Wireless technologies - Part 1

by

Tinniam.V.Ganesh
http://gigadom.wordpress.com

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Agenda – Session 1

1. Telecom and Wireless basics
2. History of Telecom
3. Digital Switching
4. Anatomy of Telephone call
5. PCM, Sampling, Nyquist criteria
6. Multiplexing
7. Principles of digital switching, time slot interchange
8. Signaling events, ISUP Call flow
9. Recap
10. SS7 Protocol Stack
11. SS7 Layers
12. Wireless Technology Terminologies
13. Recap
14. Quiz

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Trends in Telecom

Technology Realization Period

Strowger, Electromechanical ~1877 - 1975
Crossbar relays. Operator
exchanges intervention

Digital Time slot interchange. ~1965 onwards
Switches Entirely digital

Softswitch Separation of control ~1996 onwards
and bearer signaling. IP
as transport mechanism

IMS SIP, SDP signaling. All ~ 2000 onwards
IP Core.

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Historical beginnings of
Telecom…

Samuel Morse invents telegraph in 1837.

Alexander Graham Bell invents telephone in 1874.

Marconi experiments with wireless telegraph

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Early switching exchanges

The initial exchanges were electro mechanical viz.
Strowger and Cross bar exchange
Later the exchanges became entirely digital and were known
as Electronic Switching System (ESS)

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Information transmitted as electrical signals

Mouth piece converts audio
signal to electrical signal

Electrical signal transmitted
over twisted pair

Electrical signal converted to
vibrations in earpiece

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Digital Switches
• Digital Switches

• Sample voice signal
• Digitize voice samples
• Convert to Pulse Code Modulation
• Multiplex at sending end and de-multiplex at receiving end
• Perform Time slot switching or Time Slot Interchange

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Pulse Code Modulation

Voice is transmitted using Pulse Code Modulation.

At the sending the voice signal is sampled, and modulated
before transmission

At the receiving end the signal is demodulated to obtain the
original signal

Pulse-code modulation (PCM) is a digital representation of an
analog signal where the magnitude of the signal is sampled
regularly at uniform intervals, then quantized to a series of
symbols in a numeric (usually binary) code.

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Bandwidth of human voice
Audible speech is in the range of 300 Hz to 4 KHz.

Sampling & quantization

Sampling is the reduction of a continuous signal to a discrete signal

Quantization is the process of approximating a continuous range of values (or a
very large set of possible discrete values) by a relatively small set of discrete
symbols or integer values.

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Nyquist sampling frequency

Nyquist sampling frequency requires that in order to faithfully reproduce a
signal at the receiving end the sampling frequency should be twice that of
highest frequency

Voice bandwidth is 300 Hz – 4 KHz.

Hence the sampling frequency should be 8 KHz.

Sampling a sine wave

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Calculations in PCM

8 bits per PCM sample and sampled at 8 KHz

8 bits * 8000 samples per sec = 64000 bits/s = 64 Kbps

This is also known as DS0 or E0

Digitizing sampled levels

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G. 711
G.711 is an ITU-T standard for audio companding. It is primarily used in telephony.
The standard was released for usage in 1972.

G.711 represents logarithmic pulse-code modulation (PCM) samples for signals of
voice frequencies, sampled at the rate of 8000 samples/second.

A – law and µ - Law
The µ-law and A-law algorithms encode 14-bit and 13-bit signed linear PCM
samples (respectively) to logarithmic 8-bit samples. Thus, the G.711 encoder will
create a 64 kbit/s bitstream for a signal sampled at 8 kHz.

There are two main compression algorithms defined in the standard, the µ-law
algorithm (used in North America & Japan) and A-law algorithm (used in Europe
and the rest of the world).

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Multiplexing
In telecommunications , multiplexing, is used to refer to a process where
multiple analog message signals or digital data streams are combined into one
signal over a shared medium. For example, in telecommunications, several
phone calls may be transferred using one wire.

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Time-Division Multiplexing

In Time-Division Multiplexing (TDM) two or more signals or bit streams are
transferred simultaneously as sub-channels in one communication channel. The
time domain is divided into several recurrent timeslots of fixed length, one for
each sub-channel. A sample byte or data block of sub-channel 1 is transmitted
during timeslot 1, sub-channel 2 during timeslot 2, etc.

Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8

Time

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Standards in PCM transmission
There are 2 main standards in the world for transmission of PCM signals

T-Carrier – This is used in the North American market
E-Carrier – This is used for European market

T1 – 24 channels * 64 Kbps = 1.544 Mbps

E1 – 32 channels * 64 Kbps = 2.048 Mbps

Level North American European

0 64 Kbps 64 kbps

1 1.544 Mbps (T1) 2.048 Mbps (E1)

2 6.312 Mbps (T2) 8.448 (E2)

3 44.736 Mbps (T3) 34.368 (E3)

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Digital switches
Digital switches aka as Electronic switches receive digitized voice samples.
 Voice is sampled and digitized
 Digitized PCM voice samples come to the digital switch
Switching or connecting callee and called party happens in memory by
switching the voice samples in two different time slots
Switching happens through a Time-Space-Time switching fabric

Signaling
&
Control

Time
T Line Slot Line T
D Interfaces Inter- Interfaces D
M M
change

Architecture of a traditional circuit switch

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Circuit Switching - Time Slot Interchange
Functionality

5 7 Time Slot 7 5
Interchange
k
i
i
k

Data in i 5 Data
out

k 7 Read Address
Write Address
k i

Speech memory
i k

Time slot counter

Connection
18 memory
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Signaling events in Telecom network

1. Off-hook or origination
2. Dialing
3. Ringing and Ring Back Tone (RBT)
4. Answer
5. Disconnection

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Terminations at a Digital switch

Digital switches connect the following terminations

3.Normal landlines or lines.
4.Trunk Lines (E1,E2,T1,T2 etc)

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Classes of Telecom switches
• Class 5 switCh – This switch has both lines and trunks. This switch
also supports features like call forwarding, call hold etc

Class 5 switch

• Class 4 switCh – This switch only supports trunks. This is also
known as a Transit switch

Class 5 switch Class 4 switch Class 5 switch

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ISUP Call Flow

Switch A Switch B
A dials digits
Initial Address Message (IAM) B’s phone rings..

