Couverture GPRS 18/09/06 15:34 Page 2 - International … · · 2008-07-08assessment of the need...

Couverture GPRS 18/09/06 15:34 Page 2

White Paper

GPRS for ERTMS

General Packet Radio Servicefor European Rail Traffic Management System

1 ERTMS Background 4

2 Current status of GSM-R 6

3 Current status of ETCS 8

4 Identification of potential limitations with CSD for ETCS 8

5 Analysis of GSM-R capacity solutions 10

5.1 Analysis of non-GPRS technologies 10

5.1.1. Cell planning techniques 10

5.1.2. Half-rate Codex 14

5.1.3. Frequency hopping 14

5.1.4. Additional spectrum in the F- and P-GSM bands 15

5.1.5. ETCS Level 1 16

5.1.6. Summary 17

5.2 GPRS as GSM-R capacity solution 18

5.2.1. How could GPRS adress capacity issues 19

5.2.2. Summary of the technical feasibility of moving to GPRS 21

5.3. Summary of perceived benefits of moving to GPRS 25

6 Conclusions and Way forward 26

6.1 Economic evaluation 26

6.2 Standards development 27

6.3 Product development 27

6.4 Next steps for development activities 28

7 List of abbreviations 30

8 Appendix 1 - Group participation 31

9 Appendix 2 - Key input documents 32

Contents

Prepared by the UIC GPRS Ad-hoc GroupCoordination and graphics: Daniel Tessèdre - UIC/Communication Department

Printing: ECGISBN: 2-7461-1191-8 - Copyright Deposit: September 2006

GPRS for ERTMS - White Paper

The purpose of this document is to provide an outlineassessment of the need to enhance GSM-R network capacityand to review the key technology solutions available.The intention is to prepare for the future, NOT todestabilise the ETCS specification process.The first European corridor would not be affected by this work.If the Railways wish to go ahead with this initiative, adevelopment path toward IP-based solutions has to be agreed.This implies that a generational shift is required in the signallingworld.

The GPRS for ERTMS White Paper provides the outline businesscase for supporting the use of the General Packet Radio Service(GPRS) for the European Rail Traffic Management System(ERTMS) and other data applications and it specifically considersthe potential for introducing GPRS to support ETCS.

The document also includes proposals for steps to beundertaken to prove whether GPRS (and the introduction of IP-based protocols) is feasible as future method for datatransmission in the railway environment and it proposes anoutline plan for the development of working systems.

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1 Interoperability definesthe ability of safe and

uninterrupted trainmovements.

4

Rail traffic management systems are traditionally conceived and maintained on

a national basis.Today a multiplicity of totally different CC (Control-Command)

systems exist, which makes cross-border efficiency and the utilisation of train

sets and locomotives difficult and limits the potential benefit of an open and

large procurement market, thus of interoperability1.

Technical interoperability, which is measured by the amount of CC systems

onboard (amount of antennas installed underneath the vehicle) is the necessary

precondition to permit trains to run freely on the whole interoperable network

and on international corridors.

ERTMS (European Rail Traffic Management System) began as a European

project (the European Commission had decided that there should be one

unique CC system in Europe). Today ERTMS is a universal solution gaining in

worldwide influence as more and more countries implement GSM-R and ETCS.

The goal of ERTMS is to have one single and common train management

system, unified standard equipment, thus allowing full interoperability and open

procurement market. Gone will be the days were the locomotive had to be

changed at each border (sometimes even the wagons!) or when trains had to

have several control systems on board (i.e. Thalys has 7 control systems on

board to be operable in 4 countries).

ERTMS is a system which allows interoperability and all parties (railway

associations, European Union, railway operators and industry) commonly agree

that ERTMS is the right technological solution for interoperability and the

future train signalling system. The Concerned (European Commission, UIC,

CER, UNIFE and EIM) signed a Memorandum of Understanding in March 2005

establishing the basic principles of the EU deployment strategy. With this

Memorandum the Railway agencies, Industry and the European Union declare

their vision and commit to implement a single European system of train control.

The member states of the European Union have to develop their national

master plan of ERTMS deployment; these all together will enable a European

Master Plan of Deployment.

1 ERTMS Background


ERTMS has three layers:

1. ETCS (European Train Control System: command and control

components)

2. GSM-R (GSM for trains: telecommunications component)

3. ETML (European Traffic Management Layer: traffic management

component)

ETCS exists in three levels of implementation, which do not build on each

other:

• ETCS level 1 is installed in parallel to existing CC Systems.This version

is often sought for rails already in action.

• ETCS level 2 means that only ETCS is employed as CC System.There

are no more trackside signals and full cab signalling is achieved. This

solution is often employed for newly built lines.

