Liaison statement
LS on Clarification of M3UA usage in 3GPP networks
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State | Posted |
---|---|
Submitted Date | 2008-02-07 |
From Group | 3GPP |
From Contact | Susanna Kooistra |
To Group | IETF |
To Contacts | gonzalo.camarillo@ericsson.com |
Response Contact | zhaoyuyi@chinamobile.com |
Technical Contact | zhaoyuyi@chinamobile.com |
Purpose | For action |
Deadline | 2008-04-11 Action Taken |
Attachments | (None) |
Body |
3GPP TSG CT WG4 Meeting #38 C4-080568 Puerto Vallarta, MEXICO, 28th Jan ¨C 1st Feb 2008 Title: LS on Clarification of M3UA usage in 3GPP networks Response to: Release: Rel-8 Work Item: Source: TSG CT WG4 To: IETF Cc: None Contact Person: Name: Zhao yuyi Tel. Number: +86 13901009967 E-mail Address: zhaoyuyi@chinamobile.com Attachments: None. 1. Overall Description: 3GPP defines an IP based SS7 signalling network using M3UA/SCTP/IP as transport layer, SPs such as HLR, MSC can communicate with each other directly by accessing to this IP based signalling network.. Address translation, GTT management, SCTP Association configuration are handled separately from the basic signalling transport. According to 3GPP TR29.801, when deploying a large scale signalling network based on IP, it is better to separate the network into several sections, keep the number of SPs in each section in an appropriate degree. SGs are needed between different sections to simplify the GT data and converge the SCTP association data. And it is recommended that M3UA should be used on the SG-SP interface, while M2PA may be used on the SG- SG interface. As same as the traditional TDM based SS7 signalling network, an IP based SS7 signalling network also provides signalling network management functions, such as signalling traffic management, signalling link management , and signalling route management, to insure the availability and traffic transport capacity of a signalling network in case of failures and congestion. For a large scale signalling network based on IP with SGs , the usage of M2PA on SG- SG interface can help to realize the signalling network management between different sections. But M3UA can not fulfil the signalling network management within a section completely at present, the extension of it for this application is needed. The reason and the proposal for the extension will be discussed in this paper. Figure1: M3UA used within a signalling section 2 The scenarios of M3UA usage in 3GPP networks Within a section of a large scale signalling network based on IP with SGs, the normal signalling transport route between two SPs will transit a SG. When the destination SP is not available£¨Scenario 1£©, the SG must notify the source SP to choose another route. And when the user part of the destination SP is not available £¨Scenario 2£©, the SG must also notify the source SP to stop the signalling traffic. M3UA is designed for SP-(TDM)-SG-(IP)-IP SP and IP SP-(IP)-IP SP applications, so the network level management function isn¡¯t required. SSNM(SS7 Signalling Network Management) messages defined in M3UA are only used for interworking with SS7. M3UA specification doesn¡¯t define signalling network management function for the IP SP-(IP)-SG-(IP)-IP SP application. Scenarios 1: the destination SP is not available In Scenario 1, when SG1 find the destination SP (AS,SP2) in IP domain is not available, and there is no connection between SG1 and SG2 or the connection is not available. Assuming there is no signalling available towards SG2, it is a matter of M3UA spec interpretation whether SG1 sends or not a DUNA (M3UA) message to SP1 upon failure of signalling towards SP2. M3UA spec does not prohibit this, but it seems there is a bit of unclarity on whether SSNM msg can be sent by the SG in the context of a AS->SG-AS interworking, while it is very clear that SG can send such message in the context of SEP -> SG -> AS. In result, the source SP (AS,SP1) doesn¡¯t know the route is unavailable and still sends traffic to SG1, which makes the signalling transport failure. Figure2: Scenario 1 ¨C the destination SP is not available Scenarios 2: the user part of the destination SP is not available In Scenario 2, if multiple user parts are associated with single AS in SP2, M3UA does not allow SP2 to send DUPU to SG1 when the user part of the destination SP(AS, SP2 ) is not available, In result, the source SP (AS,SP1) doesn¡¯t know the user part of SP2 is unavailable and still sends traffic to SP2 , which makes the signalling transport failure. One solution is to associate a single user part to an AS . So when user part is unavailable, AS announces that it is unavailable too by sending DUNA to SG1. SG1 gets aware that AS of SP2 is not available / inactivated. And then afterwards still a matter of interpretation on whether SG1 sends or not a DUNA/DUPU to SP1. In addition , DUPU contains no DPC field to indicate the address of the source SP(AS, SP1) which is the originator of the message( DATA) that triggered the DUPU. Figure3: Scenario 2 ¨C the user part of the destination SP is not available IETF is kindly asked to see if it is necessary to clarify in M3UA RFC that SSNM messages are sent not only for an interworking between MTP3 to M3UA (SP ¨C > SG -> AS), but also for signalling from M3UA to M3UA (AS -> SG -> AS), and provide feedbacks to CT4 about this issue. 3. Actions: To IETF: 1) IETF is kindly asked to see if it is necessary to clarify in M3UA RFC that SSNM messages are sent not only for an interworking between MTP3 to M3UA (SP ¨C > SG -> AS), but also for signalling from M3UA to M3UA (AS -> SG -> AS), and provide feedbacks to CT4 about this issue. 2) what is IETF¡¯s recommendation to solve the mentioned problem? 4. Date of Next CT4 Meetings: CT4#38bis (Rel-8) 7th ¨C 11th April 2008 South Korea CT4#39 5th ¨C 9th May 2008 Cape Town, SOUTH AFRICA |