Address Complete Message (ACM)

B Answers

Answer Message (ANM)
A disconnects

Release Message (REL)
B disconnects
Release Complete (RLC)

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Wireless
Networks
Wireless networks support wireless telephone calls using cell phones.
The digital switch in a wireless network is called a MSC.

The network elements in a wireless network are
5.MSC – Mobile Switching Center. This network element is switches the
wireless calls between the calling and called mobile telephone
6.HLR – Home Location Register - This is a database and stores the feature
supported by each mobile phone viz. IMEI number, IMSI, features
subscribed by the subscriber
7.BTS – Base Transceiver Station. This network element keeps track of the
location of mobiles and the forwards the digitized voice to the MSC
8.BSC – Controls several BTS
9.SCP – Service Control Point – Supports Intelligent Network
10.VLR – Visitor Location Network – Keeps tracks mobiles roaming in its
network

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Wireless Network

HLR SCP

Mobile Switching Centre
(MSC) VLR
BSC
BTS

Other
MSC

BTS

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Benefits of the circuit switches

Digital Switches have the following merits
 Are very feature rich. Lucent’s 5ESS has close to 3000 features
 Support 99.9999 % (6 nine’s) availability
Support all regulatory services like 911, CALEA etc

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SIGNALING SYSTEM 7 (SS7)

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WHAT IS COMMUNICATION ?
• Communication is used between 2 network elements to exchange information.
• There are 2 types of domains in the communication world
 Data communication
 Telecommunication

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DIFFERENCES BETWEEN TELECOM & DATACOM

Telecommunication Data Communication

Network used for making voice calls Network used for transferring data from
between telephones one computer to another

Telephones were the end points Computers were the end point

Uses protocols like ISUP, ISDN Predominantly uses TCP/IP

Network elements are MSC, HLR, SCP Network elements are Routers, hubs,
etc ATMs, bridges etc
Uses circuit switching Uses packet switching

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NETWORKS OF TODAY …
• In the networks of today telecommunication networks are used to download data
e.g.GPRS

• Data networks are used for making Voice Calls e.g. VOIP

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WHAT IS SIGNALING ?
• Signaling refers to the exchange of information between network elements
• Signaling between network elements follows a specific protocol
• A Protocol refers to the set of rules for communicating between the elements

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WHAT IS SS7 SIGNALING ?
 Signaling System 7 was devised by ITU-T (formerly known as CCITT)
 Initially the signaling in trunks used to happen on the same channel in which
the voice call used to occur. Hence call setup, digits etc would use the same
line as the actual voice circuit
 In SS7 a separate channel is allocated just for signaling. This is known as
Out-Of- Band signaling

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SS7 SIGNALING
• Signaling happens in a separate channel outside of the voice channels
• A separate timeslot is used to transfer signaling messages like call setup,
teardown etc
• This is also known as Common Channel Signaling (CCS)

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ADVANTAGES OF OUT OF BAND SIGNALING
• Allows signaling at any phase of the call
• Allows upto 56 Kbps of signaling information

Switch A Switch B

Voice Trunk

Signaling Link

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SS7 STACK

CAP,MAP
…
Application layer
ISUP,TUP..
TCAP

SCCP Network layer
MTP 3 Network layer
MTP 2 Data link layer

MTP 1 Physical layer

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SS7 LAYERS
• MTP – Message Transfer Part
• SCCP – Signaling and Connection Control Part
• TCAP – Transaction Capabilities Application Part
• CAP – CAMEL Application Part
• ISUP – ISDN User Part
• MAP – Mobile Application Part

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SS7 PROTOCOLS
SS7 protocols can be classified as call related and non-call related

• Call related protocols – ISUP (ISDN User Part), B-ISUP (Broadband – ISUP)

• Non-call related protocols –
– INAP (Intelligent Network Application Part)
– CAP (CAMEL Application Part)
– MAP (Mobile Application Part)
– …

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SS7 STANDARD BODIES
• The SS7 standard body for North American market is ANSI (American National
Standards Institute). The ANSI versions are ANSI ISUP, ANSI TCAP etc.

• The SS7 standard body for European market is ETSI (formerly CCITT). The ETSI versions
of the protocols are ETSI ISUP, ETSI TCAP etc.

• There are minor variations in the protocols by the two standard bodies.

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SS7 Link speeds

There are 2 main standards in the world for transmission of PCM
signals

T-Carrier – This is used in the North American market
E-Carrier – This is used for European market

T1 – 24 channels * 64 Kbps = 1.544 Mbps

E1 – 32 channels * 64 Kbps = 2.048 Mbps

Level North American European

0 64 Kbps 64 kbps

1 1.544 Mbps (T1) 2.048 Mbps (E1)

2 6.312 Mbps (T2) 8.448 (E2)

3 44.736 Mbps (T3) 34.368 (E3)

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SS7
• Signaling System Number 7 (SS#7 or C7) is the protocol used by the
telephone companies for interoffice signaling. In the past, in-band signaling
techniques were used on interoffice trunks. This method of signaling used
the same physical path for both the call-control signaling and the actual
connected call. This method of signaling is inefficient and is rapidly being
replaced by out-of-band or common-channel signaling techniques.

