SMS Roaming Tutorial March 22, 2006

1. SMS Roaming Tutorial March 22, 2006 0.2 Version

2. Introduction • This session will cover the way SMS roaming works today • Basics of signaling and billing • Aim – new for some, review for others – background information for ongoing SMS roaming work • We won’t cover: • What is SMS • Why is SMS important • Possible future solutions

3. Signaling for SMS • High-level overview of the network elements and signaling messages used for SMS • Network signaling (i.e. ANSI-41) and air interface • Initial message flows are roaming-independent

4. Network Elements • These are the ANSI-41 network elements involved in SMS: • Message Center (MC) – aka Short Message Service Center (SMSC). Store and forward function for messages. End-point for SMS communication with a Mobile Station (MS) • Mobile Switching Center (MSC) – Includes (for this presentation) the VLR and Base Station. ANSI-41 to IS-2000 interface, and relay point for SMS messages • Home Location Register (HLR) – Stores subscriber location and profile information. Doesn’t see actual SMS message contents

5. Service Authorization • How to tell that a serving MSC supports SMS? • SMS_Address parameter included in Registration Notification sent from serving MSC • Indicates “the current routing address of the Serving MSC for the purpose of short message termination to a MS …” • Although it can be different, everyone seems to use the transport layer address (Point Code or Global Title Address) of the MSC • How to tell that a subscriber is authorized for SMS? • In subscriber profile stored in HLR: SMS_OriginationRestrictions and SMS_TerminationRestrictions parameters • These can have some fancy values, but the easiest to understand (and most widely supported) are 0 – Block All, and 3 – Allow All • See backup slide for more detail

6. Mobile-Terminated (MT) SMS Message Flow - Simple 2 MSC HLR 3 4 5 1. Message arrives at MC, addressed to MS 4. MC sends message to MSC using the address received in the previous step – SMS Delivery Point To Point (SMDPP) message MC 2. MC queries HLR for MS location – SMS Request (SMSREQ) message MS 1 5. MSC delivers message to MS over the air 3. HLR checks subscriber is authorized, returns address (SMS_Address from registration time)

7. MT SMS Message Flow – Delayed Delivery 2 MSC HLR 3 4 8 5 9 û 7 1 - 4. As per previous slide 6 MC 5. MS goes into coverage hole, message delivery fails. MSC sets “SMS Delivery Pending” flag for MS 9. Message is delivered successfully to MS 7. System access plus pending flag trigger MSC to send advice to MC that MS is available – SMSNotification (SMSNOT) message MS 1 Other notification scenarios are possible – if HLR knows that subscriber is unavailable, it will issue the SMSNOT instead of the MSC – see backup slide 6. Some time later, MS returns to coverage, makes system access 8. MC resends SMDPP

8. Mobile-Originated (MO) SMS – Indirect Routing • Indirect routing means that the message is routed through the originator’s MC: 2 1 MSC MC 3 MS 1. The MS originates a short message 2. The MSC sends the message to the MC for this MS (SMDPP) 3. The MC analyzes the destination address, and routes the message on. If the destination is a MS which belongs to another MC, the message will be sent to that MC

9. Mobile-Originated (MO) SMS – Direct Routing • With direct routing, the serving MSC delivers the message “directly” to the destination (or destination MS’s MC) • The originator’s MC is not involved (unless it’s the same as the destination MC) • Simpler message flow, but more work for the serving MSC – analysis of destination address • Not recommended for roaming MC MSC MS

10. Air Interface • Over the air, SMS carried in IS-2000 Data Burst Message (DBM) • Inside the DBM, message contents are defined by IS-637 • Parameters and subparameters include: • Teleservice – Application ID e.g. WAP, Voice Mail, Text Messaging • Addressing information – see next slide • Time Stamp • Delivery Receipt request • And of course the actual User Data • Some of these are also carried explicitly in ANSI-41, others are just encapsulated IS-637 • A sample message is available in a backup slide

11. Message Addressing • There are multiple address parameters for SMS, especially in ANSI-41: • SMS_OriginatingAddress • SMS_OriginalOriginatingAddress • SMS_OriginalOriginatingSubaddress • MSID • And many more! • Addresses can change/disappear at different points in the message flow, and vary for Direct/Indirect • Some procedural changes between ANSI-41 Rev D and Rev E on how to populate – Rev E is much easier to follow! • … Addressing can be difficult!

12. International Roaming • Now, subscriber is in a different country to his/her home network: • Call flows are essentially the same, but what new challenges does this bring?

