1. Wireless Networks and 2G
Sowjanya Talasila
Kalpana Uppalapati
Karthik Dhoopati
Sudheer Adumulla

2. Agenda Introduction to Wireless Networks 2G Architecture
SS7 and IS-95 protocols
Connection Management
Radio resource management
MSC-MSC interfaces and protocols

3. Advantages of Wireless
Reduced Cost
Accuracy of data
User mobility( Stay connected to the network)
Flexible
Return on investment and increased productivity

4. Limitations
Energy constraints
Variability in network performance

5. Wireless media
Fading
Interference

6. Types of wireless networks
Centralized
User terminals communicate with access points only
Non-centralized
Communication not limited between user terminals and access points

7. Comparision Services Coverage area Limitation Examples Cellular
Handheld phones
Continuous
Limited bandwidth
AMPS, IS-95
WLAN
Extended LAN
Local environments
Limited range
IEEE a,b,g
GPS
3D position,
velocity
Anyplace on earth
Cost
GNSS,
NAVSTAR

8. Wireless Network Mobile Switching Center (MSC) Mobile Data Set
Base Station Controller (BSC)
PSTN
Mobile Voice Unit
Packet Network
Packet Inter-Working Function
Base Transceiver System (BTS)
Challenge is to keep connection and not loose any data during handoff operation

9. Components Base Transceiver System (BTS)
Consists of one or more transceivers at a single location
Base Station Controller (BSC)
Provides allocation and management of radio resources
Mobile Switching Center (MSC)
Provides and controls mobile access to PSTN

10. Contd.. Public Switching Telephone Network (PSTN)
Landline calls initiated from cell get connected via this network

11. Handoff
The technique of handing over a call from one access point to another (as the user moves from one cell to another) without the call getting terminated is handoff

12. Contd..

13. Types of handoff
Soft handoff
Hard handoff

14. Contd..

15. Access Techniques Time Division Multiple Access (TDMA)
Frequency Division Multiple Access (FDMA)
Code Division Multiple Access (CDMA)

16. CDMA o r “Spread Spectrum”
Contd..
FREQUENCY
TIME
User 3
User 2
User 1
TDMA
FREQUENCY
TIME
FDMA 1 2 3
TIME
FREQUENCY
CODE
CDMA o r “Spread Spectrum”
User 3
User 2
User 1

17. Mobile Systems Single high powered transmitters High coverage
Limited number of subscribers

18. Cellular Concept Number of low power transmitters
Large number of subscribers
Increased system capacity without adding more spectrum

19. Frequency reuse
Frequency reuse refers to the use of same radio channels on the same carrier frequency to cover different areas which are seperated by a significant distance

20. Contd..

21. Different generations
1G – Analog, only voice communication
2G – Digital, only voice communication, SMS
2.5G – Digital, voice communication, simple web browsing
3G – Digital, data, voice communication , Multimedia

22. Interfaces and Protocols
Bsc-msc interface and protocols.
Msc-msc interface and protocols.

23. IS-95 Interfaces
A Interface (BSC-MSC) .. This interface is between the BSC and the MSC. It supports both the control plane and user plane
Abis Interface (BTS-BSC)—This is the interface between the BSC and BTS. This is internal interface and generally proprietary
B Interface (MSC-VLR) This interface is defined by TIA IS-41

24. IS-95 interface (cont..)
C Interface (MSC-HLR) This interface uses IS-41 messaging as well
D Interface (HLR-VLR) – HLR-VLR signaling is based on IS-41 as well. It sits on top of SS7
E Interface (MSC-MSC)– Inter MSC signaling is defined in IS-41
L interface (MSC-IWF) This interface allows the ability for circuit switched data in second generation networks
Um Interface (BS-MS) – This is the air interface between the mobile and the network

25. Multiple Access CDMA Benefits of CDMA:
unique digital codes are used to differentiate subscribers
codes are shared by both MS and BS
all users share the same range of radio spectrum
Benefits of CDMA:
Capacity increases: 4 to 5 times (GSM)
Improved call quality
Simplified system planning
Enhanced privacy
Improved coverage characteristics
Increased talk time for portables
Bandwidth on demand

26. CDMA There are two CDMA common air interface standards:
Cellular ( MHz) - TIA/EIA/IS-95A
PCS ( MHz) - ANSI J-STD-008
They are very similar in their features, with exceptions of the frequency plan, mobile identities, and related message fields.
IS-95A
45 MHz spacing for forward & reverse channel
Permissible frequency assignments are on 30 kHz increments

27. Forward CDMA Channel of IS-95A
From BSS to MS
It carries traffic, a pilot signal, and overhead information.
Pilot is a spread but unmodulated
Pilot and overhead channels establish the system timing and station identity.
Pilot channel is also used in the mobile-assisted handoff (MAHO) process as a signal strength reference.