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SS7 Stack

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SS7 Layers
Physical Layer (MTP-1)
• This defines the physical and electrical characteristics of the signaling links of the SS7
network. Signaling links utilize DS–0 channels and carry raw signaling data at a rate of
56 kbps or 64 kbps (56 kbps is the more common implementation).

Message Transfer Part—Level 2 (MTP-2)
• The level 2 portion of the message transfer part (MTP Level 2) provides link-layer
functionality. It ensures that the two end points of a signaling link can reliably
exchange signaling messages. It incorporates such capabilities as error checking, flow
control, and sequence checking.

Message Transfer Part—Level 3 (MTP-3)
• The level 3 portion of the message transfer part (MTP Level 3) extends the functionality
provided by MTP level 2 to provide network layer functionality. It ensures that messages
can be delivered between signaling points across the SS7 network regardless of whether
they are directly connected. It includes such capabilities as node addressing, routing,
alternate routing, and congestion control.

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SS7 Layers (contd.)
Signaling Connection Control Part (SCCP)
• The signaling connection control part (SCCP) provides two major functions that are
lacking in the MTP. The first of these is the capability to address applications within a
signaling point. The MTP can only receive and deliver messages from a node as a whole;
it does not deal with software applications within a node.
• While MTP network-management messages and basic call-setup messages are
addressed to a node as a whole, other messages are used by separate applications
(referred to as subsystems) within a node. Examples of subsystems are 800 call
processing, calling-card processing, advanced intelligent network (AIN), and custom
local-area signaling services (CLASS) services (e.g., repeat dialing and call return). The
SCCP allows these subsystems to be addressed explicitly.

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SCCP
• The second function provided by the SCCP is Global Title translation, the ability to
perform incremental routing using a capability called global title translation (GTT). GTT
frees originating signaling points from the burden of having to know every potential
destination to which they might have to route a message. A switch can originate a
query, for example, and address it to an STP along with a request for GTT. The receiving
STP can then examine a portion of the message, make a determination as to where the
message should be routed, and then route it.
• For example, calling-card queries (used to verify that a call can be properly billed to a
calling card) must be routed to an SCP designated by the company that issued the
calling card. Rather than maintaining a nationwide database of where such queries
should be routed (based on the calling-card number), switches generate queries
addressed to their local STPs, which, using GTT, select the correct destination to which
the message should be routed. Note that there is no magic here; STPs must maintain a
database that enables them to determine where a query should be routed. GTT
effectively centralizes the problem and places it in a node (the STP) that has been
designed to perform this function.
• In performing GTT, an STP does not need to know the exact final destination of a
message. It can, instead, perform intermediate GTT, in which it uses its tables to find
another STP further along the route to the destination. That STP, in turn, can perform
final GTT, routing the message to its actual destination.
• Intermediate GTT minimizes the need for STPs to maintain extensive information about
nodes that are far removed from them. GTT also is used at the STP to share load among
mated SCPs in both normal and failure scenarios. In these instances, when messages
arrive at an STP for final GTT and routing to a database, the STP can select from among
available redundant SCPs. It can select an SCP on either a priority basis (referred to as
primary backup) or so as to equalize the load across all available SCPs (referred to as
load sharing).

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ISUP
ISDN User Part (ISUP)
• ISUP user part defines the messages and protocol used in the establishment and tear
down of voice and data calls over the public switched network (PSN), and to manage the
trunk network on which they rely. Despite its name, ISUP is used for both ISDN and
non–ISDN calls. In the North American version of SS7, ISUP messages rely exclusively
on MTP to transport messages between concerned nodes.

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SS7 Layers (contd.)
Transaction Capabilities Application Part (TCAP)
• TCAP defines the messages and protocol used to communicate between applications
(deployed as subsystems) in nodes. It is used for database services such as calling card,
800, and AIN as well as switch-to-switch services including repeat dialing and call
return. Because TCAP messages must be delivered to individual applications within the
nodes they address, they use the SCCP for transport.

Operations, Maintenance, and Administration Part (OMAP)
• OMAP defines messages and protocol designed to assist administrators of the SS7
network. To date, the most fully developed and deployed of these capabilities are
procedures for validating network routing tables and for diagnosing link troubles. OMAP
includes messages that use both the MTP and SCCP for routing.

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SS7 Layers (contd.)
Mobile Application Part (MAP) messages sent between mobile switches and databases to
support user authentication, equipment identification, and roaming are carried by
TCAP. In mobile networks (IS-41 and GSM) when a mobile subscriber roams into a new
mobile switching center (MSC) area, the integrated visitor location register requests
service profile information from the subscriber's home location register (HLR) using MAP
(mobile application part) information carried within TCAP messages.
• The Mobile Application Part (MAP), one of protocols in the SS7 suite, allows for the
implementation of mobile network (GSM) signaling infrastructure. The premise behind
MAP is to connect the distributed switching elements, called mobile switching centers
(MSCs) with a master database called the Home Location Register (HLR). The HLR
dynamically stores the current location and profile of a mobile network subscriber. The
HLR is consulted during the processing of an incoming call. Conversely, the HLR is
updated as the subscriber moves about the network and is thus serviced by different
switches within the network.
• MAP has been evolving as wireless networks grow, from supporting strictly voice, to
supporting packet data services as well. The fact that MAP is used to connect NexGen
elements such as the Gateway GPRS Support node (GGSN) and Serving Gateway
Support Node (SGSN) is a testament to the sound design of the GSM signaling system.
• MAP has several basic functions:
• Mechanism for a Gateway-MSC (GMSC) to obtain a routing number for an incoming call
• Mechanism for an MSC via integrated Visitor Location Register (VLR) to update
subscriber status and routing number.
• Subscriber CAMEL trigger data to switching elements via the VLR
• Subscriber supplementary service profile and data to switching elements via the VLR.