13. International Roaming - Challenges • Network interconnection • No real difference here to voice roaming • SMS_Address is a transport layer identifier hiding in the MAP layer – treat with care • Addressing and other ANSI-41 differences • Different networks may do things differently – e.g. MIN vs MDN as originating address – need to understand your own network • Direct Routing • Serving MSC now has to understand “dial plan” of home network – short codes, other carriers etc – hard: not recommended • Identification of MC • Need to provision MSC with MC address for foreign MSID ranges (or use Global Title) • Billing • Will deal with separately

14. Roaming Service Provider • As per voice, an RSP can assist in network interconnection • RSP can simplify routing rules – all messages go via RSP • If the RSP terminates the messages at the ANSI-41 layer, they can potentially mitigate some interworking issues: • E.g. resolve addressing differences between home and serving networks • The RSP may also be able to provide billing information to the serving and/or home network

15. MSC Intercarrier SMS - An Aside • Intercarrier SMS is messaging between subscribers of two different networks • MC - MC leg may be SMPP, SMTP or ANSI-41 HLR MC MC MSC Operator A Operator B • Different to roaming! • A single message scenario may be both

16. SMS Roaming Billing • Issues with billing are seen as an impediment to wider deployment of SMS roaming • How are operators billing today? • Requirements • Characteristics of Current Networks • Current Solutions • Current Challenges

17. Billing - Requirements • High-level assumptions about what operators want • Serving Operator: • Get paid for providing a service to inbound roamers • Home Operator: • Charge own subscribers for SMS • Cover costs including payment to Serving Operator Subscriber Home Operator Serving Operator

18. Characteristics of Current Networks • Low low pricing at home – bulk, unlimited etc • CDR Production: Home û MSC MC Serving No MSC CDR – no record of message in serving network! MC CDR used by home operator to bill subscriber • Direct Routing provides even less information!

19. Current Solutions for Roaming Billing • For Serving Operator (to charge Home Operator): • Bill & Keep – i.e. don’t bother to recover money • MSC CDRs after all – some network vendors can offer this • Network Probe - sniff/intercept ANSI-41 links and generate billing record • Generate CIBER from either of above two methods • Use RSP bulk billing – Proprietary RSP solution: sum SMS events, price and apply to net settlement position • For Home Operator (to bill subscriber & cover intercarrier cost): • Bill & Keep – no intercarrier cost • Use MC CDR – price to cover intercarrier component • Use CIBER – as per voice – add markup and charge subscriber – not common practice today

20. Current Billing Challenges • For Serving Operator: • RSP bulk billing proprietary to a particular RSP. May be restricted to when Home and Serving Operators are customers of same RSP • Bulk solution only – not auditable to per-SMS level • For Home Operator: • Differential charging – base subscriber charging on roaming location • Ensure that varying costs from different Roaming Partners are covered • Via RSP – MC may not receive any information that will allow it to identify true serving market • No RSP – may not want to populate billing system with all RP MSC point codes if included on MC CDR • Different charging philosophy - What to do if Serving Operator wants to charge for MT but Home doesn’t? • For both Home and Serving Operators: • Cost of billing system change – any change from status quo implies billing system changes – may be hard to justify for current SMS roaming volumes

21. Final Thought… SMS Roaming Works! • It’s not perfect, but customers are using the service, and operators are making money today 

22. Thank you! • Comments & Suggestions welcome: dsalek@qualcomm.com • Get involved: join the Voice & SMS Working Group • To join, send email to: lmackay@qualcomm.com

23. Backup slides • MDN-based MC • Multiple MCs • HLR-initiated SMSNOT • IS-2000 trace example • ANSI-41 trace example • CIBER example for SMS • Subscriber Provisioning Details

24. MDN-based MC • ANSI-41 didn’t account for Wireless Number Portability in SMS operations: • SMS_Request has MSID as a mandatory parameter • MC may only know Mobile Directory Number (MDN) • IS-841 addresses this issue – either MSID or MDN can be used • Standard is written to minimize impacts on serving system

25. Multiple MCs • ANSI-41 states: “There is only one home MC for each MS …” • However some operators send MT-SMS from more than one MC for the same subscriber • Handling of SMS_Notification becomes difficult • Any solution in the home network that relies on custom MSC capabilities will have problems when roaming

26. HLR Registration SMS Notification & Delivery 2 3 4 5 MSC 1 MC HLR-Initiated SMS_Notification • If the HLR knows the subscriber is unavailable (e.g. inactive), it will maintain the SMS Delivery Pending Flag at the time of the SMS_Request, and send the SMS_Notification when the mobile is known to be available:

27. IS-2000 Air Interface Trace Example • MT SMS sent over the Traffic Channel • Originating Address changed to protect the innocent

28. ANSI-41 Trace Example • MO SMS captured between MSC and MC • Identifying information has been removed

29. CIBER SMS Example • MO SMS – record sourced from network probe • Identifying information has been removed

30. Subscriber Provisioning Details • SMS_OriginationRestrictions: • SMS_TerminationRestrictions: