-
Notifications
You must be signed in to change notification settings - Fork 10
/
draft-ietf-ccamp-optical-impairment-topology-yang.xml
7648 lines (7022 loc) · 283 KB
/
draft-ietf-ccamp-optical-impairment-topology-yang.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<?xml version='1.0' encoding='utf-8'?>
<?xml-model href="rfc7991bis.rnc"?>
<rfc
xmlns:xi="http://www.w3.org/2001/XInclude"
docName="draft-ietf-ccamp-optical-impairment-topology-yang-16"
category="std"
consensus="true"
ipr="trust200902"
submissionType="IETF">
<?rfc strict="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="no"?>
<?rfc text-list-symbols="o*+-"?>
<?rfc toc="yes"?>
<front>
<title abbrev="Opt. Impairment-Aware Topo YANG Model">
A YANG Data Model for Optical Impairment-aware Topology</title>
<author initials="D." surname="Beller" fullname="Dieter Beller" role="editor">
<organization>Nokia</organization>
<address><email>Dieter.Beller@nokia.com</email></address>
</author>
<author initials="E." surname="Le Rouzic" fullname="Esther Le Rouzic">
<organization>Orange</organization>
<address><email>esther.lerouzic@orange.com</email></address>
</author>
<author initials="S." surname="Belotti" fullname="Sergio Belotti">
<organization>Nokia</organization>
<address><email>Sergio.Belotti@nokia.com</email></address>
</author>
<author initials="G." surname="Galimberti" fullname="G. Galimberti">
<organization>Individual</organization>
<address><email>ggalimbe56@gmail.com</email></address>
</author>
<author initials="I." surname="Busi" fullname="Italo Busi">
<organization>Huawei Technologies</organization>
<address><email>Italo.Busi@huawei.com</email></address>
</author>
<date year="2024" month="July" day="5" />
<area>Routing</area>
<workgroup>CCAMP Working Group</workgroup>
<abstract>
<t>
In order to provision an optical connection through optical
networks, a combination of path continuity, resource availability,
and impairment constraints must be met to determine viable and
optimal paths through the network. The determination of appropriate
paths is known as Impairment-Aware Routing and Wavelength Assignment
(IA-RWA) for WSON, while it is known as Impairment-Aware Routing and
Spectrum Assignment (IA-RSA) for SSON.
</t>
<t>
This document provides a YANG data model for the impairment-aware TE
topology in optical networks.
</t>
</abstract>
</front>
<middle>
<section title="Introduction" anchor="sect-1">
<t>
In order to provision an optical connection (an optical path)
through a wavelength switched optical networks (WSONs) or spectrum
switched optical networks (SSONs), a combination of path continuity,
resource availability, and impairment constraints must be met to
determine viable and optimal paths through the network. The
determination of appropriate paths is known as Impairment-Aware
Routing and Wavelength Assignment (IA-RWA) <xref target="RFC6566"/>
for WSON, while it is known as IA-Routing and Spectrum Assigment
(IA-RSA) for SSON.
</t>
<t>
This document provides a YANG data model for the impairment-aware
Traffic Engineering (TE) topology in WSONs and SSONs. The YANG model
described in this document is a WSON/SSON technology-specific Yang
model based on the information model developed in
<xref target="RFC7446"/> and the two encoding documents
<xref target="RFC7581"/> and <xref target="RFC7579"/> that developed
protocol independent encodings based on <xref target="RFC7446"/>.
</t>
<t>
The intent of this document is to provide a YANG data model, which
can be utilized by a Multi-Domain Service Coordinator (MDSC) to
collect states of WSON impairment data from the Transport PNCs to
enable impairment-aware optical path computation according to the
ACTN Architecture <xref target="RFC8453"/>. The communication
between controllers is done via a NETCONF <xref target="RFC8341"/>
or a RESTCONF <xref target="RFC8040"/>. Similarly,this model can
also be exported by the MDSC to a Customer Network Controller (CNC),
which can run an offline planning process to map latter the services
in the network.
</t>
<t>
It is worth noting that optical data plane interoperability is a
complex topic especially in a multi vendor environment and usually
requires joint engineering, which is independent from control plane
and management plane capabilities. The YANG data model defined in
this draft is providing sufficient information to enable optical
impairment aware path computation.</t>
<t>
Optical data plane interoperability is outside the scope of this
draft.
