1、 International Telecommunication Union ITU-T H.248.44 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2007) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS Infrastructure of audiovisual services Communication procedures Gateway control protocol: Multi-level precedence and pre-emption package ITU-T
2、Recommendation H.248.44 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND 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
3、 procedures H.240H.259 Coding of moving video H.260H.279 Related systems 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 multim
4、edia services H.360H.369 Supplementary services for multimedia H.450H.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 ap
5、plications and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559 Mobile multimedia collaboration inter-working procedures H.560H.569 BROADBAN
6、D AND TRIPLE-PLAY MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. H.248.44 (01/2007) i ITU-T Recommendation H.248.44 Gateway control protocol: Multi-level precedence and pre-emption package Summ
7、ary This Recommendation defines a package to provide signals and procedures necessary to realize multi-level precedence and pre-emption applications under H.248. While bandwidth and overload control, as well as judicious use of the Priority and Emergency ContextAttributes go a long way toward achiev
8、ing these goals, existing systems also utilize tonal signals to inform end-users about the nature of the traffic, whether their current call is being pre-empted and whether or not their origination is being treated as priority traffic. These systems find a wide range of applications, including milit
9、ary command and control, government priority traffic and many disaster recovery and relief efforts. Priority traffic control and pre-emption are especially important in the time span immediately following a disaster when communications resources may be scarce. Source ITU-T Recommendation H.248.44 wa
10、s approved on 13 January 2007 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. H.248.44 (01/2007) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunica
11、tion 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
12、(WTSA), 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 fa
13、ll within ITU-Ts purview, the necessary standards 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 R
14、ecommendation is voluntary. However, the Recommendation 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 s
15、uch as “must“ and the negative equivalents are 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 Recomm
16、endation may involve the use of a claimed Intellectual 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 appr
17、oval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB
18、patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2007 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. H.248.44 (01/2007) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviation
19、s 1 5 Conventions 1 6 Multi-level Precedence and Pre-emption Package . 1 6.1 Properties 2 6.2 Events. 2 6.3 Signals 2 6.4 Statistics 3 6.5 Procedures 3 Bibliography. 6 ITU-T Rec. H.248.44 (01/2007) 1 ITU-T Recommendation H.248.44 Gateway control protocol: Multi-level precedence and pre-emption packa
20、ge 1 Scope This Recommendation defines a package that provides signals for use with precedence features, such as those used by military, government and disaster recovery applications. The support of this package is optional. 2 References The following ITU-T Recommendations and other references conta
21、in 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 encouraged to investigate the
22、 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 document, the status of a R
23、ecommendation. ITU-T H.248.1 ITU-T Recommendation H.248.1 (2005), Gateway control protocol: Version 3. 3 Definitions This Recommendation defines the following terms: 3.1 precedence: The assignment of a priority level to a call. 3.2 pre-emption: The seizing of resources which are in use by a call of
24、a lower precedence by a higher level precedence call in the absence of idle resources. 4 Abbreviations This Recommendation uses the following abbreviations: eMLPP enhanced Multi-level Precedence and Pre-emption Service IEPS International Emergency Preference Scheme MG Media Gateway MGC Media Gateway
25、 Controller MLPP Multi-level Precedence and Pre-emption 5 Conventions None. 6 Multi-level Precedence and Pre-emption Package Package Name: Multi-level Precedence and Pre-emption Package Package ID: prectn (0x009f) 2 ITU-T Rec. H.248.44 (01/2007) Description: This package defines signals and procedur
26、es for use with precedence and pre-emption features, such as those used by military, government and disaster recovery applications. Version: 1 Extends: None 6.1 Properties None. 6.2 Events None. 6.3 Signals 6.3.1 Preset Conference Notification Tone Signal Name: Preset Conference Notification Tone Si
27、gnal ID: preconf (0x0001) Description: Generate preset conference notification tone, indicating that some conferees have not yet entered the conference. The physical characteristic of preset conference notification tone is available in the gateway. Signal Type: Brief Duration: Provisioned Additional
28、 parameters: None 6.3.2 Preset Conference Precedence Notification Tone Signal Name: Preset Conference Precedence Notification Tone Signal ID: pcprec (0x0002) Description: Generate preset conference precedence notification tone, which is a provisionable alternative to the preset conference notificati
29、on tone. The physical characteristic of preset conference precedence notification tone is available in the gateway. Signal Type: Brief Duration: Provisioned Additional parameters: None 6.3.3 Precedence ringing tone Signal Name: Precedence Ringing Tone Signal ID: precrt (0x0003) Description: Generate
30、 precedence ringing tone, indicating that the call has importance above that of normal calls. The physical characteristic of precedence ringing tone is available in the gateway. Signal Type: TimeOut Duration: Provisioned Additional parameters: None ITU-T Rec. H.248.44 (01/2007) 3 6.3.4 Pre-emption t
