TETRA Inter System Interface (ISI)

An update and review of specific issuesJohn Cox

CEO TETRA MoU Association

Inter System Interface (ISI)• An important part of the TETRA standards suite• Defines interoperability between radio networks• Published by ETSI (European Telecommunications

Standards Institute)• Korean National version published by TTA (Korean

Standardisation Organisation)

ISI usage

ISI

Country A Country B

International cross-border cooperation

ISI Usage

Subnetwk ASubnetwk B

ISI

National Multivendor Cooperation

ISI Usage

User A NetworkUser B Network

ISI

Local In Country Cooperation

Interoperability Certification Process• Managed by TETRA MoU Association• Ensures genuine multi-vendor market for

operators, users and suppliers of TETRA• TETRA Interoperability Profile (TIP)

specifications are produced to…– Guide the implementation and– Give detailed instructions for conducting

Interoperability test sessions• Test sessions are carried out under the

supervision of an independent Italian Government Organisation, ISCTI

Status of ISI TIP’s – June 2005• Comprehensive set of TETRA ISI TIP’s have been published for the

implementation of operational network solutions:– Individual Call– Mobility Management– Short Data Service– Group Call– Voice Transmission Format– Lower Layer Protocols

• Test Plan Documents– Original Plan – reviewed by Member’s Enquiry (ME)– Revised Plan – about to re-enter the ME stage

• ISI and related Test Sessions– Air Interface Migration tested April 2005 (required for terminals to roam across

an ISI)– ISI test

• Planned for later in 2005• Awaiting manufacturers to inform TETRA MoU Association that they are ready

3-Country Pilot -Interworking Verification Project

• Tested interworking between national networks• Security agencies from Belgium, Germany & the

Netherlands participated• Equipment

– Networks from Motorola & Nokia– Terminals from Motorola, Nokia and other manufacturers

• Phase 1 report concluded “… that the European TETRA standard provides the communication requirements for the future emergence of a new dimension of co-operation of security agencies in Europe.”

• Full report available at www.3countrypilot.com

Developments after the 3-Country Pilot

• Functional Requirements Specification developed • Produced by combined group working from:

– Belgian and Dutch Security Agencies– Motorola and Nokia

• Scope – detail the communicating technology needs based on the development scenarios (the practical tests carried out by multi-agency teams during the pilot)

• Specification now an ETSI Technical Report – TR 101 448

ETSI Project TETRA – additional ISI specifications• TR 101 448 analysed by ETSI Project TETRA and TETRA ISI

TIP Working Group• New work item established, supported by

– Astrid (Belgian Public Safety)– ISC (The Netherlands Public Safety)– Motorola– Nokia

• New requirements for TETRA ISI TIP specification identified• Additional functionality for group attachment through the

ISI to the TETRA ISI Mobility Management standard• ETSI Project TETRA has been replaced by TETRA Technical

Committee

Update on specific functions supported by current ISI TIP specification

• Priority call & Emergency call– Can be delivered through ISI allowing emergency call to

continue on other side of ISI

• Individual call– Test plan currently at ME stage – anticipated to be

completed by the end of June 2005– No restoration during migration – not identified as

necessary by 3-Country Pilot teams

• Group call– Not covered in ISI TIP as calls can be re-established by

Late Entry or by pushing PTT once

Encrypted functionality and the ISI

• Current ISI TIP’s are ready for air interface encryption with Dynamic Cipher Key (DCK)

• Over The Air Rekeying (OTAR) and Group Cipher Key (GCK) functions could all be included if they become user organisation requirements

Group attachments across the ISI

• Current situation– ISI TIP’s assume that group attachments are done in the

network where the radio is registered using a local ‘agent’

• New ETSI work item identified– Work in progress to allow the network identifier part of

the group number to be delivered across the ISI to enable direct attachment from the other side of the ISI

• TIP and test case will be updated when the content of the new standard is finalised

Dynamic Group Number Assignment across the ISI• DGNA handling logic is same as for

Group Attachments:– DGNA is performed in the network where the

radio is located– DGNA message sent by the dispatcher located

in the same network as the radio

• Current ISI TIP’s do not support DGNA between networks

Radio Enable/ Disable across the ISI

• Amendment to current ISI TIP was identified in 3-Country Pilot

• ISI TIP Working Group suggestion:– Enabling/disabling should be linked with

authentication– Home network of a stolen radio would not

grant other networks a permission to authenticate that radio

• Modification to the ISI standards NOT needed if this proposal is accepted by users

Packet Mode Data Call across the ISI

• IPI (Internetwork Packet Interface) is Packet Data Gateway standard for TETRA

• ETSI reference is ETSI TS 101 747 ‘IP Interworking (IPI)’

• Same interface as ALREADY used to connect TETRA packet core networks to the Internet

• Additional specification to cover packet data NOT required

End to end encryption across the ISI

• Current ISI TIP's support end-to-end encryption

• ISI delivers TETRA voice frames transparently through the interface

• SwMI’s should be expected to transport end-to-end encrypted communication as long as they are:– Compliant with SFPG recommendations, and – Can support ISI connectivity

Future revisions of documents • Drafting work for TIP’s and Test Plans is done by

voluntary resources from the manufacturers• Manufacturer priorities typically depend on demand

from the operators and users• In general, ISI work has high priority• Required amendments are quite minor• Time required to make the identified revisions is shorter

than the time required to produce the ISI Test Plans

• Conclusion– ‘revision’ work would NOT be the limiting factor in the time-to

market for interoperable TETRA ISI

Sources of further information

www.tetramou.com

www.3countrypilot.com

www.etsi.org

Thank you

John CoxChief Executive OfficerTETRA MoU Association

john.cox@tetramou.com