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ISUP
• ISUP (ISDN User Part) defines the messages and protocol used in the establishment and
tear down of voice and data calls over the public switched telephone network (PSTN),
and to manage the trunk network on which they rely. Despite its name, ISUP is used for
both ISDN and non–ISDN calls. In the North American version of SS7, ISUP messages
rely exclusively on MTP to transport messages between concerned nodes.
• ISUP controls the circuits used to carry either voice or data traffic. In addition, the state
of circuits can be verified and managed using ISUP. The management of the circuit
infrastructure can occur both at the individual circuit level and for groups of circuits.
• Services that can be defined using ISUP include: Switching, Voice mail, Internet offload.
ISUP is ideal for applications such as switching and voice mail in which calls are routed
between endpoints.
• When used in conjunction with TCAP and SIGTRAN, ISUP becomes an enabler for
Internet offload solutions in which Internet sessions of relatively long duration can be
isolated from relatively brief phone conversations.

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IMSI

The IMSI (International Mobile Subscriber Identity) is a unique 15-digit code used to
identify an individual user on a GSM network.
The IMSI consists of three components:
– Mobile Country Code (MCC)
– Mobile Network Code (MNC)
– Mobile Subscriber Identity Number (MSIN)
– The IMSI is stored in the Subscriber Identity Module (SIM).
– It is also used for acquiring other details of the mobile in the Home Location
Register (HLR) or as locally copied in the Visitor Location Register.
– The IMSI is used in any mobile network that interconnects with other
networks, in particular CDMA and EVDO networks as well as GSM networks.
This number is provisioned in the phone directly

IMSI - 310150123456789
MCC 310 USA
MNC 150 AT&T
MSIN 123456789 MSIN

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TMSI
TMSI –Temporary Mobile Subscriber Identity

• A TMSI is used to protect the true identity (IMSI) of a subscriber. It is issued by and
stored within a VLR (not in the HLR) when an IMSI attach takes place or a Location
Area (LA) update takes place. At the MS it is stored in the MS’s SIM. The issued TMSI
only has validity within a specific LA.

• Since TMSI has local significance, the structure may be chosen by the administration. It
should not be more than four octets.

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MSISDN
MSISDN
• MSISDN is a number uniquely identifying a subscription in a GSM or
a UMTS mobile network. Simply put, it is the telephone number of the SIM card in a
mobile/cellular phone. This abbreviation has several interpretations, the most
common one being "Mobile Subscriber Integrated Services Digital Network Number".
• The MSISDN together with IMSI are two important numbers used for identifying a
mobile subscriber. The latter identifies the SIM, i.e. the card inserted in to the mobile
phone, while the former is used for routing calls to the subscriber.
• The MSISDN represents the ‘true’ or ‘dialled’ number associated with the subscriber.
It is assigned to the subscriber by the network operator at registration and is stored
in the SIM.

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IMEI
IMEI
• The International Mobile Equipment Identity or IMEI is a number, usually unique,to
identify GSM, WCDMA, and mobile phones, as well as some satellite phones. It is
usually found printed inside the battery compartment of the phone. It can also be
displayed on the screen of the phone by entering *#06# into the keypad on most
phones.
• The IMEI number is used by the GSM network to identify valid devices and therefore
can be used for stopping a stolen phone from accessing the network in that country.
For example, if a mobile phone is stolen, the owner can call his or her network
provider and instruct them to "ban" the phone using its IMEI number

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MSRN
MSRN – Mobile Station Roaming Number

The MSRN is a temporary, location-dependant ISDN number issued by the parent VLR to all
MSs within its area of responsibility. It is stored in the VLR and associated HLR but not
in the MS. The MSRN is used by the VLR associated MSC for call routing within the
MSC/VLR service area.

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Intelligent Network
G M S C

g sm S S F
C

g sm S R F g sm S C F H L R

D

g sm S S F V L R
B
M S C

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INAP
• Intelligent Network Application Part (INAP) is the signaling protocol used in Intelligent
Networking. Developed by the International Telecommunication Union(ITU), IN is
recognized as a global standard. Within the International Telecommunications Union, a
total functionality of the IN has been defined and implemented in digestible segments
called capability sets. The first version to be released was Capability Set 1 (CS-1).
Currently CS-2 is defined and available. The CAMEL Application Part (CAP) is a
derivative of INAP and enables the use of INAP in mobile GSM networks.

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Service Switching Point (SSP)
• Service Switching Point (SSP) is a physical entity in the Intelligent Network that
provides the switching functionality. SSP the point of subscription for the service user,
and is responsible for detecting special conditions during call processing that cause a
query for instructions to be issued to the SCP.
• The SSP contains Detection Capability to detect requests for IN services. It also contains
capabilities to communicate with other physical entities containing SCF, such as SCP,
and to respond to instructions from the other physical entities. Functionally, an SSP
contains a Call Control Function, a Service Switching Function, and, if the SSP is a
local exchange, a Call Control Agent Function. It also may optionally contain Service
Control Function, and/or a Specialized Resource Function, and/or a Service Data
Function. The SSP may provide IN services to users connected to subtending Network
Access Points.
• The SSP is usually provided by the traditional switch manufacturers. These switches
are programmable and they can be implemented using multipurpose processors. The
main difference of SSP from an ordinary switch is in the software where the service
control of IN is separated from the basic call control.

