1、 International Telecommunication Union ITU-T Series HTELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Supplement 6(04/2006) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSControl load quantum for decomposed gateways ITU-T H-series Recommendations Supplement 6 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL A
2、ND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects H.230H.239 Communication procedures H.240H.259 Coding of moving video H.260H.279 Related sys
3、tems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture for audiovisual and multimedia services H.360H.369 Supplementary services for multimedia H.450
4、H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile multimedia collaboration applications and services H.520H.529 Security for mobile multimedia sy
5、stems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559Mobile multimedia collaboration inter-working procedures H.560H.569 BROADBAND AND TRIPLE-PLAY MULTIMEDIA SERVICES Broadband multimedia services o
6、ver VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. H series Supplement 6 (04/2006) i Supplement 6 to ITU-T H-series Recommendations Control load quantum for decomposed gateways Summary This Supplement defines a baseline for control load metrics for H.248 syst
7、ems with focus on performance engineering parameters relevant for control processing in H.248 network nodes, on correspondent performance design objectives relevant for H.248 network nodes, and on examples of traffic models. Source Supplement 6 to ITU-T H-series Recommendations was agreed on 13 Apri
8、l 2006 by ITU-T Study Group 16 (2005-2008). Keywords H.248, load control, NGN, performance, traffic model. ii H series Supplement 6 (04/2006) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunicatio
9、n Standardization Sector (ITU-T) is a permanent 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 (WT
10、SA), which meets every four years, establishes 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
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16、rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. H series Supplement 6 (04/2006) iii CONTENTS Page 1 Paradigm shift Motivation . 1 1.1 Purpose . 1 1.2 Scope and initial objectives 1 1.3 Linearity assumption 2 2 Refe
17、rences. 2 3 Terminology and definitions. 3 3.1 Session versus Call. 3 3.2 General definitions . 3 3.3 BHxA-related definitions . 4 4 Abbreviations 6 4.1 Mathematical symbols 8 5 Basic model for 2-party communication services 9 5.1 Network model . 9 5.2 Session variants 10 6 Processing performance 14
18、 6.1 Idealized model 14 6.2 Session processing performance. 15 6.3 Context processing performance 15 6.4 H.248 performance classes. 16 7 Capacity 19 7.1 Theoretical capacity 19 7.2 Engineered capacity 19 8 Reference Control Load 19 8.1 Session Processor load parameters. 20 8.2 Context Processor load
19、 parameters 20 9 Session-to-Context relation 21 9.1 Background. 21 9.2 1:1 relationship . 22 9.3 1:N relationship 23 10 Extensions for the basic control load quantum. 25 10.1 Extension factors 25 10.2 Throughput reduction factors . 26 10.3 Reduced effective throughput in case of extended H.248 conte
20、xt processing. 26 Appendix I Fundamental relations 26 I.1 Relation between Effective Multiplication Factor and Extension Factor e . 26 iv H series Supplement 6 (04/2006) Page Appendix II Basic traffic models for H.248 systems 27 II.1 Lost context model . 27 II.2 Overload Control Model. 27 II.3 Combi
21、ned control/user plane model for H.248 Contexts of type “Circuit-to-X“ . 32 II.4 Effective throughput versus Context Holding Time: CoCPS= f(COHT). 36 II.5 Overload Control Model for access gateways 38 II.6 Overload Control Model for ITU-T Rec. H.248.11 . 40 Appendix III Examples of control processin
22、g capacity computations . 42 H series Supplement 6 (04/2006) 1 Supplement 6 to ITU-T H-series Recommendations Control load quantum for decomposed gateways 1 Paradigm shift Motivation The successful control load quantum in traditional circuit-switched networks (CSN): Busy Hour Call Attempts (BHCA), f
23、or a time unit hour, respectively denoted as Call Attempts per Second (CAPS), for a time unit second, as well as the corresponding control performance quantum Busy Hour Call Completions (BHCC), respectively denoted as Call Completions per Second (CCPS), are misleading in H.248 network nodes. NOTE 1
24、“Traditional“ refers to the call definition and control load understanding according to ITU-T Rec. Q.543 4, the control performance framework for digital switching systems. See also ITU-T Rec. Y.1530 5. An H.248-based packet-switched network (PSN) is (1) architecturally different in comparison to le
25、gacy CSNs, particularly in the following three principal aspects: decomposed control structure into H.248 MGC and H.248 MG, whereby the main vertical control processing portion is part of the controller; server approach, by centralizing the distributed control of many legacy switching systems into a
26、 few number of session control servers; and the typical 1:N relation with regard to the MGC-to-MG ratio. It is obvious that any reuse of legacy terminology requires a careful handling and common understanding. NOTE 2 The reuse of BHCA, CAPS, etc., is possible in H.248 environments, particularly in t
27、he scope of PSTN/N-ISDN service emulation. But it is not recommended, particularly due to potential misunderstandings and the PSTN/ISDN extending scope of H.248. Additionally, the architectural motivation for the network is based on a technical incentive that requires a “BHCA mapping“ on H.248 netwo
28、rk nodes: implying that a knowledge of (2) load control and overload protection mechanisms is a prerequisite for understanding the underlying control load quantum. For example, the H.248.11 Overload Control Package defines a tight cooperation principle between a MGC and associated MGs; H.248.11 appl
29、ies the same principles to load quantification. (3) A third aspect concerns relating the pure Packet-to-Packet (Pa2Pa) MG application with session control protocols at a MGC level, i.e., without the presence of a direct call relationship (e.g., 3GPP IP Multimedia Subsystem IMS). 1.1 Purpose This Sup