• ETCS level 3 adds to level 2 a train integrity function to replace the

conventional train detection, the train becomes self-detecting.

Traffic management has become of increasing importance in the rail sector for

ensuring customer-friendly and efficient services. Trains can only be exploited

safely and efficiently with adequate means for signalling, train control and

communications and the harmonisation of the systems improve trans-border

rail services over long distances. ERTMS combines all these advantages and

many more.

One of the actual questions is if the frequency capacity of the GSM-R is large

enough to enable full operation of ETCS level 2 and 3 regardless of the

geographical location, it has to also work in a bottle neck. A UIC Ad Hoc

Working Group has analysed the implementation of GSM-R and its future

developments.The Working Group realised that capacity problems risk to arise

and has analysed all possible solutions.

5

ERTMS Background

6

In July 2006 GSM-R covers 24% of the railway networks of the implementing

European countries (Belgium, Croatia, Czech Republic, Finland, France,

Germany, Hungary, Italy, Netherlands, Norway, Spain, Switzerland, Sweden and

UK), Norway has implemented 40% of its planned total network (amounting to

some 1 400km), Germany has 24 000km on air (85% of the planned total), the

Netherlands has 3 000km on air (100% of planned total) and Italy has 6 000km

on air (70% of planned total) and implementation is also moving ahead swiftly

in the other countries.The total planned line penetration of GSM-R amounts

to 74% of the combined networks of these countries (fig. 3).

Figure 3: Status of GSM-R implementation in Europe

2 Current status of GSM-R


2 For example, basedon a standard 7 cell

repeat pattern (fig. 2), thisnumber of frequencies

could give rise to between15 and 22 traffic

channels per cell. Thesetraffic channels will beshared between ETCS(one per active train)

and GSM-R voice(one per active voice or

non-ETCS data call).

3 For the purposes ofillustration, the limits of

capacity are likely to bereached in a cell with 22

traffic channels whenmore than 15 ETCS

onboard units areengaged in data calls

(assuming that 7 trafficchannels will be sufficientto support all other voice

and non safety relatedcalls).

7

The frequency band allocated for Railway use for GSM-R is limited to 4MHz

(fig. 1), meaning that 19 frequencies are available, providing a limited number2 of

circuit switched traffic channels for voice or data transmission.

Figure 1: GSM-R spectrum and surrounding frequency band

Some Railways have identified that the actual GSM-R capacity is unlikely to be

able to support ETCS level 2 and 3 in densely trafficked areas3 (in addition to

the other data and voice applications), as each ETCS onboard unit engaged in a

data call (and each voice and non-ETCS data call) will occupy an entire traffic

channel.Additional capacity will therefore be needed for ETCS Level 2 and 3. It

can be achieved by modifying and enhancing the existing networks and has the

advantage of providing sufficient capacity for all future needs from the outset

while keeping an interesting implementation cost versus the financial benefit

(i.e. the implementation strategy will be influenced by the net present value of

the investment).

Although economically expedient, this approach is likely to prove problematic

from a radio design perspective. Subsequent enhancements will inevitably be

influenced by economic factors, which will reduce the scope of the change. For

example: full optimisation of the network may only be possible by moving a

large number of existing cell sites, but economics will favour the retention of as

many existing sites as possible.

Figure 2:The 7-cell repeat pattern

Current status of GSM-R

3 Current status of ETCS

Currently, the work on ETCS is focusing on completing the suite of documents

supporting ETCS SRS version 2.3.0 and is working towards the development of

version 3.0.0.

SRS version 2.3.0 does not mention the use of GPRS. However the issue of

GPRS and ASCI is included as a priority 2 open point in Annex G of the Control

Command and Signalling TSI.

In terms of future updates to the ETCS specifications, it is essential that the

system is not allowed to diverge because of differing railway requirements.This

would dramatically increase the cost of specification and the cost of the

equipment itself.Any enhancements to ETCS to allow it to operate over GPRS

need to be subjected to formal standardisation and must be available in time to

meet the railways’ application needs.

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4 Identification of potential limitationswith CSD for ETCS

The current use of circuit switched data (CSD) for ETCS means that a

dedicated connection per train must be maintained.The average ETCS data rate

of the connection however is low (and data transfer is variable in nature) and

is, from that perspective, spectrally inefficient.

Application studies undertaken by a number of railways have shown that it is

likely that there will be problems in accommodating all ETCS trains and GSM-R

users in some densely trafficked areas. “Key Location Capacity Requirement

Analysis (SYS-TEL-REP-015)” [O-8606], for example, performs an analysis of

the likely capacity issues that would arise from the use of circuit switched data

to support ETCS in a number of different areas of the UK. In the case of

Clapham Junction, the report concluded that GSM-R capacity would be

marginal to insufficient.

