Vo IP Contents What is Vo IP Background

Vo. IP Contents • What is Vo. IP • Background & Benefit • Vo. IP Concepts • What is H. 323 • Another Vo. IP Protocol SIP • Considerations

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

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

3. Vo. IP Concepts OSI-7 layer q International Standards Organization’s Open System Interconnection 7 layer Reference Model. q Defines functional layers needed for communication between 2 or more network end-points. q Message delivery requires each function layer. 7 Application Interactive Voice (Vo. IP) 6 Presentation Codec 5 Session 4 Transport 3 Network 2 Data Link 1 Physical RTP, RTCP & UDP IP, Diffserv Ethernet UTP Cat 5 3/20

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

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

3. Vo. IP Concepts Layer 3 Network q IP (Internet Protocol) actually lower layer neutral. q IP Packet Network, IP defines packet content w/Sender, Receiver address and IPv 4 header. q IPv 4 Packet Header 20 bytes (five 32 -bit words) include: Ø Type of Service byte (Diffserv code point) Ø Header & Packet size Ø Sequence Ø Fragmentation flag, Offset Ø Type of transport (TCP/UDP) Ø Check sums and DLL CRC q Router protocols exist at this layer. 6/20

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

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

3. Vo. IP Concepts Layer 6 Presentation q To conserve LAN/WAN bandwidth, codec applies compression at encoding, common Codecs: Ø Ø 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. 729 A, CS-ACELP, 8 kbps q Codec is selected from “Capability” message, may be predefined. q Silence suppression using VAD (Voice Activity Detection) and CNG (Comfort Noise Generation). 9/20

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

4. What is H. 323? General q Multimedia communication(audio, data & video) over an unreliable network, aimed at IP and UDP. q Application Layer control protocol. q An umbrella standard employs many other protocols by reference and Annex. Feature Protocol Call Signaling H. 225 (Q. 931) Media Control H. 245 Audio Codecs G. 711, G. 723, G. 729 Video Codecs H. 261, H. 263 FAX T. 38 Media Transport RTP/RTCP Security H. 235 Supplementary SVC H. 450 11/20

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

4. What is H. 323? Protocol Architecture H. 323 Stack Audio Apps G. 711 G. 729 G. 723. 1 Video Apps H. 261 H. 263 Terminal control and management RTCP H. 225. 0 RAS H. 225. 0 Call signaling H. 245 Control signaling RTP UDP TCP IP Link Layer 802. 3 13/20 T. 120 Data

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

5. Another Vo. IP Protocol - SIP General SIP (Session Initiation Protocol) q SIP: Establish multi-media communications sessions IETF’s RFC-2543. q Text based protocol, similar to HTTP, SIP URLs SIP: me@myco. com. q Low layer neutral, Reliable (TCP) or Unreliable (UDP), packet or byte network. q Client/Server Application layer control protocol. q SIP Entities include User Agents and proxy, registrar, location servers, redirect server. q Session has unique Call ID (call leg id) with CSeq (command sequence) for each transaction controlled by a Call Agent. 15/20

5. Another Vo. IP Protocol - SIP Protocol Architecture SIP Stack Audio Apps G. 711 G. 729 G. 723. 1 Video Apps H. 261 H. 263 Terminal control and management SDP SIP SAP/Q. 931 RTP/RTCP UDP TCP IP Link Layer, 802. 3 16/20

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

6. Considerations Qo. S (Quality of Service) q IP a “best effort” network, packet may be delayed or discarded at router/switch. q Codec, highly compressed voice requires significant processing power and time, DSPs common. Ø 723. 1 delay 37. 5 msec (30 msec frame + 7. 5 msec look-ahead) Ø 729 A delay 15 msec (10 msec frame + 5 msec look ahead) q Bandwidth Required = (Packet header + payload). Ø IP/UDP/RTP packet headers = 40 bytes Ø Adding header & payload, 723. 1 needs 17 Kbps q Diff. Serv prioritizes packets at layer 3 with TOS byte. q 802. 1 p/Q, priority & queuing at layer 2, with TOS bit in Ethernet packet. 18/20

6. Considerations NAT (Network Address Translation) q NAT server controls use of scarce Public IP addresses. q NAT generally not compatible with standard Vo. IP protocols. q H. 323 Ø NAT assigns public IP address and port for outgoing request changing address & port in original packet Ø 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. IP = yyy. yy 2 IP = yyy. yy 1 IP = yyy. yyn Internet IP = xxx LAN Router running NAT Private IP Address 19/20

6. Considerations Firewalls q Firewalls Ø Ø Ø 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. q Most Firewalls support H. 323/SIP traffic Local Network Internet Firewall 20/20

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