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 2: Switching Network 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 • Motivation for wireless networks • Basic Terminology • Protocol stack • Course objective • Term paper • First assignment: send your goals

3. References and Links • IEEE Wireless Communications, IEEE’s primary wireless magazine. Easy to read articles. Good quality, refereed articles. http://www.comsoc.org • IEEE Communications, IEEE’s primary communications magazine. Approximately 50% is wireless related. Easy to read articles. Good quality, refereed articles. http://www.comsoc.org

4. References and Links, (Cont) • RCR, Weekly publication. Most articles/stories on-line. Registration on-line also at: http://www.rcrnews.com • Wireless Week, Weekly publication. Most articles/stories on-line. Registration on-line also at: http://www.wirelessweek.com • http://www.fair-rite.com for free US spectrum allocation poster

5. References and Links, (Cont) • http://www.fcc.gov for spectrum allocation for US market, who has what, latest rulings, etc. • http://www.phonescoop.com/glossary

6. How Do We Make A call? • A caller dials some digits on it phone • Waits for the called person to answer • Then they talk • How does this connection happen? Network

7. Access Network • Direct Connection • Fast, but very unpractical

8. Access Network • Operator in central location • Delay, not good for large networks

9. Access Network • Central Switching • Predictable delay, Limited subscribers, Relatively cost effective

10. Access Network • Hierarchical Switching • Predictable delay, “unlimited” number of subscribers, cost effective

11. Hierarchical Network • A group of subscribers are directly connected to one local switching center, “Local Switch” • Local switching centers are connected to each other or to a higher level switch, “Tandem Switch” • The hierarchy continues as high as needed. Other types of switches are, Access Tandem, Regional, International

12. Hierarchical Network • Access Tandem • Tandem • Local • Subscriber

13. PSTN Structure • The network discussed above is how PSTN (Public Switched Telephone Network) is structured. • The number of levels in the hierarchy is dependent on the network operator and the traffic. • What happens between these nodes?

14. Voice and Signaling • Signaling is used to transfer information between entities for the purpose of carrying traffic or performing other functions/ services. • Rules governing the signaling between entities are called protocols. • There are many signaling protocols, however Signaling System Number 7 is the most commonly used of all

15. Why SS7? • SS7 permits separation of voice and signaling traffic and is used between switching nodes • This permits using different networks for each task • This opens the door for many functions not available before, such as data base services (800 number services, Intelligent networks, and many others)

16. SCP SS7 STP Why SS7?, (Cont) STP: Signal Transfer Point SCP: Switching Control Point, stores translation Tables

17. 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

18. OSI Model for SS7, (Cont) • MUP: Mobile User Part • MTUP: Mobile Telephony User Part • TCAP: Transfer Control Application Part • ISUP: ISDN User Part • MAP: Mobile Application Part

19. OSI Model for SS7, (Cont) • INAP: Intelligent Network Application Part • OMAP: Operation and Maintenance Application Part • MTP: Message Transfer Part • SCCP: Signaling Connection Control Part

20. TDMA Network Structure • TDMA network consists of the following elements • Mobile station (MS) or mobile phone • Base Station (BS) and antenna • Mobile Switching Center (MSC) and Gateway Mobile Switching Center (GMSC) • Visitor Location Center (VLR) • Home Location Center (HLR)

21. TDMA Network Structure • Home Location Center (HLR) • Authentication Center (AUC) • Equipment Identification Center (EIC)

22. TDMA Network Structure, (Cont) PSTN AUC EIC GMSC/MSC /VLR HLR Base station controller BSC BSC BSC Air interface Base station Mobile station Base station Base station

23. TDMA Network Structure (Cont) • BSC: Detect Mobile Station activity, receive and send signals between MS and MSC, collect measurements, propagate system information, etc. • MSC: Perform call set up functions, communicate mobile activity to VLR and HLR, send and receive MS related information to them, etc • GMSC: Perform as an MSC and gateway to other networks such as PSTN. In reality every MSC also acts as GMSC

24. TDMA Network Structure (Cont) • VLR: Maintain a data base of the MS in the coverage area of the MSC, containing MS features, registration information, etc. Practically, each MSC is co-located with its own VLR, although it is possible that several MSC share one external VLR • HLR: Maintain a database of each MS belonging to the network together with some dynamic and some static information.