</t>
<t>
This document augments the generic TE topology YANG model defined
in <xref target="RFC8795"/> where possible.
</t>
<t>
The optical impairment aware topology for a WSON/SSON network
based on the YANG data model defined in this document is intended to
be used for exposing the network topology including optical
impairments. Therefore, the topology information that is typically
provided by a Transport PNC is assumed to be read-only (ro) data,
i.e., not configurable (read-write). This may change when the same
optical impairment-aware topology model is used for other use cases
than exposing the network topology. E.g, for a path computation
engine, where topological elements could be added in the context of
a what-if scenario analysis. This is outside of the scope of this
document.
</t>
<t>
This document defines one YANG module: ietf-optical-impairment-
topology (<xref target="sect-3"/>) according to the new Network
Management Datastore Architecture <xref target="RFC8342"/>.
</t>
<section title="Terminology" anchor="sect-1.1">
<t>
Refer to <xref target="RFC6566"/>, <xref target="RFC7698"/>, and
<xref target="G.807"/> for the key terms used in
this document.
</t>
<t>
The following terms are defined in <xref target="RFC7950"/> and are
not redefined here:
</t>
<t><list style="symbols"><?rfc subcompact="yes"?>
<t>client</t>
<t>server</t>
<t>augment</t>
<t>data model</t>
<t>data node</t>
<?rfc subcompact="no"?>
</list></t>
<t>
The following terms are defined in <xref target="RFC6241"/> and are
not redefined here:
</t>
<t><list style="symbols"><?rfc subcompact="yes"?>
<t>configuration data</t>
<t>state data</t>
<?rfc subcompact="no"?>
</list></t>
<t>
The terminology for describing YANG data models is found in
<xref target="RFC7950"/>.
</t>
<t>
The term ROADM in this document refers to the term "multi-degree
reconfigurable optical add/drop multiplexer (MD-ROADM)" as defined
in <xref target="G.672"/>. It does not include local optical
transponders, which can be co-located in the same physical device
(managed entity).
</t>
<t>
The term WDM-node refers to a physical device, which is managed as
a single network element.
</t>
<t>
The term WDM-TE-node refers to those parts of a WDM-node (physical
device) that are modeled as a TE-node as defined in
<xref target="RFC8795"/>, which may include a ROADM and/or multiple
local optical transponders(OTs). Hence, a WDM-TE-node may only
contain OTs.
</t>
<t>
The term "WDM-TE-network" refers to a set of WDM-TE-nodes as defined
above that are interconnected via TE-links carrying WDM signals.
These TE-links may include optical amplifiers.
</t>
<t>
The term "add/drop TE-link" refers to a TE-link representing the
media channel between a transceiver's media port of a remote optical
transponder (OT) and an add/drop port of the ROADM in the adjacent
WDM-node. The add/drop TE-link typically carries a single OTSi
signal (modulated optical carrier).
</t>
<t>
The term "bundled add/drop TE-link" refers to the TE-link bundling
concept as defined in <xref target="RFC8795"/>. Multiple component
links, add/drop TE-links in this case, are bundled into a single
bundled add/drop TE-Link.
</t>
</section>
<section title="Tree Diagram" anchor="sect-1.2">
<t>
A simplified graphical representation of the data model is used in
Section 2 of this this document. The meaning of the symbols in
these diagrams is defined in <xref target="RFC8340"/>.
</t>
</section>
<section title="Prefixes in Data Node Names" anchor="sect-1.3">
<t>
In this document, names of data nodes and other data model objects
are prefixed using the standard prefix associated with the
corresponding YANG imported modules, as shown in
<xref target="tab-prefixes-and-corresponding-yang-modules"/>.
</t>
<texttable title="Prefixes and corresponding YANG modules"
anchor="tab-prefixes-and-corresponding-yang-modules" style="full">
<ttcol> Prefix</ttcol>
<ttcol> YANG module</ttcol>
<ttcol> Reference</ttcol>
<c>oit</c>
<c>ietf-optical-impairment-topology</c>
<c>[RFCXXXX]</c>
<c>l0-types</c>
<c>ietf-layer0-types</c>
<c><xref target="I-D.ietf-ccamp-rfc9093-bis"/></c>
<c>nw</c>
<c>ietf-network</c>
<c><xref target="RFC8345"/></c>
<c>nt</c>
<c>ietf-network-topology</c>
<c><xref target="RFC8345"/></c>
<c>tet</c>
<c>ietf-te-topology</c>
<c><xref target="RFC8795"/></c>
</texttable>
<t>
[Editor's note: The RFC Editor will replace XXXX with the number
assigned to the RFC once this draft becomes an RFC.]
