1、 International Telecommunication Union ITU-T G.7714/Y.1705TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2005) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Data over Transport Generic aspects Transport network control aspects SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE
2、, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Operation, administration and maintenance Generalized automatic discovery for transport entities ITU-T Recommendation G.7714/Y.1705 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NE
3、TWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIE
4、R 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 CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND
5、DIGITAL LINE SYSTEM G.900G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 General G.7000G.7099 Transport network control aspects G.7700G.7799 ETHERNET OVER TRANSPORT
6、 ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.7714/Y.1705 (08/2005) i ITU-T Recommendation G.7714/Y.1705 Generalized automatic discovery for transport entities Summary This Recommendation describes the discover
7、y process for transport entities, their sub-processes and basic interactions in a protocol-neutral manner. Source ITU-T Recommendation G.7714/Y.1705 was approved on 22 August 2005 by ITU-T Study Group 15 (2005-2008) under the ITU-T Recommendation A.8 procedure. Keywords Auto-discovery, discovery age
8、nt, layer adjacency discovery, transport capability exchange. ii ITU-T Rec. G.7714/Y.1705 (08/2005) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a perm
9、anent organ of ITU. ITU-T is responsible for studying 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, establi
10、shes the topics for study by the ITU-T study groups which, 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 stand
11、ards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Reco
12、mmendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents a
13、re used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed In
14、tellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not rec
15、eived notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2006 All rights reserve
16、d. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.7714/Y.1705 (08/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Terms and definitions . 2 4 Abbreviations 2 5 Conventions 3 6 Discovery process overview. 3 7 Disco
17、very trigger process . 4 8 Layer Adjacency Discovery (LAD) 4 8.1 Methods for layer adjacency discovery 5 8.2 Timescales for layer adjacency discovery 6 9 Transport entity capability exchange 7 10 Requirements 8 10.1 Discovery agent 8 10.2 (T)CPs under the responsibility of a Discovery Agent 8 10.3 D
18、iscovery process instance. 8 10.4 Discovery of a transport entity . 8 10.5 Discovery of a unidirectional transport entity 9 10.6 Discovery of a bidirectional transport entity 9 10.7 Discovery of transport entity capabilities. 9 11 Discovery messages 9 11.1 LAD process. 10 11.2 TCE process 11 12 Disc
19、overy state machine descriptions. 11 12.1 LAD state machine. 12 12.2 TCE state machine 15 Appendix I Discovery process state machines 19 Appendix II Mapping of TCE state machine to RFC 1661 LCP state machine . 21 Appendix III Rationale for removal of CELA process. 22 ITU-T Rec. G.7714/Y.1705 (08/200
20、5) 1 ITU-T Recommendation G.7714/Y.1705 Generalized automatic discovery for transport entities 1 Scope This Recommendation describes the discovery process for transport entities (Link Connection, Trail and Network Connection). Their sub-processes and basic interactions within the Discovery process a
21、re described in a protocol-neutral manner. Other aspects of discovery, such as further specification of mechanisms, protocols and how discovery may be used by applications, is outside the scope of this Recommendation. This version of ITU-T Rec. G.7714/Y.1705 allows the discovery process to be used b
22、y the Management Plane as well as the Control Plane1. In this Recommendation, the Discovery Agent is broken down into the following discovery processes: a) Discovery Trigger; b) Layer Adjacency Discovery; c) Transport Entity Capability Exchange. 2 References The following ITU-T Recommendations and o
23、ther references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encourag
24、ed to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone docume
25、nt, the status of a Recommendation. ITU-T Recommendation G.805 (2000), Generic functional architecture of transport networks. ITU-T Recommendation G.806 (2004), Characteristics of transport equipment Description methodology and generic functionality. ITU-T Recommendation G.852.2 (1999), Enterprise v
26、iewpoint description of transport network resource model. ITU-T Recommendation G.853.1 (1999), Common elements of the information viewpoint for the management of a transport network. ITU-T Recommendation M.3100 (2005), Generic network information model. ITU-T Recommendation G.8080/Y.1304 (2001), Arc
27、hitecture for the automatically switched optical network (ASON), plus Amendment 2 (2005). _ 1The 2001 version of ITU-T Rec. G.7714/Y.1705 assumed discovery was limited to use by the Control Plane. 2 ITU-T Rec. G.7714/Y.1705 (08/2005) 3 Terms and definitions This Recommendation makes use of the follo
28、wing terms defined in other ITU-T Recommendations. 3.1 Access Point (AP): See ITU-T Rec. G.805. 3.2 Connection Termination Point (CTP): See ITU-T Rec. M.3100. 3.3 continuity supervision: See ITU-T Rec. G.806. 3.4 Discovery Agent (DA): See ITU-T Rec. G.8080/Y.1304. 3.5 link: See ITU-T Recs G.852.2 an
29、d G.853.1. 3.6 link connection: See ITU-T Rec. G.805. 3.7 network connection: See ITU-T Rec. G.805. 3.8 Subnetwork Point (SNP): See ITU-T Rec. G.8080/Y.1304. 3.9 trail: See ITU-T Rec. G.805. 3.10 Trail Termination Point (TTP): See ITU-T Rec. M.3100. 4 Abbreviations This Recommendation uses the follo
30、wing abbreviations: AP Access Point CI Characteristic Information CP Connection Point CTP Connection Termination Point DA Discovery Agent DCN Data Communication Network DT Discovery Trigger ID Identifier LAD Layer Adjacency Discovery LC Link Connection LCP Link Control Protocol LRM Link Resource Man
