s, namely G.8265.1, G.8275.1, and G.8275.2. Although the previously covered recommenda- tions describe the solution, the network, and the clocks, it is the profiles that are implemented on the elements that make up the nodes of the world's networks. If there are any questions about the implementation or interoperability of these protocols during testing, acceptance, initial deployment, or day-to-day operations, then the recommendations on the individual profiles are the place to answer any questions or resolve any disagreements. Commonly, there is only a single profile deployed in a network, but some mobile operators may run a combination of frequency support using G.8265.1 alongside one of the two phase profiles: G.8275.1 and G.8275.2. Note, however, that many network elements only contain enough hardware to implement a single clock, SO it is not possible for them to be a PTP clock in multiple clock do- mains at the same time. See "Chapter 12. Operating and Verifying Timing Solutions", for details on the hardware design of clocks. G.8265.1: Precision Time Protocol Telecom Profile for Frequency Synchronization ITU-T G.8265.1 is the PTPoIP profile used to transport frequency in a packet network. From the scope of the recommendation: The profile specifies the [IEEE 1588] functions that are necessary to ensure network ele- ment interoperability for the delivery of frequency only. The profile is based on the archi- tecture described in [ITU-T G.8265] and definitions described in [ITU-T G.8260]. This Recommendation also specifies some aspects necessary for use in a telecom environ- ment which are outside the scope of, and complement the PTP profile. The profile completes the picture, as it is the protocol implementation that delivers the solution out- lined in the architecture and network topology recommendations. This recommendation includes the following main topics, annex, and appendix: Details on the use of PTP for frequency distribution, including selection of some PTP options available in IEEE 1588-2008. This in