- 2 - COM XI-R 74-E 1.1.2 Draft Recommendation Q.50 SIGNALLING BETWEEN CIRCUIT MULTIPLICATION EQUIPMENTS (CME) AND INTERNATIONAL SWITCHING CENTRES (ISC) 1. Introduction This Recommendation contains principles and examples of signalling between ISC (exchanges) and their associated circuit multiplication equipments. (In call modification is for further study.) Circuit multiplication equipments may have integral echo control and A/u law converter functions. The information in this Recommendation is compatible with the control procedures for such devices. 2. Definitions relating to CME 2.1 Digital circuit multiplication equipment (DCME) and CME DCME and CME constitute a general class of equipment which permits concentration of a number of trunks on a reduced number of transmission channels. DCME in particular permits concentration of a number of 64 kbit/s PCM encoded trunks on a reduced number of digital transmission channels. 2.2 Speech interpolation; digital speech interpolation (DSI) A method of profiting from the time instants when a speaker is not active, which is indicated by a speech detector. The channel is then used by another speaker. The signals carried by a transmission channel therefore represent interleaved bursts of speech signals derived from a number of different trunks. 2.3 Low rate encoding (LRE) Speech coding methods with bit rates less than 64 kbit/s, e.g. the 32 kbit/s transcoding process defined in G.721 applied to speech coded according to G.711. 2.4 Speech activity The ratio of the time speech and corresponding hangover occupies the trunk to the total measuring time, averaged over the total number of trunks carrying speech. 2.5 CME gain The trunk channel to transmission channel multiplication ratio, which is achieved through application of CME, including LRE and/or speech interpolation (DSI). - 3 - COM XI-R 74-E FIGURE 1/Q.50 CME gain Note - For a complete discription of bearer channels, see Recommendation G.dcme. 2.6 Trunk A bidirectional connection consisting of a forward channel and a backward channel between the ISC and CME not subject to LRE or DSI operation. 2.7 Transmission channel - bearer channel One channel of the connection between the transmit unit and receive unit of corresponding CME. 2.8 Freeze-out The condition when a trunk channel becomes active and cannot immediately be assigned to a transmission channel, due to lack of available transmission capacity. 2.9 Freeze-out fraction The ratio of the sum of the individual channel freeze-outs to the sum of the active signals and their corresponding hangover times and front end delays, for all trunk channels over a fixed interval of time, e.g. one minute. 2.10 Transmission overload The condition when the freeze-out fraction or average bits per sample goes beyond the value set in accordance with speech quality requirements. 2.11 Operating modes 2.11.1 Point-to-point mode (see Figures 2a/Q.50 and 2b/Q.50) Point-to-point - Using Figure 2a/Q.50 for reference, the transmit side CME concentrates N trunks into N/G transmission channels, where G is the CME gain. - 4 - COM XI-R 74-E At the receive side, the receiving CME simply reconstitutes the N trunks from the N/G transmission channels. FIGURE 2a/Q.50 Point-to-point unidirectional FIGURE 2b/Q.50 Point-to-point two origins unidirectional FIGURE 2/Q.50 Multi-clique for two origins and two destinations unidirectional The example in Figure 2b/Q.50 also shows a point-to-point mode. From the switching point of view there could be a difference between the configurations in Figures 2a/Q.50 and 2b/Q.50. For transmission of alarms it has also to be considered, that different exchanges may be connected to one CME. 2.11.2 Multi-clique mode (see Figure 3/Q.50) Multi-clique mode - in this mode the pool of transmission channels is sub-divided into several independent pools (cliques) or fixed capactiy, each being for an individual destination. If a part of the cliques capacity is not used, it cannot be used for another destination. - 5 - COM XI-R 74-E FIGURE 3/Q.50 Multi-clique mode (only one direction shown) 2.11.3 Multi-destination mode A DCME operational mode where input trunk channel traffic is interpolated over a pool of available transmission channels for all destinations having traffic in the pool. The transmit trunk channels are designated to receive trunk channels at corresponding locations. Figure 4/Q.50 shows a unidirectional system block diagram for a multi- destination mode with two transmit and two receive DCME units. - 6 - COM XI-R 74-E FIGURE 4/Q.50 Multi-destination mode (only one direction shown) 3. Requirements for control 3.1 Reasons for use of circuit multiplication equipments (CME) Circuit multiplication equipments are used in order to reduce the 3.2 Integration of CMEs into the telephone network Normally, when an exchange needs an outgoing circuit, the only question is whether or not a circuit is available. In this example, the call may be blocked if all of the circuits are unavailable through traffic or maintenance. If the same call encounters a CME, the possible outcomes are more complex. - 7 - COM XI-R 74-E (and for 3.1 kHz audio, if appropriate) through DSI systems (i.e., not through internal pre-assignment), the establishment and disestablishment of connections between the CMEs have to be initiated from the outgoing exchange. 