Page 1168 - 5G Basics - Core Network Aspects

2 Transport aspects

transparent transcoding (TTT) of the client signal to reduce the bit rate of the signal to fit the OPUk
payload bandwidth;
– constant bit rate client signals into OPU1, OPU2, OPU3 or OPU4 respectively using a client agnostic
generic mapping procedure (GMP) possibly preceded by a timing transparent transcoding (TTT) of
the client signal to reduce the bit rate of the signal to fit the OPUk payload bandwidth;

– other constant bit rate client signals into OPUflex using a client agnostic bit-synchronous mapping
procedure (BMP);

– packet streams (e.g., Ethernet, MPLS, IP) which are encapsulated with the generic framing
procedure (GFP-F);
– test signals;

– continuous mode GPON constant bit rate client signal into OPU1 using asynchronous mapping
procedure (AMP);
– continuous mode XGPON constant bit rate client signal into OPU2 using asynchronous mapping
procedure (AMP);
– FlexE-aware client signal into OPUflex using bitsynchronous mapping procedure (BMP);
– FlexE Client client signal into OPUflex using idle mapping procedure;

– packet streams (e.g., Ethernet, MPLS, IP) which are encapsulated with the Idle mapping procedure
(IMP)

into OPU.

17.1 OPU client signal fail (CSF)
For support of local management systems, a single-bit OPU client signal fail (CSF) indicator is defined to
convey the signal fail status of the CBR and Ethernet private line client signal mapped into an OPU at the
ingress of the OTN to the egress of the OTN.
OPU CSF is located in bit 1 of the PSI[2] byte of the payload structure identifier. Bits 2 to 8 of the PSI[2] byte
are reserved for future international standardization. These bits are set to all-0s.
OPU CSF is set to "1" to indicate a client signal fail indication, otherwise it is set to "0".
NOTE – Equipment designed prior to Edition 3.0 of the Recommendation will generate a "0" in the OPUk CSF and will
ignore any value in OPUk CSF.

17.2 Mapping of CBR2G5, CBR10G, CBR10G3 and CBR40G signals into OPUk

The mapping of a CBR2G5, CBR10G or CBR40G signal (with up to 20 ppm bit-rate tolerance) into an OPUk
(k = 1,2,3) may be performed according to the bit-synchronous mapping procedure based on one generic
OPUk frame structure (see Figure 17-1). The mapping of a CBR2G5, CBR10G or CBR40G signal (with up to
45 ppm bit-rate tolerance) into an OPUk (k = 1,2,3) may be performed according to the asynchronous
mapping procedure. The mapping of a CBR10G3 signal (with up to 100 ppm bit-rate tolerance) into an
OPUk (k = 2e) is performed using the bit-synchronous mapping procedure.
NOTE 1 – Examples of CBR2G5, CBR10G and CBR40G signals are STM-16 and CMGPON_D/U2 (refer to
[ITU-T G.984.6]), STM-64 and CMXGPON_D/U2 [ITU-T G.987.4] and STM-256. An example of a CBR10G3 signal is
10GBASE-R.
NOTE 2 – The maximum bit-rate tolerance between an OPUk and the client signal clock, which can be accommodated
by the asynchronous mapping scheme, is 65 ppm. With a bit-rate tolerance of 20 ppm for the OPUk clock, the client
signal's bit-rate tolerance can be 45 ppm.

NOTE 3 – For OPUk (k=1,2,3) the clock tolerance is 20 ppm. For OPU2e the clock tolerance is 100 ppm and
asynchronous mapping cannot be supported with this justification overhead.

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