TU-T Recommendations for Frequency in Packet Networks The ITU-T frequency timing recommendations for packet networks are divided into two groups, but there is some overlap, SO precise categorization is not always easy. One group includes the recom- mendations that apply to physical timing in a network designed to transfer packets (namely SyncE). The other group includes the recommendations that apply when transporting frequency using the packets themselves (namely PTP and other techniques used with circuit emulation). However, some recommendations, such as G.8261, apply more generally to both cases. The recommendations covered in this section include Packet-based frequency and circuit emulation network limits: G.8261, G.8261.1 Synchronous Ethernet clocks: G.8262, G.8262.1 Carrying timing quality in packet networks (ESMC): G.8264 8.3.1 Packet-Based Frequency and Circuit Emulation This section is still concerned with the transport of frequency, but this time the recommendations are for when a frequency signal is carried using packet-based techniques rather than a physical method. The most common use case for this section is for networks implementing circuit emulation (CEM) as a replacement for end-to-end TDM circuits. But many mobile networks also use these methods to provide frequency synchronization for 2G/3G networks in those circumstances where a physical method (such as SyncE) is either not available or too expensive. G.8261: Timing and Synchronization Aspects in Packet Networks ITU-T G.8261 defines numerous characteristics of frequency synchronization in packet networks. It specifies the limits of network jitter and wander that should not be exceeded. It also stipulates the minimum tolerance of the network node to jitter and wander at the TDM and synchronization inter- faces. From the scope of the recommendation: This Recommendation defines frequency synchronization aspects in packet networks. It specifies the maximum network limits of jitter and wander that shall not be exceeded. It specifies the minimum equ