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CDS Introduction


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Contents

1 Circuit Switched Data Server (CDS) ................................................... 51.1

CDS in the MSC Server (MSS) system .................................................. 6

1.2

CDS in the Integrated MSC Server (MSS) ............................................. 7

1.3 CDS in the Standalone MSC Server (MSS) ........................................... 91.4

CDS shared by the Multimedia Gateways (MGW) ................................ 10

1.5 CDS benefits ........................................................................................ 11

2 CDS functionality ............................................................................... 13

3 CDS interfaces ................................................................................... 15

4

CDS hardware architecture ............................................................... 17

4.1

CDS architecture .................................................................................. 184.2

Functional units in the CDS .................................................................. 19

4.3 CDS redundancy principles .................................................................. 214.4 CDS availability .................................................................................... 224.5

CDS mechanical design and power supply .......................................... 23

4.6 Capacity of the CDS ............................................................................ 264.7

Typical power consumption of the CDS ............................................... 27

5

Site requirements for the CDS .......................................................... 29

5.1 Exchange room layout ......................................................................... 305.2 Cable structures ................................................................................... 31


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Summary of changes

Date Version Name Change comment

19/08/2009 0.1 ChaducLaurent

Creation of an update training document fromSR3.0

30/06/2010 0.2 PubateSatienpoch

Editing for SR4.0

01/02/2012 0.3 CharfeddineSassi

Updated to SR4.1


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1.2 CDS in the Integrated MSC Server (MSS)Operators can move to the MSS system by integrating the MSS functionality inthe existing MSC by doing a software and hardware upgrade. In this system theoperator uses the existing Time Division Multiplex (TDM) interfaces in the MSCand additionally has access to the IP/ATM backbone transport provided by theMGW.

In the Integrated MSS system, the operator has the choice of connecting thePCM lines from the Base Station Subsystem (BSS) either to the Integrated MSSor to the MGW.

For the CS data calls the operator can utilise the existing InterworkingFunctionality (IWF) in the Integrated MSC Server for both the data calls coming

to the MSS or for the data calls coming to the MGW. If the operator needs moreIWF resources than the integrated IWF provides or if the operator does not wantto connect TDM lines between the MGW and the MSS, then the CDS can beconnected to the MGW.

If the CDS is used, part of the data calls, for example, those coming to theMGW, are served by the CDS and the data calls coming to the MSS are servedby the integrated IWF.

The CDS is used only for the data calls for which the A/Iu-interface is connectedto the MGW.


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Figure 1 CDS in the Integrated MSS system

For more information on Integrated MSS, see the Nokia Siemens NetworksMSC Server product description.


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1.3 CDS in the Standalone MSC Server (MSS)The Standalone MSS is a network element that does not have user planeconnections.

The Standalone MSS basically offers the GSM intelligence or the control plane,and the user plane is transported through the MGW.

In this system the CDS must be used for the CS data calls requiring theInterworking Functionality (IWF).

Figure 2 CDS in the Standalone MSS system


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1.4 CDS shared by the Multimedia Gateways (MGW)

To optimise the Interworking Functionality (IWF) resources in the network, theoperator can share the use of the CDS among several MGWs.

Figure 3 CDS shared by MGWs

In the figure above the CDS is located on the MGW1 site. The MSS controls theCDS through MGW1 or MGW2 depending on where the data calls come from.The controlling interface between the MSS and the MGW is a standardH.248/Megaco, whereas the interface between the MGW and the CDS consistsof a Nokia Siemens Networks proprietary control interface over TCP/IP (NPI)and the user plane from the MGW to the CDS is TDM PCMs (E1/T1).


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1.5 CDS benefitsThe CDS provides modularity and scalability both on the network and NetworkElement (NE) level.

On the network level the CDS is used by several MGWs because it is notphysically integrated in any particular MGW. This provides scalability on thenetwork level.

The CDS NE itself comes in different sizes and provides the modularity andscalability on the NE level.

Because of the network and NE level scalability the operator configures thenetwork for CS data calls according to the exact needs. The platform is modular

by nature and therefore allows the operator to start with a smaller configurationand increase the capacity later as necessary.

