Southern Methodist University Fall 2003 EETS 8316/NTU CC745-N Wireless Networks

1. Southern Methodist University Fall 2003 EETS 8316/NTU CC745-N Wireless Networks Lecture 3: Mobility Management, Air Interface Instructor: Jila Seraj email: jseraj@engr.smu.edu http://www.engr.smu.edu/~jseraj/ tel: 214-505-6303

2. Review In the last meeting we discussed • Basic Structure of PSTN • SS7 as an application of OSI model and its significance in PSTN • Basic structure of a wireless networks • Basic functionalities of wireless networks

3. Access Network

4. Access Network

5. SCP SS7 STP Why SS7

6. OMAP Layer 4-7 INAP MAP ISUP TCAP MUP OSI Model for SS7 SCCP Layer 3 MTP Layer 1-2 Signaling link function, Signaling link physical requirement

7. TDMA Network Structure PSTN AUC EIC GMSC/MSC /VLR HLR Base station controller BSC BSC BSC Air interface Base station Mobile station Base station Base station

8. Basic Functions • Registration • Power Up/Power Down Registration • Location Area Update Registration • Periodical Registration • Initiating a call • Receiving a call • Paging is the process of searching for an MS in the network. Location Areas are needed to make paging efficient

9. Location Area, MSC border MSC-1 LA-1 MSC-1 LA-2 MSC-1 LA-3 MSC-2 LA-1 MSC-2 LA-2

10. Handoff • Movement into a different cell requires MTSO to automatically transfer call to another base station without interruption • Hard handoff: “break before make”, connection is broken then re-established • Soft handoff: temporarily connected to two or more base stations simultaneously before dropping all but one

11. Handoff, (cont) • Initiation: Base station detects measured signal strength drops below threshold (first generation) or mobile station detects signal from another base station is stronger than current base station (second generation) • Resource reservation: frequencies are reserved with new base station • Execution: actual handoff of connection • Completion: unneeded resources are cleared

12. Handoff Challenge • Measured signal strength drop is caused by momentary fading • Handoff must be completed before signal strength drops below a minimum acceptable level • No channels are free at nearby base stations, causing call connection problems, dropped calls. • If mobile station moves to another cellular system (controlled by different MTSO), an intersystem handoff is required - more complicated

13. Handoff, Cont. • There are three type of handoffs • MS controlled handoff • Network controlled handoff • Mobile assisted handoff (MAHO) • D-AMPS and CDMA use MAHO, AMPS uses network controlled handoff. • Capabilities required for the MS are taken into account.

14. BS BS BS Target MSC #2 Target MSC #1 PSTN Serving MSC HANDMREQ HANDMREQ HANDMREQR Handoff, Cont.

15. BS BS Target MSC #1 PSTN Serving MSC FACDIR FACDIRR MSONCH Handoff, Cont.

16. BS BS New Serving MSC PSTN Anchor MSC Handoff, Cont. • What happens if we go back to the anchor MSC? • IS-41 has handoff back facility • What if a third MSC gets involved? • Path minimization process

17. 6 BS 7 BS BS Serving MSC PSTN Anchor MSC 4 Target MSC HANDTHIRD 1 FACDIR 2 FACDIRR 3 HANDTHIRDR 5 MSONCH 8 FACREL 9 FACRELR 10 Path Optimization Process

18. BS BS BS MSC PSTN Anchor MSC New Serving MSC Call Path after path minimization process Path Optimization Process, (cont)

19. More On Roaming • Registration • Power up/down • periodical • New system • Call origination • MS Service Qualification • validation information (billing) • Service profile information, features, restrictions…

20. More On Roaming, cont.. • MS Location Update Process • Location update at registration • Location cancellation, AKA de-registration • MSC triggered • MSINACT with or without De-registration parameter • Bulkdereg, remove all mobiles associated with the MSC • HLR triggered • Location update in another switch • Administrative actions • Data failure in HLR