3.3 Factors for signalling functions determination The functional requirements for signalling between CMEs and exchanges are determined by the type of CME with its capabilities and limitations, and by the types of bearer services it supports. The remote control of echo control devices and A/u-law converters, if they are integrated into the CME, is accomplished either by the terminal or test equipment or directly from the ISC (based on call set up information/signalling information). Requirements and actions for control of ECD are described in CCITT Recommendation Q.115. - 8 - COM XI-R 74-E 3.3.1 Circuit multiplication equipment and physical location There are different types of CME which are being used or will most likely be used in the international telephone network, each with its own capabilities and limitations: a) 32 kbit/s low rate encoding (LRE); b) analogue speech interpolation equipment; c) digital speech interpolation (DSI) with 64 kbit/s PCM; d) combined 32 kbit/s LRE and DSI e) 16 kbit/s LRE. The location of certain types of CME relative to the exchange determines the choice of signalling interface. These CMEs can be located at the ISC or remote from the ISC (e.g., at an earth station). Certain types of signalling interfaces may be more practical when these CMEs are co-located with the ISC, and others may be more practical when they are remote from the ISC. Therefore, the location of the CME needs to be considered when choosing the signalling between ISC and CME. When the CME is remote from the ISC, the link between the ISC and CME could be composed of digital or analogue transmission path. Both conditions have different equipment configurations and different signalling requirements (see section 7). 3.3.2 Bearer services supported on CME links Up to four basic bearer service types are supported or will likely be supported by CMEs in the international network: - speech bearer service (full duplex, analogue or digital); - 3.1 kHz audio bearer service (full duplex); - 64 kbit/s unrestricted bearer service (full duplex); - alternate speech/64 kbit/s unrestricted bearer service (full duplex); - 9 - COM XI-R 74-E TABLE 1/Q.50 Bearer services supported in CMEs in relation to CME-exchange signalling 4. Bearer services and CME techniques in the context of signalling Table 1/Q.50 gives the relationship between CME techniques and the four bearer services identified in  3.3.2 with regard to their supportability and the need for CME-exchange message transfer. The signalling function requirements are categorized on the basis of bearer services supported by the different CME techniques. For speech bearer services, only transmission resource management (TRM) information alone is adequate especially for CMEs employing speech interpolation. The objective of this provision is to maintain the reduction of transmission quality within tolerable limits. In addition to TRM information, external call set-up message (CSM) exchange is needed for bearer services involving on-demand 64 kbit/s unrestricted service in contemporary digital circuit multiplication equipment (32 kbit/s LRE and DSI). - 10 - COM XI-R 74-E 5. Division of functionality between the exchange and the CME 5.1 CME dynamic load control process TRM information is based on traffic load measurements at the local and distant CMEs. Therefore in the multi-destination and multi-clique mode of operation, TRM information is provided for each destination/clique separately. A universal arrangement is proposed for handling transmission resource management (TRM) information between CME and an exchange. The TRM information is dynamically presented to the exchange in one of two states for each bearer service. The states are called "available" and "not available". Logic within the CME is used to determine which of the two states should be indicated to the exchange regardless of any condition at the exchange. When a CME encounters a "not available" state for a