PSTN and TDM Analysis and Simulation

7/28/2019 PSTN and TDM Analysis and Simulation

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PSTN and TDM Analysis and Simulation

Move the mouse over different interfaces shown in the network diagram below to knowmore details

PSTN and TDM Analysis and Simulation

Analysis and simulation All trafic types (Voice, Digits, Tones, Fax, and Modem) All protocols (HDLC, ISDN, SS7, GSM, GPRS, CDMA 2000, TRAU, PPP, UMTS,

Frame Relay, V5.x, SAHDLC)

All interfaces (Analog, T1, E1, T3, OC-3, STS-1, STM-1) Analyze and simulate thousands of channels Includes broadest range of test and simulation for echo testing Compliance testing per G.168/G.160, scripting/automation VoIP and TDM networks fully covered Network-wide intrusive and non-intrusive test/monitoring solutions TCP/IP remoting, centralized collection & database in addition to a variety of probes for

VoIP, Wireless and TDM networks

BTS to BSC Interface


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Complete GSM protocol analysis - VisitGSM Protocol Analyzerpage. Complete TRAU protocol analysis - VisitTRAU Protocol Analyzerpage. Complete TRAU voiceband analysis - VisitTRAU PDApage. TRAU protocol and traffic emulation - VisitTRAU Toolboxpage andTRAU

Traffic Playback

BSC to MSC Interface Complete GSM protocol analysis - VisitGSM Protocol Analyzerpage. Complete GPRS protocol analysis - VisitGPRS Protocol Analyzerpage.

MSC to STP Interface Complete SS7 protocol analysis and emulation for traffic and signalling

DCOSS provides SS7 protocol emulation (traffic and signalling) - VisitDCOSSpage andSS7 emulationpage.

Complete SS7 protocol analysis - VisitSS7 Protocol Analyzerpage.

MSC to IXC / CO Interface Complete traffic and signalling emulation and analysis

DCOSS provides protocol emulation (traffic and signalling) - VisitDCOSSpage andAll available protocolspage.

Complete Protocol analysis - VisitProtocol Analysispage. Complete Protocol emulation - VisitProtocol Emulationpage.

STP to STP Interface Complete signalling emulation and analysis
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DCOSS provides SS7 protocol emulation (traffic and signalling) - VisitDCOSSpage andSS7 emulationpage.

Complete SS7 protocol analysis - VisitSS7 Protocol Analyzerpage.

CO / EO to CO / EO Interface Complete analysis and emulation

T1, E1 analysis - Visithardware platformspage. T3, OC-3, STM-1 analysis - VisitUltra T3page andOC-3 / STM-1page. DCOSS provides protocol emulation (traffic and signalling) - Visit

DCOSSpage andAll available protocolspage.

Analog interfaces - VisitDCOSS APSpage andVQuad with Analogoptionpage.

Fax and Modem Interfaces - VisitDCOSS emulationpage andfax andmodem analysispage.

Complete SS7 Protocol Analysis - VisitSS7 Protocol Analyzerpage. Complete CAS Protocol Analysis - VisitProtocol Analysispage.

Public Switched Telephone Network - PSTN

Public switched telephone networks are communication systems that are available to the public to allowusers to interconnect communication devices. Public telephone networks within countries andregions are standard integrated systems of transmission and switching facilities, signaling processors,and associated operations support systems that allow communication devices to communicate with eachother when they operate.

This figure shows a basic overview of the Public Switched Telephone Network (PSTN) as deployed in atypical metropolitan area. PSTN customers connect to the end-office (EO) for telecommunicationsservices. The EO processes the customer service request locally or passes it off to the appropriate endor tandem office. As Different levels of switches interconnect the parts of the PSTN system, lower-

level switches are used to connect end-users (telephones) directly to other end-users in a specificgeographic area. Higher-level switches are used to interconnect lower level switches.
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Public Switched Telephone Network - PSTN Diagram

Switches within the PSTN send control messages to each other, usually through a separate control-signaling networkcalled signaling system number 7 (SS7). The SS7 network is composed ofsignaling transfer points (STPs) and service control point (SCP) databases. A STP is used to route

packets of control messages through the network. SCP's are databases that are used by the network toprocess or reroute calls through the network (such as 800 number toll free call routing). SS7 alsoprovides for the newer features such as incoming call identification and automatic call rerouting used by

some service companies that provide 24/7, worldwide dial-in support.

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E1 Link / Circuit

- details and notes about the E1 link or circuit, the most commonly used circuit within the E

carrier system. Includes E1 frame and frame format.