</t>
</section>
</section>
<section title="Reference Architecture" anchor="sect-2">
<section title="Control Plane Architecture" anchor="sect-2.1">
<t>
<xref target="Figure-1"/> shows the control plane architecture.
</t>
<figure align="center" title="Scope of RFC AAAA" anchor="Figure-1">
<artwork><![CDATA[
+--------+
| MDSC |
+--------+
Scope of this ID -------> ||
| ||
| +------------------------+
| | OPTICAL |
+---------+ | | DOMAIN | +---------+
| Device | | | CONTROLLER | | Device |
| config. | | +------------------------+ | config. |
+---------+ v // || \\ +---------+
______|______ // || \\ ______|______
/ OT \ // || \\ / OT \
| +--------+ |// __--__ \\| +--------+ |
| |Vend. A |--|----+ ( ) +----|--| Vend. A| |
| +--------+ | | ~-( )-~ | | +--------+ |
| +--------+ | +---/ \---+ | +--------+ |
| |Vend. B |--|--+ / \ +--|--| Vend. B| |
| +--------+ | +---( OLS Segment )---+ | +--------+ |
| +--------+ | +---( )---+ | +--------+ |
| |Vend. C |--|--+ \ / +--|--| Vend. C| |
| +--------+ | +---\ /---+ | +--------+ |
| +--------+ | | ~-( )-~ | | +--------+ |
| |Vend. D |--|----+ (__ __) +----|--| Vend. D| |
| +--------+ | -- | +--------+ |
\_____________/ \_____________/
^ ^
| |
| |
Scope of RFC AAAA Scope of RFC AAAA
]]></artwork>
</figure>
<t>
Note: The RFC Editor will replace AAAA above with the number
assigned to the RFC once draft-ietf-ccamp-dwdm-if-param-yang will
become an RFC.
</t>
<t>
The topology model developed in this document is an abstracted
topology YANG model that can be used at the interfaces between the
MDSC and the Optical Domain Controller (aka MPI) and between the
Optical Domain Controller and the Optical Device (aka SBI) in
<xref target="Figure-1"/>.
It is not intended to support a detailed low-level DWDM interface
model. DWDM interface model is supported by the models presented in
<xref target="I-D.ietf-ccamp-dwdm-if-param-yang"/>.
</t>
</section>
<section title="Optical Transport Network Data Plane"
anchor="sect-2.2">
<t>
This section provides the description of the optical transport
network reference architecture and its relevant components to
support optical impairment-aware path computation.
</t>
<t>
<xref target="Figure-2"/> shows the reference architecture.
</t>
<figure title="Reference Architecture for Optical Transport Network"
anchor="Figure-2">
<artwork><![CDATA[
+-------------------+ +-------------------+
| WDM-Node 1 | | WDM-Node 2 |
| | | |
| PA +-------+ BA | ILA | PA +-------+ BA |
| +-+ | | +-+ | _____ +--+ _____ | +-+ | | +-+ |
--|-| |-| ROADM |-| |-|-()____)-| |-()____)-|-| |-| ROADM |-| |-|--
| +-+ | | +-+ | +--+ | +-+ | | +-+ |
| +-------+ | optical | +-------+ |
| | | | | fiber | | | | |
| o o o | | o o o |
| local | | local |
| transponders | | transponders |
+-------------------+ +-------------------+
OTS MCG OTS MCG
<---------> <--------->
OMS MCG = TE-link
<-------------------------------->
BA: Booster Amplifier (or egress amplifier)
PA: Pre-Amplifier (or ingress amplifier)
ILA: In-Line Amplifier
MCG: Media Channel Group
]]></artwork>
</figure>
<t>
BA (WDM-node 1) is the egress Amplifier and PA (WDM-node 2) is the
ingress amplifier for the OMS Media Channel Group (MCG) in the
direction from left to right in <xref target="Figure-2"/>.
</t>
<t>
According to <xref target="G.807"/>, a Media Channel Group (MCG)
represents "a unidirectional point-to-point management/control
abstraction that represents a set of one or more media channels that
are co-routed. A media channel group (MCG) is bounded by a pair of
media ports."
