© 2005 Cisco Systems, Inc. All rights reserved. IPTX v2.01-1 Introducing Cisco CallManager Express Understanding VoIP Challenges and Solutions. - презентация

1 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Introducing Cisco CallManager Express Understanding VoIP Challenges and Solutions

2 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v IP Network IP is connectionless. IP provides multiple paths from source to destination.

3 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Packet Loss, Delay, and Jitter Packet loss –Loss of packets severely degrades the voice application. Delay –VoIP typically tolerates delays up to 150 ms before the quality of the call degrades. Jitter –Instantaneous buffer use causes delay variation in the same voice stream.

4 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Consistent Throughput Throughput is the amount of data transmitted between two nodes in a given period. Throughput is a function of bandwidth, error performance, congestion, and other factors. Tools for enhanced voice throughput include: –Queuing –Congestion avoidance –Header compression –RSVP –Fragmentation

5 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Reordering of Packets IP assumes that packet-ordering problems exist. RTP reorders packets.

6 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Reliability and Availability Traditional telephony networks claim percent uptime. Data networks must consider reliability and availability requirements when incorporating voice. Methods for improving reliability and availability include: –Redundant hardware –Redundant links –UPS –Proactive network management

7 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Bandwidth Implications of Codec

8 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Impact of Voice Samples

9 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Data-Link Overhead Ethernet: 18 bytes of overhead MLP: 6 bytes of overhead Frame Relay Forum 12 (FRF.12): 6 bytes of overhead

10 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Total Bandwidth Required

11 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Effect of VAD

12 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Summary This lesson presented these key points: IP networks need to use QoS parameters and protocols to adequately support VoIP. The characteristics of IP contribute to voice-traffic problems, including packet loss, delay, and jitter. Different codecs have different bandwidth requirements. Voice sample size affects the bandwidth that is required. Overhead in Layer 2 protocols affects the bandwidth that is used. Codec, Layer 2 protocol, sample size, and VAD must all be used when calculating VoIP bandwidth.

13 © 2005 Cisco Systems, Inc. All rights reserved. IPTX v Summary (Cont.) VAD can lower bandwidth use as much as 35 percent. QoS mitigates delay, jitter, and packet loss in converged voice and data networks. QoS supports dedicated bandwidth, improves loss characteristics, avoids and manages network congestion, shapes network traffic, and sets traffic priorities across the network.

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