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Service Control Point (SCP)
• Service Control Point (SCP) validates and authenticates information from the service
user, processing requests from the SSP and issuing responses.The SCP stores the
service provider instructions and data that direct switch processing and provide call
control. At predefined points during processing an incoming or outgoing call, the switch
suspends what it is doing, packages up information it has regarding the processing of
the call, and queries the SCP for further instruction. The SCP executes user-defined
programs that analyze the current state of the call and the information received from
the switch. The programs can then modify or create the call data that is sent back to
the switch. The switch then analyzes the information received from the SCP and follows
the provided instruction to further process the call.
• Functionally, an SCP contains Service Control Function (SCF) and optionally also
Service Data Function (SDF). The SCF is implemented in Service Logic Programs (SLP).
The SCP is connected to SSPs by a signalling network. Multiple SCPs may contain the
same SLPs and data to improve service reliability and to facilitate load sharing between
SCPs. I

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Intelligent Peripheral (IP)
• Intelligent Peripheral (IP) provides resources such as customized and concatenated
voice announcements, voice recognition, and Dual Tone Multi-Frequencies (DTMF) digit
collection, and contains switching matrix to connect users to these resources. The IP
supports flexible information interactions between a user and the network.
Functionally, the IP contains the Special Resource Function. The IP may directly
connect to one or more SSPs, and/or may connect to the signalling network.

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SS7 APPLICATION LAYER
• At the application layer there are the following protocols
• Call related
– ISDN User Part (ISUP) supports basic telephone call connect/disconnect between
end offices.
• Non-call related
– CAP – Camel Application Part is used to access a database ,the SCP and influence
the call

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SS7 SIGNALING ARCHITECTURE
There are 3 main elements in SS7 signaling architecture

SSP – These are SS7 capable digital switches
STP – These are SS7 capable network elements that route incoming SS7 messages to the
correct destination
SCP – These are databases which take part in non-call related SS7 signaling

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ISUP CALL FLOW
Switch A Switch B
A dials digits
Initial Address Message (IAM) B’s phone rings..

Address Complete Message (ACM)

B Answers

Answer Message (ANM)
A disconnects

Release Message (REL)
B disconnects
Release Complete (RLC)

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ISUP
A simple call flow using ISUP signaling is as follows:
Call set up: When a call is placed to an out-of-switch number, the originating SSP transmits
an ISUP initial address message (IAM) to reserve an idle trunk circuit from the
originating switch to the destination switch. The destination switch rings the called party
line if the line is available and transmits an ISUP address complete message (ACM) to the
originating switch to indicate that the remote end of the trunk circuit has been reserved.
The STP routes the ACM to the originating switch which rings the calling party's line and
connects it to the trunk to complete the voice circuit from the calling party to the called
party.

Call connection: When the called party picks up the phone, the destination switch
terminates the ringing tone and transmits an ISUP answer message (ANM) to the
originating switch via its home STP. The STP routes the ANM to the originating switch
which verifies that the calling party's line is connected to the reserved trunk and, if so,
initiates billing.

Call tear down: If the calling party hangs-up first, the originating switch sends an ISUP
release message (REL) to release the trunk circuit between the switches. The STP routes
the REL to the destination switch. If the called party hangs up first, or if the line is busy,
the destination switch sends an REL to the originating switch indicating the release
cause (e.g., normal release or busy). Upon receiving the REL, the destination switch
disconnects the trunk from the called party's line, sets the trunk state to idle, and
transmits an ISUP release complete message (RLC) to the originating switch to
acknowledge the release of the remote end of the trunk circuit. When the originating
switch receives (or generates) the RLC, it terminates the billing cycle and sets the trunk
state to idle in preparation for the next call.

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SS7 VS OSI STACK

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Questions ?

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Quiz 1
1. PCM is the technique where the magnitude of the signal is sampled and digitized.
a) True b) False
2. The bit rate of DS0 or E0 PCM channel is
a) 56 Kbps b) 2 Mbps c) 64 Kbps d) 8 Khz
3. Time division multiplexing is
a. Transferring multiple lower rate channels onto higher bit rate channel
b. Sampling a signal in multiples of time
c. Using several carrier frequencies to multiplex a channel
d. Uses G.711 law
4. T Carrier is North American market and E Carrier is European
a. True b. False
5. The principle of digital switching is based on
a. Mapping IP addresses to port numbers
b. Performing layer 2 switching
c. Based on Time slot interchange
d. OSI Network layer

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Quiz 1
1. Which of the below is not a signaling event
a. Off hook b. On –hook c. Ringing d. conversation
2. Central Offices are usually
a. Class 4 switch b. Class 5 switch c. Classless switch d. Class 3 switch
3. What is the ISUP message that is returned when B party answers
a. ACM b) ANM c) REL d) IAM
4. Which element is not usually considered as a part of a wireless network
a. HLR b. MSC c. Router d. VLR
10. Which of the following is true of SS7 protocol
a. is an out-of-band signaling b. Uses in-band signaling c. Devises by IETF d. is based on OSI
11. Which of the following is not a function of the SCCP Layer
a. Routing to Signaling points b. Routing to subsystems c. Performing electrical properties d.
Doing flow control
12. A person’s mobile number is
a. IMSI b. IMEI c. TMSI d. MSISDN
13. The IN architecture does not include
a. SSP b. SCP d. IP e. HLR

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Agenda – Session 2
Evolution of Wireless Technologies
2. Comparison of SS7 & OSI stack
3. 1G
4. 2G
5. 2.5G
6. 3G
7. 3.5G
8. 4G
9. Recap
10. TDMA, FDMA, CDMA
11. CDMA Basics
12. GSM Architecture
13. Access, Core Network
14. Cellular concepts - Roaming, Registration, Handoff
15. Traffic Engineering concepts
16. Recap
17. Quiz 2

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First Mobile radio 1924

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First Generation Systems (1G)

