1、 _ - CCITT RECMN*E*820 72 M 4862571 0576537 708 INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING E.820 (1 0/92) CALL MODELS FOR SERVEABILITY AND SERVI
2、CE INTEGRITY PERFORMANCE Recommendation E.820 FOREWORD The CCIT (the International Telegraph and Telephone Consultative Committee) is a perm,anent organ of the International Telecommunication Union (ITU). CCIT- is responsible for studying technical, operating and tariff questions and issuing Recomme
3、ndations 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 Recommendations by the members of CCIT betwee
4、n Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation E.820 was revised by Study Group II and was approved under the Resolution No. 2 procedure on the 30th of October 1992. CCIT NOTE In this Recommendation, the expression “Administrati
5、on” is used for conciseness to indicate both a telecommunication administration and a recognized private operating agency. O ITU 1993 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and micro
6、film, without permission in writing from the ITU. CCITT RECNN*E.BZO 92 W 4862593 0576541 366 W Recommendation E.820 CALL MODELS FOR SERVEABILITY AND SERVICE INTEGRITY PERFORMANCE (revised 1992) Introduction This Recommendition is one of a set of closely related Recommendations concerned with accessi
7、bility and retainability of the telephone service, as listed below. The CCITT, considering (a) that there is a desire to establish overall objectives for the Quality of Service as perceived by the users; (b) that such objectives can then be used as a basis for the design, planning, operation and mai
8、ntenance of telecommunication networks and their components parts; (c) that a model is necessary in order to relate the various serveability and integrity measures to the different call phases; (d) that Recommendation E.800 contains terms and definitions for the Quality of Service, reliability and a
9、vailability performances and related characteristics of the service and network, recommends that the call models given in this Recommendation shall be used by Administrations to design, plan, operate ,and maintain their networks, taking into account the objectives given in Recommendations: E.845 Con
10、nection accessibility objectives; E.850 Connection retainability objectives. Note - Refer also to Recommendation E.830: Models for allocation and evaluation of serveability and service integrity. 1 Call models for serveability and integrity performance The simplified models given in 5 3 illustrate t
11、he main phases of different types of calls. It also interrelates these phases to the service-related performance concepts and their principle measures as well as to the main causes of failure in the establishment and retention of such a call and its subsequent billing. The models also indicate where
12、, in this series of phases, user actions or mistakes may influence the call. 2 Comments to the models and their applications 2.1 Contributions to causes of cull failitre It is generally recognized that the various parts of a national or international network may be of different importance to the suc
13、cessful completion of the vrarious phases of a call. For example, the network accessibility is mainly determined by the telephone set, the subscriber line and the local exchange; the connection accessibility by the exchanges, uransmission network and signalling network used; the billing integrity is
14、 dependant on the charging facilities used by the network parts that constitute the connection and the equipment for processing the billing information, etc. In some Administrations, the telephone set is not considered as a part of the network and in that case it is not included in the concepts of n
15、etwork performance. Recommendation E.820 (10/92) 1 - CCITT RECMN*E.BZO 92 M LI862591 05765Y2 2T2 M 2.2 Time aspects of measures Depending on the intended application of the measures indicated in the call models, it may be appropriate to express these measures by the distribution. Consequently the di
16、stribution may be estimated taking appropriate sampling intervals, over a sufficiently long observation time, in order to get enough data for covering rare situations. 2.3 Space aspects of averages The measures as indicated in call models could be applied to calls between particular destinations as
17、traffic weighted averages over a number of destinations, etc. However it should be noted that several averages may mask the user perception, particularly when there is a large spread among the different directions. In this case, better information is given by the distribution of measures over the di
18、fferent directions. Each relevant Recommendation should clearly specify which alternative(s) to use. 3 3.1 3.1.1 3.1.2 3.1.3 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 2 Call models Call models for services supported by telephone network Telephone call See Figure 1E.820. Facsimile call See Figure 2lE.820. Da
