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2 Transport aspects

Appendix XI

Derivation of recommended ODUflex(GFP) bit-rates and examples of
ODUflex(GFP) clock generation

(This appendix does not form an integral part of this Recommendation.)

XI.1 Introduction
The recommended bit-rates for ODUflex(GFP) are provided in Table 7-8. While in principle an ODUflex(GFP)
may be of any bit-rate, there are a variety of reasons for recommending particular rates:
– To encourage a common set of bit-rates which can be expected to be supported by multiple
manufacturers.
– To provide the largest amount of bandwidth possible within a given amount of resource (number
of tributary slots) independent of the ODUk over which the ODUflex(GFP) may be routed.
– To maintain the number of tributary slots required if the ODUflex(GFP) must be rerouted, e.g.,
during a restoration.
– To satisfy a protocol requirement for ODUflex hitless resizing that a resizable ODUflex must occupy
the same number of tributary slots on every ODUk path over which it is carried, and that a resize
operation must always add or remove at least one tributary slot.

XI.2 Tributary slot sizes

ODUflex(GFP) is mapped via GMP into a certain number of 1.25G tributary slots of a HO OPU2, OPU3, or
OPU4 . Each of these have different tributary slot sizes:

238 476columns
OPU 2 _TS   4 STM 16  1249409.62 0 kbit/s  20ppm
237 3808columns
238 119columns
OPU 3 _TS   16 STM 16  1254703.72 9 kbit/s  20ppm
236 3808columns
238 47 5 . columns
OPU 4 _TS   40 STM 16  1301709.25 1 kbit/s  20ppm
227 3808columns

An ODUflex(GFP) that occupies 8 or fewer tributary slots may be routed over OPU2, OPU3, or OPU4. The
smallest tributary slot that may be encountered along the route of the ODUflex(GFP) is that of OPU2. Even
if the initially selected route does not chose a link of OPU2, the ODUflex(GFP) should be sized to a multiple
of the OPU2 tributary slot size to preserve the possibility to restore the ODUflex(GFP) over a route that
includes OPU2 without changing the size of the ODUflex or the number of tributary slots it occupies.
An ODUflex(GFP) that occupies at least 9, but no more than 32 tributary slots may be routed over OPU3 or
OPU4. It does not fit over OPU2. Therefore such an ODUflex may be sized to a multiple of the OPU3
tributary slot size. Even if the initially selected route does not chose a link of OPU3, the ODUflex(GFP)
should be sized to a multiple of the OPU3 tributary slot size to preserve the possibility to restore the
ODUflex(GFP) over a route that includes OPU3 without changing the size of the ODUflex or the number of
tributary slots it occupies.
An ODUflex(GFP) that occupies at least 33, but no more than 80 tributary slots may only be carried via
OPU4, and may therefore take advantage of the full size of the OPU4 tributary slot size.
A small margin must be left between the ODUflex(GFP) size and the integral multiple of the tributary slot
size to accommodate possible clock variation along a sequence of OPUk links without overflowing the range
of Cm in the GMP mapper.

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