1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T Series G TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Supplement 54 (07/2015) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Ethernet linear protection switching ITU-T G-series Recommendations Sup
2、plement 54 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIE
3、R TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS
4、 CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRA
5、NSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. G series Supplement 54 (07/2015) i Supplement 54 to ITU-T G-series Recommendations Ethernet linear protection switching
6、Summary Supplement 54 to ITU-T G-series Recommendations provides supplemental information to Recommendation ITU-T G.8031/Y.1342. It provides examples of network application scenarios involving Recommendation ITU-T G.8031/Y.1342. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-
7、T G Suppl. 54 2015-07-03 15 11.1002/1000/12574 _ * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/ 11830-en. ii G series Supplement 54 (07/2015) FOREW
8、ORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying
9、technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups wh
10、ich, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO an
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16、 by any means whatsoever, without the prior written permission of ITU. G series Supplement 54 (07/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 4 Abbreviations and acronyms 1 5 Conventions 2 6 Introduction . 2 7 Ethernet linear protection to support dual parenting pro
17、tection . 2 7.1 Protected Ethernet connection configuration over a PON system . 3 7.2 Solution description 4 7.3 Ethernet elements in a protected Ethernet connection over a dual parented PON 5 G series Supplement 54 (07/2015) 1 Supplement 54 to ITU-T G-series Recommendations Ethernet linear protecti
18、on switching 1 Scope Supplement 54 to ITU-T G-series Recommendations provides supplemental information to ITU-T G.8031. It provides examples of network application scenarios involving ITU-T G.8031. 2 References ITU-T G.984.1 Recommendation ITU-T G.984.1 (2008), Gigabit-capable passive optical networ
19、ks (GPON): General characteristics. ITU-T G.7710 Recommendation ITU-T G.7710/Y.1701 (2012), Common equipment management function requirements. ITU-T G.8013 Recommendation ITU-T G.8013/Y.1731 (2015), OAM functions and mechanisms for Ethernet based networks. ITU-T G.8031 Recommendation ITU-T G.8031/Y.
20、1342 (2015), Ethernet linear protection switching. ITU-T G Suppl. 51 Supplement ITU-T G Suppl. 51 (2012), Passive optical network protection considerations. 3 Definitions None. 4 Abbreviations and acronyms This Supplement uses the following abbreviations and acronyms: AIS Alarm Indication Signal APS
21、 Automatic Protection Switching BNG Broadband Network Gateway CCM Continuity Check Message C-EC Customer Ethernet Connection CPE Customer Premises Equipment EC Ethernet Connection ETH ETHernet MAC Layer FOP Failure Of Protocol GPON Gigabit-capable Passive Optical Network MAC Media Access Control MEG
22、 Maintenance Entity Group MEP Management entity group End Point MEPID MEG End Point Identifier OAM Operations, Administration and Maintenance 2 G series Supplement 54 (07/2015) OLT Optical Line Termination ONU Optical Network Unit PON Passive Optical Network S-EC Service Ethernet Connection SF Signa
23、l Fail SNC/N Subnetwork Connection protection with Non-intrusive monitoring SNCP Subnetwork Connection Protection SNC/S Subnetwork Connection protection with Sub-layer monitoring S-VID Service VLAN Identifier TCM Tandem Connection Monitor UNI User Network Interface VLAN Virtual Local Area Network 5
24、Conventions None. 6 Introduction This Supplement provides supplemental information to ITU-T G.8031. It describes the suitability of ITU-T G.8031 for network technologies (e.g., gigabit-capable passive optical network dual parenting protection ITU-T G.984.1). 7 Ethernet linear protection to support d
25、ual parenting protection Figure 7-1 shows an Ethernet connection between customer premises equipment (CPE) and a broadband network gateway (BNG) over a passive optical network (PON) system and an aggregation backhaul/metro network. The optical line termination (OLT) is the head-end chassis that term
26、inates the PON system on the network side using Ethernet interfaces and the optical network unit (ONU) terminates the PON system on the customer side. Each ONU has one or more user network interfaces (UNIs; Ethernet interfaces) to connect to different CPEs. Although the Ethernet traffic passes throu
27、gh the PON system transparently, the PON system controls the transmissions at a lower layer between the two Ethernet interfaces. Figure 7-1 Elements of a connection between CPE and a BNG over a PON and backhaul G series Supplement 54 (07/2015) 3 In a dual parented type B PON protection configuration
28、 (Figure 7-2), a 2:N optical splitter is used to connect the ONUs to two different OLTs. Figure 7-2 General physical configuration of a dual parented type B PON protection 7.1 Protected Ethernet connection configuration over a PON system Figure 7-3 illustrates the initial connection configuration be
29、tween ONUs and the aggregation Ethernet switch on the network side. Figure 7-3 Initial PON system connection configuration and protected Ethernet connections The ONUs are activated on the “working“ port of OLT A, and the service traffic will flow between ONUs and the Ethernet switch through OLT A. T
30、he “protection“ port in OLT B will be on standby, thus not transmitting, but listening to upstream optical power from all ONUs. Therefore, OLT B in the “protection“ state behaves like an open switch for all Ethernet traffic. It is important to stress that, at any given time, either none or at most o
