 profile. The reason for this is that the IEEE 1588 standard views a boundary clock as a component in a sync net- work rather than a bridge between two networks, and all the nodes in a given network have to operate with the same profile to be able to interwork. O-RAN on the other hand views the backhaul and fronthaul networks as separate-as indeed they are in terms of 296 Open Radio Access Network (O-RAN) Systems Architecture and Design Grand Master Front Switch PTP View of Slave Master Slave Network Slave PTS (G8275.1) FTS (G8275.2) DU bridge two PTP network types FIGURE 8-25 Mixed PTP profiles. PTP, Precision time protocol. dataflow-and, therefore, there is no requirement for PTP running on the backhaul net- work synchronizing the O-DU to operate in the same way as PTP on the fronthaul network from the O-DU to the O-RUs, even though time itself is flowing from one network to the other. Instead, the O-DU in this case is actually operating as what is called a gateway clock or Interworking Function by ITU-T. Again, this is something that the ITU-T standards do not currently address beyond acknowledging the existence of, and is another case of the where the need-driven requirements of a standard such as O-RAN precede the more formal adoption of an idea by ITU-T. O-RAN sync equipment requirements We now need to turn our attention away from the network as a whole and concentrate on the requirements of the individual O-RU and O-DU equipment when it comes to synchroni- zation. For the purposes, this discussion we will concentrate on a fronthaul network in an Chapter 8 Synchronization in open radio access networks 297 LLS-C1 or LLS-C2 configuration-in other words, a network in which the O-RUs are all syn- chronized using PTP to their associated O-DU, either through a point-to-point fronthaul link (LLS-C1) or through one or more FSHs of routers (LLS-C2). The O-RAN specification is currently designed to consider two use cases-networks sup- porting contiguous carrier aggregation (Category A) or networks only supporting non