The first thing that Call Center owners and IT managers should be looking before they start searching for a new call center VoIP provider is their internet bandwidth or internet speed as some may call it, both the upload and the download are importants to complete a call, when you talk you are sending packages and when your interlocutor talks you are receiving, so both upload/download must be simetric. Let’s say you have 10 computers connected to a predictive dialer making four simultaneous calls per agent at 8kbps (at this point i suppose you are using audio codec g729 on your softphones which compresses the data at 8kbps) each would be 32kbps and those 4 computers will be using other web aplications, CRM’s and even the Dialer web GUI.
Something else that you should be looking for is the reliability of your VoIP provider, if there is at least a little of packet loss, hight latency or jitter your VoIP calls are going to be deficient.
Visit this link to learn how to select the Codec g729 on your Softphone: https://switch2voip.us/contact-support/byod/configuring-your-softphone-x-lite-x-ten-or-eye