Known limitations with circuit switched data in addition to the capacity issues

raised above are as follows:

• call set-up times

• cell handover errors

• management of dropped calls (including detection of dropped calls)

• management of RBC-RBC handovers (the circuit switched solution

requires two mobiles and two traffic channels for seamless RBC-RBC

handovers)

• in addition, “sleeping” ETCS units require access to the radio network

(for example during entry to an RBC area and when entering/exiting

sleeping mode

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Identification of potential limitations with CSD for ETCS

Smaller cells

5.1.1 Cell planning techniques

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5 Analysis of GSM-R capacity solutions

To find a solution to the future problematic of limited GSM-R capacity, the UIC

has set up a GPRS Ad-Hoc Working Group as part of the ERTMS/GSM-R

Project to identify and analyse possible solutions.

The following solutions were considered:

• Cell planning techniques (e.g. microcells and picocells)

• Half-rate codec

• Frequency hopping

• Additional frequencies

• Use of ETCS Level 1

• GPRS

5.1 Analysis of non-GPRS technologies

The following alternative techniques to packet switching (GPRS) were

considered in terms of their suitability for increasing GSM-R capacity to

support ETCS.

The use of smaller cells will increase the available GSM-R network capacity

within certain limits (this is elaborated below – fig.4), but it will inevitably result

in a greater number of cell handovers for moving subscribers.This will ultimately

give rise to a lower quality of service, because more cell handovers mean more

handover transmission breaks and more dropped calls due to handover failures.

Figure 4: Use of smaller cells

Whilst the use of smaller cells can increase the capacity for voice and data

point-to-point communications, it would not be as beneficial for group and

broadcast call traffic. Group and broadcast calls use resources in every cell in

the group/broadcast call area. Splitting those cells would therefore often result

in proportionally increasing the number of cells per area, thus resulting in little

or no net capacity gain.

Moreover, one of the key limitations of this approach is that it will serve to

reduce the distance between base stations. This will ultimately give rise to

increased levels of radio interference even if effective power control of base

stations and mobiles can be employed (this is an issue regarding the use of

power control at high speed for group calls).

Microcells and picocells

“Microcells” is the name given to small radio cells used as part of a mobile

telecommunications network. Microcells typically have diameters of 1 to 2

kilometres and are mainly used in cities.

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Analysis of GSM-R capacity solutions

Even smaller than these are “picocells”, whose diameters are often only a few

hundred metres. Larger radio cells, typically with diameters of the order 10 to

30 kilometres are known as "macrocells".

Micro- and picocells are often used as means of overlaying additional coverage

on top of an existing macrocell network. The introduction of a number of

strategically positioned microcells and picocells (in addition to the backbone

macrocell network) could provide additional capacity particularly in areas such

as some stations and shunting yards (refer to fig.5).

Picocells are especially effective in enclosed environments such as buildings,

because these structures can help to shield the picocell and the mobile

equipment it serves from interferences generated by external macrocells (and

vice versa).

Figure 5: Use of micro/picocells

Micro- and picocells can, however, have a detrimental effect on interference and

their introduction can necessitate significant changes to the frequency plan (and

possibly even the cell plan) within a given area.This is particularly true for GSM-R

networks, which have relatively few available frequencies compared to public

GSM.

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Furthermore, the use of this technique could have a severe effect on the quality

of service due to issues with cell handovers. For example, consider the

handover issues associated with a fast-moving train passing through a station

served by one or more micro- or picocells. If the train were travelling at

200km/h, and the cell had a diameter of 0.5km, two successive handovers may

occur within a 9 second period, resulting in potential disruption to ETCS

communications.

Conclusions from analysis of cell planning techniques

The use of smaller cells is a valuable technique for the GSM-R network planner

and will be used to optimise the GSM-R network capacity as part of any

coherent network design process. A compromise often needs to be made

between delivery of the desired capacity (particularly in densely trafficked

areas) and the quality of service that is required from the network. Cell size is

an important parameter that will be used by the GSM-R network planner to try

to adjust this balance as favourably as possible to support the operational needs

of the railway.

Interference and handover issues limit the amount by which the cell sizes can

be practically reduced. Furthermore, the reduction of cell size in an existing

network will result in the need to move and add a large number of base stations

and may therefore prove to be economically undesirable. However, this

technique will be used by cell planners in the design of new networks to get

the most favourable compromise between quality of service and network

capacity.

