一：ODCa、ODCb、ODCr、ODCp的意义：（8251资料里有介绍 ）
This annex contains the requirements for the ODUk Clock (ODC). Here, the term clock refers to a clock filtering and/or generating circuit. Four ODC types are defined, for different applications
(see A.2):
1) ODCa for asynchronous mapping of constant bit rate (CBR) clients (e.g. generic CBRx
client, RS client, etc.) and variable bit rate (VBR) clients (e.g. VP client, GFP client, etc.)
into ODUk, asynchronous multiplexing of ODUj clients into ODUk (k > j), generation
of Test/NULL signals and for AIS and OCI generation;
2) ODCb for bit-synchronous mapping of CBRx clients into ODUk;
3) ODCr for 3R regeneration of the ODUk signal; and
4) ODCp for demapping of constant bit rate (CBR) clients and demultiplexing of ODUj
clients from ODUk (k > j).
The ODCa and ODCb generate the timing signal for the ODUk and OTUk signals produced by an
OTN network element. The ODCr generates the timing signal for the OTUk produced by a 3R
regenerator. The ODCp generates the timing signal for a demapped CBRx client signal or
demultiplexed ODUj signal.
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看来我还是比较聪明的哦！嘿嘿，自己表扬一下！！！