Because several CDSs can be connected to one MGW, the operator providesload sharing and redundancy which eliminate a single point of failure situationwhich might occur if only one Interworking Functionality (IWF) is used for all CSdata calls.

Modular Structure

The CDS is designed with a modular structure enabling a distributed processingarchitecture.

This makes the network elements easier to install to suit any network size andeliminates the need to over-invest in hardware at the network start-up.

Low power consumption and ease of installation are achieved with compactdesign and highly integrated components, which also facilitates expansion asthe network grows.

For more information on the modular structure of the CDS, see Engineering forCircuit Switched Data Server (CDS).

Scalability

It is important for the operator to optimally dimension their networks, as well asall the individual network elements.

To support this principle, the CDS is designed so that it is not physically tied toany particular MGW but can be connected to several MGWs to provide optimal

IWF functionality on the network level.Additionally, the CDS is fully scalable from small configurations (224 datachannels per CDS) to large ones (1,792 data channels per CDS). The CDS iscompact in size even with the maximum configuration, which is an importantfactor when the operators want to keep their fixed costs at a minimum level.

Reliability

As with any product, reliability is a consumer requirement. The DX MSCtechnology is used as a basis in the CDS. In the products available today and inthe future products Nokia Siemens Networks provides an extremely high rate of


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reliability and availability of network elements, by backing up functional units aswell as software with redundancy techniques such as 2N or N+1.

To increase reliability the operator can connect more than one CDSs to an

MGW. If, for instance, there are two CDSs connected to an MGW, the operatorcan share the load of the CS data calls between these two CDSs. If one of theCDSs goes down then the other one can be used to provide the IWFfunctionality for the CS data calls without any service interruption.


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2 CDS functionality

The CDS provides the same interworking functionality as the integrated IWFfunctionality.

It is logically part of the MGW user plane but it is a separate network elementthat is connected to the MGW.

The functions of the CDS depend on the services and the type of the fixednetwork. The CDS is required to convert the protocols used in the PLMN tothose used in the appropriate fixed network. The CDS is not used when theservice implementation in the PLMN is directly compatible with that of the fixednetwork (for example, 56/64 kbit/s transparent data services).

The typical services requiring the use of interworking functionality are:

non-transparent Asynchronous bearer services

transparent synchronous bearer services requiring rate adaptation

transparent facsimile group 3 teleservice

High Speed Circuit Switched Data (HSCSD) services

14.4 kbit/s data traffic channel

V.42bis data compression and compression on V.120

asymmetric data connection

H.324 multimedia modem calls

data call handovers between 3G and 2G

The interworking functionality is not used with the following services:

32 kbit/s transparent data service (rate adaptation in the MGW)

56/64 kbit/s transparent data services

H.324 multimedia Unrestricted Digital Information/Restricted Digital

Information

(UDI/RDI) calls


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3 CDS interfaces

At the higher level, the CS data call connections are controlled by the MSSwhich uses the device control protocol H.248/Mecago to establish thenecessary terminations and connections in the MGW.

According to the instructions received from the MSS through H.248/Mecago, the

MGW connects the User Plane (UP) to the CDS and controls the CDS asshown in the following figure. The user plane interface (TDM UP in the figure) isa TDM interface and the control plane is a Nokia Siemens Networks proprietyinterface over Stream Control Transmission Protocol (SCTP) or TCP/IP (NPICP in the figure).

Figure 4 MSS-MGW and CDS-MGW interface


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4 CDS hardware architecture

The CDS hardware is based on the i-series Nokia Siemens Networks DX 200platform and it uses Intel Pentium embedded processors.

The possibility to build different modular CDSs according to capacityrequirements is a good example of the versatility of the hardware architecture.


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4.1 CDS architecture

The CDS consists of the Compact Data Service Units (CDSU) connected to theGroup Switch (GSW). The CDSUs are controlled from the CMM (CentralMemory and Marker combined) where the AS7 cards are also located. Themeasurement functions are integrated in the Operation and Maintenance Unit(OMU). The E1/T1 interface is used for the user plane coming from the MGW.The Local Area Network (LAN) interface is used for the O&M and for thepropriety control signalling between the MGWs and the General Signalling Unit(GSU).

