ctively, based on their priority. The three strategies for discarding cells are: 1. Complete buffer sharing with pure pushout - Cells are permitted to pass into the network for transmission until the buffer is full, at which time a new high-priority cell can push out a buffered low-priority cell and new cells push out buffered cells of equal priority. 2. Partial buffer sharing with nested sharing for different loss priorities - A threshold is assigned to each priority and cells of a particular class are allowed to enter the buffer only if the current queue length is less than the corresponding threshold. 3. Expelling policy - Cells are squeezed out by cells of higher priority and when the number of high-priority cells exceeds a threshold, then low-priority cells at the head of the queue are expelled until high-priority cell reaches the head of the queue and is then transmitted. CTD is the elapsed time between a cell's exit at the source and its entry at the des- tination. Subscribers using CBR or Variable Bit Rate - real time (VBR-rt) service categories need to specify this parameter. An IP router attached to an ATM network might delay some cells in order to reduce the peak rate and rate variance without affecting throughput. A Motion Pictures Experts Group (MPEG) code operating in a situation where delay is not a problem might operate in CBR mode. CDV, sometimes called "cell jitter", compares the inter-cell traffic departure of a given connection with its inter-cell arrival. Subscribers to CBR or VBR-rt services must specify this value as a parameter of their desired QoS. Each of these QoS parameters is established in the traffic contract between a sub- scriber and the ATM network. Conformance for CBR, VBR-rt, VBR-nrt and UBR connections are given in the "conformance definition". Provided the subscriber sends ATM User-to-Network Interface (UNI) traffic which conforms to ATM traffic specifications, the network will deliver the QoS that was negotiated. Particular difficulties arise in ATM traffic management becaus