Overcoming the VoIP and wireless security challenges of TETRA (PowerPoint)

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					Overcoming the VoIP and wireless
security challenges of TETRA

               Bert Bouwers
         Rohill Technologies B.V.

1               VoIP for TETRA
Contents of Presentation
•   Introduction to VoIP
•   Applications of VoIP for TETRA
•   Standards for VoIP
•   Advantages and disadvantages of VoIP
•   Security concerns
•   Case study: IP network as TETRA network backbone
•   Conclusion

2                      VoIP for TETRA
Introduction to VoIP
• VoIP = Voice over the Internet Protocol
• Uses IP for call setup and speech transfer
• Can be deployed over any IP network
    – Internet
    – Intranet
    – Local Area Network (LAN) using Ethernet
• Transparant operation over
    – Routers
    – Switches
    – Hubs

3                         VoIP for TETRA
Applications for VoIP
• Generic applications for VoIP
    – Low cost long distance calling
    – Telephony over Ethernet (PABX using VoIP)
    – Enterprise communication (individual and conference calls)
• VoIP applications specific to TETRA
    – Telephony interfacing to VoIP capable PABX and PSTN
    – Interfacing to LAN connected Line Dispatch Stations
    – As backbone to Base Stations and Switches

4                          VoIP for TETRA
Application #1: telephony interfacing
                                  Media Gateway
                                  Controller (SIP)
              Station             or Gatekeeper
               Site                   (H.323)

                                         IP-capable                Traditional
                        TETRA           PABX/PSTN                    PSTN
                         SwMI           (softswitch)

                                                  VoIP                   Standard
                                                 phone                    phone

5                               VoIP for TETRA
Application #2: line dispatcher interface
                                                 Media Gateway
               Base                              Controller (SIP)
               Site                              or Gatekeeper

                        TETRA                            Ethernet
                         SwMI                              LAN
                                   over LAN

                                                 Line Dispatch      Line Dispatch
                                                    Station            Station

6                               VoIP for TETRA
Application #3: as backbone
     Base           TETRA               Optional
                     SwMI            Media Gateway
                                     Controller (SIP)
                                     or Gatekeeper


     Base                            Station
    Station                           Site


7              VoIP for TETRA
Standards for VoIP
• H.323
    –   Standardised by the ITU
    –   First version of standard is published in 1996
    –   Complex operation, inflexible
    –   Well established
• Session Initiative Protocol (SIP)
    –   Standardised by IETF
    –   First draft published in 1999
    –   Simple, powerful, extensible
    –   Fast growing support, especially for 3G applications

8                             VoIP for TETRA
Generic advantages of VoIP
• Integrated network for voice and data
    – No separate PABX needed in enterprise environment
    – Simultaneous access to the Internet and voice services
• Cost optimization for long distance calling
    – Utilises cheap, flat rate Internet connection
• Feature rich compared to ISDN and POTS
    – Powerful voice conferencing capabilities
    – Whiteboarding and video conference capabilities
    – Integration with Web and E-mail

9                            VoIP for TETRA
Generic disadvantages of VoIP
• Speech delay
     – Caused by voice compression and network latecy
     – Jitter in IP networks require additional buffering
• Interruptions in speech transfer
     – Occurs due to lost packets or delayed arrival of packets
     – Mainly caused by congestion problems in the network
• Lower speech quality
     – Caused by voice compression – standard PCM (64 kbps) is too
• Standards battle will go on for at least the next 2 years

10                           VoIP for TETRA
TETRA specific VoIP challenges
• TETRA ACELP speech vocoder is not a generic vocoder
     – Not available as “plug-in” for PC-based VoIP applications
     – Not available as vocoder in commercial VoIP gateways
     – Therefore transcoding is necessary, causing additional
       degradation of voice quality
• Extra delay caused by transport over TETRA slots
     – TETRA standard already causes a significant speech delay
• Security issues
     – TETRA networks generally require high level of security, not
       offered by the public Internet

11                          VoIP for TETRA
Security concerns of VoIP
•    Denial-of-service Attack
•    Forking
•    Reflection Attack
•    Multi-Proxy Authentication
•    Encryption Limitations
•    Cancel Security
•    NAT and Firewall Transversal

See for details

12                           VoIP for TETRA
Is VoIP suitable for TETRA networks ?
• Telephony interfacing
     – Yes: VoIP capability offers seamless integration with VoIP
       capable PABX and PSTN
• Interconnection to Line Dispatch Stations
     – Yes: VoIP provides low delay voice services to LAN connected
       PC based Line Dispatch Stations
     – In addition, data services (TCP/IP, Email, WAP) can utilise the
       same LAN connection to the TETRA SwMI
• As backbone between SwMI and Base Stations
     – No: VoIP introduces too much delay, causes an unpredictable
       performance and requires too much bandwidth

