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Network Convergence


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  • So in summary, a combination of internet driven demand, enabling technologies and regulatory changes are driving the growth. No great surprise with these drivers, they’ve been around a while, however, the pace of change is getting quicker.
  • More predictions: i.e.. Data will be 5x Voice traffic by 2000 Data will be 23x Voice traffic by 2005.
  • This shows where we are today and ...
  • … how the network is converging - a true hybrid in terms of both technologies and services delivered.
  • 15
  • 13 When it is present in a system, the Gatekeeper shall provide the following services:  Address Translation - The Gatekeeper shall perform alias address to Transport Address translation. This should be done using a translation table which is updated using the Registration messages described in Section 7. Other methods of updating the translation table are also allowed.  Admissions Control - The Gatekeeper shall authorize LAN access using ARQ/ACF/ARJ H.225.0 messages. This may be based on call authorization, bandwidth, or some other criteria which is left to the manufacturer. It may also be a null function which admits all requests.  Bandwidth Control - The Gatekeeper shall support BRQ/BRJ/BCF messages. This may be based on bandwidth management. It may also be a null function which accepts all requests for bandwidth changes.  Zone Management - The Gatekeeper shall provide the above functions for terminals, MCUs, and Gateways which have registered with it as described in Section 7.2. The Gatekeeper may also perform other optional function such as:  Call Control Signalling - The Gatekeeper may choose to complete the call signalling with the endpoints and may process the call signalling itself. Alternatively, the Gatekeeper may direct the endpoints to connect the Call Signalling Channel directly to each other. In this manner, the Gatekeeper can avoid handling the H.225.0 call control signals. The Gatekeeper may have to act as the network as defined in Q.931 in order to support supplementary services. This operation is for further study.  Call Authorization - Through the use of the H.225.0 signalling, the Gatekeeper may reject calls from a terminal due to authorization failure. The reasons for rejection may include, but are not limited to, restricted access to/from particular terminals or Gateways, and restricted access during certain periods of time. The criteria for determining if authorization passes or fails is outside the scope of this Recommendation.  Bandwidth Management - Control of the number of H.323 terminals permitted simultaneous access to the LAN. Through the use of the H.225.0 signalling, the Gatekeeper may reject calls from a terminal due to bandwidth limitations. This may occur if the Gatekeeper determines that there is not sufficient bandwidth available on the network to support the call. The criteria for determining if bandwidth is available is outside the scope of this Recommendation. Note that this may be a null function, i.e. all terminals are granted access. This function also operates during an active call when a terminal requests additional bandwidth.  Call Management - For example, the Gatekeeper may maintain a list of ongoing H.323 calls. This information may be necessary to indicate that a called terminal is busy, and to provide information for the Bandwidth Management function.  Gatekeeper management information data structure. For further study. Bandwidth reservation for terminals not capable of this function. For further study. Directory services. For further study.
  • This chart lists every signalling phases involved to set up a call. It is currently requires a large number of messages and will be improved in the future.
  • RTP Services Payload Type ID Sequence Numbering Timestamp Delivery Monitoring Synch. Source ID (end point ID not dependent on Net ID.) RTCP Quality Monitoring Header Compression is used to keep payload to header ratio high for efficiency 20ms @ 8kbs = 20byte payload RTP + UDP + IP = 12 + 8 + 20 (bytes) = 40byte Header 2x Payload! Fragmentation and Interleave of large packets reduces residency on slow links 1500 Byte MTU Takes 215Ms to Transmit on 56Kb Link MLPPP on single interface at frag level IETF Draft memo - draft-ietf-issll-isslow-mcml-01.txt
  • Transcript

    • 1. Voice over IP
    • 2. Communications Industry Revolution Future Market for Communications Services 1.8T$
      • Network Technology
      • Moore’s Law
      • Fiber BW = 2 X Moore’s Law
      • Demand
      • Client-Server applications
      • Web services
      • Outsourcing
      • Regulatory Changes
      • Telecom ‘96
      • WTO Feb ’97
      • EC ‘98
    • 3. Voice and Data Growth Data Traffic Time Voice About now! 2000 x5 2005 x23
    • 4. Today’s Mixed Networks Virtual Private Networks Managed Network Services Internet Services Wireless Services Voice Services Transport IP Frame Relay ATM Voice-centric Infrastructure
    • 5. The Converging Network Virtual Private Networks Managed Network Services Internet Services Wireless Services IP Voice Services FR + ATM Legacy Infrastructure
    • 6. Frost & Sullivan predict - 4/98
    • 7. Little affect on PSTN '97 '98 '99 '00 '01 '02 0% 20% 40% 60% 80% 100% '98 '99 '00 '01 '02 World telephony traffic IP PSTN Frost & Sullivan, April 1998
    • 8. VoIP Standards & Organizations
        • ITU-T—H.323
        • IMTC—VoIP
    • 9. H.323 Infrastructure Intranet Telephone Network Gatekeeper H.323 Terminal Router Proxy Gateway H.320 (Over ISDN) H.324 (Over POTs) Speech Only (PSTN) H.323 Corp LAN Real-Time Network V V
