Network emulation provides the capability of evaluating distributed applications on a stand-alone system: Applications can be exposed to adverse and repeatable network conditions without requiring complex testbeds. This paper describes the design and implementation of a portable and object-oriented network emulator targeted to the development and test of Java-based Internet applications. The emulator is based on instrumented sockets, say EmuSockets, able to emulate the behavior of links with a given bandwidth and communication delay. The emulator is organized modularly, so that it is possible to plug-in user-defined classes for bandwidth and delay figures generation. Carrying out experiments with EmuSockets is as simple as running the tested application code on a single host.