(up to about 20 per study group). These subgroups focus on specific areas based on the goals of the current study period (at the time of this writing, the 2017-2020 study period is currently ending). With a new study period can come a change in priorities and focus. As outlined in Chapter 4, the specific section of the ITU-T that is concerned with timing is known as Question 13 (Q13), which is part of Study Group 15 (SG15). Collectively, this group is referred to as Q13/15, and SO the following section deals with this group in more detail. 8.1.1 ITU-T Study Group 15 and Question 13 Study Group 15 develops recommendations that define technical specifications for networks, tech- nologies and infrastructures for transport, access, and home. The 19 individual questions within SG15 encompass a wide range of communications technologies such as passive optical networks (PON), optical fibers, Dense Wavelength Division Multiplexing (DWDM), Course Wavelength Di- vision Multiplexing (CWDM), and digital subscriber line (DSL). The questions also cover various other optical systems, such as optical transport network (OTN), packet transport network (PTN), and metro transport network (MTN). Question 13 of SG15 (abbreviated to Q13 or Q13/15) is responsible for network synchronization and time distribution performance and the recommendations that flow from this work. As a com- ponent of its tasks, Q13/15 also cooperates with several other SDOs, such as the following: Institute of Electrical and Electronics Engineers (IEEE) 1588, for PTP IEEE 802.1 and 802.3, for Ethernet Bellcore/Telcordia Technologies (now a division of Ericsson) and the American National Stand- ards Institute (ANSI), which developed the General Requirements (GR) standards for synchron- ous optical network (SONET) Alliance for Telecommunications Industry Solutions (ATIS), accredited by ANSI and also a sec- tor member and major contributor to the ITU and an organizational partner of the 3GPP 3rd Generation Partnership Project (3GPP), which is the principal organiz