13                           VoIP for TETRA
Case study: VoIP as backbone
• Assumptions
     – Base Stations are connected to SwMI via an IP network
     – SwMIs are interconnected to eachother using an IP network
     – IP network is privately owned (Intranet, not Internet)
     – Network includes high speed (> 2 Mbps) as well as low speed
       (64 kbps) interconnections
     – H.323 standard is selected for VoIP
     – Coded ACELP speech (60 ms speech frames, 7,200 bps) is
       used for transferring speech packets

14                         VoIP for TETRA
IP routing via low-speed link
     Information to/
       from node 2                                               Delay caused by
                                                                 Gathering 60 ms speech packet
           TCP                                                   IP packet verification
         protocol                            1                   Routing decision

                    IP Router                                    Typical transit delay: 50 – 90 ms
                                                                 per node, depending on:
                                                                 Link speed
            IP                     IP                            Utilisation of link
         protocol               protocol            2
          stack                  stack

           Port                Port
        to node 1           to node 3

     Information to/      Information to/                    3
       from node 1          from node 3

15                                          VoIP for TETRA
VoIP efficiency
 VoIP packet format, send every 60 ms
          IP          UDP                 RTP                  Coded ACELP payload
        160 bit       64 bit             128 bit                      432 bit

 … but also the RTCP must be send for flow control, say every 2 seconds
          IP                    TCP                           RTCP
        160 bit                160 bit                        312 bit

 Calculation of efficiency
 RTP packets: total 160 + 64 + 128 + 432 = 784 bits per 60 ms
 Per second, this is 784 x ( 1000 / 60 ) = 13,067 bps
 Efficiency = 432 bit Coded ACELP / 784 x 100% = 55 %
 RTCP packet: total 160 + 160 + 312 = 632 bits, or 316 bits per second
 Total throughput required = 13,067 + 316 = 13,383 bps

16                                           VoIP for TETRA
VoIP delay
     Delay caused by node processing
     Received by node                IP     UDP   RTP   ACELP

     IP decoding


     IP encoding

     Transmitted by node                                           IP    UDP    RTP   ACELP

       CPU time         Transmission time                       Delay: 50 – 90 ms

     Delay caused by IP decoding, routing and IP encoding is affected
     by CPU performance and RTOS choice

17                                          VoIP for TETRA
Other notes
• Note also
     – Processing time can fluctuate due to CPU load, causing variable
       delay, whereby worst case delay must be considered for end-to-
       end delay
     – At the end-point, data should be buffered to ensure continuous
       voice playback
     – TRCP packets will interleave RTP packets, of which the delay
       should be added once for the full path, because no RTP packet
       can be send then
     – Transmission of time slots via TETRA Base Stations shall be
       synchronous, requiring worst-case delay to be used as reference

18                          VoIP for TETRA
Alternative solutions for VoIP
• Summary of requirements
     – Reliable, determistic behaviour, low delay, high efficiency
• Solution: TetraNode Streaming Protocol (TNSP)
     –   Synchronous operation, well suitable for TETRA
     –   Low transit delay of < 2 ms per node
     –   Highly efficient: 32 kbps per TETRA Base Station
     –   Can operate over E1, T1, ISDN, G.703 64 kbps, etc.
     –   Offers transparent transport of IP (IP over TNSP)
     –   Includes Play & Play mechanism for simple system expansion
     –   Includes line quality monitoring mechanism, similar to E1/T1

19                           VoIP for TETRA
• VoIP is a promising technology, well suitable for
  connecting peripheral equipment to a TETRA network
• VoIP is not suitable as a backbone, because of
     – Additional speech delay caused by VoIP
     – Possible interruptions of speech transfer
     – Voice quality (transcoding issues)
     – Lack of necessary high speed networks in rural areas
     – Security issues of the public Internet, requires private network
     – TETRA requires highly synchronous transmission of time slots
     Proprietary solutions are needed to solve problems above

20                           VoIP for TETRA
Additional concerns
•    VoIP currently mainly based on proprietary solutions
•    Two competing standards: no clear winner yet
•    Quality of Service issues not yet resolved
•    Encryption requires additional overhead, adding to the
     already substantional call setup and speech delay

21                       VoIP for TETRA

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