Centralized radio access network (CRAN) is getting considerable attention in 5G radio access network infrastructure because of supporting deployments of small cells at a massive scale. In particular, CRAN enables network operators to enhance network coverage and capacity without interference with one cell solution and centralized radio processing. This centralization decreases both the network capital and operational expenditures. However, all these technological advancements bring considerable challenges in the transport infrastructure of 5G such as the evolution of the mobile front haul (FH) interface which imposes strict latency and bandwidth requirements on the transport layer. In this paper, the architectural changes that CRAN brings in 5G cellular networks and the intrinsic demands of the FH transport network is discussed. Different techniques that constrain FH requirements to make it cost-efficient are also surveyed. The overall motivation of this work is to achieve the optimal FH transport solution through a passive optical network.