E-Carrier / E1 tutorial includes:

E Carrier tutorial E1 link / circuit E1 interface

The E1 link or circuit is probably the most commonly used format within the E carrier system. It

is used for connecting a variety of elements within a network - typically small exchanges, mobile

base stations and the like will use E1 circuits.

E1 Applications and standards

The E-carrier standards form part of the overall Synchronous Digital Hierarchy (SDH) scheme.

This allows where groups of E1 circuits, each containing 30 circuits, to be combined to produce

higher capacity. E1 to E5 are defined and they are carriers in increasing multiples of the E1format. However in reality only E3 is widely used and this can carry 480 circuits and has an

overall capacity of 34.368 Mbps.
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Physically E1 is transmitted as 32 timeslots and E3 has 512 timeslots. Unlike Internet data

services which are IP based, E-carrier systems are circuit switched and permanently allocate

capacity for a voice call for its entire duration. This ensures high call quality because the

transmission arrives with the same short delay (Latency) and capacity at all times. Neverthelessit does not allow the same flexibility and efficiency to be obtained as that of an IP based system.

In view of the different capacities of E1 and E3 links they are used for different applications. E1

circuits are widely used to connect to medium and large companies, to telephone exchanges.

They may also be used to provide links between some exchanges. E3 lines are used where highercapacity is needed. They are often installed between exchanges, and to provide connectivity

between countries.

E1 basics & E1 frame format

An E1 link runs over two sets of wires that are normally coaxial cable and the signal itselfcomprises a nominal 2.4 volt signal. The signalling data rate is 2.048 Mbps full duplex and

provides the full data rate in both directions.

To provide signal structure, there is a frame that has been devices. The E1 frame format has been

devised to provide a frame of 32 time slots of octets, i.e. 8 bits each which are numbered 0 to 31,

or as more often seen, TS0 to TS31. Obviously TS stands forTime Slot. The E1 frame repetitionrate is 8000 Hz.

E1 Frame Format

The E1 frame Time Slots are nominated TS0 to TS31 and they are allocated to differentpurposes:

TS0: This E1 frame time slot is used for synchronisation, alarms and messages. It is reserved forframing purposes, and alternately transmits a fixed pattern. This allows the receiver to lock onto

the start of each frame and match up each channel in turn. The standards allow for a full Cyclic

Redundancy Check to be performed across all bits transmitted in each frame.

TS1 - TS15: These time slots are used for user data TS16: E1 signalling data is carried on TS16. This includes control, call setup and teardown.

These are accomplished using standard protocols including Channel Associated Signalling (CAS)


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where a set of bits is used to replicate opening and closing the circuit. Tone signalling may also

be used and this is passed through on the voice circuits themselves. More recent systems use

Common Channel Signalling (CCS) such as ISDN or Signalling System 7 (SS7) which sends short

encoded messages containing call information such as the caller ID. Data may also be carried on

this time slot.

TS17 - TS31: These E1 frame times slots are used for carrying user dataSeveral options are specified in the original CEPT standard for the physical transmission of data.

However an option or standard known as HDB3 (High-Density Bipolar-3 zeros) is used almost

exclusively.

>


E Carrier System

- details, notes and tutorial about the E carrier telecommunications system used for

telecommunications links.



The E carrier system has been created by the European Conference of Postal and

Telecommunications Administrations (CEPT) as a digital telecommunications carrier scheme forcarrying multiple links. The E-carrier system enables the transmission of several (multiplexed)

voice/data channels simultaneously on the same transmission facility. Of the various levels of theE-carrier system, the E1 and E3 levels are the only ones that are used.

E carrier beginnings

The life of the E carrier standards started back in the early 1960s when Bell Laboratories, wherethe transistor was invented some years earlier, developed a voice multiplexing system to enable

better use to be made of the lines that were required, and to provide improved performance of theanalogue techniques that were used.

The step of the process converted the signal into a digital format having a 64 kbps data stream.The next stage is to assemble twenty four of the data streams into a framed data stream with an
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overall data rate of 1.544 Mbps. This structured signal was called DS1, but it is almost

universally referred to as T1.

In Europe, the basic scheme was taken by what was then the CCIT and developed to fit the

European requirements better. This resulted in the development of the scheme known as E

carrier - the E standing for Europe or European.

The E1 designation can be seen to refer to not only the system itself but also raw data rate.

