terraces Each protocol offers an interface to its users and expects one from the layers on which it builds > Syntax and semantics strike again Data formats Interface characteristics, e.g. IP service model Protocols build upon each other 》 Add value E.g, a reliable protocol running on top of IP 》 Reuse E.g oS provides TCP, so apps don't have to rewrite 66 Interfaces Each protocol offers an interface to its users, and expects one from the layers on which it builds » Syntax and semantics strike again – Data formats – Interface characteristics, e.g. IP service model Protocols build upon each other » Add value – E.g., a reliable protocol running on top of IP » Reuse – E.g., OS provides TCP, so apps don’t have to rewrite