DSP Calculator
For easier DSP calculation, a DSP calculator apparatus is accessible at the afterward URL (and
requires adapted login accreditation for the Cisco website):
http://www.cisco.com/cgi-bin/Support/DSP/dsp-calc.pl
The afterward archetype shows how to account the adapted DSPs to arrange the following
media assets on a distinct gateway:
Router model: Cisco 2811
Cisco IOS release: 12.4(6)T
Installed articulation interface cards (VICs): Onboard aperture 0, VWIC2-1MFT-T1/E1 used
as a PRI T1 with 23 articulation agent channels
Number of G.711 calls: 23
Number of transcoding sessions: 8 G.711 to G.729a
Number of conferences: 4 mixed-mode conferences
Follow these accomplish to accomplish the calculation:
Step 1. Select the actual router model, in this case Cisco 2811.
Step 2. Select the actual Cisco IOS release: mainline release, T alternation release, or special
release, as apparent in Figure 2-15. In this case, 12.4(6)T is selected.
Different Cisco IOS releases ability advance to altered DSP calculations because
the firmware of a DSP depends on the Cisco IOS adaptation used.
Step 3. Select the adapted VIC configuration. In this case, VWIC2-1MFT-T1/E1
(T1 voice) is selected. The T1 articulation advantage is all-important because the VWIC2
supports both E1 and T1.
Step 4. Specify the best cardinal of calls for a specific codec or fax configuration.
In this case, a abounding T1 is configured for PRI—that is, 23 G.711 calls, as
illustrated in Figure 2-16.
DSP Calculator (Steps 1 and 2)
104 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
Select the router model.
Select the Cisco IOS release.
1
2
3 Select router VICs. 4 Specify the number of calls.
Figure 2-16 DSP Calculator (Steps 3 and 4)
Note A full T1 PRI supports only 23 voice channels. A T1 channel associated signaling
(CAS) or a T1 configured for Nonfacility Associated Signaling (NFAS) can support as many
as 24 voice channels.
Step 5. Specify the number of transcoding sessions with the appropriate codec. In
this example, 8 G.711 to G.729a sessions are required.
Step 6. Specify the number of conferences required on the gateway, either singlemode
G.711 or mixed-mode conferences, as demonstrated in Figure 2-17.
Chapter 2: Considering VoIP Design Elements 105
Note A full T1 PRI supports only 23 voice channels. A T1 channel associated signaling
(CAS) or a T1 configured for Nonfacility Associated Signaling (NFAS) can support as many
as 24 voice channels.
Specify the number of conferences.
5 Specify the number of transcoding sessions.
6
Figure 2-17 DSP Calculator (Steps 5 and 6)
Step 7. After entering all parameters, you can calculate the required DSP resources.
For our example, five C5510 DSPs need to be deployed, as shown in
Figure 2-18.
Figure 2-18 DSP Calculator (Step 7)
Table 2-13 summarizes the DSP requirements for the specified media resources.