The introduction of micro- and picocells may provide additional capacity in

some areas without the need for extensive changes to existing network

infrastructure. This method is likely to prove particularly effective in areas

enclosed by buildings and some types of geological features. However, the

deployment of this solution will not be suitable in all locations due to

degradation in the quality of service resulting from higher interference and

handover issues.


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5.1.3 Frequency hopping

Cell planning techniques are therefore not useable in all cases to solve the need

for enhanced capacity. The benefit that can be realised from using these

techniques is fundamentally limited by the need to compromise between

capacity, interference and increased numbers of handovers.

5.1.2 Half-rate CODEC

The half-rate CODEC enables two voice calls to use the same GSM-R timeslot,

thereby effectively doubling the network capacity for this type of call. Use of the

half-rate CODEC would therefore improve efficiency of voice network usage

and could therefore liberate more capacity for ETCS data.

However, the use of the half-rate CODEC to support data transmission is not

currently supported by GSM equipment. It is understood that there are no

plans to extend half-rate to data communications for the foreseeable future and

there are possible problems regarding the quality of service.

In areas where circuit switched ETCS data communications utilise the majority

of the GSM-R network capacity, the use of the half-rate CODEC for voice will

provide only a marginal capacity benefit.

Frequency hopping is a method which enables the mobile (and base station) to

transmit and receive each successive GSM timeslot or group of timeslots on a

different frequency. The mobile receives the list of frequencies that are to be

used, the hopping sequence and an index offset (to enable different mobiles to

be allocated exclusive slot combinations) from the base station.

In a system not using frequency hopping, some communications could be

continuously degraded by co-channel or adjacent channel interference from

another call within the same service area (this applies only to networks where the

frequency reuse is sufficiently tight to allow these levels of interference to arise).14


Frequency hopping effectively “spreads” system co-channel and adjacent

channel interference, thus helping to alleviate the problem of continuous

degradation. As a result, frequency hopping could allow a tighter frequency

reuse pattern to be employed, thus giving rise to increased network capacity.

However, GSM-R networks have relatively few frequency channels compared to

public GSM networks, so it is unlikely that the full advantages of frequency

hopping could be realised in a GSM-R implementation. The use of frequency

hopping may also have a detrimental effect on GSM-R functionalities (e.g. for

the late entry of trains into emergency call areas) due to a reduced number of

available notifications in each Notification Channel block.

Furthermore, a key disadvantage of this method is that in a heavily loaded

network, frequency hopping will often give rise to brief periods (i.e. several

milliseconds) of comparatively poor transmission quality. Although this can be

tolerated for most voice communications (providing that the signal quality

during the majority of the timeslots is adequate), it could prove to be highly

detrimental to ETCS data communications.

Germany has made enquiries to its spectrum authorities about securing

additional spectrum in the E-GSM band. All GSM-R mobiles are capable of

operation across the whole GSM 900 band. Therefore, there should be no

interoperability issues arising from the use of additional GSM 900 spectrum in

particular countries.

This approach is only valid in countries where the spectrum is not in use or

can be secured. In a significant number of other countries, further frequencies

are very unlikely to be available.

5.1.4 Additional spectrum in the E- and P-GSM bands


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5.1.5 ETCS Level 1

“Islands” of ETCS Level 1 could be used in place of ETCS Level 2/3 in densely

trafficked areas to reduce the demand on GSM-R. However, this would

necessitate the installation of infill, either Eurobalises or Euroloop. The latter

would result in large amounts of cabling in these areas. It is an economic

imperative of many ETCS business cases not to have to put up signals on

expensive structures and perpetuate national signalling systems.

Figure 6: ERTMS/ETCS Level 1 without infill

Radio infill could be utilised for ETCS level 1 (fig.7), however this is not likely

to be a suitable technique for dense areas due to the number of GSM-R traffic

channels required if circuit switched data transmission is used.

Figure 7: ERTMS/ETCS Level 1 with infill

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The GPRS Ad-Hoc Working Group has performed an analysis of these

techniques and has concluded that the use of these methods alone will not

provide a satisfactory solution to the capacity problems associated with the

implementation of ETCS Level 2/3 in densely trafficked areas, based on the use

of circuit switched data transmission in all areas.

Even in cases where sufficient capacity could be provided in such areas, the

majority of the available traffic channels would be needed for ETCS

communications. As mentioned before, the utilisation of these connections is

low.This, combined with the large number of circuits needed for ETCS, means

that the overall utilisation of the GSM-R spectrum is likely to be inefficient (or

at best sub-optimal). Furthermore, very little capacity would be available for

non-critical voice communications and other applications.

5.1.6 Summary


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5.2 GPRS as GSM-R capacity solution

GPRS is an international standard for the transfer of packet data and is widely

available in public GSM networks.This standard is now robust and can therefore

also be used for railway applications.

