1、 ATIS-1000623.2014 Digital Subscriber Signalling System Number 1 (DSS1) Signalling Specification for the User Bearer ServicesAMERICAN NATIONAL STANDARD FOR TELECOMMUNICATIONS As a leading technology and solutions development organization, ATIS brings together the top global ICT companies to advance
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11、 Notice of Disclaimer and b) The information processing and actions that take place at the user side and the net- work side. A user can have multiple user signalling connections simultaneously via the same D-channel, with each user signalling connection being identified by a different call reference
12、 value. 4.1 States for the User Signalling Bearer Service This clause defines the basic call control states for user-to-user signalling not associated with circuit-switched calls. The procedures for call control are given in clause 7. 4.1.1 Call States at the User Side of the Interface The states th
13、at may exist on the user side of the user-network interface are defined in 2.1.1 of ATIS-1000607. The Call Delivered (U4), Call Received (U7), Disconnect Request (U11), and Disconnect Indication (U12) states are not supported. 4.1.2 Network Call States The states that may exist on the network side o
14、f the user-network interface are defined in 2.1.2 of ATIS-1000607. The Call Delivered (N4), Call Received (N7), Disconnect Request (N11), and Disconnect Indication (N12) states are not supported. 4.1.3 Call States Associated with the Global Call Reference Clause 2.2 of ATIS-1000607defines the states
15、 that the protocol may adopt using the global call reference. 7 ATIS-1000623.2014 Table 1 - Messages for the user signalling bearer service 5 Message Functional Definitions packet mode in the transfer mode field; user information layer 2 protocol is ITU-T Recommendation Q.921 and user information la
16、yer 3 protocol is ATIS-1000607 in the layer and protocol identification fields; b) Channel identification information element: 15 ATIS-1000623.2014 exclusive in the preferred/exclusive field; D channel in the D-channel indicator field; no channel in the channel selection field. NOTE A SETUP message
17、for an incoming USBS call is very similar to the SETUP message used for notification of an incoming packet-mode call on the D-channel. In fact, if there is no map- ping of ITU-T Recommendation X.25 facilities to ITU-T Recommendation Q.931 information elements, the only difference rests in the coding
18、 of the User information layer 3 protocol, where this octet indicates “T1.607” for USBS, and “X.25 packet level” for D channel packet. If the network determines that the requested user signalling bearer service is not authorized or is not available, the network shall initiate call clearing in accord
19、ance with 5.3.2(1) of ANSI T1.607 or by sending a RELEASE message as described in 5.3.3 and 5.3.4 of ATIS-1000607 with one of the following causes: a) #57 “bearer capability not authorized”; b) #58 “bearer capability not presently available”; c) #63 “service or option not available, unspecified”; d)
20、 #65 “bearer service not implemented”; e) #21 “call rejected”; f) #42 “switching equipment congestion”; g) #29 “facility rejected”. The called user accepts the user signalling bearer service request by sending a CONNECT message toward the calling user. After the called user has received a CONNECT AC
21、KNOWLEDGMENT message, it may begin sending USER INFORMATION messages. Once the calling user receives a CONNECT message, it can begin sending USER INFORMATION messages. 7.3 Transfer of USER INFORMATION Messages Once an end-to-end signalling connection is established for the user signalling bearer ser
22、vice, both users can transfer information between themselves by transferring USER INFORMATION messages across the user- network interface. The network provides for the transfer of such messages from the called to the calling side and vice versa. The USER INFORMATION message includes the Call referen
23、ce, the Protocol discriminator, and the User-user information elements as defined in clause 6. The More data information element may also be sent by the source user to indicate to the remote user that another USER INFORMATION message will follow, containing information belonging to the same block of
24、 data. The use of the More data is not supervised by the network. 7.4 Congestion Control of USER INFORMATION Messages The network or user will flow-control, when needed, the transfer of USER INFORMATION messages from its local peer by means of a CONGESTION CONTROL message containing a Congestion lev
25、el information element. Two indications of congestion level are specified: “receive not ready” and “receive ready”. On receipt of the former, the user or network should suspend sending USER INFORMA- TION messages; on receipt of the latter, sending may recommence. After having sent a “receive not rea
26、dy” indication, the network or user shall discard USER INFORMATION messages that are subsequently received. The network or user will send a CONGES- TION CONTROL message with a “receive not ready” indication whenever a USER INFOR- MATION message is locally discarded, if it is possible. The CONGESTION
27、 CONTROL message shall also include a cause #43 “access information discarded”. 16 ATIS-1000623.2014 If USER INFORMATION messages are received at a rate that exceeds the flow control limit set by the network, the network shall discard the messages that cannot be handled and respond to the first disc
28、arded message with the congestion level specified as “receive not ready”. The CONGESTION CONTROL message shall also include a cause #43 “access information discarded”. The network shall notify the user that flow control restriction has been removed by sending a CONGESTION CONTROL message with the co
29、ngestion level specified as “receive ready” to indicate that further messages may be sent. This message may be sent, as an implementation option, either (a) immediately upon removal of flow control restriction, (b) in response to the first USER INFORMATION message received following the removal of f