</t>
</section>
<section title="OTS and OMS Media Channel Group" anchor="sect-2.3">
<t>
According to <xref target="G.807"/>, an
OTS Media Channel Group (MCG) represents a topological construct
between two adjacent amplifiers, such as:
</t>
<figure>
<artwork><![CDATA[
(i) between a WDM-TE-node's BA and the adjacent ILA,
(ii) between a pair of ILAs,
(iii) between an ILA and the adjacent WDM-TE-node's PA.
]]></artwork>
</figure>
<t>
<xref target="G.807"/> defines an OMS MCG as "The topological
relationship between the media port on a filter or coupler where a
set of media channels are aggregated and the media port on a filter
or coupler where one or more media channel is added to or removed
from that aggregate. All of the media channels that are represented
by the OMS MCG must be carried over the same serial concatenation of
OTS MCGs and amplifiers."
</t>
<t>
An OMS MCG originates at the ROADM in the source WDM-node and
terminates at the ROADM in the destination WDM-node traversing the
Booster Amplifier (BA) and the Pre-Amplifier (PA) in the WDM-nodes
as well as the In-Line Amplifiers (ILAs) between the two WDM-nodes.
</t>
<t>
An OMS MCG can be decomposed into a sequence of OTS MCGs and
amplifiers.
</t>
<t>
An OMS MCG traverses a sequence of elements such as BA, fiber
section, ILA, PA, and concentrated loss wherever there is an
insertion loss caused for example by a fiber connector.
</t>
<t>
In TE-topology terms, the OMS MCG is modeled as a WDM TE-link
interconnecting two WDM-TE-nodes. A network controller can retrieve
the optical impairment data for all the WDM TE-link elements defined
in the layer-0 topology YANG model.
</t>
<t>
The optical impairments related to the link between remote optical
transponders, located in a different WDM-TE-node (an IP router with
integrated optical transponders for example), can also be modeled
as a WDM TE-link using the same optical impairments as those defined
for a WDM TE-link between WDM-TE-nodes (OMS MCG). In this scenario,
the node containing the remote optical transponders can be
considered as WDM-TE-node with termination capability only and no
switching capabilities.
</t>
<t>
A WDM TE-link is terminated on both ends by a link termination point
(LTP) as defined in <xref target="RFC8795"/>.
Links between WDM nodes in optical transport networks are typically
bidirectional.
Generally, they have different impairments in the two directions and
hence they have to be modeled as a pair of two unidirectional
TE-links following the <xref target="RFC8795"/> modeling approach.
Unlike TE-links, which are unidirectional, the LTPs on either end
of the TE-link pair forming the bidirectional link, are
bidirectional as described in
<xref target="I-D.ietf-teas-te-topo-and-tunnel-modeling"/> and the
pair of unidirectional links are connected to the same bidirectional
LTP on either end of the link pair.
</t>
<section title="Optical Tributary Signal (OTSi)" anchor="OTSi">
<t>
The OTSi is defined in ITU-T Recommendation G.959.1, section 3.2.4
<xref target="G.959.1"/> as "Optical signal that is placed within a
network media channel for transport across the optical network. This
may consist of a single modulated optical carrier or a group of
modulated optical carriers or subcarriers."
The YANG model defined below assumes that
a single OTSi consists of a single modulated optical carrier. This
single modulated optical carrier conveys digital information.
Characteristics of the OTSi signal are modulation scheme (e.g. QPSK,
8-QAM, 16-QAM, etc.), baud rate (measure of the symbol rate), pulse
shaping (e.g. raised cosine - complying with the Nyquist inter
symbol interference criterion), etc.
</t>
<t>
Path computation needs to know the existing OTSi signals for each
OMS link in the topology to determine the optical impairment impact
of the existing OTSi signals on the optical feasibility of a new
OTSi signal and vice versa, i.e., the impact of the new OTSi on the
existing OTSi signals. For determining the optical feasibility of
the new OTSi, it is necessary to know the OTSi properties like
carrier frequency, baud rate, and signal power for all existing
OTSi signals on each OMS link.
</t>
<t>
Additionally, it is necessary for each WDM-TE-node in the network to
know the OTSi signals that are added to or dropped from an WDM
TE-link (OMS MCG)link as well as the optical power of these OTSi
signals to check whether the WDM-TE-node's optical power constraints
are met.