28. Overhead Channels
There are three types of overhead channel in the forward link:
pilot, is required in every station
sync
paging
Pilot channel
pure short code with no additional cover or information content
always code channel zero
a demodulation reference for the mobile receivers and for handoff level measurements
carries no information
all stations use the same short code, distinguished by the phase

29. Overhead Channels Sync Channel Paging channel
sync channel carries timing and system configuration information
data rate is always 1200 bps
Paging channel
used to communicate with MSs when they are not assigned to a traffic channel
successful accesses are normally followed by an assignment to a dedicated traffic channel
paging channel may run at either 4800 or 9600 bps
each BS must have at least one paging channel per sector, on at least one of the frequencies in use

30. Traffic Channel Traffic channels Timing
assigned dynamically, in response to MS accesses, to specific MS
always carries data in 20 ms frames
carry variable rate traffic frames, either 1, 1/2, 1/4, or 1/8 of 9600 bps
rate is independently variable in each 20 ms frame
the 800 bps reverse link power control subchannel is carried on the traffic channel by puncturing 2 from every 24 symbols transmitted.
Timing
all base stations must be synchronized within a few microseconds

31. Overhead Messages System Parameter Message:
configuration of the Paging Channel
registration parameters
parameters to aid pilot acquisition
Access Parameter Message
configuration of the Access Channel
control parameters used to stabilize the Access Channel
Neighbor List Message
time offset of the pilot
basic neighbor configuration
CDMA Channel List Message
CDMA frequency assignment that contain Paging Channels

32. Paging Channel Messages
Page Message:
contains pages to one or more mobile stations.
Order Message:
a broad class of messages used to control a particular MS.
Channel Assignment Message:
let BS to assign a MS to the traffic channel
change Paging Channel Assignment

33. Access Channel
Access Channel provides communications from MS to BS when MS is not using a Traffic Channel.
All Access Channel use 4800 bps mode
Access Channel Message:
call origination
response to pages
orders
registrations
Control of Access Channel transmission is accomplished through the Access Parameter Message sent on the Paging Channel

34. Connection Management
Mobile Origination
Mobile Termination
Call clearing procedure

35. Call origination

36. Call termination

37. Supplementary services
Call waiting
Three way calling
Message notification on the paging system
Message notification on the traffic channel

38. Call waiting

39. Three way calling

40. Call paging on paging/traffic channel

41. Radio Resource Management
Purpose:
Keeps a state of Radio Resources
Allocates Physical Radio Resources
Allocates Scrambling Codes (UL)
Allocates Spreading Codes (DL)
Knows Radio Network Configuration and State Data
Informs PS for current resources state

42. Radio Resource Management
Handles QoS
Controls Cell Capacity and Interference in order to provide an optimal utilization of the wireless interface resources.
Includes RRM Mechanisms:
Power Control
Handover
Call Admission Control
Load Control
Packet Scheduling
Resource Management

43. Handoff Based on Types Signal Quality (thresholds)
Traffic Level (maximum cell capacity or maximum threshold)
User Mobility
Faster movements many handovers
Types
Softer (BSsection1  BS section2)
Soft (BS1  BS2)
Hard (lose connectivity, change frequency)

44. Contd..

45. 2G Access Technologies Frequency division multiple access (FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)

46. FDMA
FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth
Used mainly for analog transmission

47. TDMA
A narrow band that is 30 kHz wide and 6.7 milliseconds long is split time-wise into time slots
Voice data takes up significantly less transmission space
TDMA has three times the capacity of an analog system
Operates in either 800MHz(IS-54) or 1900MHz(IS-136) frequency bands

48. CDMA
After digitizing data, spreads it out over the entire available bandwidth
Multiple calls are overlaid on each other on the channel, with each assigned a unique sequence code.
CDMA is a form of spread spectrum
At the receiver, that same unique code is used to recover the signal