21. MS Location Management, Border Case • Multiple access problem • IS-41 revision C has a procedure for HLR to determine the best serving system based on the signal quality information received from each system • MSC uses the signal quality information to accept or deny registration cancellation.21

22. Paging • Paging is used when there is a terminating call to a mobile station. • Finding a mobile subscriber requires some work, since its location is not known • The call towards the mobile subscriber is routed towards gateway MSC. • Gateway MSC consults HLR to find the mobiles location

23. Paging, cont.. • HLR looks up in its directory to find the current MSC of the mobile • The address of the current MSC is sent back to the gateway MSC. • Based on that information gateway MSC routes the call to the visiting MSC. • Visiting MSC checks with VLR to find the Location Area for the mobile. All cells in that Location Area are pages simultaneously.

24. Paging, cont.. • Mobile station hears the page and respond to it. • Several base stations in the area might hear the page response. They all report to MSC that the mobile is in their coverage area together with signal level data • MSC filters between these reports and chooses the one that has the strongest signal.

25. Paging, cont.. • MSC chooses an idle voice channel in the chosen Base Station and prepares to set up a voice channel connection. • MSC send a message to HLR informing that the mobile is found together with other useful information such as signal strength, Location Area, etc. • HLR updates its database and forwards the visiting MSC address to the gateway MSC.

26. Paging, cont.. • Gateway MSC has now sufficient information to connect to the visiting MSC. • Gateway MSC send call set up request to the visiting MSC, which sets up the call • What happens when more than one MSC report to GMC that the mobile is its coverage area?

27. Paging, cont.. • When HLR receives more than one response, it chooses the MSC with strongest signal. • It send the address of the chosen VMSC to the gateway MSC and informs other MSC that the call is off. • How does HLR know it has received response from all MSCs? Internal timer

28. Primer on RF • The radio frequencies are grouped into bands. • Each set of bands are dedicated to different purposes by FCC • Each frequency is logically divided into time slots for communication between mobile station and the base station. • Some time slots are reserved for user traffic, such as voice and data and other for signaling purposes.

29. DCCH Reverse Forward SPACH RACH BCCH SCF Reserved PCH ARCH SMSCH FBCCH EBCCH SBCCH Cellular DCCH Structure

30. Cellular DCCH Structure, cont.. • RACH = Random Access Channel • SPACH = SMS, Paging and Access response Channel • PCH = Paging Channel • ARCH =Access Response Channel • SMSCH = SMS Channel

31. Cellular DCCH Structure, cont.. • BCCH= Broadcast Channel • F-BCCH = Fast Broadcast Control Channel • E-BCCH = Extended Broadcast Control Channel • S-BCCH = SMS Broadcast Control Channel • SCF = Shared Channel Feedback • Reserved!

32. Cellular DCCH Structure, cont.. • DCCH Structure: sent on F-BCCH, indicates the structure of DCCH • Access Parameters: sent on F-BCCH, provides data necessary to access RACH. Power level, maximum number of attempts, authentication information • Control Channel Selection parameters: sent on F-BCCH, provides channel reselection parameters

33. Cellular DCCH Structure, cont.. • Registration Parameters: sent on F-BCCH, indicates type of registration, power up, power down, new system, location area, forced and periodic. Also indicates options for de-registration, foreign system registration • System Identity: sent on F-BCCH, identity and type of system (public, private, residential), protocol version, mobile country code. System identity is 15 characters long text.

34. BCCH Message Set • Neighbor Cell: sent on E-BCCH. Included is also reselection criteria for each neighbor cell. Up to 24 neighbor cells can be defined

35. SPACH Message Set • Analog voice channel designation: sent on ARCH, contains channel number, power level, SAT, and protocol version • Digital traffic channel designation: sent on ARCH, contains DTC channel number, etc. • Directed retry, sent on ARCH, forces the mobile to access another DCCH from its neighbor list. Used when resources are not available.