</t>
<t>
The optical impairment-aware topology YANG model below defines the
OTSi properties needed for optical impairment-aware path computation
including the spectrum occupied by each OTSi signal. The model also
defines a pointer (leafref) from the OTSi to the transceiver module
terminating the OTSi signal.
</t>
<t>
The OTSi signals in the YANG model are described by augmenting the
network and each OTSi signal is uniquely identified by its
otsi-carrier-id, which is unique within the scope the OTSiG [see
<xref target="OTSiG" /> below] the OTSi belongs to.
</t>
</section>
<section title="Optical Tributary Signal Group (OTSiG)"
anchor="OTSiG">
<t>
The OTSiG is defined in ITU-T Recommendation G.807
<xref target="G.807"/> as a "set of optical tributary signals (OTSi)
that supports a single digital client".
Hence, the OTSiG is an electrical signal that is carried by one or
more OTSi's. The relationship between the OTSiG and the the OTSi's
is described in <xref target="G.807"/>, section 10.2.
The YANG model below supports both cases: the single OTSi case
where the OTSiG contains a single OTSi (see <xref target="G.807"/>,
Figure 10-2) and the multiple OTSi case where the OTSiG consists of
more than one OTSi (see <xref target="G.807"/>, Figure 10-3).
From a layer 0 topology YANG model perspective, the OTSiG is a
logical construct that associates the OTSi's, which belong to the
same OTSiG. The typical application of an OTSiG consisting of more
than one OTSi is inverse multiplexing. Constraints exist for the
OTSi's belonging to the same OTSiG such as: (i) all OTSi's must be
co-routed over the same optical fibers and nodes and (ii) the
differential delay between the different OTSi's may not exceed a
certain limit. Example: a 400Gbps client signal may be carried by 4
OTSi's where each OTSi carries 100Gbps of client traffic.
</t>
<t>
All OTSiGs are described in the YANG model by augmenting the network
and each OTSiG is uniquely identified by its otsi-group-id, which is
unique within the network. Each OTSiG also contains a list of the
OTSi signals belonging to the OTSiG.
</t>
<figure align="center" title="MC Example containing all 4 OTSi
signals of an OTSiG" anchor="Figure-3">
<artwork><![CDATA[
OTSiG
_________________________/\__________________________
/ \
m=7
- - - +---------------------------X---------------------------+ - - -
/ / / | | / / /
/ / /| OTSi OTSi OTSi OTSi |/ / /
/ / / | ^ ^ ^ ^ | / / /
/ / /| | | | | |/ / /
/ / / | | | | | | / / /
/ / /| | | | | |/ / /
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12
--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---
n = 4
K1 K2 K3 K4
]]></artwork>
</figure>
</section>
<section title="Media Channel (MC)" anchor="MC">
<t>
<xref target="G.807"/> defines a "media channel" as "A media
association that represents both the topology (i.e., the path
through the media) and the resource (i.e., frequency slot or
effective frequency slot) that it occupies." In this document,
the term "channel" is occasionally used to indicate the resource
of an MC (i.e., frequency slot or effective frequency slot),
without representing topology.
</t>
<t>
In this document, an end-to-end MC is defined as a type of MC,
which is formed by the serial concatenation of all the MCs from
source Transceiver media ports to destination transceiver media
ports.
This end-to-end MC is defined across all the ROADM nodes along the
end-to-end optical path with the same nominal central frequency n
and frequency slot of width m, which represents the effective
frequency slot of the end-to-end MC.
An end-to-end MC can carry a single OTSi, or multiple OTSi signals
belonging to the same OTSiG.
</t>
<t>
<xref target="G.807 Amd1"/> defines a "network media channel (NMC)"
as "a type of media channel that is formed by the serial
concatenation of all media channels between the media port of a
modulator and the media port of a demodulator". The modulator and
demodulator are integral functions of a transceiver and their media
ports do not necessarily coincide with the media port of the
transceiver, which is associated with the transceiver's physical
optical port. Due to this difference, the end-to-end MC is defined
above and is used in this document.
</t>
<t>
In section <xref target="Prot"/>, the term "end-to-end MC path" is
used to describe the topological aspect of the end-to-end MC, i.e.,
the path through the media (see: <xref target="G.807 Amd1"/>,
section 7.1.2). This is in line with the TE path defined in
<xref target="RFC8795"/>, section 3.9, where the TE path is defined
as "an ordered list of TE links and/or TE nodes on the TE topology
graph" interconnecting a pair of tunnel termination points (TTPs).
