Introduction TETRA over IP

Bert Bouwers

Rohill Technologies B.V.

Agenda

• TETRA-over-IP (ToIP) basics• Benefits of TETRA-over-IP• Myths about TETRA-over-IP• Potential difficulties and concerns• Guidelines for ToIP system evaluation• Summary of facts

TETRA-over-IP basics

• Use the Internet Protocol (IP) to connect Base Stations and SwMI together

• Real TETRA-over-IP requires efficient mechanisms to transport both call setup signalling and speech / data traffic

• ToIP is a compromise solution. There is a considerable debate whether IP is the best solution or should be avoided.

TETRA-over-IP networking

• Can be deployed over any IP network– Internet– Intranet– Local Area Network (LAN) using Ethernet

• Transparent operation over– Routers– Switches– Hubs

Conventional TETRA network

PABX, PSTN,ISDN

Intranet /Internet

Other TETRAnetwork

NetworkManagement

LineDispatcher

IP gateway,Firewall

SwMI

TETRA-over-IP network

PABX, PSTN,ISDN

Intranet /Internet

Other TETRAnetwork

NetworkManagement

LineDispatcher

ISI / IPIgateway

Telephonygateway

IP gateway,Firewall

Databaseserver

Ethernet LAN

Benefits of TETRA-over-IP (1)

• One architecture for multiple purposes– Transport of TETRA traffic and signalling– Exchange of Status, SDS and Packet Data– Integrated platform for Network Management

(SNMP, HTTP)

NetworkManagement

Benefits of TETRA-over-IP (2)

• Large part available as COTS– Routers and switches

– PC based platforms for database servers and telephony gateways

– System software – Windows or Linux

Benefits of TETRA-over-IP (3)

• Support of virtually any type of network topology

Star topology

Meshed topology

Ring topology

Benefits of TETRA-over-IP (4)

• Resilience for link failures– If proper network topology

is selected

• Resilience for network component failures– If distributed and replicated

databases and redundant TETRA network components are used

Does ToIP save costs ?

• NO, not really, because– A separate, private IP network is needed for

ToIP to prevent delays and ensure security– Additional routers are needed to interconnect

the IP components to line circuits (Synchro-nous V.35 / V.11, ISDN, DSL, Frame Relay)

– IP uses more bandwidth because of packet headers (IP, UDP, TCP)

Is ToIP a standard ?

• NO, not really, because– Current ToIP solutions are not compatible with

industry-standard Voice-over-IP (VoIP) standards, such as H.323 and SIP

– Each manufacturer has defined its own protocols for call establishment, transport of speech, database synchronization, etc.

– IP is not the same as Ethernet: optimizations on the Ethernet level may prevent the use of standard IP router equipment

Why not use H.323 or SIP ?

• Additional call setup delay because of negotiation through MGC or Gatekeeper

• Additional speech delay due to increased packet length and session control

• No TETRA ACELP gateways available on the market, thus transcoding is needed to realise an open solution, resulting in degradation of speech quality

Potential difficulties of ToIP

• Extra speech and call setup delay caused by serialisation of data packets within radio sites and IP routers

• Jitter caused by queuing of packets in IP infrastructure – requires additional buffering of speech packets

• Risk of packet loss or delayed packets due to network congestion

Additional concerns

• Prioritisation of different packets – TETRA speech traffic needs higher priority

then call setup, SDS and Network Management– Should be based on open standards, otherwise

benefits of using COTS will disappear

How to deal with these difficulties

• Use plenty of extra bandwidth to ensure low serialisation delays and reduction of packet delay and packet loss – typically four times minimum required bandwidth

• Establish a separate IP network for networking TETRA system components

• Use QoS mechanisms such as MPLS to allow prioritisation of IP packets

Criteria for system evaluation (1)

• Required bandwidth for IP links– Is it available and also cost effective ?

• Are the proposed IP routers and links suitable for mission-critical applications ?– Evaluate reliability of equipment (MTBF)– Observe link reliability – avoid DSL and WLAN !

• Level of resilience in case of link failures– Is the network topology designed in such a way

that continuous operation is ensured in case of link failures ?

Criteria for system evaluation (2)

• Level of system resilience– Are databases replicated for redundancy ?– Are the proposed link bandwidths sufficient for

database synchronisation all over the network ?

• Is the system based on open standards and platforms ?– Multi-vendor availability of routers, switches– Hardware platform and operating systems– Can the equipment be networked with standard IP

routers, not only on Ethernet level ?

Summary of Pros and Cons+ Offers a convergent network

for TETRA speech, signalling, messaging and network management

+ Potential to use COTS equipment and software

+ Potential to provide resilience in case of link failures

+ Networking flexibility – find optimum balance between link cost and resilience

– Extra bandwidth required for overhead of IP packets

– Extra call setup and speech delay caused by serialisation of data over low-speed links

– Risk of packet loss and non-sequential arrival of packets

– Additional cost for router equipment

– IP equipment and networks not always suitable for mission-critical applications

Conclusion

• IP is a proven solution for data transport, and maturing for real-time voice transport

• For mission critical use, including encryption, protocols and platforms have to be substantionally optimized

• Use of IP will increase price and require sufficient bandwidth on each site

• Increase of call setup time and speech delay is unavoidable

Thank you for your attention !

Questions ?

Glossary (1)

ACELP Algebraic Code-Excited Linear Predictive

DefinitionAbbrev. Description

ETS 300 395-2

COTS Commercial Off The Shelf -

DSL Digital Subscriber Line TS 101 388

HTTP Hyper Text Transfer Protocol RFC 2616

IP Internet Protocol RFC 791

IPI Internet Protocol Interworking EN 301 747

ISDN Integrated Services Digital Network TBR 003

ISI Inter System Interface EN 300 392-3

LAN Local Area Network IEEE 802.3

Glossary (2)

MGC Media Gateway Controller

DefinitionAbbrev. Description

RFC 3054

MPLS Multiprotocol Label Switching In progress

MTBF Mean Time Between Failure MIL-HDBK-217

PABX Private Automated Branch Exchange -

PC Personal Computer -

PSTN Public Switched Telephone Network -

QoS Quality of Service See RFC 2990

SDS Short Data Service EN 300 292-2

SIP Session Initiation Protocol RFC 3261

Switching and Management Infrastructure

SNMP Simple Network Management Protocol

DefinitionAbbrev. Description

RFC 1157

SwMI EN 300 392-1

TCP Transmission Control Protocol RFC 793

TETRA Terrestrial Trunked Radio EN 300 39x

ToIP TETRA over Internet Protocol -

VoIP Voice over Internet Protocol See SIP/H.323

UDP User Datagram Protocol RFC 768

WLAN Wireless Local Area Network IEEE 802.11

Glossary (3)