E carrier system basics

More specifically E1 has an overall bandwidth of 2048 kbps and provides 32 channels each

supporting a data rate of 64 kbps. The lines are mainly used to connect between the PABX

(Private Automatic Branch eXchange), and the CO (Central Office) or main exchange.

The E1 standard defines the physical characteristics of a transmission path, and as such it

corresponds to the physical layer (layer 1) in the OSI model. Technologies such as ATM andothers which form layer 2 are able to pass over E1 lines, making E1 one of the fundamental

technologies used within telecommunications.

A similar standard to E1, known as T1 has similar characteristics, but it is widely used in North

America. Often equipment used for these technologies, e.g. test equipment may be used for both,

and the abbreviation E1/T1 may be seen.

E carrier link formats and data rates

Within the E carrier system there is a hierarchy of different levels of the system. The overall Ecarrier system is designed so that the base level or E0 signal rate is designed so that each higher

level can multiplex a set of lower level signals.

The framed E1 link is able to carry 30 E0 data channels. In addition to this there is a furthersignalling channel required for the operation of the system.

High level E carrier links carry 4 signals from the level below.

It will be seen that the data rates achieved are not the exact multiples of the lower level links that

might be expected. It is found that each level has a capacity greater than would be expected fromsimply multiplying the lower level signal rate. For example the E2 data rate is 8.448 Mbit/s and

not 8.192 Mbit/s which equates to the E1 rate multiplied by 4.

The reason for this is that less overhead and signalling data is required when the higher rate E

carrier links are used.


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E carrier link designation Data Rate

E0 64 kbps

E1 2.048 Mbps

E2 8.448 Mbps

E3 34.368 Mbps

E4 139.264 Mbps

E5 564.992 Mbps

Future

E1 and also T1 are well established for telecommunications use. However with new technologiessuch as ADSL, DSL, and the other IP based systems that are now being widely deployed, thesewill spell the end of E1 and T1. Nevertheless they have given good service over many years, and

they will remain in use as a result of this wide deployment for some years to come.


E1 Interface & Specification

- details and notes about the E1 interface, specification, connector types, signals, etc..



The E1 interface requires accurate definition in a standard or specification to ensure that

equipment from different suppliers is able to operate together.

With E1 systems widely deployed around Europe and the rest of the world, the E1 interface hasbeen defined in a standard or specification to ensure its successful operation.

The E1 physical interface defines the various parameters required to ensure correct electrical

operation of the circuit.
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E1 interface basics

The E1 standard is defined under the specification or standard G.703 which is defined by the

ITU-T - International Telecommunications Union, Telecommunication Standardisation Sector.

The ITU G.703 standard sets down the various physical parameters for the physical interface.

These include a number of elements.

Parameter Specification limits or details

Pulse shape Normally rectangular

Conductor pairs in each directionOne coaxial line (i.e.

centre and outer

conductors)

One symmetrical pair(e.g. twisted conductor

pair)

Test load impedance 75 ohms (resistive) 120 ohms (resistive)

Peak voltage of Mark condition 2.37 V 3 V

Peak voltage of space 0 0.237 V 0 0.3 V

Ratio of the amplitudes of positive and

negative pulses at the centre of the

pulse interval

0.95 - 1.05

Ratio of the widths of positive and

negative pulses at the nominal half

amplitude

0.95 - 1.05

Nominal pulse width 244 ns

The attenuation of the transmission lines used for carrying he data needs to be characterised aswell. The standard assumes a f law, and that the loss at the basic frequency of operation, 2048kHz should be in the range 0 to 6 dB (minimum value). This loss must take into account any lossincurred in the digital distribution frame between the terminal equipments. In other words the

loss required is between the driver and receiver.


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Typical E1 interface connectors and implementation

The E1 interface uses a differential format using different transmit and receive pairs.

The most common physical formats for the data transmission are two coaxial cables terminated

in BNC connectors, or twisted pairs terminated with RJ-48C connectors.

The RJ-48C connector has a total of eight connections.

Signal Name RJ-48C Connector BNC

Transmit Tip 5 TX BNC centre pin

Transmit Ring 4 TX BNC outer

Receive Tip 2 RX BNC centre pin

Receive Ring 1 RX BNC outer

Receive Shield 3

Transmit Shield 6

Not assigned 7

Not assigned 8

E1 lines are widely used for a variety of applications including Voice, Internet Access, X.25,

Multiplexed data, ISDN, ATM and more. For example they are widely used for small exchanges

and also for connecting mobile phone base stations to large switching centres. Both E1 lines are

frequently connected to X.21, V.35 or other connections via network interface converters beforeconnection to the communications equipment.