bearer service (either locally or remotely), it presents this indication to the exchange so it will stop routing new calls to the CME for that bearer service even if there are free, unseized circuits available. The exchange will continue to prohibit calls to the CME until it receives an "available" indication for the bearer service which will be sent by the CME when both, locally and remotely, there is no overload. This DLC information is therefore directly influencing the circuit selection process in the exchange during call set-up for each bearer service separately. The circuit selection in the exchange is a check whether or not a free unseized circuit is suitable for a certain bearer service type, for which a new call is to be accommodated. For example, the exchange would select a free circuit for a speech call if "speech capacity available" is indicated, irrespective of the indications for other bearer service types. If the DCME link is unable to accommodate additional new 64 kbit/s calls, all free unseized circuits within the exchange will be marked accordingly. Even though the generation of bearer service related TRM information with DCMEs may be in part mutually dependent (i.e., no capacity for speech implies no capacity for any other bearer service types but not necessarily vice-versa), separate signalling and processing for each bearer service type are necessary to allow different future CMEs to develop independently. 5.2 Call set-up process According to Table 1/Q.50, the contemporary digital circuit multiplication equipment, having the capability to support on-demand all four identified bearer services, in addition to providing TRM to the exchange, requires call set-up messages (CSM) (from the exchange) for selecting bearer services. For the 64 kbit/s unrestricted bearer service, a circuit is selected if "unrestricted capacity available" is indicated, and a CSM in the form of Seizure/Select request is forwarded to the DCME. An acknowledgement (positive or negative) is set as soon as possible even if capacity is available, to account for possible call set-up rejects other than due to capacity limitations on the DCME link. - 11 - COM XI-R 74-E The positive acknowledgement will be used by the ISC to initiate the interexchange signalling to the next ISC (e.g. transmission of the IAM of Signalling System No. 7). A failure to establish a 64 kbit/s circuit between CMEs must be reported to the DSG as soon as the condition has been identified by the CME to the ISG by using an out-of-service message. The out-of-service message is considered by the ISC to be equivalent to the alarm signal defined in Recommendation Q.33. The ISC will take release actions (if appropriate) as specified in Recommendation Q.33,  4. The released 64 kbit/s message from the ISC will be positively acknowledged after proper completion of the DCME circuit disestablishment process. Failure to complete this process shall be notified to the ISC using an out-of-service message and the DCME will put the circuit in a blocked condition. After the failure condition is removed, this circuit will be in idle condition and a back-in-service message shall be sent to the ISC. Under a 64 kbit/s unrestricted dual seizure situation, the non- controlling ISC will initiate a release of the DCME connection using procedures defined in the appropriate inter ISC signalling system protocol. If the DCME is unable to re-establish a remotely released 64 kbit/s duplex connection, it shall indicate this abnormal situation to the appropriate ISC by out-of- service. The information elements and procedures necessary to support the alternate 64 kbit/s speech bearer services are for further study. FIGURE 5/Q.50 Typical ISC/CME information flows - 12 - COM XI-R 74-E 5.3 Inter-dependency between dynamic load control and call set-up process To allow a standard method of interworking with inter-exchange signalling systems it is important to adopt the functional interdependency between TRM and CSM as described above. 6. Control information elements between exchange and CME The amount of control information elements utilized between the exchange and the CME depends on the capabilities of the CME and the exchange. Two categories of CME signalling capabilities are recognized. The first category of CME (Type 1) is capable of only transmitting signals from the CME to the exchange (e.g. DLC see Table 3/Q.50). The second category of CME (Type 2) is able to transmit and receive signals to/from the exchange. Tables 2/Q.50, 3/Q.50 and 4/Q.50 give a set of information elements and their flow on the control link between the exchange and the CME for the second category of CME. 6.1 Information elements for Type 1 CME Type 1 CME only should use the following information elements (m = mandatory; o = optional). 