Furthermore, GPRS has been included as an option in the EIRENE

specifications and has been successfully implemented in the railway

environment for non-safety critical data applications.

GPRS enhances GSM data services significantly by providing end-to-end packet

switched data connections.

GPRS is particularly useful for applications where short bursts of data

communications activity are interspersed with relatively long periods of

inactivity.

GPRS can support several simultaneous data sessions by inserting data packets

from one data session into the gaps between the data packets in another data

session.

GPRS uses IP internally to provide end-to-end packet services, therefore every

active GPRS mobile must have an IP address associated with it. Depending on

the configuration, the mobile may have a fixed IP address or, alternatively, the

network will allocate an IP address to the mobile dynamically from a pre-

determined range4.4 If fixed IP addresseswere to be used for ETCS,

each train mobile wouldneed to be allocated apermanent IP address.

This raises interoperabilityissues for roaming trains,

as each country mayneed to be allocated

specific IP address ranges.Dynamic IP addresses, in

contrast, might beexpected to make more

efficient use of the IPname-space, but this mayincrease session initiation

times.

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GPRS uses radio resources only when data is actually sent. The channel

utilisation for some applications is therefore significantly more efficient, leading

to a more economic use of the available bandwidth.

Communication between mobile users and the network are managed as

sessions, although there is no permanent end-to-end connection. Once a

session has been established, users can be continuously on-line without using

network resources when data is not being sent. Data packets can be

transmitted rapidly when communication is required. In this way, a given amount

of radio bandwidth can be shared between multiple users simultaneously.

Figure 8: GPRS allows multiple users to share a single time slot

In addition, GPRS has the potential to provide faster data transmission, to

improve the handling of RBC-RBC handovers and thus could provide more

efficient solutions for key management. It should also be noted that further

improvements to GPRS (principally to the speed of data transmission) could be

realised by enhancing the network and mobiles with Enhanced Data for GPRS

Evolution (EDGE)5 . Figure 9 illustrates the raw data rates that can be achieved

with the available coding schemes (the figures are in kbps).

Figure 9: High performance coding schemes brought in by EDGE modulation

5.2.1 How could GPRS address the capacity issues?

5 EDGE is not areplacement for GPRS; it is

an improvement in thebearer and would improve

the data rate.Furthermore, there shouldbe no further implications

on ETCS as a result ofchanging from a GPRS

bearer to a GPRS bearerenhanced by EDGE.


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Depending on network configuration, GPRS can support seven subscribers

interspersing their data on each available packet data traffic channel (c.f. circuit

switched data where only one user can be supported on each traffic channel –

fig.8).This restriction results from the addressing header (known as the USF or

Uplink State Flag) that is used to identify which GPRS data packets belong to

which mobile. As the USF is three bits long, a maximum of eight (23) mobile

users can be distinguished per packet data traffic channel, however due to

implementation constraints, one of these values is reserved for system use (see

section 6.6.4.1 of GSM 03.64 (ETSI TS 101 350) for further details on the USF

and dynamic allocation of radio resources).

The number of packet data traffic channels required to support GPRS

communications is therefore the greater of the following two parameters:

• The number of packet data traffic channels required to support the

desired data throughput

• and the number of subscribers concurrently wishing to send data over

the network divided by eight.

Due to the complexities highlighted, it is not possible to quantify the precise

capacity gain that will be realised from the use of GPRS to support ETCS

without undertaking detailed modelling work. This modelling ideally needs to

encompass railway operational scenarios in order to derive the real-time ETCS

data throughput and should also consider the air interface behaviour. Please see

O-8633 (Remit for GPRS Study) for an approach to the modelling work that is

proposed to be undertaken to help resolve this issue.

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In assessing the technical feasibility of using GPRS to support ETCS, a number

of key input papers have been reviewed and some new technical papers have

been produced. A full list of the material considered by and produced by the

GPRS Ad-Hoc Working Group is provided in Appendix B.

The remainder of this section provides a summary of some of these key input

papers, the important technical issues that they describe and a summary of

their conclusions.

O-8608/O-2703: GPRS a new bearer for ETCS?

This paper considers the pros and cons of GPRS and circuit switched data,

provides some ideas on how GPRS/IP could be used to support ETCS and

discusses the implications.

The paper draws the following conclusions:

1) When introducing IP, railways may benefit from cost-effectiveness,

economies of scale and future-proofness6 . Introducing IP probably leads

to a cost increase in the near term but likely to an overall cost reduction

in the future. Using IP/GPRS as a data bearer for ETCS looks promising

but further study is required for a final answer on feasibility.