30、low control restriction, or (c) in both cases. The Congestion control procedure should be regarded as local. Congestion control procedure for remote applications is not covered by this standard. 7.5 Throttling of USER INFORMATION Messages The user equipment shall provide a means to throttle USER INF
31、ORMATION messages sent to the network. A maximum of 16 USER INFORMATION messages shall be sent in any 10-second interval with a long-term average of no more than 0.8 messages per second. NOTE Some networks may establish other rates of information. An example of an algorithm that may be used to achie
32、ve throttling is as follows: In each direction of data transmission, a Burst Capability of sending n messages is immediately available where n initially equals the value of the Burst parameter x. The value of n is decremented by one for every message sent by the user and incremented by y at regular
33、intervals of T, subject to the limitation that n may not exceed x, i.e., n + y x. The Burst parameter is set to a value of x =16. The replenishment parameter y is set to a value of y = 8. The internal timer T is set to a value of T = 10 seconds. 7.6 Call Clearing The clearing of an established user
34、signalling bearer service connection can be initiated by the user or network by sending a RELEASE message. The clearing procedure followed and the timers involved are the same as those for clearing a circuit-switched connection as described in 5.3.3 and 5.3.4 of ATIS-1000607 with the exception that
35、no B-channel resources are released. 7.7 Handling of Error Conditions In the event of a data link reset of failure, all USBS connections on the D-channel shall be released as in 7.6. For data link resets, the clearing messages shall indicate cause #41, “temporary failure”, to both local and remote u
36、sers. For data link failures, the clearing message to the remote user shall indicate cause #27, “destination out of order”, and the local USBS connection shall be cleared internally. Handling of other error conditions is defined in 5.8 of ATIS-1000607. 17 ATIS-1000623.2014 7.8 RESTART Procedures If
37、a RESTART message is received with the Restart indicator information element coded as “all interfaces”, or coded as “single interface” and the indicated interface includes the D-channel, then all USBS connections on the D-channel shall be released. The clearing message to the remote users shall incl
38、ude cause #43 “temporary failure”. 8 List of System Parameters The detailed description of timers is found in clause 9 of ATIS-1000607. 8.1 Timers in the Network Side The timers specified in 9.1 of ATIS-1000607are maintained in the network side of the interface. 8.2 Timers in the User Side The timer
39、s specified in 9.2 of ATIS-1000607are maintained in the user side of the interface. 18 ATIS-1000623.2014 Annex A: Summary of Departures from ITU-T Recommendation Q.931 (I.451) (informative) The departures of this standard from the provisions of ITU-T Recommendation Q.931 (I.451) are summarized in th
40、is annex. Each clause containing a departure is identified and the difference is briefly described. Clause 1, Purpose, scope, and structure: This clause recognizes the more limited scope of the USBS standard. There is no equivalent to the clause describing the structure. Clause 2, Normative referenc
41、es: There is no equivalent to this clause. Clause 3, Definitions: There is no equivalent to this clause. Subclause 6.5.7, User-user: A new note was added to define OSI high-layer protocols as Layer 4 and above. Subclause 7.2, Call establishment: A note was added to this subclause identifying the sim
42、ilarities and differences between a USBS call and other packet calls on the D-channel. Three additional cause values, #21, #42, #29, were added. Subclause 7.4, Congestion control of USER INFORMATION messages: When the network discards messages, it is required to include cause #43 in the CONGESTION C
43、ON- TROL message. A paragraph was added to define the network options when the flow con- trol restriction is removed. Subclause 7.5, Throttling of USER INFOR- MATION messages: This subclause was modified for clarity, including specifying the average number of messages. The status of the flow control
44、 algorithm was changed from a requirement to one possible implementation. Subclause 7.7, Handling of error conditions: The procedure to follow in the event of a data link reset was clarified. Subclause 7.8, RESTART procedures: The procedure to follow in the event of a RESTART message was added. 19 A
45、TIS-1000623.2014 Annex B: Bibliography (informative) These standards are listed for information only and are not essential for the completion of requirements of this standard. ATIS-1000603.1993(R2009), Telecommunications Integrated services digital network (ISDN) Minimal set of bearer services for t
46、he primary rate interface4ATIS-1000604.1990(R2013), Telecommunications Integrated services digital network (ISDN) Minimal set of bearer services for the basic rate interface5ATIS-1000609.1999(R2009), Telecommunications Interworking between the ISDN user-network interface protocol and the signalling
47、system number 7 ISDN user part6ATIS-1000614.1991(R2012), Telecommunications Integrated services digital network (ISDN) Packet mode bearer service category description7ANSI X3.100-1989, Information systems Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) fo
48、r operation with packet-switched data networks (PSDN), or between two DTEs, by dedicated circuit8ITU-T Recommendation I.122, Framework for providing additional packet mode bearer services, 19889ITU-T Recommendation I.231, Circuit Mode Bearer Services, 19889ITU-T Recommendation I.232, Packet Mode Bea
49、rer Services, 19889ITU-T Recommendation I.320, ISDN protocol reference model, 19889ITU-T Recommendation I.430, Basic user- network interface layer 1 specification, 19889ITU-T Recommendation Q.920, ISDN user- network data link layer General aspects, 19889ITU-T Recommendation Q.930, ISDN user- network interface layer 3: General aspects, 19889ITU-T Recommendation X.200, Reference model of open systems interconnection for ITU-T applications, 19889ITU-T Recommendation X.210, OSI layer service conventions, 19889ITU-T Recommendation X.612, Information Technology