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴커 � � � � Type of information elements � Used (m) or (o) � 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴캑 � � � �1. No capacity for speech available � (m) Note a � � � � �2. Channel(s) available for speech � (m) Note a � � � � �3. Out-of-service � (o) � � � � �4. Back-in-service � (o) � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴켸 Note a - Speech includes 3.1 kHz audio. - 13 - COM XI-R 74-E TABLE 2/Q.50 Information elements for transmission resource management (load control) CME/ISC (Type 2) 旼컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴� 쿟ype of information� Notes 쿏irection of� Procedures; Use � � element (Note a) � � the � of the � � � 쿶nformation � information � � � � element � elements � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.1 No capacity � No bearer capacity � CME-->ISC � � 쿺 for speech � for additional trunk(s) � � � � available � available � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.2 Channel(s) � This information element � CME-->ISC � � 쿺 available for � is sent to notify the � � � � speech � end of "No capacity for � � � � � speech available" � � � � � condition � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.3 No trunk(s) � No bearer capacity for � CME-->ISC � � 쿽 available for � additional 3.1 kHz audio � � � � 3.1 kHz audio � trunk(s) available � � � � Note 1 � � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.4 Trunk(s) � This information element � CME-->ISC � � 쿽 available for � is sent to notify the � � � � 3.1 kHz � end of "No trunk � � � � Note 1 � available for 3.1 kHz � � � � � audio" condition � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.5 No 64 kbit/s � No bearer capacity for � CME-->ISC � � 쿺 capacity � additional 64 kbit/s � � � � available � trunk(s) available � � � � Note 2 � � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.6 Acknowledgement� � ISC-->CME � � 쿽 of "No 64 � � � � � kbit/s capacity� � � � � available" � � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.7 Trunk(s) � This information element � CME-->ISC � � 쿺 available for � is sent to notify the end� � � � 64 kbit/s � of "No 64 kbit/s capacity� � � � � available" overload � � � � � condition � � � 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �1.8 Acknowledgement� � ISC-->CME � � 쿽 of trunk(s) � � � � � available for � � � � � 64 kbit/s � � � � 읕컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴� Note a - Each information element may be sent as a message or may be implicit by the lack of a signal (e.g. the CME may send a signal for no capacity for speech available and remove the same signal to indicate trunks available for speech). m = mandatory for this type of CME o = optional for this type of CME - 14 - COM XI-R 74-E TABLE 3/Q.50 Information elements for seizure/release (CME/ISC (Type 2)) 旼컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴� 쿟ype of information � Notes 쿏irection of� Procedures; use � � elements � � the � of the � � � 쿶nformation � information � � � � element � elements � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.1 64 kbit/s 쿞ent when 64 kbit/s � ISC-->CME � � 쿺 select/ 쿬ircuit is required via � � � � seizure 퀃he DCME (Note 3) � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.2 Trunk 쿐xplicit or implicit � ISC-->CME � � 쿺 identity 쿶nformation to assign an � � � � 쿶nformation element to a � � � � 퀂pecific trunk � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.3 64 kbit/s pos. 쿞ent if 64 kbit/s request� CME-->ISC � � 쿺 Acknowlegement 쿬an be satisfied � � � � �(Note 4) � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.4 64 kbit/s NACK 쿞ent if a 64 kbit/s � CME-->ISC � � 쿺 퀁equest cannot be � � � � 퀂atisfied � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.5 Release 쿞ent by the originating � ISC-->CME � � 쿺 64 kbit/s 쿔SC to indicate that a � � � � �64 kbit/s circuit is not � � � � 퀁equired any longer � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.6 3.1 kHz 쿝equest to allocate data � ISC-->CME � � 쿽 service/select 쿽ptimized facilities � � � � seizure � � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.7 3.1 kHz 쿞ent if 3.1 kHz service � CME-->ISC � � 쿽 service, pos. 