Calculating Bandwidth Requirements参考.ppt

Describe Cisco VoIP Implementations Calculating Bandwidth Requirements 影响带宽的因素 Factors Influencing Bandwidth Bandwidth Implications of Codecs Codec称为多媒体数字信号编解码器 不同的Codec有不同的带宽需求 Codec bandwidth is for voice information only No packetization overhead includedCodec Bandwidth的带宽仅仅描述了不同的Codec的带宽需求,其不包含IP overheadData-link overheadTunneing overhead How the Packetization Period ImpactsVoIP Packet Size and Rate High packetization period results in:长打包周期会导致: Larger IP packet size (adding to the payload)较大的IP包大小(加大载荷) Lower packet rate (reducing the IP overhead)较低打包频率(减少IP负载) VoIP Packet Size and Packet Rate Examples Data Link Overhead Is Different per Link Security and Tunneling Overhead IP packets can be secured by IPsec.可以使用IPsec来保护IP数据包. Additionally, IP packets or data-link frames can be tunneled over a variety of protocols.IP数据包或数据链路层帧可以使用隧道穿越多协议的环境. Security and Tunneling Overhead (Cont.) Characteristics of IPsec and tunneling protocols are:IPsec和隧道协议特征: The original frame or packet is encapsulated into another protocol.原始的数据帧被封装到其它的协议中. The added headers result in larger packets and higher bandwidth requirements.附加的报头会产生较大数据包和较高的带宽需求. The extra bandwidth can be extremely critical for voice packets because of the transmission of small packets at a high rate.额外的带宽消耗对于语音数据包是致命的.因为较小数据包在传输中可以获得较高传输速率. Extra Headers in Security and Tunneling Protocols Example: VoIP over IPsec VPN G.729 codec (8 kbps) 20-ms packetization period No cRTP IPsec ESP with 3DES and SHA-1, tunnel mode Total Bandwidth Required for a VoIP Call Total bandwidth of a VoIP call, as seen on the link, is important for: Designing the capacity of the physical link设计和规划链路容量 Deploying CAC部署CAC Deploying QoS部署QoS Total Bandwidth Calculation Procedure Gather required packetization information:确定编解码算法和打包周期 Packetization period (default is 20 ms) or size打包周期(默认20ms)或打包大小 Codec bandwidth编解码需要带宽 Gather required information about the link:确定链路相关信息: cRTP enabled是否使用cRTP Type of data-link prot