 For cases where multiple links share the same synchronization source, the concept of a bundle of ports is introduced in ITU-T G.781. And the recommendation is that an NE is required to generate QL-DNU (do not use) or QL-DUS (do not use for synchronization) on all the ports of the bundle, when any one of them has been selected as the reference source. This use of DNU/DUS on all ports of a bundle makes sure that timing loops are avoided for links made up of a bundle of ports. 6.6.1 Enhanced ESMC Although ESMC has worked well to carry quality levels in Ethernet packet networks, now there are new, more accurate, enhanced clocks being specified by the ITU-T. The previously existing ESMC specification was not able to describe the quality of these new clocks, SO the ITU-T has defined new enhanced ESMC (eESMC) values to describe the new clock types. These clock types include en- hanced versions of both the PRC/PRS and the PRTC. This change was made to reflect the new SSM values that the ITU-T introduced into G.781 for the same reason. In addition, ITU G.8262.1 specifies an enhanced Ethernet equipment clock (eEEC), which also needs a new ESMC value to describe it. Amendment 1 of ITU-T G.8264 (2018-03) defines these new eESMC values for these enhanced clock types. The new SSM codes for eESMC are referred to as enhanced SSM (eSSM) codes, and the value is carried in an enhanced QL TLV. Table 6-5 de- scribes the formats of the fields in the enhanced QL TLV from the amended G.8264. Table 6-5 Enhanced QL TLV Format Octet Number Size/bits Field 8 bits Type: 0x02 16 bits Length: 00-14 8 bits Enhanced SSM code 64 bits SyncE clockIdentity of the originator of the extended QL TLV 8 bits 8 bits Number of cascaded eEECs from nearest SSU/PRC/ePRC 8 bits Number of cascaded EECs from nearest SSU/PRC/ePRC 16-20 40 bits Reserved Source: ITU-T G.8264, Table 11-5 Note that the normal QL TLV (refer to Table 6-4) is always sent as the first TLV in all the ESMC PDUs (for both EECs and eEECs), and any clock supporting eESMC includes the enhance