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Wireless Networks and 2G
Sowjanya TalasilaKalpana Uppalapati
Karthik DhoopatiSudheer Adumulla
Agenda
Introduction to Wireless Networks 2G Architecture SS7 and IS-95 protocols Connection Management Radio resource management MSC-MSC interfaces and protocols
Advantages of Wireless
Reduced Cost Accuracy of data User mobility( Stay connected to the network) Flexible Return on investment and increased
productivity
Limitations
Energy constraints
Variability in network performance
Wireless media
Fading
Interference
Types of wireless networks
Centralized
User terminals communicate with access points only
Non-centralized
Communication not limited between user terminals and access points
Comparision
Services Coverage area
Limitation
Examples
Cellular Handheld phones
Continuous
Limited bandwidth
AMPS, IS-95
WLAN Extended LAN
Local environments
Limited range
IEEE 802.11a,b,g
GPS 3D position,
velocity
Anyplace on earth
Cost GNSS,
NAVSTAR
Wireless Network
Mobile Data Set
PSTN
PacketNetwork
MobileVoice Unit
Base Transceiver System (BTS)
Base Station Controller
(BSC)
Mobile Switching
Center (MSC)
Packet Inter-Working Function
Challenge is to keep connection and not loose any data during handoff operation
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
Contd..
Public Switching Telephone Network (PSTN)
Landline calls initiated from cell get connected via this network
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
Contd..
Types of handoff
Soft handoff
Hard handoff
Contd..
Access Techniques
Time Division Multiple Access (TDMA)
Frequency Division Multiple Access (FDMA)
Code Division Multiple Access (CDMA)
Contd..
FREQUENCY
TIME
FDMA
1 2 3
FREQUENCY
TIME
User 3
User 2
User 1
TDMA
TIME
FREQUENCY
CODE
CDMAo r “Spread Spectrum”
User 3
User 2
User 1
Mobile Systems
Single high powered transmitters
High coverage
Limited number of subscribers
Cellular Concept
Number of low power transmitters
Large number of subscribers
Increased system capacity without adding more spectrum
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
Contd..
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
Interfaces and Protocols
Bsc-msc interface and protocols. Msc-msc interface and protocols.
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
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
Multiple Access
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
CDMA
There are two CDMA common air interface standards: Cellular (824-894 MHz) - TIA/EIA/IS-95A PCS (1850-1990 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
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.
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
Overhead Channels
Sync 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
Traffic Channel
Traffic channels 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
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
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
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
Connection Management
Mobile Origination Mobile Termination Call clearing procedure
Call origination
Call termination
Supplementary services
Call waiting Three way calling Message notification on the paging system Message notification on the traffic channel
Call waiting
Three way calling
MS BS MSCtime comment
a
bFlash with Information
Flash with Information
c
dFlash with Information
Flash with Information (2nd party called address)
e
fFlash with Information
Flash with Information
g
hFlash with Information
Flash with Information
Call paging on paging/traffic channel
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
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
Handoff
Based on 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)
Contd..
2G Access Technologies
Frequency division multiple access (FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)
FDMA
FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth
Used mainly for analog transmission
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
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
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
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
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
SwitchA
SwitchB
Voice Trunks
Signaling Link
Functions of SS7
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
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
SSP/STP/SCP SSP
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
SS7 Protocol Stack
Physical
Data Link
Network
Transport
Session
Presentation
Application
Message Transfer Part Level 1
OS
I R
efe
ren
ce M
od
el
Message Transfer Part Level 2
Message Transfer Part Level 3
ISDNUserPart
SCCP
TransactionCapabilitiesApplications
Part
Te
lep
ho
ne
Us
er P
art
SS
7 P
roto
col S
tack
Message Transfer Part (MTP)
Message Transfer Part Level 1
Message Transfer Part Level 2
Message Transfer Part Level 3
ISDNUserPart
SCCP
TransactionCapabilitiesApplications
Part
Te
lep
ho
ne
Us
er P
art
SS
7 P
roto
col S
tack
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
ISDN User Part (ISUP)
Message Transfer Part Level 1
Message Transfer Part Level 2
Message Transfer Part Level 3
ISDNUserPart
SCCP
TransactionCapabilitiesApplications
Part
Te
lep
ho
ne
Us
er P
art
SS
7 P
roto
col S
tack
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)
Telephone User Part (TUP)
Message Transfer Part Level 1
Message Transfer Part Level 2
Message Transfer Part Level 3
ISDNUserPart
SCCP
TransactionCapabilitiesApplications
Part
Te
lep
ho
ne
Us
er P
art
SS
7 P
roto
col S
tack
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
Signalling Connection Control Part (SCCP)
Message Transfer Part Level 1
Message Transfer Part Level 2
Message Transfer Part Level 3
ISDNUserPart
SCCP
TransactionCapabilitiesApplications
Part
Te
lep
ho
ne
Us
er P
art
SS
7 P
roto
col S
tack
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
Transaction Capabilities Applications Part (TCAP)
Message Transfer Part Level 1
Message Transfer Part Level 2
Message Transfer Part Level 3
ISDNUserPart
SCCP
TransactionCapabilitiesApplications
Part
Te
lep
ho
ne
Us
er P
art
SS
7 P
roto
col S
tack
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
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
References
Few websites found through Google:-
www.intellinet-tech.com/Solutions/wirelessnetworks.htm
www.informit.com/articles/article.asp?p=26330
Few Slides from Dr.Dantu’s 5520 course
uestions?
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