#1EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Southern Methodist University Fall 2003 EETS 8316/NTU CC745-N Wireless Networks Lecture 2: Switching Network Instructor : Jila Seraj tel:

#2EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Review In the last meeting we discussed  Motivation for wireless networks  Basic Terminology  Protocol stack  Course objective  Term paper  First assignment: send your goals

#3EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU References and Links  IEEE Wireless Communications, IEEE’s primary wireless magazine. Easy to read articles. Good quality, refereed articles.  IEEE Communications, IEEE’s primary communications magazine. Approximately 50% is wireless related. Easy to read articles. Good quality, refereed articles.

#4EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU References and Links, (Cont)  RCR, Weekly publication. Most articles/stories on-line. Registration on-line also at:  Wireless Week, Weekly publication. Most articles/stories on-line. Registration on-line also at:  for free US spectrum allocation poster

#5EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU References and Links, (Cont)  for spectrum allocation for US market, who has what, latest rulings, etc. 

#6EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#7EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Access Network  Direct Connection  Fast, but very unpractical

#8EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Access Network  Operator in central location  Delay, not good for large networks

#9EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Access Network  Central Switching  Predictable delay, Limited subscribers, Relatively cost effective

#10EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Access Network  Hierarchical Switching  Predictable delay, “unlimited” number of subscribers, cost effective

#11EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#12EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Hierarchical Network  Access Tandem  Tandem  Local  Subscriber

#13EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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?

#14EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#15EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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)

#16EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Why SS7?, (Cont) SCP SS7 STP STP: Signal Transfer Point SCP: Switching Control Point, stores translation Tables

#17EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU OSI Model for SS7 TCAP MAP ISUP INAP MUP OMAP Layer 4-7 SCCP MTP Layer 3 Signaling link function, Signaling link physical requirement Layer 1-2

#18EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#19EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#20EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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)

#21EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU TDMA Network Structure  Home Location Center (HLR)  Authentication Center (AUC)  Equipment Identification Center (EIC)

#22EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU HLR TDMA Network Structure, (Cont) PSTN Base station Air interface Base station GMSC/MSC /VLR BSC Base station controller Mobile station AUC EIC

#23EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#24EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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.

#25EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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.

#26EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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.

#27EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#28EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area LA 1 LA 2 LA3 MSC1 MSC2

#29EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#30EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Power Up Registration  Mobile station sends Registration to BS VMSCHLR VLR 1

#31EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Power Up Registration, (cont)  MSC checks with VLR and finds out the MS does not have a record in VLR VMSCHLR VLR 1 2

#32EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Power Up Registration, (cont)  MSC requests information from HLR. HLR send relevant information after AUC and EIC approve the MS VMSCHLR VLR 1 2 3

#33EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Power Up Registration, (cont)  MSC updates the VLR with MS information, provides the MS with temporary identity and ciphering keys. VMSCHLR VLR

#34EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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.

#35EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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

#36EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Crossing MSC Boundaries Registration  Every time an MSC crosses the boundary between two MSCs, it re-register with the new MSC New VMSC HLR New VLR Old VLR Old VMSC 1

#37EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC 1 2  The new MSC checks with VLR and finds out the MS does not have a record in VLR

#38EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC  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

#39EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC  HLR sends a message to the Old MSC to de-register the MS

#40EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC  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

#41EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC  HLR now sends the requested data about the MS to the new MSC 7

#42EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC  The new MSC updates the New VLR with the MS data 7 8

#43EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Location Area Update Registration New VMSC HLR New VLR Old VLR Old VMSC  The new MSC confirms the registration and provides the MS with temporary identity and ciphering keys

#44EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU Questions?

#45EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU 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.

#46EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU References  Provide name of some good magazine and web pages.