AS is a #logical network segment that contains several Network Devices# especially Routers# under a common administration sharing a common routing strategy. An AS is typically identified using 16-bit autonomous system number (ASN) given by the American Registry of Internet Numbers (ARIN), an Internet Service Provider (ISP) or a network administrator. It is a basic unit in Routing inside AS involves #IGP whereas routing outside AS involves #EGP.
The router inside the AS that connects to other AS is called the edge router.
Summarisation of IP Address will happen when there is a need to transfer the information to different AS.