31、ne OLT PON port is active and passing Ethernet traffic through the OLT. Therefore the optical power splitter, together with the OLT PON ports, is equivalent to a selector bridge and a merging selector. On the backhauling/metro links, a protected Ethernet connection is configured between the Ethernet
32、 switch and the Ethernet UNI at the ONU via the two OLTs. Ethernet operations, administration and maintenance (OAM) messaging must also be configured on all Ethernet connections using ITU-T G.8013. Management entity group end points (MEPs) must be configured at each active UNI 4 G series Supplement
33、54 (07/2015) of each ONU and a maintenance entity group (MEG) formed with its opposite peer or peers in the Ethernet switch. As shown in Figure 7-4, the two ports connecting the Ethernet switch to the two OLTs are associated in a 1:1 subnetwork connection protection (SNCP) switching using ITU-T G.80
34、31. Continuity check messages (CCMs) flow between the two MEPs over the Ethernet connections. To detect the signal fail condition in the upper part of Figure 7-4, the Ethernet switch has two Ethernet MEP sink functions that monitor non-intrusively the working and protection input ports. In the lower
35、 part of Figure 7-4, the Ethernet switch has an Ethernet MEP function on the working and protection input ports. Note that the path through OLT B is interrupted (open connection) as the PON transmitter is turned OFF and the Ethernet traffic is blocked in both directions. Figure 7-4 Ethernet OAM and
36、MEP association for 1:1 SNCP with non-intrusive monitoring (SNC/N) (upper) and 1:1 SNCP with sub-layer monitoring (SNC/S) (lower) protection configurations The Ethernet connections between the UNI and the port at the Ethernet switch are identified by a service virtual local area network (VLAN) ident
37、ifier (S-VID). Such service Ethernet connections (S-EC) may carry a user signal, or an aggregate of customer Ethernet connection (C-EC) signals, each one identified by a customer VLAN identifier. The S-ECs are protected. 7.2 Solution description The restoration solution is illustrated in Figure 7-5.
38、 Upon failure, loss of signal (from all active ONUs) is detected at the active and standby OLT PON ports. The active OLT PON port transits to standby state and turns its transmitter off, thus stopping all Ethernet traffic passing through the OLT, including all CCMs associated with the affected S-ECs
39、. The OLT PON port that was on standby also detects the loss of signal and transits to active state where it turns its transmitter on and takes control of all ONUs in the PON (refer to ITU-T G Suppl. 51). Once the ONUs are reconnected to OLT B, the Ethernet traffic flow on the protection route is re
40、stored and the CCM flows resume over the protection route back to the Ethernet edge switch. G series Supplement 54 (07/2015) 5 Figure 7-5 Restoration solution at a glance for 1:1 SNC/N (upper) and 1:1 SNC/S (lower) protection configurations The Ethernet edge switch asserts a signal fail (SF) conditi
41、on for those S-ECs where CCMs have stopped being received and switches both directions of affected S-ECs traffic together over to the protection route. It is important to note that individual ONUs in the PON are not protected; protection switching is triggered only when the entire PON (i.e., all ONU
42、s) or OLT fails. 7.3 Ethernet elements in a protected Ethernet connection over a dual parented PON The two associated OLT PON ports in a dual parented PON, controlled by their state within the PON system, can interrupt traffic in both directions. At any one time, the PON internal protocol only allow
43、s one of them to be active and transmitting and receiving traffic, while the associated PON port will be on standby blocking all traffic in both directions. In order to establish a protected Ethernet connection, a 1:1 SNCP should be configured in the Ethernet switch. The defect conditions are detect
44、ed by the MEP sink function, which are the inputs to the protection switching process, i.e., based on the local signal OK/failed condition information. On the access side of the protected Ethernet connection, the optical splitter and the two OLT PON ports perform the selector bridge/merging selector
45、 process where automatic protection switching (APS) is not configured. Therefore the ETH_C function in the Ethernet switch, due to the absence of incoming APS messages, will detect the defect failure of protocol (FOP) time out. Although this defect does not result in any consequent action, the assoc
46、iated alarm severity should be configured to “not alarmed“ (see clause 7.1.3.1 of ITU-T G.7710). When holding down the link, the protecting OLT will insert an Ethernet media access control (MAC) layer alarm indication signal (ETH AIS) in the Ethernet connection. The ETH MEP_Sk function will detect t
47、hen the ETH AIS defect. Because this is not a primary alarm condition, its severity should be set to “Not Alarmed“ so that no unnecessary alarm is present. The Ethernet elements for this application are illustrated in Figure 7-6. 6 G series Supplement 54 (07/2015) Figure 7-6 Ethernet elements in a p
48、rotected connection over a dual parented PON for 1:1 SNC/N (upper) and 1:1 SNC/S (lower) protection configurations For the SNC/N protection scenario, the two tandem connection monitor MEPs (TCM MEP) associated with the same MEG are configured in the Ethernet customer port interface of the ONU and in
49、 the up (network facing) port of the Ethernet switch. Unidirectional switching requires the configuration of a TCM MEP sink (TCM MEP_Sk) function on each of the Ethernet switch ports facing the OLT. This TCM MEP_Sk function non-intrusively monitors the signal. These TCM MEP_Sk functions should be added to the same MEG as the two TCM MEP_So functions. For the SNC/S protection scenario, the three MEPs (TCM MEP) associated with the same MEG are configured in the Ethernet customer port in
