As the name suggests, this marshaller adds a version short to the start of any stream when writing, enabling similar VersionAwareMarshaller instances to read the version short and know which specific marshaller implementation to delegate the call to. For example, CacheMarshaller200 , is the marshaller for JBoss Cache 2.0.x. JBoss Cache 2.1.x, say, may ship with CacheMarshaller210 with an improved wire protocol. Using a VersionAwareMarshaller helps achieve wire protocol compatibility between minor releases but still affords us the flexibility to tweak and improve the wire protocol between minor or micro releases.