1. A method for transmitting a packet by a Moving Picture Experts Group (MPEG) media transport (MMT) transmitting entity in a broadcasting system, the method comprising:identifying an MMT asset that is a data unit for which composition information for presentation and delivery characteristic information for delivery is defined, wherein the MMT asset includes at least one media processing unit (MPU), the at least one MPU comprises one of timed media data or non-timed media data, and a first MPU included in the MMT asset is identified by a unique identifier of the MMT asset and a sequence number of the first MPU in the MMT asset;
generating at least one first MMT packet based on the at least one MPU;
transmitting the at least one first MMT packet,
wherein the method further comprises:
transmitting at least one second MMT packet generated based on the composition information, wherein the composition information includes information for spatial relationship and for temporal relationship among the plurality of MMT assets including the MMT asset; and
transmitting at least one third MMT packet generated based on the delivery characteristic information, wherein the delivery characteristic information includes loss tolerance information indicating whether or not lossy delivery for the asset is allowed.