 states the problem at the outset: Table 6.5 Expected Slip Performance in Holdover Stratum Level Slips in Day 1 Slips in Week 1 1 or less 1 or less Source: Ref. 9, Table 5-1, p. 5-2. DIGITAL NETWORKS International digital links will be required to interconnect a variety of national and interna- tional networks. These networks may be of the following form: (a) A wholly synchronized network in which the timing is controlled by a single refer- ence clock. (b) A set of synchronized subnetworks in which the timing of each is controlled by a reference clock but with plesiochronous operation between the subnetworks. (c) A wholly plesiochronous network (i.e., a network where the timing of each node is controlled by a separate reference clock). Plesiochronous operation is the only type of synchronization that can be compatible with all three types listed. Such operation requires high-stability clocks. Thus Rec. G.811 states that all clocks at network nodes that terminate international links will have a long-term frequency departure of not greater than 1 X 10-11. This is further described in what follows. The theoretical long-term mean rate of occurrence of controlled frame or octet (time slot) slips under ideal conditions in any 64-kbps channel is consequently not greater than 1 in 70 days per international digital link. Any phase discontinuity due to the network clock or within the network node should result only in the lengthening or shortening of a time signal interval and should not cause a phase discontinuity in excess of one-eighth of a unit interval on the outgoing digital signal from the network node. Rec. G.811 states that when plesiochronous and synchronous operation coexist within the international network, the nodes will be required to provide both types of operation. It is therefore important that the synchronization controls do not cause short-term frequency departure of clocks, which is unacceptable for plesiochronous operation. 6.12.3 Digital Network Performance Requirements 6.12.3.1 Blocking Probability. 