Figure 5 Hardware configuration of the CDS


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4.2 Functional units in the CDSFrom the hardware point of view a Functional Unit is a set of plug-in units thatare inserted into one cartridge. From the software point of view a FunctionalUnit performs a set of operations that from the network element configurationviewpoint can be seen as one entity. This allows flexible hardwareconfigurations that ensure optimal use of floor space.

The CDS functional units are briefly described in Table Functional units in theCDS.

For a detailed description of the units, see Engineering for Circuit SwitchedData Server (CDS).

Functional unit DescriptionCentral Memory and Marker (CMM) The central memory handles the routingfunctions. The Marker controls and supervises the GSW, hunts for free circuitsand is responsible for establishing and releasing all connections.

Clock and Alarm Buffer Unit (CLBU) The duplicated CLBUs distribute the clocksignals (generated by the CLSUs) to the units in the same cabinet. The CLBUalso collects the wired alarms from the units whose timing it handles andtransfers them further to the OMU.

Clock System Unit (CLSU) CLSUs generate the clock signals, necessary forsynchronising the functions of the CLS, and transmit them further to the CLBUunits in the other cabinets.

Compact Data Service Unit (CDSU) The CDSU offers standard circuit switcheddata services, which include modem-based digital connections towards thePSTN and digital connections towards the ISDN.

General Signalling Unit (GSU) The GSU takes care of the data call controlfunctions in the CDS and interfaces with the CM and M (CMM), Group Switch(GSW) and the LAN unit.

Exchange terminal (ET) The ET performs the electrical synchronization andadaptation of an external PCM line.

Group Switch 512 (GSW 512) The GSW is the switching fabric of the CDS. It iscontrolled by the CMM and performs the switching of data calls coming from theMGW through the PCM circuits.

LAN Switch Unit (LANU) The LAN switches are used to collect control-planetraffic between different cabinets and it provides the external interface for theO&M and for the proprietary control signalling between the MGW and the CDS.

Message Bus (MB) The duplicated MB has a transfer rate of 32 Mbytes/s and itis controlled by the

Message Bus Interface plug-in units (MBIF-B).


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Functional unit Description

Central Memory andMarker (CMM)

The central memory handles the routing functions. TheMarker controls and supervises the GSW, hunts for freecircuits and is responsible for establishing and releasing allconnections.

Clock and Alarm BufferUnit (CLBU)

The duplicated CLBUs distribute the clock signals (generatedby the CLSUs) to the units in the same cabinet. The CLBUalso collects the wired alarms from the units whose timing ithandles and transfers them further to the OMU.

Clock System Unit

(CLSU)

CLSUs generate the clock signals, necessary for

synchronising the functions of the CLS, and transmit themfurther to the CLBU units in the other cabinets.

Compact Data ServiceUnit (CDSU)

The CDSU offers standard circuit switched data services,which include modem-based digital connections towards thePSTN and digital connections towards the ISDN.

General Signalling Unit(GSU)

The GSU takes care of the data call control functions in theCDS and interfaces with the CM and M (CMM), Group Switch(GSW) and the LAN unit.

Exchange terminal (ET)

The ET performs the electrical synchronization and

adaptation of an external PCM line.

Group Switch 512 (GSW512)

The GSW is the switching fabric of the CDS. It is controlled bythe CMM and performs the switching of data calls comingfrom the MGW through the PCM circuits.

LAN Switch Unit (LANU)

The LAN switches are used to collect control-plane trafficbetween different cabinets and it provides the externalinterface for the O&M and for the proprietary control signallingbetween the MGW and the CDS.

Message Bus (MB)The duplicated MB has a transfer rate of 32 Mbytes/s and it iscontrolled by the Message Bus Interface plug-in units (MBIF-

B).

Operation andMaintenance Unit (OMU)

The OMU acts as an interface between the user and thesystem. It is used for local operations and maintenancepurposes, for controlling application configuration and systemfiles, starting tests, traffic measurements, and statistics.

Table 1 Functional units in the CDS.


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4.3 CDS redundancy principles

Reliability is one of the most important considerations when investing in any product and

Nokia Siemens Networks provides an extremely high rate of reliability with the NetworkSubsystem (NSS) network elements by backing up every crucial part of the system.