</t>
<figure align="center" title="MC Example containing both OTSi signals
of an OTSiG" anchor="Figure-4">
<artwork><![CDATA[
m=8
+-------------------------------X-------------------------------+
| | |
| +----------X----------+ | +----------X----------+ |
| | OTSi | | OTSi | |
| | ^ | | | ^ | |
| | | | | | | |
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12
--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+-
| n=4 |
K1 K2
<------------------------ Media Channel ----------------------->
]]></artwork>
</figure>
<t>
The frequency slot of the MC is defined by the n value defining the
central frequency of the MC and the m value that defines the width
of the MC following the flexible grid definition in
<xref target="G.694.1"/>. In this model, the effective frequency
slot as defined in <xref target="G.807"/> is equal to the frequency
slot of this MC. It is also assumed that ROADM devices
can switch MCs.
For various reasons (e.g. differential delay), it is preferred to
use a single MC for all OTSi's of the same OTSiG. It may however not
always be possible to find a single MC for carrying all OTSi's of an
OTSiG due to spectrum occupation along the OTSiG path.
</t>
</section>
<section title="Media Channel Group (MCG)" anchor="sect-2.3.4">
<t>
ITU-T [G.807] defines the Media Channel Group MCG as
"A unidirectional point to point management/control abstraction
that represents a set of one or more media channels that are
co-routed."
The YANG model below assumes
that the MCG is a logical grouping of one or more MCs that are used
to to carry all OTSi's belonging to the same OTSiG.
</t>
<t>
The MCG can be considered as an association of MCs without defining
a hierarchy where each MC is defined by its (n,m) value pair. An MCG
consists of more than one MC when no single MC can be found from
source to destination that is wide enough to accommodate all OTSi's
(modulated carriers) that belong to the same OTSiG. In such a case
the set of OTSi's belonging to a single OTSiG have to be split
across 2 or more MCs.
</t>
<figure align="center" title="MCG Example with 2 MCs"
anchor="Figure-5">
<artwork><![CDATA[
MCG1 = {M1.1, M1.2}
__________________________/\________________________
/ \
M1.1 M2 M1.2
____________/\____________ _____/\_____ ____/\____
/ \/ \/ \
- - - +---------------------------+-------------+-----------+ - - -
/ / / | | / / / / / / | | / / /
/ / /| OTSi OTSi OTSi |/ / / / / / /| OTSi |/ / /
/ / / | ^ ^ ^ | / / / / / / | ^ | / / /
/ / /| | | | |/ / / / / / /| | |/ / /
/ / / | | | | | / / / / / / | | | / / /
/ / /| | | | |/ / / / / / /| | |/ / /
-7 -4 -1 0 1 2 3 4 5 6 7 8 ... 14 17 20
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n=0 n=17
K1 K2 K3 K4
]]></artwork>
</figure>
<t>
The MCG is relevant for path computation because all end-to-end MCs
belonging to the same MCG have to be co-routed, i.e., have to follow
the same path. Additional constraints may exist (e.g. differential
delay).
</t>
</section>
</section>
<section title="Optical Amplifiers" anchor="optical_amps">
<t>
Optical amplifiers are used in WDM networks for amplifying the
optical signal in the optical domain without any optical to
electrical and electrical to optical conversion. Three
main optical amplifier technologies are existing today:
<ul spacing="compact">
<li>Erbium Doped Fiber Amplifiers (EDFAs)</li>
<li>Raman Amplifiers</li>
<li>Semiconductor Optical Amplifiers (SOAs)</li>
</ul>
</t>
<t>
In today's WDM networks EDFAs and Raman amplifiers are widely used.
Raman amplifiers have become attractive due to their large spectral
gain bandwidth, which can be quite flat, with similar or even lower
noise figures compared to EDFAs. On the other hand, Raman amplifiers
consume more power and are usually more expensive than EDFAs.
</t>
<t>
Raman amplifiers are distributed amplifiers where an optical pump
signal is injected typically in opposite direction to the optical
signal that is amplified (backward pump, counter-propagating pump
light). Injecting the optical pump signal in the same direction is
also possible (forward pump, co-propagating pump light).
