y the mobile opera- tor or by a wholesale provider of xHaul services; in most cases the services will be termi- nated by an enhanced cell site gateway. The increased number of cells and the stricter time accuracy requirements will necessi- tate innovative timing solutions. Network dynamicity and slicing require tighter interworking between NMSs (and/or SDN controllers) of transport networks and mobile networks. 6.6.2 Market Drivers To outline major market drivers that steer and shape the xHaul development, let's first ana- lyze the key changes from 4G mobile backhauling to 5G xHaul (more precisely, combined 4/5G xHaul). Figure 6.6.2 depicts a high-level picture of such migration. 4G mobile backhaul (we can neglect the 4G fronthaul as it was commercially deployed in only a few countries) might be characterized by the following essential qualities: On the whole, connecting radio sites to centralized locations that host contents and appli- cations. The exceptional case was the MEC, which was introduced to bring contents closer to users (e.g.with local CDN), but not successful in 4G. Single class-of-services for all applications. Static pre-provisioned connections ("pipes") with star or ring topology; typically, not direct X2 connections between eNBs, but via an aggregation node. Semi-static network management. 5G xHaul dramatically changes these basic features and entails new ones, specifically: 6 Enabling Technologies 4GLTE Internet Content/Apps Backhaul Aggregation P2P/Ring Backbone Backhaul Network Core(s) ((HII)) Internet (v)CU ((III) ) Content Content/Apps xHaul Aggregation ((IIII)) Backbone Content RU+DU (v) DU xHaul Network Figure 6.6.2 Evolution of the backhaul transport network. Connectivity to highly distributed contents and applications that require various trans- port attributes: RAN-related - fronthaul (e.g. CPR/eCPRI) delay, packet delay variation (PDV), HARQ delay, different data rates for different NG-RAN functional splits (see Chapter 4). Application-related - eMBB, URLLC, mMTC use cases with higher