The scaling of CMOS technology causes a widening gap between the performance of on-chip communication and computation. This calls for a communication-centric design flow. The MANGO network-on-chip architecture enables globally asynchronous locally synchronous (GALS) systemon- chip design, while facilitating IP reuse by standard socket access points. Two types of services are available: connection-less best-effort routing and connection-oriented guaranteed service (GS) routing. This paper presents the core-centric programming model for establishing and using GS connections in MANGO. We show how OCP transactions are packetized and transmitted across the shared network, and illustrate how this affects the end-to-end performance. A high predictability of the latency of communication on shared links is shown in a MANGO-based demonstrator system.