31、ager MS Multiplexing Section NC Network Connection NE Network Element PPP Point-to-Point Protocol RS Regenerator Section Rx Receive SNP Subnetwork Point TAP Termination and Adaptation Performer TCE Transport Entity Capability Exchange TCP Termination Connection Point ITU-T Rec. G.7714/Y.1705 (08/200
32、5) 3 TTP Trail Termination Point Tx Transmit VC Virtual Container 5 Conventions In this Recommendation the notation “R-n“ is used to identify requirements. The notation (T)CP is used to represent a TCP or a CP. 6 Discovery process overview The overall discovery process for transport entities is illu
33、strated in Figure 6-1. It is a generic process that is applicable to any layer of multilayer networks as described in ITU-T Rec. G.805. There is no proscribed location or distribution for the entities that support the discovery process (e.g., management systems, NEs, etc.). It shall be possible for
34、the Management Plane to enable and disable the discovery process and individual sub-processes that will be discussed in subsequent clauses. As shown in Figure 6-1, the discovery process is documented for the three sub-processes: Discovery Trigger (DT), Layer Adjacency Discovery (LAD) and Transport E
35、ntity Capability Exchange (TCE)2. The DT process is responsible for triggering the LAD and TCE processes. The DT process is realized through the Discovery Agent (DA). The LAD process is used for deriving an association between two TCPs/CPs that form a network connection/link connection in a particul
36、ar layer network. The association discovered through layer adjacency discovery is valid as long as the trail supporting the link connection is valid. Preconditions of the LAD process include knowledge of the (T)CP IDs. The TCE process is used for exchanging information about the capabilities of the
37、transport entities (e.g., Link Connections, Trails) in order to facilitate the negotiation of an agreed set of capabilities. Preconditions of the TCE process include knowledge of the Layer Adjacency information and the local capabilities information. NOTE If Layer Adjacency has been preconfigured, t
38、he LAD process may be omitted. _ 2TCE was called SCE (Service Capability Exchange) in ITU-T Rec. G.7714/Y.1305 (2001). 4 ITU-T Rec. G.7714/Y.1705 (08/2005) Figure 6-1/G.7714/Y.1705 Discovery sub-process interaction diagram The following clauses describe in detail the sub-processes that encompass dis
39、covery, i.e., DT, LAD and TCE. A detailed description of the interfaces and message exchanges is provided in clause 11. 7 Discovery trigger process The discovery trigger process is enabled by the Management Plane, which specifies the types of scenarios that need to be supported. The scenario profile
40、 has multiple parameters including whether or not particular discovery sub-processes are supported, what type, under what conditions, and what management information needs to be provided under each condition. The default profile is a policy decision. For example: Whether LAD is used. If LAD is not u
41、sed, the Management Plane shall provide (T)CP binding information. If LAD is used, what type (Type 1 or Type 2 as described in 8.1), and under what conditions (return-to-service triggered or continuous as described in 8.2). Whether TCE is used. If TCE is not used, the Management Plane shall provide
42、local and remote end information. If TCE is used, the detailed capabilities of the end point transport entities shall be provided, as governed by policy. 8 Layer Adjacency Discovery (LAD) The discovery process for transport entities takes place on a per-layer basis, consistent with ITU-T Rec. G.805.
43、 The LAD process is used to discover the association between the end points of a link connection (LC) or network connection (NC) within a particular layer (i.e., between the two TCP/CPs that constitute a connection). A pre-condition for the discovery process is that (T)CP IDs shall exist for the end
44、 points being discovered. It shall be possible for the Management Plane to enable and disable the LAD process on a per-(T)CP basis. The LAD process involves the sending of discovery and discovery acknowledgement messages between the end points of a LC or NC in a particular layer, shown as “A“ and “Z
45、“ in Figure 6-1. The LAD process at the A-end starts by periodically sending discovery messages to the Z-end containing information that allows the Z-end to determine the A-ends (T)CP ID and the Discovery Agent (DA) ID scoping the (T)CP ID. When the Z-end has received that message, it sends a discov
46、ery acknowledgement message back to the A-end that contains: the information the Z-end has received from the A-end; ITU-T Rec. G.7714/Y.1705 (08/2005) 5 the information about the Z-end where the discovery message was received. The exchanged information allows both sides to identify the A-Z unidirect
47、ional connection. This process is performed in parallel for the Z-A direction to identify the Z-A unidirectional connection. After both unidirectional connections associated with a (T)CP have been identified, the unidirectional links are verified to be between the same pair of (T)CPs. If they are no
48、t, a misconnection is detected and reported. If the two unidirectional links are between the same pair of (T)CPs, the LAD process is assumed to be complete. The Management Plane may then stop the LAD process or keep it active to continually supervise the adjacency. Figure 8-1/G.7714/Y.1705 Layer adj
49、acency discovery Example The example in Figure 8-1 illustrates discovery processes applied in both the client and server layers to discover layer network topology. Two APs that are associated over a server layer network connection form a trail at the server layer. In this example, the server layer trail supports the association of three pairs of CPs in the client layer to form a client layer link composed of three LCs. Here the LAD process discovers the association between the two TCPs
