1、i CCITT REMCN*In255. 3 90 m 4862593 05633b7 5 m INTERNATIONAL TELECOMMUNICATION UN ION CCITT 1.255.3 TH E INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES MULTI-LEVEL PRECEDENCE AND PREEMPTION SERVICE (
2、MLPP) Recommendation 1.255.3 Geneva 1990 INTERNATIONAL TELECOM M U NI CATI0 N UN CCITT TH E INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE ON 1.255.3 CAPABILITIES MULTI-LEVEL PRECEDENCE AND PREEMPTION SERVICE (MLP
3、P) Recommendation 1.255.3 Geneva 1990 CCITT REMCN*I=255. 3 90 4862593 O563369 9 FOREWORD The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCIIT is responsible for studying technical, operating and ta
4、riff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendat
5、ions by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation 1.255.3 was prepared by Study Group I and was approved under the Resolution No. 2 procedure on 2 July 1990. CCIIT NOTE In this Recommendation, the
6、 expression “Administration“ is used for shortness to indicate both a telecommunication Administration and a recognized private operating agency. O IT 1990 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including
7、photocopying and microfilm, without permission in writing from the ITU. Recommendation 1.255.3 MULTI-LEVEL PRECEDENCE AND PREEMPTION SERVICE (MLPP) 1 Definition The multi-level precedence and preemption (MLPP) service provides prioritized call handling service. This service has two parts - precedenc
8、e and preemption. Precedence involves assigning a priority level to a call. Preemption involves the seizing of resources, which are in use by a call of a lower precedence, by a higher level precedence call in the absence of idle resources. Users in networks that do not support this service will not
9、be affected by this service. 2 Description 2.1 General description The MLPP service is provided as a network providers option to a domain of a network. The domain can be the whole network or a subset of the network. The MLPP service applies to all network resources in the domain that is in common us
10、e. The maximum precedence level of a subscriber is set at the subscription time by the service provider, based on the subscribers need. The subscriber may select a precedence level up to and including the maximum precedence level subscribed to, on a per call basis. Precedence calls (MLPP calls that
11、have a higher precedence than the lowest level of precedence) that are not responded to by the called party (e.g. call unanswered and/or unacknowledged, called party busy with call of equal or higher precedence, or called party busy and non-preemptable) are diverted to a predetermined alternate part
12、y. This alternate party may be another subscriber or a network operating position. Preemption may take one of two forms. First the called party may be busy with a lower precedence call which must be preempted in favour of completing the higher precedence call from the calling party. Second, the netw
13、ork resources may be busy with calls, some of which are of lower precedence than the call requested by the calling party. One or more of these lower precedence calls must be preempted to complete the higher precedence call. There are three characteristics of preemption: - any party whose connection
14、was terminated (whether that resource is reused or not) must receive a distinctive preemption notification; - any called party of an active call that is being preempted by a higher precedence call should be required to acknowledge the preemption before being connected to the new calling party (see 0
15、 2.2 for definition of active call); and - when there are no idle resources, preemption of the lowest lower level of precedence resources shall occur. A call can be preempted any time after the precedence level of the call has been established and before call clearing has begun. The MLPP service is
16、not intended to provide preemption of users that do not subscribe to the MLPP service. The service provides for preemption of calls within the MLPP domain, which consists of the resources belonging to the users that subscribe to the MLPP service. In other words, calls that are originated by, or made
17、 to, non-MLPP users will not be preempted. Calls that are originated by MLPP subscribers may be preempted by calls of higher precedence only in networks that support this service. Recommendation 1.255.3 1 CCITT REMCN*Im255. 3 i0 m 48b2591 05b1171 7 2.2 Specifc terminology Precedence is the priority
18、associated with a call. Aprecedence call is a call with precedence level higher than the lowest level of precedence. An MLPP call is a call that has a precedence level established and is either being set up (Le. before alerting) or is set up. User A is a party of the MLPP call and is not the called
19、party of the precedence call. User B is the other party of the MLPP call and is the called party of the precedence call. User C is the party who initiates the precedence call to user B. An active call is a call that has the connection established and the calling and called parties are active on the
20、call. Response timer TK is started when the service provider notifies the called user of a precedence call (for example, this would be the preemption notification if preemption occurs at the user interface). This timer establishes the time that user B has to accept the precedence call from user C. T
21、he length of this timer is in the range of 4-30 seconds. An alternate party is the party to which a precedence call will be diverted. Diversion will occur either when the response timer TK expires, when the called party is busy on a call of equal or higher precedence, or when the called party is bus
22、y with access resources non-preemptable. Alternate party diversion is an optional terminating feature that is subscribed to by the called party; thus, the alternate party to which a precedence call is diverted is specified by the called party at the time of subscription. 2.3 Qualifeations on the app
23、licability to telecommunications services This supplementary service is considered meaningful when applied to the telephony teleservice, speech, 3.1 kHz audio, 7 kHz audio, and 64 kbit/s unrestricted bearer services. Furthermore, it may be meaningful when applied to other services. 3 Procedures 3.1
24、Provisionlwithdrawal For a given ISDN number, a maximum authorized precedence level may be subscribed to for each service or collectively for all services. The service provider should provide the capability of combining 3.1 kHz audio and speech for the purpose of assigning subscription options. Subs
25、criber options are summarized below: 2 Recommendation 1.255.3 Subscriber options Maximum authorized precedence levela) Alternate party Access resource non-preemptableb) Value - O (Flash Ovemde: highest) - 1 (Flash) - 2 (Immediate) - 4 (Routine: lowest) - 3 (Priority) - NO - Yes - network operating p
26、osition - alternate party directory number - NO - Yes A call of higher precedence level can preempt calls of lower precedence. For example, a Flash call can preempt Immediate, Priority, or Routine cab. A user having this option will not experience preemption of calls by higher precedence calls, if t
27、he cause for preemption would be due to called party busy condition. However, the user may still experience preemption of calls due to a lack of service provider resources other than the users own access resources. b) 3.2 Normal procedures 3.2.1 Activationldeactivationlregistration (None identified.