For optical amplifiers, the YANG model defines Raman pump light
attributes describing the direction (raman-direction) with respect
to the signal that is amplified and optical frequency and power for
the pump light source(s) contained in the raman-pump list. These
Raman amplifier-specific attributes are optional as they are only
applicable to Raman amplifiers. For determining the optical
amplifier type, i.e., to figure out whether an optical amplifier is
a Raman amplifier, the type-variety attribute is used.
Due to the distributed nature of the Raman amplifier it is difficult
to clearly separate the amplifier from the fiber span into which the
pump signal is injected. From a topology modeling perspective, the
Raman amplifier is modeled as two OMS line elements:
</t>
<t>
<list style="numbers"><?rfc subcompact="yes"?>
<t>
a passive fiber element accounting for the fiber loss only
and not the resulting loss including the Raman gain</t>
<t>
an amplifier element providing all optical amplifier properties
(gain, tilt, etc.). On the OMS-link, the amplifier element is
placed where the pump is located and the geolocation information
also indicates the location of the pump.
</t>
<?rfc subcompact="no"?>
</list>
</t>
<t>
Amplifiers can be classified according to their location along the
TE-link (OMS MCG). There are three basic amplifier types: In-Line
Amplifiers (ILAs), Pre-Amplifiers and Booster Amplifiers. ILAs are
separate physical devices while Pre-Amplifiers and Booster
Amplifiers are integral elements of a WDM-node. From a data modeling
perspective, node-internal details should not be modeled and should
be abstracted as much as possible. For Pre-Amplifiers and Booster
Amplifiers, however, a different approach has been taken and they
are modeled as TE-link elements as they have the same optical
impairments as ILAs.
</t>
<t>
ILAs may have a variable optical attenuator on the ingress side
(in-voa attribute) allowing to control the input power of the WDM
signal (OMS MCG) entering the gain stage of the ILA. It may also
have a variable optical attenuator on the egress side, which allows
to control the optical power of the WDM output signal (OMS MCG) of
the ILA. The actual-gain attribute reflects the gain of the ILA gain
stage and does not include the attenuation of the in-voa and/or
out-voa.
</t>
<t>
To support the modeling of multi-band (e.g., C + L band) and
multi-stage (cascaded) amplifiers as depicted in
<xref target="multi-band_multi-stage_amp"/>, the OMS element that
describes an optical amplifier may contain an unordered list of
amplifier-elements. The position of the element is based on the
following attributes:
</t>
<t>
<ul spacing="compact">
<li>
lower-frequency and upper-frequency describing the frequency
band the set of amplifier-elements are operating in.
</li>
<li>
stage-order describing the sequential order of the cascaded
amplifier-elements for the frequency band.
</li>
</ul>
</t>
<t>
The detailed representation of the amplifier stages is not always
mandatory. Abstraction is allowed as long as the optical impairments
of the multi-stage amplifier are modeled properly.
For example, the detailed representation of the cascaded elements is
needed in case the amplifier supports both amplification of the
signal as well as the DGE function described in
<xref target="DGE_subsection"/>.
</t>
<t>
Multi-band amplifiers like the dual-band amplifier depicted in
<xref target="multi-band_multi-stage_amp"/> have a band-separating
filter at the input and a band-combining multiplexer combining all
the bands at the output. This filter and multiplexer functions are
not modeled explicitly and their optical impairments are subsumed
in the optical impairments of the amplifier components.
</t>
<figure align="center" title="Example of a Dual-band, Multi-stage
Amplifier with DGE Functionality" anchor="multi-band_multi-stage_amp">
<artwork><![CDATA[
Dual-band, Multi-stage Amplifier with DGE
+-----------------------------------------------+
| |
| C BAND |
| lower/upper-frequency |
| | |
| +-----------+----------+ |
| | | |
| OA1 DGE OA2 |
| |\ +---+ |\ |
| | \ | | | \ |
--->o---+------------->| +----+ +-----+ +-->+---o--->
| | | / | | | / | |
| | |/ +---+ |/ | |
| | stage-order = 1 2 3 | |
| | | |
| | | |
| | stage-order = 1 2 3 | |
| | |\ +---+ |\ | |
| | | \ | | | \ | |
| +------------->| +----+ +-----+ +-->+ |
| | / | | | / |
| |/ +---+ |/ |
| OA1 DGE OA2 |
| | | |
| +-----------+-----------+ |
| | |
| lower/upper-frequency |
| L BAND |
| |
+-----------------------------------------------+
]]></artwork>
</figure>
<t>
ILAs are placed at locations where the optical amplification of the
WDM signal is required on the TE-link (OMS MCG) between two
WDM-TE-nodes nodes.
