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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 5 QoS in a SOHO Virtual Private Network for IP Telephony
Solutions
For the one- and two-box cable solutions (illustrated in
·
The IP phone handles classification of the VoIP bearer and control traffic. The IP phone marks its
traffic at Layer 2 with a CoS of 5 for bearer traffic and 3 for control traffic. It marks its traffic at
Layer 3 with a DHCP PHB label of EF for bearer traffic and AF31 for control traffic.
·
QoS is provided via DOCSIS version 1.1. DOCSIS 1.1 provides Layer 2 QoS services that enable a
cable solution to provide bandwidth guarantees for VoIP traffic.
It is important to note that QoS in cable environments is not accomplished through the Modular QoS CLI
configuration. Instead, a DOCSIS policy is downloaded to the cable router when it boots. Then the router
enforces the policy as it transmits traffic.
illustrates this download process.
Figure 5-9
DOCSIS 1.1 Configuration Downloaded to a Cable Router
highlights specific options in the cable modem DOCSIS 1.1 configuration that are required
to provide the bandwidth and scheduling guarantees for VoIP traffic.
Example 5-3
Cable DOCSIS 1.1 Extracts for QoS
18 (Maximum Number of CPE) = 10
22 (Upstream Packet Classification Block)
T01 (IP ToS Range & Mask) = 160.160.224
Match IP Prec 5
T02 (IP Protocol) = 256
T02 (Source MAC Addr) = 0-8-21-3a-29-7e
Match MAC
23 (Downstream Packet Classification Block)
T01 (IP ToS Range & Mask) = 160.160.224
Match IP Prec 5
T05 (Destination Address) = 10.91.20.4
Match IP address
T06 (Destination Mask) = 255.255.255.255
24 (Upstream Service Flow Block)
S19 (Unsolicited Grant Size) = 300
Bandwidth
S20 (Nominal Grant Interval) = 20000
Timeslot
In this example:
·
Options 22 and 23 specify traffic source and destination.
·
Option 24 specifies the bandwidth guarantee being granted to the VoIP traffic.
IP
IP
IP
Two-box
Third-party modem
Single-box
Cisco
806/1710
Cisco 9x5
uBR7246
PIX 501
Cable
backbone
To head
end
74926