30、plement introduces BHCOA (Busy Hour Context Attempts) as a baseline control load metrics for H.248 systems, and defines a control load quantum based on a basic H.248 context. It includes the definition of performance engineering parameters relevant for control processing in H.248 network nodes and t
31、he definition of performance design objectives relevant for H.248 network nodes. This Supplement also provides examples of processing capacity calculations. 1.2 Scope and initial objectives The objectives of the current edition are: identification of the need for an extended performance engineering
32、framework in the context of decomposed control platforms; introduction of new terminology (such as BHCoA, BHSA, effective multiplication factor); 2 H series Supplement 6 (04/2006) initial definition of a control processing model; initial definition of H.248 Context-based performance classes; and bas
33、ic relations of load and performance parameters according to the defined performance framework. The initial scope is to achieve consensus on a qualitative basis, the natural next step would be then to commence quantitative performance investigations. 1.3 Linearity assumption Linearity is assumed. Al
34、so, first-order traffic engineering calculations frequently use linearization approximations, particularly in the context of control load estimations (like BHCaA)1. 2 References 1 ITU-T Q-series Suppl. 31 (2000), Technical Report TRQ.2141.0: Signalling requirements for the support of narrow-band ser
35、vices over broadband transport technologies Capability Set 2 (CS-2). 2 ITU-T Vocabulary: SANCHO Database (ITU-T Sector Abbreviations and Definitions for a Telecommunications Thesaurus Oriented database), http:/www.itu.int/sancho. 3 ITU-T Recommendation E.600 (1993), Terms and definitions of traffic
36、engineering. 4 ITU-T Recommendation Q.543 (1993), Digital exchange performance design objectives. 5 ITU-T Recommendation Y.1530 (2004), Call processing performance for voice service in hybrid IP networks. 6 VILLAR (J.E.): Traffic Calculations in SPC Systems, 8th ITC, November 1976. 7 ITU-T Recommend
37、ation E.492 (1996), Traffic reference period. 8 ITU-T Recommendation E.500 (1998), Traffic intensity measurement principles. 9 ITU-T Recommendation E.501 (1997), Estimation of traffic offered in the network. 10 ITU-T Recommendation E.502 (2001), Traffic measurement requirements for digital telecommu
38、nication exchanges. 11 ITU-T Recommendation E.503 (1992), Traffic measurement data analysis. 12 ITU-T Recommendation E.508 (1992), Forecasting new telecommunication services. 13 ITU-T Recommendation E.529 (1997), Network dimensioning using end-to-end GOS objectives. 14 ITU-T Recommendation E.711 (19
39、92), User demand modelling. 15 Generic Requirements for Voice over Packet End-to-End Performance. Telcordia GR-3059-CORE (March 2000). 16 Switching System Overload Control Generic Requirements. Telcordia TR-NWT-001358, (September 1993). 17 LSSGR: Traffic Capacity and Environment. Telcordia GR-517-CO
40、RE (December 1998). _ 1For example, 6: The assumption of a linear relationship between processor occupancy and offered load (BHCA) holds well in steady-state, fault-free conditions with a constant call-type distribution, up to the designed occupancy level for overload capacity. H series Supplement 6
41、 (04/2006) 3 18 ETSI TR 182 015, Architecture for control of processing overload in next generation networks. 3 Terminology and definitions 3.1 Session versus Call The telecommunication network specific term “call“ is often translated to the term “session“ for packet-switched connectionless networks
42、 (e.g., Internet). The notion of a session is also fundamental to IP-based NGN architectures. A session extends the traditional notion of a call in telecommunication networks. An “H.248 session/call“ and the associate creation of an “H.248 Context“ is typically triggered by a specific Call Control P
43、rotocol (e.g., SS7 TUP, SS7 ISUP, BICC, DSS1, H.225/H.245, etc.), or a Session Control Protocol (e.g., SIP, SIP-I, SIP-T, NGN-SCP) events. The differentiation between a “call“ and a “session“ is transparent and is actually not too relevant from an H.248 perspective. Both may be used interchangeably
44、from the Gateway Control Protocol point of view. The key control association is fundamentally the H.248 Context. NOTE 1 ITU-T Rec. E.600 3 defines the individual terms “call“, “call attempt“, and “busy hour“, primarily in the context of BHCaA (Busy Hour Call Attempts). See also the ITU-T terms and d
45、efinitions database 2. NOTE 2 SIP uses the notions of “call“, “session“ and “dialog“ in different aspects (see IETF documents). In order to avoid confusion with the legacy BHCA definition, it is recommended that the terms “BHSA“ and “BHCoA“ be used in the context of H.248 network nodes. That is the
46、reason why the term Session is continuously used in this Supplement. 3.2 General definitions 3.2.1 session/call: Session or Call is a generic term related to the creation, modification and deletion of an H.248 Context (in a MG). Normally, a qualifier is necessary to make clear the aspect being consi
47、dered, e.g., session attempt. This definition is aligned with ITU-T Rec. E.600 3. 3.2.2 session/call attempt: Session/Call Attempt is an attempt to achieve the creation of one or more new H.248 Context(s) in the MG. This definition is aligned with ITU-T Rec. E.600 3. 3.2.3 load: Load means the total
48、 number of the various types of attempts presented to a MGC (e.g., a Call attempt from a PSTN terminal or a Session attempt from a SIP user agent) or a MG (e.g., a Context Attempt by the primary MGC) during a given interval of time (i.e., offered load). This definition is aligned with the performanc
49、e objectives of ITU-T Rec. Q.543 4. 3.2.4 session load: See Figure 1. 3.2.5 context load: MG Context Load; see Figure 1. 3.2.6 processor: Processor denotes the logical entity responsible for all control processing work. The technical realization may be very different, from a single CPU to multi-processor systems, in any form of cluster organization (e.g., distributed, hierarchical, load and/or functional sharing modes, etc.