Network ArchitectureMobile Station Base Transceiver Station Base Station Controller Mobile Switching Center Gateway MSC

Home Location Register Visitor Location Register Equipment Identity Register Authentication Center

Home
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GSM Network ArchitectureA GSM network is made up of multiple components and interfaces that facilitate sending and receivingof signaling and traffic messages. It is a collection of transceivers, controllers, switches, routers, and

registers.

A Public Land Mobile Network (PLMN) is a network that is owned and operated by one GSM service

provider or administration, which includes all of the components and equipment as described below.

For example, all of the equipment and network resources that is owned and operated by Cingular is

considered a PLMN.

Mobile Station (MS)

The Mobile Station (MS) is made up of two components:

Mobile Equipment (ME) This refers to the physical phone itself. The phone must be able to operate on a

GSM network. Older phones operated on a single band only. Newer phones are dual-band, triple-band,

and even quad-band capable. A quad-band phone has the technical capability to operate on any GSM

network worldwide.

Each phone is uniquely identified by the International Mobile Equipment Identity(IMEI) number. This

number is burned into the phone by the manufacturer. The IMEI can usually be found by removing the

battery of the phone and reading the panel in the battery well.

It is possible to change the IMEI on a phone to reflect a different IMEI. This is known as IMEI spoofing or

IMEI cloning. This is usually done on stolen phones. The average user does not have the technical ability

to change a phone's IMEI.

Subscriber Identity Module (SIM) - The SIM is a small smart card that is inserted into the phone and

carries information specific to the subscriber, such as IMSI, TMSI, Ki(used for encryption), Service

Provider Name (SPN), and Local Area Identity(LAI). The SIM can also store phone numbers (MSISDN)

dialed and received, the Kc (used for encryption), phone books, and data for other applications. A SIM

card can be removed from one phone, inserted into another GSM capable phone and the subscriber will

get the same service as always.

Each SIM card is protected by a 4-digit Personal Identification Number (PIN). In order to unlock a card,


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the user must enter the PIN. If a PIN is entered incorrectly three times in a row, the card blocks itself and

can not be used. It can only be unblocked with an 8-digit Personal Unblocking Key (PUK), which is also

stored on the SIM card.

[Back to Top]

Base Transceiver Station (BTS)Base Transceiver Station (BTS) - The BTS is the Mobile Station's access point to the network. It is

responsible for carrying out radio communications between the network and the MS. It handles speech

encoding, encryption, multiplexing (TDMA), and modulation/demodulation of the radio signals. It is also

capable of frequency hopping. A BTS will have between 1 and 16 Transceivers (TRX), depending on the

geography and user demand of an area. Each TRX represents one ARFCN.

One BTS usually covers a single 120 degree sector of an area. Usually a tower with 3 BTSs will

accommodate all 360 degrees around the tower. However, depending on geography and user demand

of an area, a cell may be divided up into one or two sectors, or a cell may be serviced by several BTSs

with redundant sector coverage.

A BTS is assigned a Cell Identity. The cell identity is 16-bit number (double octet) that identifies that cell

in a particular Location Area. The cell identity is part of the Cell Global Identification (CGI), which is

discussed in the section about the Visitor Location Register (VLR).
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120 Sector

The interface between the MS and the BTS is known as the Um Interface or theAir Interface.

Um Interface

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Base Station Controller (BSC)

Base Station Controller (BSC) - The BSC controls multiple BTSs. It handles allocation of radio

channels, frequency administration, power and signal measurements from the MS, and handoversfrom one BTS to another (if both BTSs are controlled by the same BSC). A BSC also functions

as a "funneler". It reduces the number of connections to theMobile Switching Center(MSC) andallows for higher capacity connections to the MSC.

A BSC my be collocated with a BTS or it may be geographically separate. It may even be

collocated with the Mobile Switching Center (MSC).

Base Station Controller

The interface between the BTS and the BSC is known as the Abis In terf ace


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Base Station System

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Mobile Switching Center (MSC)

Mobile Switching Center (MSC) - The MSC is the heart of the GSM network. It handles call routing, call

setup, and basic switching functions. An MSC handles multiple BSCs and also interfaces with other MSC's

and registers. It also handles inter-BSC handoffs as well as coordinates with other MSC's for inter-MSC

handoffs.