31、one Signal Name: Pre-emption Tone Signal ID: preempt (0x0004) Description: Generate pre-emption tone, indicating that the call is being pre-empted for traffic of higher importance. The physical characteristic of pre-emption tone is available in the gateway. Signal Type: Brief Duration: Provisioned A
32、dditional parameters: None 6.4 Statistics None. 6.5 Procedures ITU-T H.248.1 defines the Priority ContextAttribute as an integer taking a value 0-15, with 15 being the highest and 0 being the lowest priority. It also defines two ContextAttributes, Emergency and IEPS, which allow the MGC to mark a co
33、ntext as being used for the purposes of emergency or IEPS calls, respectively. To date, there has been no formal definition of what a particular priority value means, or what the impact of the Emergency or IEPS ContextAttributes are on the priority value. ITU-T H.248.11 makes use of priority to help
34、 in ameliorating overflow at the MG, but no indication as to what a particular priority value really means has been documented. In the function of MLPP, particular calls are defined as being more important than other calls and are designated with named levels. These vary from network to network and
35、from application to application. Table 1 provides several defined priority schemas. This does not imply any linkage between different schemas and is only provided as an informal survey of different priority schemas and their definitions. Please see the appropriate definition specifications to determ
36、ine interaction requirements for a particular schema. 4 ITU-T Rec. H.248.44 (01/2007) Table 1 Existing priority schemas and algorithms Priority DSN/I.255.3 DRSN Q.735.3 ETS WPS eMLPP Flash- Override Flash- Override- Override (Note 1) 0 0 0 A (Note 2) Flash Flash- Override 1 1 1 B (Note 2) Immediate
37、Flash 2 2 2 0 Priority Immediate 3 3 3 1 Routine Priority 4 4 4 2 Routine 3 Highest Lowest 4 MLPP policy Pre-emption Pre-emption Pre-emption Priority Queuing Priority Queuing Both NOTE 1 Flash-Override-Override displaces existing calls, but once established becomes a Flash- Override call for the pur
38、poses of future pre-emptive calls. NOTE 2 A and B are only used on the local switch. For interswitch calls, A and B are treated as 0. In addition to these, one has to consider the possibility that a provider has defined a “less-than- routine“ call service level. This could be a lesser guaranteed lev
39、el of service in exchange for reduced tariffs, for example. While not common in the PSTN today, it is possible in H.248 networks and has to be considered in the scope of the priority discussion overall. In order to account for all these schemas, it is difficult to classify a particular schema as mor
40、e or less important as another schema. Largely, these schemas operate on different networks (military or government networks, as opposed to the PSTN for example) and there is no need to identify how a particular schema aligns with another schema. In terms of H.248, pre-emption is the act of forcibly
41、 removing terminations in order to free up facilities for another higher-precedence call. This allows the seizing of call/bearer resources which are in use by a call of a lower precedence by a higher level precedence call in the absence of idle resources. Ultimately, the decision that a particular c
42、all is more important than another is the domain of the MGC. The Priority, IEPS and Emergency ContextAttributes are useful in allowing the MG to decide which calls to accept and which to reject in the case of overload control. Further, it allows the MG to perform dynamic resource allocation to ensur
43、e that a particular portion of its resources are available to handle higher priority calls that may come later. The priority designation and MLPP functionality are handled completely within the MGC, and any indication to the MG is secondary to the actual execution of the MLPP functions. As indicated
44、 in Table 1, there are two common algorithms, namely, pre-emption and priority queuing. It is conceivable that both algorithms could be present in the same network. The algorithms are presented here for informational purposes: Pre-emption Schemas using a pre-emption policy may disrupt an existing ca
45、ll to make room for a higher-priority incoming call. Since calls may require different amounts of bandwidth or a different number of circuits, a single higher-priority call may displace more than one lower-priority call. ITU-T Rec. H.248.44 (01/2007) 5 Priority queuing In a priority queuing policy,
46、calls that find no available resources are queued to the queue assigned to the priority value. Unless otherwise specified, calls are queued in first-come, first-served order. Each priority value may have its own queue, or several priority values may share a single queue. If a resource becomes availa
47、ble, the MGC reattempts the call from the highest-priority non-empty queue according to the queue service policy. For first-come, first-served policies, the call from that queue that has been waiting the longest is served. Each queue can hold a finite number of pending calls. If the per-priority-val
48、ue queue for newly arriving calls is full, the MGC may deny handling for the call immediately. In addition, a priority queuing policy may impose a waiting time-limit for each priority class, whereby setup times that exceed a specified waiting time are ejected from the queue and the call is deemed to
49、 have failed. Finally, the MGC may impose a global queue size limit summed across all queues and drop waiting lower-priority calls attempts. This does not imply pre-emption, since the call was not previously established. 6 ITU-T Rec. H.248.44 (01/2007) Bibliography b-ITU-T H.460.14 ITU-T Recommendation H.460.14 (2004), Support for Multi-Level Precedence and Preemption (MLPP) within H.323 systems. b-ITU-T I.255.3 ITU-T Recommendation I.255.3 (1990), Community of interest supplementary services: Multi-level precedence and preemption service (MLPP). b-ITU
