VoIP What is VoIP Background & Benefit VoIP Concepts What is H.323 Another VoIP Protocol SIP Considerations What is VoIP Background & Benefit VoIP Concepts What is H.323 Another VoIP Protocol SIP Considerations Contents

1. What is VoIP? PSTN Router IP Network PBX ① ② 1/20 Voice is transported over Internet with compression of Audio data.

 Offices are located everywhere, cost grows heavier. 2. Background & Benefit Data 망 Voice 망 PBX Voice Data System PBX Voice  Business IP LAN/WAN grown rapidly, and Ethernet network is everywhere. Data System Voice & Data Data System PBX Voice 2/20

 International Standards Organization’s Open System Interconnection 7- layer Reference Model.  Defines functional layers needed for communication between 2 or more network end-points.  Message delivery requires each function layer. 7ApplicationInteractive Voice (VoIP) 6PresentationCodec 5SessionRTP, RTCP 4TransportTCP & UDP 3NetworkIP, Diffserv 2Data LinkEthernet 1PhysicalUTP Cat 5 3. VoIP Concepts OSI-7 layer 3/20

 VoIP standards define protocol messages and packet structure/content for each layer.  “Protocol Stack” sum of protocol layers in OSI model  Several VoIP standards:  IEEE developed H.323  IETF developed SIP  MGCP used by DOCSIS (Cable TV), disassociated Gateway  IEEE/IETF Megaco/H.248 IETF/IEEE disassociated Gateway 3. VoIP Concepts General 4/20 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 SenderReceiver Message

 Defines functions for sharing physical medium and media access.  Ethernet, 10/100 Base T LAN IEEE 802.  Uses Layer 1 as UTP Cat 5 cable.  MAC (Media Access Control) 6 byte address unique for each device.  Sometimes called MAC layer 3. VoIP Concepts Layer 2 Data Link 5/20

 IP (Internet Protocol) actually lower layer neutral.  IP Packet Network, IP defines packet content w/Sender, Receiver address and IPv4 header.  IPv4 Packet Header 20 bytes (five 32-bit words) include:  Type of Service byte (Diffserv code point)  Header & Packet size  Sequence  Fragmentation flag, Offset  Type of transport (TCP/UDP)  Check sums and DLL CRC  Router protocols exist at this layer. 3. VoIP Concepts Layer 3 Network 6/20

 Layer 4 defines controls reliability and other route characteristics.  For VoIP TCP (Transport Control Protocol) & UDP (Uniform Datagram Protocol) employed.  TCP “reliable” includes retransmit, used for VoIP network call signaling.  UDP relies on application for transport reliability, Real-time nature of voice suggests use of unreliable transport, UDP for voice packets. 3. VoIP Concepts Layer 4 Transport 7/20

 Each session (call or request) carries a unique ID.  RTP (real-time protocol) & RTCP (real-time control protocol), session statistics.  Receiver requests, application processes, e.g. for excessive delay, app could request change codec.  Call (session) control signaling messages:  request  alerting  connect  release  ReSerVation Protocol (RSVP), Quality of Service protocol. 3. VoIP Concepts Layer 5 Session 8/20

 To conserve LAN/WAN bandwidth, codec applies compression at encoding, common Codecs:  G.711, PCM codec, 64 kbps  G.726, ADPCM, 16 to 32 kbps  G.723.1, MP-MLQ/ACELP 5.3/6.4 kbps  G.729A, CS-ACELP, 8 kbps  Codec is selected from “Capability” message, may be predefined.  Silence suppression using VAD (Voice Activity Detection) and CNG (Comfort Noise Generation). 3. VoIP Concepts Layer 6 Presentation 9/20

 Inter-active Voice communications:  IP Phone call  Office to Office FAX  IP Conference Calling  Voice Mail  Unified Messaging, TTS “ reads ” s 3. VoIP Concepts Layer 7 Application 10/20

 Multimedia communication(audio, data & video) over an unreliable network, aimed at IP and UDP.  Application Layer control protocol.  An umbrella standard employs many other protocols by reference and Annex. Feature Protocol Call SignalingH.225 (Q.931) Media ControlH.245 Audio CodecsG.711, G.723, G.729 Video CodecsH.261, H.263 FAXT.38 Media TransportRTP/RTCP SecurityH.235 Supplementary SVCH What is H.323? General 11/20