19、ta call For further study. Call models for services supported by ISDN Circuit switched “overlap sending” See Figure 3lE.820. Circuit switched “en bloc sending” See Figure 4lE.820. Virtual call “Packet Terminal See Figure 5E.820. Virtiial call “non Packet Terminal” See Figure 6lE.820. Telex See Figur
20、e 7E.820. Recommendation E320 (10/92) Call hases accessibility, Pl (Note 1) Call detection Dial tone sending delay tone delay I Dial tone received i I A-subscriber : dials the I : B-subscriber Dialling : number ,(Note 2) f The call is routed to its destination I Post- dialling : Ringing : signal I T
21、ime to answer -Relea=- (The billing information is cdlected and presented to the user of the telephone service) I (Human factor related) Pjl Examples of causes of call failure Excessive dial tone delay User abandons the call attempt Dialling mistake Misrouting No tones Connection Excessive through-c
22、onnection (Note 1) Unacceptable transmission accessibility, P12 delay quality Congestion Premature release Connection retainability, i+ 41) Release failure (Note 4) Billing integriy, P4 (Note 5) Incorrect charging Incorrect billing TOZO3780-93 Note I -Network accessibility and connection accessibili
23、ty combine into service accessibility. Note 2 -The routing of the call may start before all digits have been received. Note 3 -The shaded area shows that a premature release can occur during the time to answer. Nofe 4 - The release of a call is not a separate phase in this model. A release failure m
24、ay result in network inaccessibility for a new cai. Note 5 -The biiiing integrity has been shown for completeness, but is not a part of serveability performance. FIGURE 1E.820 Moel of the serveability performance on a basic call in the telephone network Recommendation E.820 (10/92) 3 CCITT RECflN*E.
25、BZO 92 W 4862591 0576544 075 T.30 O Call phases - A A-subscriber goes off-hook Call detection Dial tone tone delay sending delay Deal I Dial tone received A-subscriber dials the : B-subscriber number I Dialling Phi The call is routed to its destination Post- dialling t : Ringing : signal I Time to a
26、nswer : Answer : Communication I I Communication iase - eA - 3B - Release (The billing information is collected and presented to the user of the I telephone service) 4 Related measures in PSTN Network accessibility, Pi, (Human or terminal factor related) p31 Connection retainability, P, (Human or te
27、rminal I Connection retainability, P, Recommendation E.820 (10/92) Related measures in facsimile call Terminal A availability, Pt , , Terminal A reliability, Pt, Billing integrity, P4 El TO203790-93 Note 1 - The biing integrity has been shown for completeness but is not a part of serveability perfor
28、mance. Note 2 -Terminal availability contains the factor in Phase A and B in Recommendation T.30. Note 3 - Terminal reliability contains the factor in Phase C, D and E in Recommendation T.30. Note 4 -The duration may depend on the network conditions. FIGURE 2E.820 Madel of the serveability performan
29、ce on a basic facsimile call g I_. CCITT RECNN*E*BZO 72 4462571 0576545 TO1 w A-subscriber and/or 4 B-subscriber go on-hook (hang up) Call phases o A-subscriber sets service t : information Dialling A-subscriber indicates service information to the network Information I Setup ack- nowledgement delay
30、 processed Setup acknowledgement call information : (B-subscriber Dialling . number, etc.) , (Note 2) tim (Cal procedure received) The cai1 is routed to its destination I I Post- dialling delay I : : Ring back indication Time to (pick-up) (RBI stops) Communication data flow I Call durr A Release (di
31、sconnect) information is collected and presented to the user of the telephone service) Related measures (Human factor related) 40 Network accessibility, Pi (Note 1) Examples of causes of cai1 failure Excessive dial tone delay Requested service not available I I User abandons the call Dialling mistak
32、e (Human factor related) psi attempt Connection accessibility, Pi2 (Note 1) Misrouting No tones Excessive through-connection delay Unacceptable transmission Zi$L.tion Terminal no answer (results in reception of disconnect) Connection retainability, P2 Premature release (cutoff call) (Note 4) Release
33、 failure (disconnect) T02038w-93 Noie I - Network accessibility and connection accessibility combine into service accessibility. Note 2 -The routing of the call may start before ali digits have been received (overlap). Note 3 -The shaded area shows that a premature release can occur during the time
34、to answer. Nore 4 - nie release of a call is not a separate phase in this model. A release failure may result in network inaccessibility for a new call. Note 5 -The billing integrity has been shown for completeness, but is not a part of serveability performance. FIGURE 3fi.820 Model for serveability
