, δ, as follows: Equally, the minimum value of jitter tolerance τ that gives a specific MBS can be calculated from the MBS as follows: In the case of ATM, where technically MBS only relates to the SCR tolerance, in the above equation the time it takes each packet to arrive, δ, is the emission interval for cells at the PCR TPCR, and the emission interval, T, is the emission interval for the SCR TSCR. Where MBS is to be the number of cells required to transport a segmented packet, the limit value in the above, τ, should be that for the SCR τSCR. However, at the UNI or an NNI, where cells at the PCR will have been subjected to delay variation, it should be the limit value for the SCR plus that for the PCR τSCR + τPCR. For variable length packets, the maximum burst size will depend on the lengths