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Introduction TETRA over IP Bert Bouwers Rohill Technologies B. V.
Agenda • • • TETRA-over-IP (To. IP) basics Benefits of TETRA-over-IP Myths about TETRA-over-IP Potential difficulties and concerns Guidelines for To. IP system evaluation Summary of facts
TETRA-over-IP basics • Use the Internet Protocol (IP) to connect Base Stations and Sw. MI together • Real TETRA-over-IP requires efficient mechanisms to transport both call setup signalling and speech / data traffic • To. IP 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 Sw. MI Network Management Line Dispatcher Other TETRA network Intranet / Internet IP gateway, Firewall PABX, PSTN, ISDN
TETRA-over-IP network Other TETRA network ISI / IPI gateway Intranet / Internet Network Management Line Dispatcher Database Telephony server gateway Ethernet LAN IP gateway, Firewall PABX, PSTN, ISDN
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) Network Management
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 Ring topology Meshed 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 To. IP save costs ? • NO, not really, because – A separate, private IP network is needed for To. IP to prevent delays and ensure security – Additional routers are needed to interconnect the IP components to line circuits (Synchronous V. 35 / V. 11, ISDN, DSL, Frame Relay) – IP uses more bandwidth because of packet headers (IP, UDP, TCP)
Is To. IP a standard ? • NO, not really, because – Current To. IP solutions are not compatible with industry-standard Voice-over-IP (Vo. IP) 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 To. IP • 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 Qo. S 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 nonsequential 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) Abbrev. Description Definition ACELP Algebraic Code-Excited Linear Predictive 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) Abbrev. Description Definition MGC Media Gateway Controller 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 - Qo. S Quality of Service See RFC 2990 SDS Short Data Service EN 300 292 -2 SIP Session Initiation Protocol RFC 3261
Glossary (3) Abbrev. Description Definition SNMP Simple Network Management Protocol RFC 1157 Sw. MI Switching and Management Infrastructure EN 300 392 -1 TCP Transmission Control Protocol RFC 793 TETRA Terrestrial Trunked Radio EN 300 39 x To. IP TETRA over Internet Protocol - Vo. IP Voice over Internet Protocol See SIP/H. 323 UDP User Datagram Protocol RFC 768 WLAN Wireless Local Area Network IEEE 802. 11