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Definition: packet over SONET

A metropolitan area network (MAN) or wide area network (WAN) transport technology that carries IP packets directly over SONET transmission without any data link facility such as ATM in between. Packet over SONET is intended to transmit data at the highest rates possible, because SONET has a smaller packet header overhead than ATM (28 bytes out of an 810-byte frame compared with 5 out of a 53-byte ATM cell). However, ATM has traditionally provided proven management and quality of service (QoS) for long haul transport. See RPR.

Transporting IP
In a LAN, IP generally runs over Ethernet. In a WAN, it typically is transported by ATM, which rides over SONET, and increasingly, directly over SONET. In the future, it is expected that IP will run directly over DWDM fiber (rightmost diagram).