To ensure reliability, different back-up techniques are used depending on the particularelement. Furthermore, each backed-up functional unit receives its power supply fromseparate DC/DC converters or from the power source of each card. The operation of thesystem is also continuously supervised so the backup can be in use quickly if a faultoccurs. These methods are used in supervising the system and ensuring properoperation.

Different back-up techniques are used depending on the situation. Some functional unitsare backed-up either by full duplication (2N), or by the N+1 redundancy principle so thatthere are more functional units available than traffic requires.

The redundancy of the different units of the CDS is shown in Table Redundancymethods of the CDS.

The Compact Data Service Unit (CDSU) data pools have no redundancy as such, formore information see Engineering for Circuit Switched Data Server (CDS). To ensurebackup, the CDS should always have at least two pools of the same kind housed incartridges with voltage inputs from different Power Distribution Fuse Units (PDFU). Formore information on PDFU-A, see Engineering for Circuit Switched Data Server (CDS).

The redundancy of small data pools (under 32 channels) is achieved, for example, byconfiguring two first pools as General Pools (CDSU), which support all data call types.

Operation and Maintenance Unit (OMU) The OMU acts as an interface between the userand the system. It is used for local operations and maintenance purposes, for controllingapplication configuration and system files, starting tests, traffic measurements, andstatistics.

Unit RedundancyGSU N+1

CMM 2N

OMU 2N

GSW 2N

CLSU 2N

CLBU 2N

LANU 2N

MB 2N

Table 2 Redundancy methods of the CDS

To ensure redundancy for the ET2 plug-in units, it is recommended that the ExchangeTerminals (ET) interfacing PCMs to the same direction are installed in cartridges or slotsfed by different PDFUs.

For more information, see Engineering for Circuit Switched Data Server (CDS) .


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4.4 CDS availability

The system is designed to meet the demanding availability requirementsaccording to ITU-T recommendation guidelines. The calculations describe thesystem from the availability point of view - presenting availability, meandowntime values, and mean operating time between system failures. Thecalculations are based on mathematical modelling and are the result of usingreliability block diagrams of the system, failure definitions used, plug-in unitfailure intensities, maintainability data, and the rules of probability theory.

Simplicity and speed of the maintenance procedures are importantconsiderations for the availability of the system. Maintenance is improved by themodular structure of the equipment, automatic fault detection procedures, andelimination of downtime by using efficient redundancy methods.

CDS HW and SW attributable unavailability (=System Outage

Performance)Based on the latest field data of CDS product quality, six months rolling sum ofthe total and major software and hardware outages is under the BellcoreTelecom standard 2 Minutes/Network Element/Year. The six months rollingsum is calculated as a sum of the latest six months period.


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4.5 CDS mechanical design and power supplyCabinets

From the M12 release onwards, the CDS is housed in an IPC209-A forcedventilation cabinet. The cabinet types used in the CDS are:

The base configuration contains one IP Cabinet C (IPCC), one cabling cabinet,and one Interworking Cabinet (IWC). The capacity of the CDS can be extendedwith three additional IWF cabinets. For more information on CDS cabinets, seeEngineering for Circuit Switched Data Server (CDS).

The dimensions of the cabinet types are the following:

IPCC 2000 x 1200 x 600 mm (78.8 x 47.3 x 23.6 in)

IWC 2000 x 900 x 600 mm (78.8 x 35.5 x 23.6 in)

The depth of the cabinet doors is included in the depth measure.

BASE Base Configuration

IWC InterWorking Cabinet


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Table 3 CDS cabinet

types

Figure 6 CDS cabinet types

Cartridges

In the design of the cartridges special attention has been paid to durability evenunder demanding conditions, along with dimensioning for optimal use of space.One cartridge usually contains the equipment of one Functional Unit.

For more information on cartridges in the CDS, see Engineering for CircuitSwitched Data Server (CDS).


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Plug-in units

The printed circuit boards of the plug-in units are multilayered and covered witha protective coating for easy handling and protection against scratches. High

quality Hard Metric connectors, which are designed in accordance with the IEC1076-4-101 standard and Standard Euro connectors are used. Both surface andhole-mounted components are used.

For more information on plug-in units in the CDS, see Engineering for CircuitSwitched Data Server (CDS).