These were analog systems
Advanced Mobile Phone Service (AMPS)
• US trials 1978; deployed in Japan (’79) & US (’83)
• 800 MHz band — two 20 MHz bands
• Still widely used in US and many parts of the world
• Uses FDMA

Nordic Mobile Telephony (NMT)
• Launched in 1981
• Sweden, Norway, Finland
• Initially 450 Mhz, later in the 900 MHz band

Total Access Communication System (TACS)
• Similar to AMPS,
• British design in 1985

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Second Generation (2G)
• Digital Systems
• Leverage technology to increase capacity
– Speech compression, digital signal processing
• Greater security against fraud
Variety of 2G Systems

IS-54 and IS-136
Uses Time Division Multiplexing (TDM). Introduced in 1990 in North America
Digital voice channels and analog control channels

IS-136
Introduced in 1994 in North America
Digital Voice and digital control channels

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Second generation 2G (contd)
GSM
GSM was developed in 1982 under Conference on European Posts and Telecommunications
(CEPT)
Formal standardization took place in 1989 under ETSI
GSM operates in 900 MHz band
Uses TDMA.

IS-95 CDMA
Both IS-136 & GSM use TDMA.
CDMA all users share same frequency. The signal from each user is modulated with a
separate code.
Introduced in 1989 by Qualcomm, San Diego, Califormia
Deployed in North America and Korea.
In North America occupies 800 Mhz band

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Interfaces between components
MS
Um

BTS VLR HLR

BSC
Abis MSC
A B H
MS C AuC
BTS GMSC
E F
Abis
EIR
A E
MSC

BSC PSTN
Um
BTS X.25
VLR
X.25
OMC Server

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GPRS (2.5 G)

GPRS
GPRS is an enhancement over the GSM and adds some nodes in the network to provide the
packet switched services. These network nodes are called GSNs (GPRS Support Nodes)
and are responsible for the routing and delivery of the data packets to and from the MS
and external packet data networks (PDN).

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GPRS Network Elements

GPRS adds 2 Network Elements to the network
 Serving GPRS Support Node (SGSN)
 Gateway GPRS Support Node (GGSN)
 Allows bit rates up to 170 kbps

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2.5G Architectural details

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Third Generation (3G)
• IMT-200 was formed to handle higher network capacity
• 144 Kbps for mobile service
• 2MBps for fixed access
• Operates in the 2Ghz band
• The main technologies were selected
• Wideband CDMA (WCDMA)
• CDMA 2000 (an evolution of IS 95 CDMA)
• TDD-CDMA and TD-SCDMA)

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3G Rel 99 Architecture

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Benefits of 3G
• High Quality Voice Service
The quality of voice falls under 3G will be much higher compared to 2G services.

Enhanced content services
3G users can download full music files, full movie files and other files at high speed.

Mobile Broadband
3G User can use his handset for high speed Internet any time anywhere (where connectivity is
available :P)

Video Services
3G user can enjoy the video call facility wherein both the caller and receiver will be able to see
each other while speaking if both have 3G services and 3G enabled handsets. 3G enables its
users to send Video mails and , Video clips.

Mobile TV
3G users can watch TV programmes of different video channels as per his liking while on the
move.

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Fourth Generation 4G

To handle even higher data throughputs we have the 4G technology
2. Long Term Evolution (LTE)
3. Wireless Interoperability for Microwave Access (WiMAX)
4. Uses an all-IP core network
5. Data rates upto 100 Mbps

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1G Technologies'

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FDMA
• Available spectrum divided into radio channels at different frequencies
• In AMPS, available spectrum is divided into 30Mhz channels
• One of the 30Khz channel assigned for call
• 2 channels one in each direction (FDD)
• Technique is known as FDD FDMA

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2G - TDMA

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TDMA
• TDMA is an assigned frequency band shared among a few users. However, each user is
allowed to transmit in predetermined time slots. Hence, channelization of users in the
same band is achieved through separation in time.

• Radio channel is divided into time slots,
• User A assigned to time slot 1, user B to time slot 2 and so on.
• We could have FDD TDMA or TDD TDMA

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Multiple radio Access techniques

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Multiple Access Methods

AMPS 30KHz carriers – Full duplex

1.25 Mhz carriers 800/1900 Mhz
Cellular/PCS Full-Duplex

US TDMA IS-136 & GSM Full Duplex
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Multiple Access Techniques

• Frequency Division Multiple Access – allocates a discrete amount of bandwidth per user
• Time Division Multiple Access – allocates unique time slots for each user
• Code Division Multiple Access – all users share the same frequency all the time. A
unique code assigned to each user allows it to be distinguished from other users

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Introduction to CDMA

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Code Division Multiple Access
• CDMA employs spread-spectrum technology and a special coding scheme (where each
transmitter is assigned a code) to allow multiple users to be multiplexed over the same
physical channel
• CDMA uses Direct Sequence spreading, where spreading process is done by directly combining
the baseband information to high chip rate binary code.

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Spread Spectrum Techniques

• Transmission of a signal has 2 characteristics
– Carrier frequency
– Bandwidth

Fc – carrier

bandwidth

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Spread Spectrum vs. other modulation

• Amplitude modulation : The bandwidth is twice the baseband on either side of the
carrier
• Frequency modulation modulates the carrier frequency with the baseband signal
• Digital modulation like QPSK give higher spectral efficiency
• In spread spectrum the transmitted signal is spread using a bandwidth much larger
than that required by mixing the data and the spreading code signal.