2) Moving from circuit switched data to GPRS is definitely about stepping

into the IP world.This has a major impact on the following areas:

a) The EURORADIO protocol stack needs to change to a full IP equivalent.

b) Mobile and fixed ETCS communication services (e.g. train-RBC and

RBC-RBC) will be IP based. ETCS will likely use services such as DNS,

DHCP, firewalls and IPsec.

c) The addressing scheme needs to be changed from an E.164 basis to an

IP basis (think for example of the ETCS balise which now communicates

an E.164 RBC number to the train).

d) For preserving co-existence of CSD and IP, protocol stacks, interfaces

and services (including Euroradio) need to be supported simultaneously.

5.2.2 Summary of the technical feasibility of movingto GPRS

6 The general opinion ofthe GPRS Ad-Hoc Working

Group was that IP has along term future (at least

25 years) so a move to IPfor ERTMS would appear

to be a reasonably future-proof decision. It seemsunlikely that the packetswitched services will beshorter lived than circuit

switched.

O-8603/O-2679: GPRS Capability Report for ETCS

The purpose of this report is to summarise from the information that has been

gathered on the technical capabilities of GPRS with respect to its suitability to

support ETCS. It makes reference to a number of the other input papers

considered by the UIC GPRS Ad-Hoc Working Group and draws their

conclusions together.

The key conclusions were as follows:

1) Dedicated GPRS Class C mobiles 7 appear to be the most suitable

choice for ETCS communications.This approach needs to be verified

and agreed. It should be noted that the GPRS Data Radio for ETCS

should be used for data communications only and, hence, interactions

with ASCI calls should not arise.

Figure 10: Proposed ERTMS on-train equipment layout

2) In the network, dynamic allocation of uplink and downlink resources

provide the most efficient use of network capacity, but gives rise to the

danger that GPRS communications will be pre-empted by voice calls

and other circuit switched communications. Fixed allocation provides a

safer alternative, however this is potentially more wasteful of resources.

The merits of using mixed allocation should also be considered.

7 This type of mobile canonly be attached

(registered) to either theGSM voice (and CircuitSwitched Data) part of

the network or the GPRS(packet switched data)

part of the network, butnot both simultaneously.When it is attached to

one part of the network, itis unable to make/receivecalls or data on the other.

See the appendedreference documents formore information about

mobile equipment classes.

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3) Since the ETCS application has its own error recovery capabilities, it is

difficult to determine which GPRS reliability class is best suited for

ETCS. It is anticipated that further study of the behaviour of the ETCS

communication layers would allow a choice to be made between all of

the available possibilities. This study should include the feasibility of

using TCP and other protocols over transparent and non-transparent

GPRS.

4) When using GPRS, there should be a negligible break in transmission

break for most RBC–RBC handovers. In theory, a single GPRS mobile

can maintain simultaneous connections with up to five RBCs.Therefore,

when handing over from one RBC to another there is no necessity to

use a second mobile to establish communications with the accepting

RBC, except when crossing borders between GSM-R networks.

5) In the case of crossing borders, a procedure similar to the two data

radio RBC-RBC handovers option currently used in circuit switched

ETCS is possible. This would require the use of a second mobile to

contact the new RBC via the new GSM-R network, whilst contact is

still established by the first mobile to the current RBC via the old

network. This procedure requires an area of overlapping coverage

between the two networks across the border.

6) Will circuit switched data communications remain the baseline for

ETCS interoperability? If so, all international trains using GPRS in their

home network will need to be capable of using circuit switched data

communications for ETCS in other networks. Similarly, trains roaming

into a GPRS capable network will need to be given the option to use

circuit switched data communications for ETCS if they are not GPRS

enabled. Onboard and network ETCS equipment may therefore be

required to support both GPRS and circuit switched ETCS

communications and be able to perform any transitions required

between the two types of connection (e.g. at borders).

O-8601: Guidance for usage of standard GPRS for railwayapplicationsThe purpose of this document is to define the applicability of standard GPRS

to railway applications. The document considers GPRS interaction with ASCI

features, draws conclusions from this analysis and gives guidance on how

standard GPRS should be implemented in the GSM-R environment. The key

conclusions and guidelines are as follows:

1) Network suppliers are ready with GPRS facilities in the GSM-R

network environment. Mobile manufacturers are ready to propose

GPRS equipment working in GSM-R/GPRS network environment.

2) According to tests already performed, Class C mobile equipment is

available and ready.The outcomes of the tests showed that there is no

interaction between GSM-R and GPRS features.