28、) 3.2.2 Invocation and operation The precedence level is selected by the subscriber on a per call basis. The subscriber may select any precedence level up to and including his maximum authorized precedence level. The service provider at the subscribers originating interface ensures that the selected
29、 precedence level does not exceed the maximum level assigned to that ISDN number. Once set for a cail, this precedence level cannot be changed. An MLPP call is automatically established with the lowest precedence unless a higher precedence is specified. 3.2.3 Operation During a call Set-up, if there
30、 is shortage of some resource, then the network can determine if resources are held by calls of lower precedence. The network can then release the lowest lower precedence call(s) and seize the necessary resources that are required to set up the higher precedence call. These resources can include int
31、er-office circuits, channels, conference bridges, and circuit-switched data circuits. The preemption operation depends on whether the network needs to preempt a common network facility such as an inter-switch trunk which is currenty being used by a different subscriber than the intended called subsc
32、riber or whether it needs to preempt a channel on the user access of the desired called subscriber. If a common network facility is preempted, both existing parties concerned are notified of the preemption and the existing connection is immediately disconnected. The new call is then set up using the
33、 preempted facility in the normal manner without any special notification to the new called party. If a called user access channel is to be preempted, both the cailed and non-called parties shall be notified of the preemption and the existing MLPP call shall be immediately cleared. The called party
34、must acknowledge the preemption before the higher precedence call is completed. The called party is then notified that a new MLPP call is available. Recommendation 1.255.3 3 CCITT RENCN*I*255. 3 90 W 48b2591 05b1373 O 3.3 Exceptional procedures 3.3.1 Activationldeactivationlregistration (None identi
35、fied.) 3.3.2 Invocation and operation If the service provider cannot comply with a precedence call request, the calling party should receive a a) b) c) d) notification that the precedence call is unsuccessful. Possible causes are: the requested precedence level is not subscribed to; equal or higher
36、precedence calls have prevented completion; the dialled number is non-preemptable; and there are no idle network resources to make a connection to the dialled number and the called subscriber belongs to a network that does not support preemption. A precedence call should be diverted to a predetermin
37、ed alternate party, which can be another subscriber or a network operating position, if the called party (user B) does not acknowledge preemption or does not answer a precedence call (a call of precedence level 0-3) before the response timer TK expires. To prevent infinite diversions, an alternate p
38、arty diversion is limited to a total of five alternate party diversion attempts. Once this limit is reached, no additional diversion attempts will be made. In the case of preemption at the user interface, if no alternate party has been specified by the called party, an unacknowledged indication will
39、 be returned for the precedence call. In addition, a precedence call should be diverted to a predetermined alternate party if the called party is busy on a call of equal or higher precedence or is busy and non-preemptable. To prevent infinite diversions, an alternate party diversion is limited to a
40、total of five alternate party diversion attempts. Once this limit is reached, no additional diversion attempts will be made. If no aiternate party has been specified by the called party, a precedence call blocked notification will be returned to the calling party for the precedence call. 4 Network c
41、apability for charging This Recommendation does not cover charging principles. Future Recommendations in the D-Series are expected to contain that information. It shall be possible to charge the subscriber accurately for the service. 5 Interworking considerations In public networks that support the
42、MLPP service, the network shall ensure that only MLPP calls from the same domain as the preempting call are a subject of preemption and that the connections of non-MLPP users are not preempted. The precedence level of a call may not be changed when interworking with other MLPP networks. A network th
43、at does not support the MLPP service is required, if bilaterally agreed, to convey the parameters of the MLPP service intact. If the parameters are received from another network, the network should pass them on with no action taken, if bilaterally agreed, and with no effect on the network that does
44、not support the MLPP service. 6 Interaction with other supplementary services The following interactions with other supplementary services apply within the MLPP domain. 6.1 Call Waiting a) The incoming call is of the lowest precedence level (precedence level 4): 1) one or more MLPP calls are of the
45、lowest precedence level: no interaction; call waiting service is invoked. 4 Recommendation 1.255.3 CCITT REflCN*Ie255- 3 90 m qBb2591 0561174 i! 2) all MLPP calls are precedence calls: Call Waiting service is invoked. If the in-band call waiting tone is being applied as a network provider option, th
46、en the tone should not be provided in this case since it would disrupt a higher precedence call. b) The incoming call is a precedence call: One or more MLPP calls are of lower precedence than the incoming call: An MLPP call of the lowest precedence level is preempted unless the called subscriber is
47、non- preemptable. If the called subscriber is non-preemptable, Call Waiting service is invoked and the precedence level of the incoming call is provided to the called user along with call waiting indication. one or more MLPP calls are of the same precedence and the rest of the MLPP calls are of high
48、er precedence than the incoming call: Call Waiting service is invoked. The precedence level of the incoming call is provided, along with call waiting indication, to the called users on MLPP calls at the same precedence level as the incoming call. If the called user is on an MLPP call at a higher pre
49、cedence level, Call Waiting service is invoked. If the in-band call waiting tone is being applied as a network provider option, then the tone should not be provided in this case, since it would disrupt a higher precedence call. All the MLPP calls are of higher precedence: Call Waiting service is invoked. If in-band call waiting tone is being applied as a network provider option, then the tone should not be provided in this case since it would disrupt a higher precedence call. 6.2 Call Transfer For a single step or a normal call transfer, the precedence level of calls is
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