49. Benefits of CDMA Capacity increases: 4 to 5 times
Improved call quality
Simplified system planning
Enhanced privacy
Improved coverage characteristics
Increased talk time for portables

50. Signaling System #7(SS7)
Signaling in Telecommunications Network
Channel Associated Signaling (CAS)
Common Channel Signaling (CCS)
Signaling System Number (SS7) is a form of Common Channel Signaling.
SS7 is a communications protocol that provides signaling and control for
various network services and capabilities

51. Switch A B Voice Trunks Signaling Link Channel Associated Signaling:
Uses In-Band Signaling
Signaling is transmitted in the same frequency band as used by voice.
Voice path is established when the call setup is complete, using the same path that the call setup signals used
Common Channel Signaling:
Uses Out-of-Band Signaling
Employs dedicated path for signaling
Voice trunks are used only when a connection is established ,not before
Faster call setup
Switch A B
Voice Trunks
Signaling Link

52. Functions of SS7 Roaming Subscriber Identification Call forwarding
Basic call setup, management and tear down
Wireless services
Roaming
Subscriber Identification
Local Number Portability (LNP)
Toll-free services (800) and premium (0907)
Advanced call features
Call forwarding
Number display
Conference/party calls

53. Properties of SS7
Interconnected network elements exchange messages using standard protocol
Uses 56 or 64 kbps bi-directional channels called signalling links
All signalling is out-of-band on dedicated channels rather than in-band
Three network nodes called signalling points
Service Switching Point
Service Transfer Point
Service Control Point
Each point has a unique number code used in messages

54. SSP/STP/SCP Used to originate, terminate and tandem calls
Can request routing information from the SCP
STP
Packet switching hub
Removes need for all Signalling Points to be interconnected
May act as a firewall between network operators
SCP
Routing databases
SSP’s and SCP’s are also called end points

55. SS7 Protocol Stack

56. Message Transfer Part (MTP)

57. Message Transfer Part (MTP)
Divided into three parts
MTP Level 1
Provides an interface to the actual physical channel over which communication takes place
CCITT recommends 64Kbps transmission whereas ANSI recommends 56 Kbps
MTP Level 2
Ensures accurate end-to-end transmission
Implements flow control, sequence validation and error checking
MTP Level 3
Provides message routing
Detects and reroutes on link failure or congestion

58. ISDN User Part (ISUP)

59. ISDN User Part (ISUP)
Defines set-up, management and release of trunk circuits for voice/data traffic
Calls that originate and terminate at the same SSP do not use ISUP
Messages are sent from a switch, to the switch where the next circuit connection is required
Call circuits are identified using circuit identification code (CIC)

60. Telephone User Part (TUP)

61. Telephone User Part (TUP)
Handles analogue circuits only
TUP is used to handle call set-up, management, release for the analogue network
Used in countries with less mature networks such as China, South America
As digital networks become the norm ISUP is replacing TUP

62. Signalling Connection Control Part (SCCP)

63. Signalling Connection Control Part (SCCP)
Provides connection oriented / connectionless services to the network
Provides Global Title Translation (GTT)
A GTT may be
800 numbers, Mobile Subscriber ID’s, etc
SCCP translates the GTT into the actual destination SSP point code and subsystem number (SSN)
SSN are codes for applications rather than standard end-points
SCCP is used as the transport layer by TCAP

64. Transaction Capabilities Applications Part (TCAP)

65. Transaction Capabilities Applications Part (TCAP)
Handles exchange of non-circuit related data between applications on the SS7 network using SCCP messages
For example
when a mobile subscriber connects to the network, TCAP carries the Mobile Application Part (MAP) messages between the mobile switches and their supporting databases used for identifying and authentication the device and subscriber
SCP’s use TCAP to query routing tables in the SCP’s

66. Transaction Capabilities Applications Part (TCAP)
TCAP has enabled the development of Intelligent Network (IN) services by supporting connectionless non-circuit related data exchange between signalling points
TCAP messages consist of
Transaction Portion
Basic packet identifier data (type, ID’s, etc)
Component Portion
May be thought of as “function calls” such as invoking, returning, rejecting, etc

67. References Few websites found through Google:-
Few Slides from Dr.Dantu’s 5520 course

68. uestions?