3) The guidelines for implementing GPRS facilities in GSM-R networks are

as follows:

a) Separate equipment should be dedicated for GSM-R circuit

switched applications (including railway emergency calls, VBS and

VGCS) to that used for GPRS applications.

b)All GPRS equipment used in such applications shall be Class C which

means that both GPRS and circuit switched services cannot be used

simultaneously and do not have any interaction with each other.

c) Network suppliers and terminal suppliers already have available

products which fulfil these requirements.

24



25

The following list summarises the perceived benefits of moving to GPRS:

1) Capacity - freeing up of GSM-R capacity for other services, cell

planning would be easier and would allow more flexibility in design to

achieve the required capacity (particularly in highly trafficked areas).

2) Spectrum - more efficient use of available spectrum.

3) Quality of service - improvements in session establishment, fewer

dropouts, etc.

4) RBC-RBC handovers - potential for smoother RBC-RBC handovers

procedures using GPRS multi-session.

5) Inter-working strategy - potential co-existence with circuit

switched data ETCS as the basis for interoperability would enable a

staged rollout of GPRS ETCS without adversely affecting

interoperability.

6) Ability to support other services and other users - as a result

of reduced demand for GSM-R radio capacity from ETCS.

7) Reduced equipment in the GSM-R Network - the capacity

improvement brought about by the implementation of GPRS may

mean that fewer items of equipment such as base station transceivers

may be needed leading to lower costs for the network.

8) Future proofing - the general opinion of the GPRS Ad-Hoc Working

Group was that IP has a long term future (at least 25 years) so a move

to IP for ERTMS would appear to be a reasonably future-proof

decision.

9) On-line key management and transfer of diagnostic data - this

may be provided simultaneously to ETCS Level 2/3 operation without

blocking cell slots for a CSD call. This data transfer could be

independent of the safety layer and the RBC using a second IP/GPRS

session.

5.3 Summary of perceived benefits of moving to GPRS

6 Conclusions and Way forward

The GPRS Ad-Hoc Working Group recommends GPRS as the solution that

should be taken forward to solve the capacity problems regarding ETCS. Most

of the techniques considered in section 7 are compatible with a GPRS system

and could help to alleviate capacity problems, improve quality of service and

therefore merit further consideration alongside GPRS.

This section proposes the way forward for the work that has been initiated by

the GPRS Ad-Hoc Working Group. The section specifically focuses on the

economic evaluation, the standards development and the product development

work that will need to be undertaken to make this concept a reality.The section

concludes with a summary of the proposed next steps for the development

activities.

6.1 Economic evaluation

In order to make the business case for developing GPRS for ETCS stack up, the

value of the perceived benefits needs to be greater or equal to the

development costs.The economic evaluation should therefore look wider than

just the problem areas for ETCS. In particular, the demand for GSM-R capacity

from other applications and the values of providing these services need to be

considered. The importance to the railways of using the GSM-R frequency

allocation in a more spectrally efficient manner needs to be factored into this

evaluation.

The economic evaluation also needs to identify when GSM-R capacity

constraints are expected to cause a real problem for circuit switched ETCS.

This issue needs to be considered in the context of national railways’ roll-out

plans for ETCS and should also consider how migration to GPRS could be best

managed to preserve railway’s economic and operational interests, and protect

interoperability. For example will the entire fleet require fitment of new ETCS

equipment or will existing circuit switched equipment be able to operate

alongside new GPRS-enabled equipment without overloading the network?

26


Conclusions and Way forward

27

6.3 Product development

In order to enable ETCS operation over GPRS, the following standards would

require an update:

- The ERTMS/ETCS Specifications (updates to these specifications are

currently managed by UNISIG).

- FFFIS for EuroRadio (updates to this specification are currently managed

by a joint UNISIG & UIC ERTMS/GSM-R Project Technical Group).

- EIRENE Specifications (updates to these specifications are currently

managed by the UIC ERTMS/GSM-R Project and it is likely that only

minor updates will be needed).

- ETSI GPRS Standards (any additional requirements needed for railway

operations should be developed by ETSI’s Rail Telecoms Project (EP-RT).