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Spread Spectrum - Characteristics
• Transmission bandwidth much larger than that of the bandwidth or rate of
the baseband data
• Transmission bandwidth dependent on the rate of the code used for
spreading

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Spread Spectrum technique
User Information 1 0 1

001010001011 110101110100 001010001011

Spread information

110101110100 110101110100

Cyclic code
generator

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Spread Spectrum - Techniques
• Four main techniques
– Direct Sequence (DS) – carrier modulated by a digital code larger than the signal
information bit rate. These systems are also called Pseudo-noise systems
– Frequency Hopping (FH) – carrier frequency shifted in discrete increments in a
pattern generated by code sequence
– Time Hopping (TH) – transmission time divided into frames and frames into time
slots. During each frame one and only one time slot is modulated with the
message.

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Direct Sequence Spread
Spectrum
Information Baseband de -
Baseband Information
bits modulation
modulation bits

PN sequence
generator PN Sequence
generator

•Commonly used due to simplicity
•Direct modulation of carrier using the PN sequence.
•Occupies the whole available spectrum.
•Modulation can be AM, FM, BPSK or QPSK
•For an information rate of 10 kbps a code rate of 1Mcps producing a spread spectrum
signal of 1 Mcps.*

•* chip – each bit in a PN sequence is called chip to distinguish it from information bits

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Frequency Hopping
• Frequencies selected from a pre-determined group within a available spectrum and
they change in order defined by a pseudo-random sequence with characteristics
similar to thermal noise

Time

f1 f2 f3 f4 …… Frequency

Each bit in pseudo sequence called “chip” to
distinguish it from data “bit”
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Frequency Hopping

Information Baseband Bandpass Baseban Information
bits modulation de - bits
filter modulati
on

PN sequence Frequency PN Sequence
generator synthesizer Frequency generator
synthesizer

On the reception side the PN sequence generator defines the centre frequency of
bandpass filter and the frequency for the demodulation process. The demodulation can
only succeed if both the transmission and reception are synchronized.

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CDMA

• Immunity to interference and higher user capacity
• Low probability of interception and jamming
• Based on the IS-95 protocol standard Operates in the 900Mhz and 1900Mhz band
• Work on development of CDMA standard is by the CDMA development group (CDG) now
known as cdmaOne

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Evolution of CDMA (contd.)
– CDMA 2000 1XEV has 2 variants
• CDMA 2000 1XEV DO – (evolution data only) capable of delivering streaming
multimedia with rates upto 2.4 Mbps in mobile environment
• CDMA 2000 1X EVDV – (evolution data and voice) capable of delivering
integrated voice and data services of upto 3.09 Mbps

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Background to GSM

• 1G : Advanced Mobile Phone Service (AMPS)
Analog, Circuit Switched, FDMA, FDD
• 2G : Global System for Mobile (GSM)
Digital, Circuit Switched, FDMA and TDMA, FDD
• 2G : Code Division Multiple Access (CDMA)
Digital, Circuit Switched, FDMA, SS, FDD

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GSM System specifications
Frequency band
Uplink 890 - 915 MHz
Downlink 935 - 960MHz
Duplex Frequency Spacing 45MHz
Carrier separation 200KHz
Frequency Channels 124
Time Slots /Frame(Full Rate) 8
Voice Coder Bit Rate 13Kbps
Modulation GMSK
Air transmission rate 270.833333 Kbps
Access method FDMA/TDMA
Speech Coder RPE-LTP-LPC

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GSM uses paired radio channels

K
UP LI N

K
N LIN
W
DO

890MHz 915MHz 935MHz 960MHz

0 124 0 124

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GSM Architecture

It provides an overview of the GSM network architecture. This includes a
brief explanation of the different network subsystems and a description
of the functionality of the elements within each of the subsystems.
• General architecture overview
• The Mobile Station (MS) Subsystem and Elements
• The Base Station Subsystem (BSS) and Elements
• BTS – Base Transceiver System
• BSC – Base Station Controller
• The Network Subsystem (NSS) and Elements

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Elements of a GSM Network

• Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)

• Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)

• Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)

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Base Station Subsystem

The BSC:
• Allocates a channel for the duration of a call
• Maintains the call:
monitors quality
controls the power transmitted by the BTS or MS
generates a handover to another cell when required

The BTS:
• Provide radio access to the mobile stations
• Manage the radio access aspects of the system

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Network Subsystem
Can be considered as a heart of the GSM Network.
All the major activities like
• Routing,
• Security functions,
• Call handling, charging,
• Operation & maintenance,
• Handover decisions,

• Various kinds of interfaces are used to communicate between the different entities.
Different methods are used to optimize and provide the quality network with the
minimum operating cost.

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Mobile Switching Center (MSC)

• Performs call switching
• Interface of the cellular network to PSTN
• Routes calls between PLMN and PSTN
• Queries HLR when calls come from PSTN to mobile user
• Inter-BSC Handover
• Paging
• Billing

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2G Architecture
ISUP

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2G Architecture
PSTN Gi Gp

GMSC GGSN

AuC
Gc
C H

HLR Gn
PSTN PSTN

Gr
D EIR

F Gf
G
VLR VLR
Gs
B B SGSN
MSC MSC
E

CN

A Gb IuCS IuPS

BSS RNS
Iur
BSC RNC RNC
Abis Iubis
BTS BTS Node B Node B
cell

Um Uu

ME

SIM-ME i/f or Cu

SIM USIM

MS
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Important cellular Concepts

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Registration
• Every mobile in the network communicates its location, and identification to
the network through the registration process
• Knowing the location allows the BTS to page the mobile when a MS
terminated call is requested.
– Power up registration occurs when the MS is turned on and enter the
mobile idle state
– Power down registration when turned off
– Timer based registration: The MS must register according to pre-
programmed timer
– Distance based registration : When it reaches a pre-specified distance
from the BTS
– Zone based registration: occurs based on internal zone configuration ,
when a MS enter a new zone
– Parameter change registration: Occurs when a parameter changes
– Ordered registration : occurs every time the system requests
registration
– Traffic channel registration: occurs when the MS registers while
requesting a traffic channel allocation

