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Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using RFC 1483 Encapsulation
Associating the Policy Map with the ATM PVC and Using TCP MSS Adjust
Fine-Tuning the Size of the PVC ATM Transmit Ring Buffer
Differentiating Between Data and Voice Packets
To give priority to voice packets, the router must differentiate between the 
entering voice and data packets. One way to differentiate the packets is to...

 
Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using RFC 1483 Encapsulation
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Configuring a Policy Map and Specifying Voice Queuing
Follow the steps below to configure a policy may and to specify voice queuing, 
beginning in global configuration mode. 
Associating the Policy Map with the ATM PVC and Using TCP 
MSS Adjust
Perform the steps below to associate the policy map with the ATM PVC and to 
use the TCP...

 
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Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using RFC 1483 Encapsulation
Fine-Tuning the Size of the PVC ATM Transmit Ring Buffer
Each PVC has a hardware output first-in first-out (FIFO) queue that temporarily 
stores packets before they are sent out to the transceiver. In order to reduce 
latency for voice packets, you may need to reduce the size of this queue. Reducing 
the queue size reduces the...

 
Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using PPP over ATM and Multilink Encapsulation
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78-5372-06 priority 480
int atm0
dsl equipment-type CPE
dsl linerate AUTO
ip tcp-mss 1452
pvc 8/35
encapsulation aaal5snap
service-policy out mypolicy
vbr-rt 1000 1000 1
tx-ring-limit 5
!
Configuring a Single-PVC Environment Using PPP 
over ATM and Multilink Encapsulation
This section describes configuring of a single-PVC...

 
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Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using PPP over ATM and Multilink Encapsulation
Another way to differentiate the packets is use IP Precedence. Usually, data 
packets have precedence 0, while voice packets have IP precedence 5. To learn 
how to configure the IP precedence for voice packets, refer to the documentation 
for your VoIP device. 
NoteIn IP Precedence, the numbers 1 through 5 identify...

 
Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using PPP over ATM and Multilink Encapsulation
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Configuring Link Fragmentation and Interleaving with Low 
Latency Queuing
Link fragmentation and interleaving (LFI) is available when you are using 
multilink PPP over ATM. 
Two types of traffic can be simultaneously transmitted over the same link: 
Large packets from heavy, delay-insensitive traffic sources
Small...

 
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Chapter 7      Router Feature Configuration
Configuring a Single-PVC Environment Using PPP over ATM and Multilink Encapsulation
Calculate the fragment size using the following formula:
fragment size = (bandwidth in kbps/8) * fragment-delay i milliseconds (ms)
In this case, the fragment size = (640/8) * 10 = 800. The fragment size is greater 
than the maximum voice packet size of 200, which is that of G.711, 20 ms. Note 
that a low fragment...

 
Chapter 7      Router Feature Configuration
Configuring a Multiple-PVC Environment
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Configuring a Multiple-PVC Environment
In a multiple-PVC environment, the traffic relies on the ATM interface to provide 
priority queuing for voice and fragmentation and interleaving. The following 
sections describe the configurations that you can use.
Voice and Data on Different Subnets
Figure 7-2 shows voice and data packets on different subnets. All voice...

 
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Chapter 7      Router Feature Configuration
Configuring a Multiple-PVC Environment
Configuration Example 
The following example shows a voice QoS configuration with all data traffic on 
the 30.0.0.1 network and all voice traffic on the 20.0.0.1 network. 
You do not need to enter the commands marked “default.” These commands 
appear automatically in the configuration file that is generated when you use the 
show running-config command.
!...

 
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Configuring a Multiple-PVC Environment
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Voice and Data on the Same Subnet Using Virtual Circuit 
Bundling
Figure 7-3 and Ta b l e 7 - 2 show voice and data packets on the same subnet using 
virtual circuit bundling. Virtual circuit bundling allows multiple PVCs on the 
same bundle. Using virtual circuit bundling and assigning precedence 5 to voice 
packets and not data packets ensures that traffic...