6.2 Standards development

In order to enable ETCS operation over GPRS, the following products would

require development by GSM-R suppliers (to be co-ordinated by the GSM-R

Industry Group):

- GSM-R Network Equipment

- Data Radio for ETCS

The following products would require development by ETCS suppliers (to be

co-ordinated by UNISIG):

- RBC

- On Board Unit

- Radio Infill Unit

- Balise

6.4 Next steps for development activities

The following GANTT chart outlines the steps that are recommended in order

to facilitate the development of GPRS for ETCS:

28


Conclusions and Way forward

29

7 List of abbreviations

8-PSK 8-Phase Shift Keying

ASCI Advanced Speech Call Items

CODEC COder DECoder

CSD Circuit Switched Data

DHCP Dynamic Host Configuration Protocol

DNS Domain Name Server

GMSK Gaussian Minimum Shift Keying

GPRS General Packet Radio Service

GSM-R Global System for Mobile communications - Railway

EDGE Enhanced Data for GPRS Evolution

E-GSM Extended-GSM

EIRENE European Integrated Radio Enhanced NEtwork

ERTMS European Rail Traffic Management System

ETCS European Train Control System

ETSI European Telecommunication Standard Institute

FFFIS Form Fit Function Interface Specification

IP Internet Protocol

IPsec IP security

MCS Modulation Coding Scheme

MORANE MObile RAdio for Networks in Europe

P-GSM Public-GSM

QoS Quality of Service

RBC Radio Block Centre

UIC Union Internationale des Chemins de Fer

UNISIG UNion Industry of SIGnalling

USF Uplink State Flag

VBS Voice Broadcast Service

VGCS Voice Group Call Service

VPN Virtual Private Network

30


Appendix 1 – Group participation

31

The following personnel have participated in the GPRS Ad-Hoc Working

Group. The names of the participants and their organisations/roles are

summarised in the following table:

Klaus Konrad UIC Chairman

Kurt Andersen UIC GSM-R Functional Group

Reiner Behnsch DB Netz

Ola Bergman Siemens

Renzo Bertolini UNISIG (Ansaldo)

Richard Bloomfield Network Rail

Philippe Branly Sagem

Sebastien Cousteix Nortel

Paolo De Cicco UIC

Valerio Diclaudio Selex

Tugrul Güner Kapsch

John Harmer UNISIG (Invensys)

Lutz Koch UNISIG (Alcatel)

Anders Malmberg Banverket

Jos Nooijen ProRail

Dominique Perrin RFF

Volker Pliquett UNISIG (Siemens)

Laurent Poutas Nortel

Robert Sarfati UIC GSM-R Operators’ Group

Peter Tiberg Siemens COM

Simon Wootton UIC Functional & Operators’ Group

Participant Organisation/role

8 Appendix 1 – Group participation

9 Appendix 2 – Key input documents

The following table summarises the documents that have been considered by

the GPRS Ad-Hoc Working Group.The documents listed in bold text have been

appended to this report for reference.

The remaining documents can be obtained from the UIC Infrastructure

Department on request.

Number Title Date Version Source

O-8600 Workshop on GPRS 22/03/2000 A3 M0001A MORANE

O-8601 Guidance for usage of Standard GPRSfor railway applications (WP3) 26/02/2003 1.0 SAGEM SA

O-8602 Critical GPRS problems 15/03/2000 - UNISIG

O-8603 GPRS Capability Report for ETCS(O-2679) 23/11/2004 0.2 UIC

O-8604 Applicability of GPRS to ERTMS(H13T9001) 21/07/1999 H13T9001 1 MORANE

O-8605 GPRS Service description Stage 2 andFunctionality of an MS supportingGPRS (SEL9905e) 24/11/1999 1.0.0 UNISIG

O-8606 Key Location Capacity Requirement UK National Analysis ERTMS(SYS-TEL-REP-015) 12/04/2005 Draft D Programme

O-8608 GPRS a new bearer for ETCS? (O-2703) 04/05/2005 1.0 UIC

O-8616 GPRS Pros and Cons (SEL0558) 15/09/2005 - UNISIG

O-8622 Proposal for GPRS Measurements(SEL0572) 15/11/2005 1.0.0 UNISIG

O-8623rev1 GPRS Interworking 20/02/2006 0.1.0 UNISIG

O-8632 Review of GPRS Specifications(SEL0569) 12/01/2006 0.1.0 UNISIG

O-8633 Remit for GPRS Study 12/01/2006 0.1 Network Rail

O-8635 Nortel/rev1 IP for ETCS in GSM-R Networks 28/06/2006 2.0 Siemens

O-8643 Capacity gains using circuit switchedrev1 spectrum efficiency techniques vs. 28/06/2006 01.02 Nortel/

GPRS packet switched. Siemens

O-8644rev1 GPRS Issues (SEL0573) 23/06/2006 0.2.0 UNISIG

O-8647 GPRS Performance Measurements(Static) 30/03/2006 1.0 Prorail

O-8648 GPRS Performance Measurements(Drive-tests) 30/03/2006 1.0 Prorail

ETSI TS Digital cellular telecommunications101 350 system (Phase 2+); General Packet

Radio Service (GPRS);Overall description of the GPRS radiointerface; Stage 2 April 2003 8.11.0 ETSI


32

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