    • 10. ITU H.323 for VoIP System Control H.245 Control Call Control H.225.0 RAS Control H.225.0 Video Codec H.261, H263 User Data Applications T.120 H.225.0 Layer Audio I/O Equipment Audio Codec G.711, G.722, G.723, G.723.1, G.728, G.729 Receive Path Delay System Control and User Interface Video I/O Equipment Session Layer and Above LAN Stack 309-E 1171_04F8_c1
    • 11. H.323 Standard suite
      • H.323: overall architecture
      • H.225: Call control, RAS
      • H.235: Security for H.323 term
      • H.332: Large group conferences
      • H.450: Supplementary services
      • H.246: Interworking with
      • Q.931: ISDN call control
    • 12. What is an H.323 Gateway? H.323 Terminal Non-H.323 Terminal H.323 Endpoint Non- H.323 Endpoint Protocol Translation and Media Transcoding H.323 Gateway
    • 13. Types of Voice over IP Gateways in the Enterprise PBX Ethernet WAN, Intranet, Internet PSTN VoIP/DSP’s TDM VoIP/DSP’s TDM VoIP/DSP’s
    • 14. VoIP Gateways for Service Providers Ethernet High Density Access Device POP WAN, Intranet, Internet VoIP/DSP’s PC-Based PSTN Switch VoIP/DSP’s VoIP/DSP’s
    • 15. H.323 Gatekeeper RAS H.323 Terminal DNS H.323 Gatekeeper Tacacs/ Radius Registration Bandwidth Management Admission/ Call Redirection Registration Database Call Redirection Database RAS Dispatch IP FR ATM VOICE
    • 16. H.323 Gatekeeper Functions
      • Mandatory services:
        • Address translation
        • Admissions control
        • Bandwidth control
        • Zone management
      • Optional services:
        • Call control signalling
        • Call authorization
        • Call management
        • Gatekeeper management information data structure
        • Directory services
      RAS- Registration, Admission and Status
    • 17. Signalling phases
      • Gateway discovery
      • Endpoint registration
      • Call setup
      • Initial communication and capability exchange
      • Establishment of audio visual communication
      • Call services : bandwidth change, status, Ad Hoc conference, call termination
      • Call termination
    • 18. Direct endpoint call signalling Gatekeeper cloud 1)ARQ 2)ACF 4)ARQ 5)ACF 3)Setup 6)Connect Endpoint 1 Endpoint 2
    • 19. Gatekeeper routed call signalling Gatekeeper cloud 1)ARQ 2)ACF 5)ARQ 6)ACF 3)Setup 8)Connect 4)Setup 7)Connect Endpoint 1 Endpoint 2
    • 20. Call Control
      • Three Types
        • Intelligent gateway
        • Gateway initiated/intelligent network (H.323 gatekeeper)
        • Intelligent network (SGCP/IPDC)
    • 21. Intelligent Gateway
      • Call control and call handling in the gateway
      • Each gateway knows about the others
      • The DialPeers map dialed numbers to IP addresses
      • SIP is also an intelligent endpoint
      dial-peer voice 24 voip destination-pattern +8.... session target ipv4: V Intranet V V 84321
    • 22. Gateway Initiated Calls—H.323 Gatekeeper
      • Defined by H.323
      • Gateways register with gatekeeper
      • Gateways initiate calls but do not know about other gateways
      • Telephony E.164-style addresses mapped to IP addresses by gatekeeper
      • H.323 gatekeepers allow scaling
      Gatekeeper Traffic Flow Call Setup PBX PBX PBX V V V
    • 23. Intelligent Network (Future) IP Network PBX Virtual Connection (per call) End-to-end Services Signaling / Backhaul Bearer Control PBX SGCP H.323 SIP Call Agent Virtual Switch Voice V V V V
    • 24. Intelligent Network (Future) IP Network Virtual Connection (per call) End-to-end Services Signaling / Backhaul Bearer Control PBX Intra-Virtual Switch Signaling SGCP PSTN/SS7 PSTN/SS7 H.323 SIP Call Agent Voice GW Virtual Switch SN, ACD, etc. Call Agent IN or Database SS7 Signaling V V
    • 25. RTP/RTCP—RFCs 1889/1890
      • End-to-end network transport function
        • Payload type identification - Voice, Video, Compression Type
        • Sequence numbering
        • Time Stamping
        • Delivery monitoring
      • RTCP (Real-Time Control Protocol) provides feedback on the quality of the distribution
      RTP Timestamp Synchronization Source (SSRC) ID 4bytes 4bytes 4bytes Sequence Number Payload Type M CC V E R
    • 26. RTP Controlling Dejitter Buffer RTP Timestamp From Router A Interframe gap of 20ms A Sender Receiver IP Network B C RouterA RouterB 10 30 50 20ms 20ms RTP Timestamp From Router A Variable Interframe Gap (Jitter) A B C 10 30 50 20ms 80ms RTP Timestamp From Router A Delitter Buffer removes Variation A B C 10 30 50 20ms 20ms V V
    • 27.
      • Background noise
      • Silence suppression
        • Comfort noise
      • Language sensitivity
      • Subjective quality (MOS)
        • MOS
      • Delay and delay variation
      • Echo cancellation
      Voice Transport Requirements Loss Bandwidth Delay VoIP Challenges in the WAN
    • 28. VoIP (G.729) Is Tolerant of “Occasional” Packet Loss
      • The friendly “retransmission” is of no use in the Voice world… late is as good as never
      • Complex “concealment strategy” in algorithm interpolates lost packets based on context
      missing packet G.729 vocoder algorithm
    • 29. How Does Echo Happen?
      • Echo is due to a reflection
      Impedance mismatch at the 2w-4w hybrid is the most common reason for echo 2 Wire Local Loop Central Office 2w-4w Hybrid Receive Direction Transmit Direction Rx & Tx Superimposed Echo is always present and as a problem is a function of the echo delay, and the magnitude of the echo
    • 30. Delay—How Much Is Too Much? Cumulative Transmission Path Delay Time (msec) 0 100 200 300 400 CB Zone Satellite Quality Fax Relay, Broadcast High Quality Delay Target 500 600 700 800 ITU’s G.114 Recommendation = 0 – 150msec 1-way delay