Geolocation information is already defined for TE nodes in
<xref target="RFC8795"/> and is also beneficial for ILAs. Therefore,
the same geolocation container has been added to the amplifier
element on an OMS link containing altitude, latitude, and longitude
as optional attributes.
</t>
<t>
One modeling consideration of the ROADM internal is to model power
parameter through the ROADM, factoring the output power from the
Pre-Amplifier minus the ROADM power loss would give the input power
to the Booster Amplifier. In other words, Power_in (@ ROADM Booster)
= Power_out (@ ROADM Pre-Amplifier) - Power_loss (@ ROADM
WSS/Filter).
</t>
</section>
<section title="Dynamic Gain Equalizers" anchor="DGE_subsection">
<t>
A Dynamic Gain Equalizer (DGE) is an optical equipment that is
capable of adjusting the optical power on a per channel basis in
order to compensate the channel power variation as a result of
variable gain or loss the DWDM signals experienced while propagating
through the network. The channel power can be configured explicitly
or in the form of power-spectral-density.
</t>
<t>
[Editor's note: This sub-section needs to be completed and is still
work in progress.]
</t>
</section>
<section title="Transponders" anchor="transponders">
<t>
[Editor's note: The relationship between the transponder and the
OTSi in the YANG model described in <xref target="sect-3"></xref>
needs further clarification and refinement.]
</t>
<t>
A Transponder is the element that sends and receives the optical
signal from a DWDM network. A transponder can comprise one or more
transceivers. A transceiver represents a transmitter/receiver
(Tx/Rx) pair as defined in ITU-T Recommendation G.698.2
<xref target="G.698.2"/>. In addition to the transceiver, which is
terminating an OTSi signal, a transponder typically provides
additional layer 1 functionality like for example aggregation
(multiplexing) of client layer signals, which is outside the scope
of this document addressing layer 0 aspects of transponders.
</t>
<t>
The termination of an OTSi signal by a transceiver is modeled as a
function of the tunnel termination point (TTP) as defined in
<xref target="RFC8795"/>.
Due to the fact that optical transport services (TE tunnels) are
typically bidirectional, a TTP is also modeled as a bidirectional
entity like the LTP described above. Moreover, a TTP can terminate
one or several OTSiG signals (tunnels) as described in
<xref target="I-D.ietf-teas-te-topo-and-tunnel-modeling"/> and each
OTSiG consists of one or multiple OTSi signals as described in
<xref target="OTSiG"/>.
Therefore, a TTP may be associated with multiple transceivers.
</t>
<t>
A transponder is typically characterized by its data/symbol rate
and the maximum distance the signal can travel. Other transponder
properties are: carrier frequency for the optical channels,
output power per channel, measured input power, modulation scheme,
FEC, etc.
</t>
<t>
From a path computation perspective, the selection of the compatible
configuration of the source and the destination transceivers is an
important factor for optical signals to traverse through the DWDM
network.
</t>
<!--<t>
A Transponder is the element that sends and receives the optical
signal from a fiber. A transponder is typically characterized by its
data rate and the maximum distance the signal can travel. Channel
frequency, per channel input power, FEC and Modulation are also
associated with a transponder. From a path computation point of
view, the selection of the compatible source and destination
transponders is an important factor for optical signal to traverse
through the fiber. There are three main approaches to determine
optical signal compatibility. Application Code based on G.698.2
<xref target="G.698.2"/> is one approach that only checks the code
at both ends of the link. Another approach is organization codes
that are specific to an organization or a vendor. The third approach
is specify all the relevant parameters explicitly, e.g., FEC type,
Modulation type, etc.
</t>-->
<t>
The YANG model defines three different approaches to describe the
transceiver capabilities (called "modes") that are needed to
determine optical signal compatibility:
</t>
<t>
<list style="symbols"><?rfc subcompact="yes"?>
<t>Standard Modes</t>
<t>Organizational Modes</t>
<t>Explicit Modes</t>
<?rfc subcompact="no"?>
</list></t>