1、CEPT T/CS*iL-OL*E 83 W 2326434 00045b 7 W Page 1 21-01 E Recommendation T/CS 21-01 (Cannes 1983) CALL HANDLING INFORMATION FLOW Recommendation proposed by Working Group T/WG 11 “Switching and Signalling” (CS) Text of the Recommendation adopted by the “Telecommunications” Commission: “The European Co
2、nference of Postal and Telecommunications Admiqistrations, considering - that basic and supplementary services should be harmonized; - that for those supplementary services for which cooperation between exchanges is required, the additional - that the elements of information to be passed between exc
3、hanges by means of additional signailing should be signalling feature according to Recommendation T/CS 20-26 11 provides a recommended basis; specified; that the way in which the additional signalling information should be passed between exchanges should be specified in conjunction with the other ca
4、fi handiing information to be pasied, especially to enable; harmonized international interworking; - that a common, unique and concise way of depicting the cd handling information flow WU speed up the process of its specification, recommends - that the members draw up specifications of the call hand
5、ling information flow for supplementary and other new - to employ for these specifications the CCIT Specification description language and caii handling sequence charts services as far as possible independently from signalling systems before working out implementations; as outlined below.” 1. CCm SP
6、ECIFICATION AND DESCRTPTION LANGUAGE Where appropriate, the processes involved in the Cali handling information flow within both the outgoing and the incoming exchange are presented in Specication and description language (SDL) form in accordance with CCITT Recommendations 2.100 to Z. 104 2. 2. CALL
7、 HANDLING SEQUENCE CHARTS When a more concise presentation of the call handling information flow is desirable and sufficient, the method Call handling sequence charts as described in the Annex to this Recommendation may be used. It is then essential to follow the rules set-out in the Annex. For the
8、time being, the Recommendations of Group T/CS 21 include call handling sequence charts in accordance with the Annex to this Recommendation. O References 11 CEPT Recommendation T/CS 20-26. Additional Signalling. 2 CCITT Recommendation Z. 100 to Z. 104. Functional specSfication and description languag
9、e (SDL). Edition of May 15, 1986 - CEPT T/CS*ZL-OL*E 3 II 2326434 0004569 9 TICS 21-01 E Page 2 Annex. Call handling sequence charts 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. The purpose of a call handling sequence chart is to show which information has to be passed between exchanges fo
10、r the call handling of a service or supplementary serviceand to show the sequence in which this should occur. Besides, a call handling sequence chart should contain all other relevant information for the understanding of the call handling process. The information in a call handling sequence chart is
11、 subdivided into the following items: (a) signalling information to be passed between exchanges; (b) signalling information to be passed from exchange to user, and vice versa; (c) audible or visual indications to be passed from exchange to user; (d) specific actions to be performed by exchanges. For
12、 each exchange which has a significant role in the call handling, a separate column is established. Signalling information to be passed between exchanges is represented by a line starting in the middle of the column of the sending exchange and ending in the middle of the column of the receiving exch
13、ange with an arrow head at the latter end. Signalling information which is to be considered as additional signalling information according to Recommen- dation T/CS 20-26 i should be specified in the form of service instructions, i.e. independent of any signalling system. The flow of signalling infor
14、mation which is not specific for the supplementary services considered may be indicated in a shortened way (e.g. normal call set-up procedure or normal clear procedure). Such an informa- tion flow may comprise different signals or messages to be passed between the exchanges concerned, possibly in bo
15、th directions. It is represented as described in paragraph 4 but with a double arrow head in the middle of the destination exchange column. Signalling information between exchanges and users is represented by a line over one half of the column representing the exchange involved. By convention, in th
16、e case of a calling subscriber, the left-hand side of the column is used, and in the case of a called subscriber, the right-hand side of the column is used. Audible indications from exchanges to users are indicated by means of an interrupted line, starting in the middle of the sending exchange colum
17、n and ending at the edge of the exchange column, to which the receiving subscriber is connected; with an arrow head at this end and according to the convention indicated in pt. 6. Specific actions to be performed by an exchange are indicated by means of clear text, which may utilize the whole width
18、of the exchange column. Where signalling information or audible or visual indication arrows cross the border between exchange columns, the separation line between the columns should be deleted. Each item, as described in pts. 4 up to and including 8, is given a reference number (rnr), which is indic
19、ated in a specific column at the left-hand side of the chart. When starting the study of a call handling sequence chart, the reference numbers should be attributed as multiples of 10 to allow for later additions. Each separate action in an exchange should be given a reference number. Different actio
20、ns in different exchanges which occur more or less in parallel may be indicated at the same height and, therefore, be given the same reference number. Signalling information and/or audible or visual indication flows starting at the same moment within the same exchange but going into opposite directi
21、ons, may be indicated on the same height and, therefore be given the same reference number. Where different conditions can occur, then in the main part of the chart the condition should be chosen which has to be met for normal service operation. Different sections should be established for cases whe
22、re the condition mentioned before is not met or where other conditions apply at that point of the call handling charts. Such sections should start with a reference number being a multiple of 100. At any point-in the chart where a jump to another section due to a different condition is possible, this
23、 should be indicated together with the starting reference number of the section to which the jump is made. At the beginning of a section to which a jump can be made, the reference number of each point which can be jumped from should be indicated. A section may end with the indication that continuati
24、on of the sequence occurs from a reference number of another section. 17. 18. 19. 20. 21. CEPT T/CS*ZL-OL*E 83 = 2326434 0004570 5 - - TICS 21-01 E Page 3 At any point in the chart where further specication of the sequence is of no interest (e.g. because the caii has been cleared, or further call ha
25、ndling occurs as for a normal caii), this should be indicated by the word end in the reference number column and in one or more exchange columns in which the last item of information is specified. An elapse of time between two successive events may, if required for clarification, be indicated with t
26、he symbol Comment may be either included in the sequence chart (if short) or by means of a separate note. A list of service instructions which are needed for the operation of the (supplementary) service should be associated with the chart together with a functional definition of each. Service instructions should be defned such that where possible they can be applied for different (supplemen- tary) services. in the corresponding exchange columns. Edition of May 15, 1986 r
