Page 1309 - 5G Basics - Core Network Aspects

Transport aspects 2

Physical layers for data interfaces such as Ethernet and Fibre Channel have historically used a clock
tolerance of 100 ppm. This range is sufficiently wide that specifying this as the clock tolerance for
ODUflex(GFP) can accommodate a variety of mechanisms for generating an ODUflex(GFP) clock and remain
within the clock tolerance range.

ODUk.ts as shown in Table 7-8 is an increment of bandwidth, which, when multiplied by a number of 1.25G
tributary slots, gives the recommended size of an ODUflex(GFP) optimized to occupy a given number of
tributary slots of a server OPUk. These values are chosen to allow sufficient margin that allows the OPUk
and the ODUflex(GFP) to independently vary over their full clock tolerance range without exceeding the
capacity of the allocated tributary slots.
The nominal values for ODUk.ts are chosen to be 186 ppm below the bandwidth of a single 1.25G tributary
slot of a server OPUk. This allows the ODUflex(GFP) clock to be as much as 100 ppm above its nominal rate
and the server OPUk to be as much as 20 ppm below its nominal clock rate, allowing approximately 66 ppm
of margin to accommodate jitter and to ensure that the largest average Cm value even in the worst-case
situation of the OPUk at -20 ppm from its nominal value and the ODUflex(GFP) at +100 ppm from its
nominal value will be one less than the maximum value (i.e., the maximum average Cm is no more than
15231 out of 15232 for ODUflex carried over OPU2 or OPU3, and no more than 15199 out of 15200 for
ODUflex carried over OPU4).

ODU2.ts
Nominal
Nominal
OPUk 1.25G TS
payload bit rate C m Bit-rate per
bit rate out of TS
1523
0
OPU2 9'995'276.962 1'249'409.620 1'249'245.570
1523
2 ODU3.ts
+20 ppm 1'249'270.555
C m Bit-rate per TS
-20 ppm 1'249'220.585 out of
1516 1523
5 0
OPU3 40'150'519.322 1'254'703.729 1'249'184.746 1'254'538.983
1523 1523 ODU4.ts
2 2
+20 ppm 1'249'209.729 1'254'564.074 C m
Bit-rate per TS
-20 ppm 1'249'159.762 1'254'513.892 out of
1458 1464 1519
104'355'975.33 7 9 8
OPU4 1'301'709.251 1'249'212.687 1'254'522.291 1'301'537.974
0 1520 1520 1520
0 0 0
+20 ppm 1'249'237.671 1'254'547.381 1'301'564.004

-20 ppm 1'249'187.703 1'254'497.200 1'301'511.943
nominal 1'249'177.230 1'254'470.354 1'301'467.133
ODUk.t
+100 ppm 1'249'302.148 1'254'595.801 1'301'597.280
s
-100 ppm 1'249'052.312 1'254'344.907 1'301'336.986

Table XI.1 – Generation of ODUflex(GFP) clock from server OPUk clock using fixed Cm

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