Cisco Cisco 1800 2800 3800 Series AP-AG 802.11a b g High-Speed WIC

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“Bandwidth remaining ratio” provides a method of balancing the minimum bit rates that traffic classes will

receive when there is congestion. The algorithm works as follows in 3-level policies:

“Bandwidth remaining” equals the 1

level shaped rate minus the 2

level strict priority rate. For

example, if the top level shaped rate is 1.5mbps and the strict priority class rate is 100kbps,

“bandwidth remaining” is 1.4mbps.

“Bandwidth remaining ratio” defines the poriton of “bandwidth remaining” for a traffic class, and

is defined in the CS3/AF3x/CS4/AF4x traffic class AND the class-default; Note that if the

“bandwidth remaining ratio” is not configured on a class in the 2

level policy (e.g. class-default)

the default value is 1, which may not be yield the desired result.

Continuing the example above, if bandwidth remaining is 1.4mbps, and a class “CS3-4” is

defined with “bandwidth remaining ratio 4” and “class-default” is defined with “bandwidth

remaining ratio 10”, class “CS3-4” will be provided a minimum of 400kbps while class “class-

default” will be provided a minimum of 1mbps. In this example, assuming the service rate was

500kbps and a voice class (strict priority) was assigned 100kbps, this is sufficient, as the “CS3-4”

class would be shaped regardless at 400kbps (so the total of the CS5/EF + CS4/AF3x/CS4/AF4x

classes do not exceed the service rate, to avoid the network dropping the excess). The sample

configuration for ISR43xx/44xx uses “bandwidth remaining ratio”.

Voice Considerations: To support voice, the bandwidth needed to support the maximum number of

simultaneous calls must be calculated. This bandwidth need is the value for the strict priority bit rate

defined in the 2

level policy’s voice traffic class. As voice packets are small in size, packet overhead

has a greater effect on the bandwidth required for a voice call. To determine the total bandwidth needed

in the strict priority queue, the amount of bandwidth per call is multipled by the maximum number of

simultaneous calls.

The bandwidth per call is determined by taking the codec type and IP overhead into account. Two

popular codecs are G.711 and G.729. The bandwidth required for various scenarios is shows below.

Codec

LAN

LTE, MPN +

DMNR

LTE, MPN +

DMNR + GETVPN

LTE, MPN +

DMVPN

LTE, MPN +

IPsec

G.711

87 kbps

96 kbps

120 kbps

131 kbps

125 kbps

G.729

31 kbps

41 kbps

65 kbps

76 kbps

70 kbps

These estimated values are based on test results,60 byte overhead for GETVPN, the IPsec overhead

calculator at

https://cway.cisco.com/tools/ipsec-overhead-calc/ipsec-overhead-calc.html

and values

from

http://www.cisco.com/c/en/us/support/docs/voice/voice-quality/7934-bwidth-consume.html

As an example, if 3 simultaneous G.729 calls over MPN with DMNR are desired, 3 x 41kbps or 123 kbps

would be set in the 2

level policy map for the strict priority class (class “CS5-EF” in the examples that

follow). Call admission control would define this site as a “location” and limit the voice traffic to 125kbps,

the phones at this site wold be in a device pool assigned to a region that supported only G.729.

More information on Unified Communications Call Admission Control can be found here:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab11/collab11/cac.html