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Voice over IP. IP Networking Overview IP assumes delay and packet ordering problems.

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Presentation on theme: "Voice over IP. IP Networking Overview IP assumes delay and packet ordering problems."— Presentation transcript:

1 Voice over IP

2 IP Networking Overview IP assumes delay and packet ordering problems

3 Voice Delay with IP Delay budget deals with one-way delay, not a round-trip! One-Way, Mouth-to- Ear Delay Description msSuitable for most delay sensitive applications like voice msStill acceptable, but starts to influence voice quality. Communication can be annoying if no actions are taken. 400 ms and greaterUnacceptable for most delay sensitive applications.

4 Understanding VoIP

5 Major VoIP Protocols VoIP ProtocolDescription H.323 ITU standard protocol for interactive conferencing. Evolved from H.320 ISDN standard. Flexible, complex. Media Gateway Control Protocol (MGCP) Emerging standard for Public Switched Telephone Network (PSTN) gateway control, thin device control. Session Initiation Protocol (SIP) IETF protocol for interactive and non-interactive conferencing. Simpler, but less mature, than H.323. Real-Time Transport Protocol (RTP) IETF standard media streaming protocol. Real-Time Transport Control Protocol (RTCP) Protocol that provides out-of-band control information for an RTP flow. Low Latency Queuing (LLQ) Priority queuing technique that uses priority queuing-class-based weighted fair queuing (PQ-CBWFQ).

6 Signaling from PBX to the Router The PBX seizes a trunk line to the router, and forwards dial digits.

7 Signaling Between Routers The Dial Plan Mapper reads the dial digits, and finds the address of the remote IP peer. The H.323 agent initiates a Q.931 call to the remote peer.

8 Signaling from Router to PBX The remote H.323 agent seizes a PBX trunk, returns a Q.931 acknowledgment to the origin, and forwards dial digits to the PBX

9 VoIP Bandwidth Consumption Coding Algorithm Voice Bandwidth (Kbps) Coded Frame Size (bytes) Voice Frames in VoIP Packet IP+UDP+RT P Header Size (bytes) Layer 2 Technology Used Layer 2 Header Size (bytes) Total Bandwidth Required G Ethernet II G MLPPP782.8 G (cRTP)MLPPP767.6 G Ethernet II (Cisco Default) G MLPPP726.8 G (cRTP)MLPPP711.6

10 VoIP QoS Building Blocks IP Network Issue Devices Affected Solutions Backbone speed and scale Backbone routers High-performance routers Packet classification Edge routers IP Precedence Bandwidth management and admission control Edge routers Voice compression Real-Time Transport Protocol (RTP) header compression Gatekeepers Congestion management Edge routers Backbone routers Weighted Random Early Detection (WRED) Queue management Edge routers Backbone routers Low Latency Queuing (LLQ) Other queuing techniques

11 RTP Header Compression RTP header compression saves bandwidth by compressing packet headers across WAN links. RTP Headers are almost always 2 Bytes long when compressed.

12 Low Latency Queuing

13 Configuring IP Precedence PrecedenceDefinition 7Network control 6Internetwork control 5Critical 4Flash-override 3Flash 2Immediate 1Priority 0Routine

14 Example: VoIP over PPP Configuration

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