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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 4 QoS in an AVVID-Enabled Wide-Area Network
QoS Recommendations for WAN Aggregation Routers
!
map-class frame-relay dTS-TO-FRTS-1536kbps
no frame-relay adaptive-shaping
service-policy output dTS-1536kbps
This command applies the dTS policy to the FR map-class.
The symbolic name of "DTS-1536kbps" represents distributed traffic shaping (DTS) and the link speed.
The following commands can be used to verify that a voice, video and data QoS policies have been
applied correctly to a Frame Relay link.
·
show policy interface
For more information, see the
Slow-Speed Frame Relay Links
Similar to high-speed Frame Relay links, slow-speed Frame Relay links require the following parameters
to be defined:
·
·
Fragment Sizes
As with all slow links, slow Frame Relay links require a mechanism for fragmentation and interleaving.
In the Frame Relay environment, the tool for accomplishing this is FRF.12. Unlike MLP LFI, which
takes the maximum serialization delay as a parameter, FRF.12 requires the actual fragment sizes to be
defined. This requires some additional calculations, as the maximum fragment sizes vary by link speed.
These fragment sizes can be calculated by dividing the recommended 10 ms of delay by 1 byte of traffic
at the provisioned line-clocking speed:
Fragment Size = (Maximum Allowed Jitter * Link Speed in kbps) / 8
For example, the calculation for the maximum fragment size for a 56 kbps circuit is:
Fragment Size = (10 ms * 56) / 8 or 70 Bytes
Fragment sizes that correspond to the recommended minimum serialization delay of 10 ms per link are
shown in second column of
Committed Information Rate and Burst
With FRTS, it is important to note that Frame Relay header flags and the CRC (which are added by the
interface driver) are not taken into account in the shaping algorithm. When the flags and CRC are
included in the CIR calculation, the value is determined by the following formula:
CIR = (Link-Speed * Maximum-Frame-Size) / (Maximum-Frame-Size + 4)
For high-speed links, this value works out to around 99%. For example, a on a T1 link:
CIR = 1536000 * 1500 / (1500 + 4)
CIR = 1536000 * 0.99734
CIR = 1531914
which is 99.7% of the link speed.
While this calculated value could be used, the difference is so negligible that for simplicity's sake the
CIR could just as well be set to the link-speed (as recommended in the