1. A network bandwidth sizing system comprising at least one branch having two or more client computers connected to a datacenter to send an input from a user to the datacenter (uplink) and to receive an output from the datacenter (downlink); the datacenter having one central server comprising a database server, a web server, and an application server for receiving, storing, and processing the input from the user to generate an output and sending the output to the user through a communication network, wherein the system determines a final value for a bandwidth to be allocated to a branch of a network of an enterprise, the system taking into account both throughput and response time requirements, the system having a processor configured to execute programmed instructions to: (a) For each class of transaction (i) expected to be conducted over the branch of the network, compute an average throughput (X i ) if a user inputs an average think time (Z i ) or computing the average think time (Z i ) if the user inputs the average throughput (X i ); (b) Compute an initial value for the bandwidth (B left ) to be allocated to the branch of the network of the enterprise that satisfies the throughput requirement, using the average throughput (X i ) a computed or input for each class of transaction (i) in step (a) and a maximum network link utilization (U i ) provided by the user as input for each class of transaction (i); (c) Compute a feasible value for the bandwidth (B right ) to be allocated to the branch of the network of the enterprise that satisfies the response time requirement, using the average think time (Z i ) computed or input for each class of transaction (i) in step (a) and the initial value computed in step (b) as inputs to an Approximate Mean Value Analysis (AMVA); and (d) Compute a final value for the bandwidth (B) to be allocated to the branch of the network of the enterprise that satisfies both the throughput and response time requirements using the following steps: Repeat Set B=(B left +B right )/2; Call AMVA (B, τ, C, N, Z, P to , P from , O, r, R); If (B is a satisfactory bandwidth) then Set B right =B; else Set B left =B; endif Until (B is a final bandwidth).