 Four “ entities ” :  Gatekeeper Zone controller, RAS channel (register, status, admit)  Gateway Provides access between disparate networks  Terminal (IP Phone) End-point, user interface device  MCU (Multi-point Control Unit) Conference controller & audio processor Internet Zone Gateways Terminals Gatekeeper W/MCU PSTN 4. What is H.323? Elements 12/20

RTP G.711 G.729 G H.261 H.263 Audio Apps Video Apps H Call signaling TCPUDP IP Link Layer RTCP H RAS H.245 Control signaling T.120 Data Terminal control and management H.323 Stack 4. What is H.323? Protocol Architecture 13/20

H.323 endpoint Gatekeeper setup ARQ ACF ARQ ACF alerting connect end session Release complete  Endpoint gets GK permission (ARQ/ACF)  ARQ request for Fast start to GK with destination & media.  Setup request between endpoints, includes media and codec.  Other messages (alerting, connect) then open audio channel.  Close audio channel (either endpoint)  Disconnect, return to idle advise to GK. Audio DRQ DCF DRQ DCF 4. What is H.323? Call Flow 14/20 RAS = black H.225 = blue H.245 = green

 SIP: Establish multi-media communications sessions IETF’s RFC  Text based protocol, similar to HTTP, SIP URLs  Low layer neutral, Reliable (TCP) or Unreliable (UDP), packet or byte network.  Client/Server Application layer control protocol.  SIP Entities include User Agents and proxy, registrar, location servers, redirect server.  Session has unique Call ID (call leg id) with CSeq (command sequence) for each transaction controlled by a Call Agent. 5. Another VoIP Protocol - SIP General SIP (Session Initiation Protocol) 15/20

RTP/RTCP G.711 G.729 G H.261 H.263 Audio Apps Video Apps UDP IP Link Layer, SIP Terminal control and management SIP Stack TCP SAP/Q.931SDP 5. Another VoIP Protocol - SIP Protocol Architecture 16/20

5. Another VoIP Protocol - SIP Call Flow INVITE+SDP 200+SDP ACK RTP/RTCP BYE 200 User Agent A Use r Agent B Proxy  Requests from the User Client include:  Invite  Ack  Cancel  Bye  Option  Register  Response message has 3-digit “ Status Code ” :  1xx Information  2xx Success  3xx Redirect  4xx Client error  5xx Server error  6xx Global failure 17/20

 IP a “ best effort ” network, packet may be delayed or discarded at router/switch.  Codec, highly compressed voice requires significant processing power and time, DSPs common.  delay 37.5 msec (30 msec frame msec look-ahead)  729A delay 15 msec (10 msec frame + 5 msec look ahead)  Bandwidth Required = (Packet header + payload).  IP/UDP/RTP packet headers = 40 bytes  Adding header & payload, needs 17Kbps  DiffServ prioritizes packets at layer 3 with TOS byte.  p/Q, priority & queuing at layer 2, with TOS bit in Ethernet packet. 6. Considerations QoS QoS (Quality of Service) 18/20

 NAT server controls use of scarce Public IP addresses.  NAT generally not compatible with standard VoIP protocols.  H.323  NAT assigns public IP address and port for outgoing request changing address & port in original packet  Far end sends H.245 request to open a logical second port on same IP address. NAT does not recognize the request on a different port and discards packet as illegal. 6. Considerations NAT NAT (Network Address Translation) Internet LAN Router running NAT IP = xxx.xxx.xxx.xxx IP = yyy.yyy.yyy.yy1 IP = yyy.yyy.yyy.yy2 IP = yyy.yyy.yyy.yyn Private IP Address 19/20

 Firewalls  Prevent unauthorized incoming access from WAN to LAN.  Prevent unauthorized outgoing access to WAN from LAN.  Typically use Allow/Deny Table of address/port.  IP address can be allowed use of defined ports.  IP address can be allowed full I/O access.  Certain applications, ftp, telnet, etc. use fixed ports.  Most Firewalls support H.323/SIP traffic 6. Considerations Firewalls InternetLocal Network Firewall 20/20

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