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Roaming
• MSs are considered ‘home’ when they are located in their home system, where they are
registered and allowed to operate
• They are roamers when they are out of their home systems
• MSs have a list of locations where they are in the ‘home system’
• Roaming is a general term referring to the extension of connectivity service in a location
that is different from the home location where the service was registered.
• the ability for a cellular customer to automatically make and receive voice calls, send
and receive data, or access other services, including home data services, when travelling
outside the geographical coverage area of the home network, by means of using a visited
network

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Handoffs

• BS Traffic not balanced: Network monitors traffic and trigger handoffs if load
not balanced among BS
• Distance limit exceeded
• Pilot signal strength below threshold the MS can initiate a handoff
• Power level exceeded – When the mobile has exceeded the power threshold
then either side can initiate a handoff

• Handoff involves the mobile moving to a new traffic channel of a different BS
• Types of handoff
– Soft Handoff – MS has simultaneous connections with two BS before a
decision is made as to which signal is stronger before breaking the
connection with the BS with the weaker signal strength (not perceived by
the user)
– Hard Handoff – There is a break before the make. Connection to old
traffic channel is broken before the connection to a new one is made
(user hears a click)

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Authentication
• The AUC does not engage directly in the authentication process, but instead generates
data known as triplets for the MSC to use during the procedure. The security of the
process depends upon a shared secret between the AUC and the SIM called the Ki. The
Ki is securely burned into the SIM during manufacture and is also securely replicated
onto the AUC. This Ki is never transmitted between the AUC and SIM, but is combined
with the IMSI to produce a challenge/response for identification purposes and
an encryption key called Kc for use in over the air communications.

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Authentication procedure

2. Algorithm id (the standard algorithms are called A3 or A8, but an operator may choose
a proprietary one). When the MSC asks the AUC for a new set of triplets for a particular
IMSI, the AUC first generates a random number known as RAND. This RAND is then
combined with the Ki to produce two numbers as follows:
3. The Ki and RAND are fed into the A3/A8 (or other operator proprietary algorithm) and a
number known as Signed RESponse or SRES is calculated.
4. The Ki and RAND are fed into a standard A5 algorithm and a number called the Kc is
calculated.
5. The numbers (RAND, SRES, KC) form the triplet sent back to the MSC. When a
particular IMSI requests access to the GSM core network, the MSC sends
the RAND part of the triplet to the SIM. The SIM then feeds this number and the Ki
(which is burned onto the SIM) into the A3/A8/proprietary algorithm as appropriate
and an SRES is calculated and sent back to the MSC. If this SRES matches with the
SRES in the triplet (which it should if it is a valid SIM), then the mobile is allowed to
attach and proceed with GSM services.
6. After successful authentication, the MSC sends the encryption key Kc to the Base
Station Controller (BSC) so that all communications can be encrypted and decrypted. Of
course, the mobile phone can generate the Kc itself by feeding the same RAND supplied
during authentication and the Ki into the A5 algorithm.

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Authentication

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Mobility Management
• Location updating- normal, periodic, IMSI attach
• Paging
• Security Management
– Preventing unauthorized users- authentication
– Maintaining Privacy of users- ciphering
• Providing roaming facility
• MM functionality mainly handled by MS, HLR, MSC/VLR.

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traffiC
EnginEEring

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Traffic Engineering

Trunk
• the telephone lines connecting one telephone switch or exchange with
another are called trunks.
Calling rate (C)
• The number of calls which arrive over a time interval

Holding time (H)
• The average duration of a call. The duartion the telephony circuits are held
during conversation

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Traffic Calculations
• The erlang describes the total traffic volume of one hour, or 3600 seconds.
• The traffic intensity, more often called the traffic, is defined as the average number of
calls in progress.

A = C x H/T

Unit: Erlang (E)
A: traffic intensity
C: number of calls arrivals during time T
H: average holding time
T: 3600 secs /1 hr

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Traffic Problem
On average, during the busy hour, a company makes 120 outgoing calls of average duration
2 minutes. It receives 200 incoming calls of average duration 3 minutes. Find the
outgoing traffic, the incoming traffic and the total traffic.

A = C x H /T

Solution
where T = 1 hour = 60 minutes
Outgoing traffic = 120 calls x 2 minutes/ 60 minutes = 4 E
Incoming traffic = 200 calls x 3 minutes/ 60 minutes =10 E
Total traffic = 4 E + 10 E = 14 E

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Traffic terms
Lost call or blocked calls
In a circuit-switched system, all attempts to make calls over a congested group of trunks
are unsuccessful. The unsuccessful call is called lost call or blocked call.

Grade of service
– probability of meeting blockage is called the grade of service (B)

Example: On average, one call in 100 will be blocked
B= 1/100 = 0.01

Grade of service is also the
• proportion of the time for which congestion exists
• probability of congestion
• probability that a call will be lost due to congestion

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Traffic calculations
Example
During the busy hour, 1200 calls were offered to a group of trunks and six calls were lost.
The average call duration was 3 minutes

The traffic offered = A = C1 x H/T = 1200 x 3 /60 = 60 E
The traffic carried = C2 x H/T=(1200-6) x 3 / 60 = 59.7 E
The traffic lost = B = C3 x H/T = 6 x 3 / 60 = 0.3 E
Grade of service = B/A = 0.3 / 60 = 0.005
The total duration of the periods of congestion = B x T = 0.005 x 3600 =18 seconds

03/22/12
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Wireless technologies - Part 1

Wireless technologies - Part 1

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