nable data services, the cable industry uses a system called Data-Over-Cable Service Interface Specification (DOCSIS), which is terminated on a cable modem in the customer premises. DOCSIS has its own timing protocol known as the DOCSIS Time Protocol, or DTP. DTP is used to provide the needed frequency and phase synchronization to the cable modems to build a two-way data network. Phase synchronization is needed to allow the cable modems to cooperate with other modems on the same cable (for instance, to use time-slots for uplink transmission). The requirement for phase in cable is currently somewhat relaxed, generally around a millisecond. However, as cable operators are now wishing to use their cable plants for back-hauling 5G mobile traffic, the synchronization performance will need to equal that of mobile (see Chapters 10 and 11). The basic problem is that DOCSIS previously was carried directly between the CCAP core and the CM, but now this has been replaced with the CIN packet network. As a result, the packet network needs to be able to pass frequency and phase synchronization to both the RPD and core devices. This enables the RPD to re-create the DTP on the coax to synchronize the cable modem and results in the CCAP functions being phase aligned with the CMs via the RPD. Figure 9-38 illustrates how this new timing is applied to the remote PHY architecture. A PRTC with a T-GM providing PTP with (optional) SyncE is placed in this new CIN network. The recommen- ded profile is the G.8275.2 telecom profile for PTS networks, using IP as a transport (many large operators deploy IPv6). Even with an unaware node or so, using PTP in this topology can very read- ily achieve one millisecond of phase alignment. DOCSIS signaling/timing SyncE SyncE Cable Cable modem modem IP/Ethernet fiber network Internet DTP over coax Converged interconnect N/W Cable Cable PTP to DTP modem modem PRTC / T-GM PTPolP Figure 9-38 Remote PHY Timing Architecture Using PTP and SyncE There are some variations on the deployment architecture, depen