1. 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

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

3.  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

4.  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

5.  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

6.  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

7.  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

8.  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

9.  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

10.  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

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

12.  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.450 4. What is H.323? General 11/20

13.  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

14. RTP G.711 G.729 G.723.1 H.261 H.263 Audio Apps Video Apps H.225.0 Call signaling TCPUDP IP Link Layer 802.3 RTCP H.225.0 RAS H.245 Control signaling T.120 Data Terminal control and management H.323 Stack 4. What is H.323? Protocol Architecture 13/20

15. 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

16.  SIP: Establish multi-media communications sessions IETF’s RFC-2543.  Text based protocol, similar to HTTP, SIP URLs SIP:me@myco.com.  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

17. RTP/RTCP G.711 G.729 G.723.1 H.261 H.263 Audio Apps Video Apps UDP IP Link Layer, 802.3 SIP Terminal control and management SIP Stack TCP SAP/Q.931SDP 5. Another VoIP Protocol - SIP Protocol Architecture 16/20

18. 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

19.  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.  723.1 delay 37.5 msec (30 msec frame + 7.5 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, 723.1 needs 17Kbps  DiffServ prioritizes packets at layer 3 with TOS byte.  802.1 p/Q, priority & queuing at layer 2, with TOS bit in Ethernet packet. 6. Considerations QoS QoS (Quality of Service) 18/20

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

21.  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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