ISCC ( Inter Server Call Control ) is used by t-servers in a multi-site environment to support call matching and data transfer. Youāll find all the details you need in the āMulti-Site Supportā section of your t-server guide.
I would recommend you to download technical tutorial #39 āUnderstanding Inter Server Call Control (ISCC)ā from Genesys Technical Support web site. It describes what ISCC is and how it works including snippets from T-Server log etc.