25. TDMA Network Structure (Cont) • Dynamic Information are those that will change by mobiles movement in the network such as its current location (which BSC), services activated (call forwarding), last registration time, etc • Static Information are those that will not change by mobiles movement in the network such as access to speed dialing.

26. TDMA Network Structure (Cont) • AUC: Authentication Center. Authenticates that the MS is who it claims to be and provide Ciphering Keys • EIC: Equipment Identification Center maintains a database of permitted equipment, stolen equipment etc.

27. 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

28. Location Area LA3 LA 1 MSC1 MSC2 LA 2

29. Roaming and Registration • When a mobile moves in the network, it is called roaming • When a mobile is powered up, it sends a registration message to BSC. • Registration informs MSC of the presence of the mobile, or that it has changed location • MSC request information about the MS from HLR, which replies with subscriber data

30. Power Up Registration • Mobile station sends Registration to BS HLR VMSC 1 VLR

31. Power Up Registration, (cont) • MSC checks with VLR and finds out the MS does not have a record in VLR HLR VMSC 1 2 VLR

32. Power Up Registration, (cont) • MSC requests information from HLR. HLR send relevant information after AUC and EIC approve the MS HLR VMSC 1 3 2 VLR

33. Power Up Registration, (cont) • MSC updates the VLR with MS information, provides the MS with temporary identity and ciphering keys. HLR VMSC 3 1 2 5 4 VLR

34. Location Area Update Registration • The coverage area of MSC is divided into location areas. Location areas are chosen by the network operator to simplify operation and improve performance of the network. • Every time an MS crosses the boundary between location areas, it re-register with the MSC.

35. Location Area Update Registration • Every time an MSC crosses the boundary between two MSCs, it re-register with the new MSC • When MS crosses MSC boundaries, HLR shall inform the old MSC to delete the entries for that MS from its VLR • Crossing MSC boundaries normally, coincides with crossing location area boundaries

36. Old VMSC HLR New VMSC 1 Old VLR New VLR Crossing MSC Boundaries Registration • Every time an MSC crosses the boundary between two MSCs, it re-register with the new MSC

37. Location Area Update Registration • The new MSC checks with VLR and finds out the MS does not have a record in VLR Old VMSC HLR New VMSC 1 2 Old VLR New VLR

38. 3 Old VMSC HLR New VMSC 1 2 Old VLR New VLR Location Area Update Registration • The new MSC requests information from HLR. HLR consults with AUC and EIC. If all was well, it notices that the MS is already registered in the old MSC

39. Location Area Update Registration • HLR sends a message to the Old MSC to de-register the MS 3 4 Old VMSC HLR New VMSC 1 2 Old VLR New VLR

40. 3 4 Old VMSC HLR New VMSC 1 6 5 2 Old VLR New VLR Location Area Update Registration • Old MSC sends a message to the old VLR to remove records of the MS. After this is done the Old MSC confirms de-registering of the MS to HLR

41. 3 4 Old VMSC HLR New VMSC 1 6 5 2 Old VLR New VLR Location Area Update Registration • HLR now sends the requested data about the MS to the new MSC 7

42. 3 4 Old VMSC HLR New VMSC 1 6 5 2 Old VLR New VLR Location Area Update Registration • The new MSC updates the New VLR with the MS data 7 8

43. Location Area Update Registration • The new MSC confirms the registration and provides the MS with temporary identity and ciphering keys. 3 4 Old VMSC HLR New VMSC 1 7 6 9 5 8 2 Old VLR New VLR

44. Questions?

45. Error correction • What is Error detection and correction • Why do need it • Some examples of error detection/correction • When due to environmental issues one or more bits in the stream of data is corrupted. • Stream of data are divided into smaller packages • Error detection is a mechanism by which the receiver of the data stream can detect that there has been an error. • Example of error detection is one bit parity • Give an example of single parity • Error detection happens when we have enough redundant data to correct the error when it happens. • Give an example of such error correction.

46. References • Provide name of some good magazine and web pages.