Mobile Switching Center

The interface between the BSC and the MSC is known as theA Interface


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A Interface

[Back to Top]

Gateway Mobile Switching Center (GMSC)

There is another important type of MSC, called a Gateway Mobile Switching Center (GMSC). The GMSC

functions as a gateway between two networks. If a mobile subscriber wants to place a call to a regular

land line, then the call would have to go through a GMSC in order to switch to the Public Switched

Telephone Network (PSTN).


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Gateway Mobile Switching Center

For example, if a subscriber on the Cingular network wants to call a subscriber on a T-Mobile network,

the call would have to go through a GMSC.

Connections Between Two Networks

The interface between two Mobile Switching Centers (MSC) is called the E Interface

E Interface

[Back to Top]

Home Location Register (HLR)

Home Location Register (HLR) - The HLR is a large database that permanently stores data about

subscribers. The HLR maintains subscriber-specific information such as the MSISDN, IMSI, current

location of the MS, roaming restrictions, and subscriber supplemental features. There is logically only

one HLR in any given network, but generally speaking each network has multiple physical HLRs spread

out across its network.

[Back to Top]

Visitor Location Register (VLR)

Visitor Location Register (VLR) - The VLR is a database that contains a subset of the information located

on the HLR. It contains similar information as the HLR, but only for subscribers currently in its Location

Area. There is a VLR for every Location Area. The VLR reduces the overall number of queries to the HLR

and thus reduces network traffic. VLRs are often identified by the Location Area Code (LAC) for the area

they service.
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Visitor Location Register

Location Area Code (LAC)

A LAC is a fixed-length code (two octets) that identifies a location area within the network. Each

Location Area is serviced by a VLR, so we can think of a Location Area Code (LAC) being assigned to a

VLR.

Location Area Identity (LAI)

An LAI is a globally unique number that identifies the country, network provider, and LAC of any given

Location Area, which coincides with a VLR. It is composed of the Mobile Country Code (MCC), the Mobile

Network Code (MNC), and the Location Area Code (LAC). The MCC and the MNC are the same numbers

used when forming the IMSI.

Location Area Identity (LAI)

Cell Global Identification (CGI)

The CGI is a number that uniquely identifies a specific cell within its location area, network, and country.

The CGI is composed of the MCC, MNC, LAI, and Cell Identity (CI)

Cell Global Identity

The VLR also has one other very important function: the assignment of a Temporary Mobile Subscriber

Identity (TMSI). TMSIs are assigned by the VLR to a MS as it comes into its Location Area. TMSIs are only

allocated when in cipher mode.

The interface between the MSC and the VLR is known as the B Interface and the interface between the

VLR and the HLR is known as the D Interface. The interface between two VLRs is called the G Interface


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GSM Interfaces

[Back to Top]

Equipment Identity Register (EIR)

Equipment Identity Register (EIR) - The EIR is a database that keeps tracks of handsets on the network

using the IMEI. There is only one EIR per network. It is composed of three lists. The white list, the gray

list, and the black list.

The black list is a list if IMEIs that are to be denied service by the network for some reason. Reasons

include the IMEI being listed as stolen or cloned or if the handset is malfunctioning or doesnt have the

technical capabilities to operate on the network.

The gray list is a list of IMEIs that are to be monitored for suspicious activity. This could include handsets

that are behaving oddly or not performing as the network expects it to.

The white list is an unpopulated list. That means if an IMEI is not on the black list or on the gray list, then

it is considered good and is "on the white list".

The interface between the MSC and the EIR is called the F Interface.

Equipment Identity Register

[Back to Top]

Authentication Center (Auc)

Authentication Center (AuC) - The AuC is responsible for generating the necessary cryptovariables for

authentication and encryptionon the network. These variables are the RAND, SRES, and Kc. The Auc also

stores the Ki for each IMSI on the network. Although it is not required, the Auc is normally physically

collocated with the HLR.
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Authentication Center

There is one last interface that we haven't discussed. The interface between the HLR and a GMSC is

called the C Interface. You will see it in the full network diagram below.This completes the introduction

to the network architecture of a GSM network. Below you will find a network diagram with all of the

components as well as the names of all of the interfaces.

Full GSM Network

Mobile Station Base Transceiver Station Base Station Controller Mobile Switching Center Gateway MSC

Home Location Register Visitor Location Register Equipment Identity Register Authentication Center

Introduction Architecture TDMA Logical Channels Authentication & Encryption Timing Advances

Speech Encoding GSM Events Cell Selection/Reselection

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PSTN and TDM Analysis and Simulation

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