Power supply

The power supply is distributed from the rectifier system and the batteriesthrough the PDFU to the cartridges, through the distribution cables. The PDFUalso contains fuses for the internal distribution cables of the cabinet and alarmcircuits for the incoming voltages, plus its own fuses. An alarm is generated if afailure occurs.

For more information, see Engineering for Circuit Switched Data Server (CDS).


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4.6 Capacity of the CDS

Maximum capacity

The maximum capacity of the CDS is 1792 CS data channels, achieved with abase configuration of one base cabinet and three Interworking (IWC) extensioncabinets.

For more information on the dimensions and the capacity of the CDS, seeEngineering for Circuit Switched Data Server (CDS).

Scalability of capacity

The capacity of the CDS is scalable from 224 CS data channels to 1792 CS

data channels.The required hardware configuration and the corresponding call handlingcapacity are presented in Table CDS data call handling capacity.

*) IWF cabinet half equipped

In the ANSI environment the maximum number of data channels is 1536.

Connectivity capacity

One CDS can be connected to several MGWs that can be connected to oneCDS. The theoretical maximum for the MGWs that can be connected to theCDS is 100. Additionally there can be up to 100 CDSs connected to one MGW.

CDS configuration Call Handling Capacity

Base configuration *) 224 data channels

Base configuration 448 data channels

Base configuration + 1IWF ext. cabinet

896 data channels

Base configuration + 2IWF ext. cabinets

1344 data channels

Base configuration + 3IWF ext. cabinets

1792 data channels

Table 4 CDS data call handling capacity


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4.7 Typical power consumption of the CDSThe typical power consumption values for fully equipped CDS cabinets are:

Power consumption

The typical estimated power consumption values for the different configurationsof the CDS are:

The typical power consumption values for the CDS minimum and maximumconfigurations:

Cabinet Power consumption

IPCC 1200 W

IWC 1100 W

Table 5 Power consumption of the CDS cabinets.

Cabinet IPCC IWC Sum power

min 1 pc 1 pc

2 cabinets 1200 W 1100 W 2300 W

max 1 pc 4 pc

5 cabinets 1200 W 4400 W 5600 W

Table 6 Power consumption of the CDS minimum and maximum configurations.


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5 Site requirements for the CDS

This section describes the exchange room layout and some basic requirementsfor the premises. For more information on the cables and cable structures, seeEngineering for Circuit Switched Data Server (CDS).


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5.1 Exchange room layout

When the equipment room houses the both DX 200 and IPA2800 networkelements, the recommended minimum distances for the cabinet rows are thefollowing:

700 mm (27.6 in) between IPA2800 network element cabinet rows.

800 mm (31.5 in) between IPA2800 network element cabinet rows and Nokia

Siemens Networks DX 200 network element cabinet rows.

In addition, each cabinet should be located in the equipment room with at least500 mm (20 in) between the end of a cabinet row and the wall.

The IC209-A cabinets are dimensioned according to ETSI recommendationsand they are suitable for raised-floor installations with standard 300 mm 300mm modules.

In layout planning, the following aspects should be considered:

cable structures for the power supply and PCM circuit cables

room for expansion cabinets

maintenance passages (at least 1200 mm or 3.9 ft wide; passage for

expansion material)

free space above the cabinet rows (height at least 500 mm, or 20 in)

the cabinets must be lined up in a single row in order from the left to right or

alternatively from right to left ('mirror image layout')

no pillars or other support structures are allowed within the free area around

the cabinets


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5.2 Cable structuresCables of peripheral devices

The connectors for the Visual Display Units (VDU) and Line Printers (LPT) usedfor temporary service operations are on the front panels of the CPU plug-inunits. The cables connect to RJ45 connectors.

The permanent VDU and LPT connections for monitoring the operations of theunits are made through the connector panels in the IPCC cabinet.

PCM trunk distribution frame

Distribution frames are not system-specific and are therefore not discussedhere.

Cable shelves

The DX 200 system construction does not comprise actual cable shelves. Onlythe cable conduits between the cabinet rows are part of the mechanicalstructure. The cable support construction arrangements for the external cablesare decided upon by the customer individually.


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Appendix


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References

1.


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Glossary


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Index


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cds introduction

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