퀁equest can be satisfied � � � � Acknowledgement� � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.8 3.1 kHz 쿞ent if 3.1 kHz service � CME-->ISC � � 쿽 service/NACK 퀁equest cannot be � � � � 퀂atisfied � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.9 Release 쿞ent to indicate � ISC-->CME � � 쿽 3.1 kHz 퀃ermination of the call � � � � service � � � � 읕컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴� - 15 - COM XI-R 74-E 旼컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴� 쿟ype of information � Notes 쿏irection of� Procedures; use � � elements � � the � of the � � � 쿶nformation � information � � � � element � elements � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.10 Speech service 쿞ent to indicate speech � ISC-->CME � � 쿽 select/seizure 퀂ervice request � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.11 Speech, pos. 쿞ent if speech request � CME-->ISC � � 쿽 Acknowledgement쿬an be satisfied � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴� � �2.12 Speech NACK 쿞ent if speech request � CME-->ISC � � 쿽 쿬annot be satisfied � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.13 Release speech 쿞ent to indicate that the� ISC-->CME � � 쿽 퀂peech circuit is not � � � � 퀁equired any longer � � Note 5 � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴� �2.14 Release 쿞ent to indicate � CME-->ISC � � 쿺 64 kbit/s pos. 퀂uccessful completion � � � � Acknowledgement쿽f Release � � � 읕컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴� - 16 - COM XI-R 74-E TABLE 4/Q.50 Information elements for maintenance (CME/ISC) Type 2 旼컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴� 쿟ype of information � Notes 쿏irection of� � elements � � the � � � 쿶nformation � � � � element � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.1 Maintenance 쿞ent for manual control, � CME-->ISC � 쿽 Release Signal 쿾lanned removal from � � � Note 5 퀂ervice � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.2 Maintenance 쿞ent to acknowledge � ISC-->CME � 쿽 Release 퀁eception of Maintenance � � � Acknowledgement 쿝elease, ISC is waiting � � � Note 5 쿯or the release of the � � � 퀃runk � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.3 CME clear of 쿞ignal sent when all � ISC-->CME � 쿽 traffic signal �(this) trunk(s) are (is) � � � (released after 쿶dle. The ISC prevents � � � maintenance 쿻ew seizures on these � � � release signal) �(this) trunk(s). � � � Note 5 � � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.4 Out-of-service 쿒eneral CME trunk � CME-->ISC � 쿺 퀅navailable signal used � � � 쿽n a per circuit basis � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.5 Out-of-service 쿞ent to acknowledge "Out-� ISC-->CME � 쿽 acknowledgement 쿽f-service signal" used � � � 쿽n a per circuit basis � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.6 Back-in-service 쿞ent after the removal � CME-->ISC � 쿺 Note 5 쿯rom service is no � � � 쿹onger necessary - used � � � 쿽n a per circuit or per � � � 쿎ME basis � � 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴� �3.7 Acknowledgement 쿢sed on a per circuit � ISC-->CME � 쿽 of "Back-in- 쿫asis � � � service" � � � 읕컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴� Notes to Table 2/Q.50 Note 1 - This information may be implicit in information element 1.1 (e.g. because 3.1 kHz audio data and speech may be supported by the same LRE algorithm or 3.1 kHz audio data is detected by the CME using inband signals (2 100 Hz) from the data terminal). Note 2 - If a defined portion of the bearer capacity is used for special call types (definition of minimum and/or maximum number of channels per call type, e.g. for 3.1 kHz audio or 64 kbit/s), a special load control information is needed for each of these call types. - 17 - COM XI-R 74-E Notes to Table 3/Q.50 Note 3 - Preassigned (DNI) 64 kbit/s channels do not need this information element. A 64 kbit/s select/seizure information element between CME and ISC is mandatory for Type 2 CME equipment, if 64 kbit/s channels are used on a demand basis. Also preassigned 64 kbit/s channels (digital non-interpolated (DNI) channels) could be used (e.g. for common channel signalling). Note 4 - Dependent on the realization of the CME there could be a longer or shorter delay for 64 kbit/s channel acknowledgement. For common channel signalling it must be ensured that the circuit establishment process between the CME is finished before signalling for this circuit has finished. Note 5 - The request for speech service may be implicit, that means, that a discrete information flow may not be required. For indication of termination (not interruption) of a call, select/seizure and release may be necessary on a per call basis. Notes to Table 4/Q.50 Note 5 - Information elements 3.1, 3.2, 3.3 and 3.6 are a set of elements that should only be used together. Information element 3.6 could also be used after "out-of-service" - information without 3.1, 3.2 and 3.3. 7.