36. SPACH Message Set, cont… • Message Waiting: sent on PCH, inform mobile a message is waiting. The message can be a voice message, SMS message or fax message. • R-DATA: sent on SMSCH, conveys point-to-point teleservice layer message. • R-DATA Accept: sent on SMSCH to acknowledge reception of R-DATA, may include a delay data.

37. SPACH Message Set, cont… • Registration Accept: sent on ARCH, informs mobile that registration is complete, may include paging frame class, current location area, and other system related information. • SPACH Notification: Sent on PCH, informs mobile that the network intends to deliver a message to it on the ARCH or SMSCH and what type of the information mobile should expect.

38. RACH Message Set • Capability Report: Informing the system of mobile’s capability, protocol version, etc. • Origination: is sent when a mobile wants to initiate a voice or data call. Includes calling party number, type of service etc. • Page Response: is sent in response to page, includes essentially the same information as in origination message, except for calling party number.

39. RACH Message Set, cont.. • R-DATA: is used to send point-to-point teleservice layer messages • R-DATA Accept: is sent to acknowledge reception of R-DATA • Registration: request registration with the network • SPACH Confirmation: is sent to network to confirm reception of SPACH notification message.

40. DTC Supervision • DTC has two associated control channels for supervision of the DTC link on layer 3. • FACCH: Fast Associated Control Channel • SACCH: Slow Associated Control Channel • These associated control channels are used in the connection phase to send and receive information.

41. FACCH Message Set, Forward • Alert with Info: sent on FACCH, causes audible or visual signal, may include calling name and number. • Base Station Ack: sent on FACCH. Acknowledges the mobile that certain message is received, such as connect, release. In the case of release message, DCCH information element might be sent to mobile.

42. FACCH Message Set, Forward , cont.. • Dedicated DTC Handoff: sent on FACCH, order mobile to change from one DTC to another DTC. • Flash with Info: sent of FACCH, used to send message waiting information or calling party number to mobile • Flash with Info Ack: sent on FACCH.

43. FACCH Message Set, Forward , cont.. • Handoff: sent on FACCH to order mobile from one DTC to another DTC or AVC • Release: sent on FACCH

44. FACCH & SACCH Message Set, Reverse • Capability Update Request: sent of FACCH • Capability Update Response: sent on FACCH • Connect, sent on FACCH • Flash with info: sent on FACCH, indicates that the user wishes to initiate a special service. • Flash with Info Ack: sent of FACCH, acknowledge receipt of Flash With Info

45. FACCH & SACCH Message Set, Reverse • Mobile Ack: Can be sent on either channel dependent on the type of message it acknowledges. Is sent as response to Alert with info, release, handoff, etc. • Release: sent of FACCH, may contain DCCH information. • Service Request: sent of FACCH, is used when mobile wished to change a service during a call.

46. Network Interfaces, TDMA • IS-41 is used for interface between MSC-VLR, MSC-HLR, HLR-VLR, MSC-MSC, MSC-PSTN, HLR-AC, MC-HLR and MC-MSC • IS-41 can be implemented on the top of MTP, X.25, or IP protocols, though MTP is the common one.

47. IS-41 Protocol Stack

48. PSTN OMC GSM Public land mobile network (PLMN) VLR MSC AUC HLR NMC A EIR BSS BSS BSC ADC BTS BTS OSS Um OSS: operation subsystem BSS: base station subsystem MS: mobile station MS MS MT TE GSM Network Structure

49. North American Numbering Plan • North American Numbering Plan consists of 10 digits, NPA-NXX-XXXX • All phone numbers follow the same structure. • NPA is the area code • NXX is the switch identifier • XXXX indicates the subscriber in the switch

50. North American Numbering Plan, cont… • Due to this structure, there is no way for a switch to identify that a number belongs to a mobile subscriber, nor can it identify the network provider. • Mobile network provider “buy” a certain number series in each area for their users. • Therefore we can not bill a caller to a mobile user for the air usage. They do it in other countries!