35、 performance on a basic circuit-switched call in ISDN based on “overlap sending Recommendation E.820 (10/92) 5 - -_ CCITT RECflN*E-820 72 4862573 O576546 74 Call phases O : A-subscriber sets service : information (service type, i destination number, etc.) Dialling time Related measures (Human factor
36、 related) hi End of dialling all call information) Call detection (Call proceeding received) dialling The call is routed to its destination ? Ring back indication Post- delay Time to answer (pick UP) Answer (B-subscriber off-hook) (RBI stops) t Communication (data flow) I Call duration A-subscriber
37、and/or B-subscriber go on-hook (hang up) Release (disconnect) (The billing information is collected and presented to the user of the telephone service) Network accessibility Connection accessibility (Note 1) i pi1 xp12 Examples of causes of call failure User abandons the call attempt Dialling mistak
38、e Misrouting No tones Excessive through-connection delay Unacceptable transmission ZE$Ltion Terminal no answer (results in reception of disconnect) Connection retainability, P2 I (Note 3) Billing integrity, P4 (Note 4) Premature release (cutoff call) Release failure (disconnect) Incorrect charging I
39、ncorrect billing TO20381 0-93 Note I - Network accessibility and connection accessibility combine into service accessibility. Note 2 - The shaded area shows that a premature release can occur during the time to answer. Note 3 - The release of a call is not a separate phase in this model. A release f
40、ailure may result in network inaccessibility for a new d. Note 4 -The billing integrity has been shown for completeness, but is not a pari of serveability performance. FIGURE 4E.820 Model for serveability performance on a basic circuit-switched call in ISDN based on ?en bloc sending? 6 Recommendatio
41、n E.820 (10192) Virtual call Dhases O : A-subscriber initiates a call ! A-subscriber sets call information : (destination number, etc.) A-subscriber (presses start-key) (Level 2 process) A-DTE sends call request packet / T The call is routed to its destination Call connection delay A-DTE receives ca
42、ll connected packet Data transfer A-DTE sends clear request packet 01 receives clear indication packet T Call A-subscriber receives a clearing clear confirmation packet (Note 3) or send clear confirmation packet initiated by B-subscribers request Examples of causes Related measures of call failure (
43、Human factor Excluding cases where a related) Network accessibility, Pll (Note 1) Connection accessibility, P12 (Note 1) Connection retainabiliity, P2 (Note 1 (The billing information is collected) Billing integriiy, P4 (Note 5) I I I basic computer initiates calls) Link level inactive Congestion /
44、the A-subscriber) (This is not known by Excessive through-connection delay Misrouting Unacceptable transmission quality Congestion caller indication) No answer DTE clearing User information transfer delay Premature release (cutoff call) Reset Congestion Incorrect charging Incorrect billing Xote I -N
45、etwork accessibility and connection accessibility combine into service accessibility. Abte 2 - nie shaded area shows that a premature release can occur during the time to await Call Connected packet. Abte 5 - nus packet has two meanings, local and end-to-end. Abte 4 - The relase of a call is not a s
46、eparate phase hi tlis model. A release failure may result in network inaccessibility for a new call. Abte 5 -The billing integrity has been shown for completeiiess, but is not a part of serveability performance. HGURE 5iE.820 Model for sereabffty performance on a virhml call (packet terminal) TO2038
47、20-93 Recommendation E.820 (10/92) 7 CCITT RECMN*E.BZO 72 W 48b2571 057b548 710 W Virtual call Dhases Related measures Examples of causes of call failure A-subscriber initiates a call processing at PAD (Link level is active) Reception of J proceed-to-dial : Dialling ; J End of dialling Y PAD sends L
48、ail request packet) The call is routed to its destination Call connection 1 A-DTE receives J call connected packet Data transfer A-DTE sends clear request packet or receives clear indication packet J T Call A-subscriber receives a clearing clear confirmation packet (Note 3) delay or send clear confi
49、rmation packet initiated by B-subscribers request I Nehivork accessibility, Pl 1 (Note 1) (Human factor related) Connection accessibility, P12 (Note 1) Connection retainability, P2 (Note 4) (The billing information is collected) Billing integrity, P4 (Note 5) Link level inactive Congestion Excessive proceed to dial signal delay (This is not known by the subscriber) Excessive through-connection delay Misrouting Unacceptable transmission quality Congestion caller indication) No answer DTE clearing User information transfer delay Premature release (cutoff
