SRST support on Cisco 3845 router

Answered Question
Dec 5th, 2008
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Hi All,


We have a cisco 3845 router and we are trying to figure out,what all hardware/software components required to configure SRST on this router. Any help would be appreciated.


Thanks


Regards

Anantha Subramanian Natarajan

Correct Answer by Nicholas Matthews about 8 years 5 months ago

For an SRST router you will technically only need DSPs (PVDM) if you have an analog connection.


Generally, you will have an analog port for SRST so that phones can dial out of the system, but all you wish to have is intra-system DN reachability, you wouldn't use DSPs.


If this helps clear up the question at all.


Use the DSP calculator to figure out your DSP situation:

http://www.cisco.com/cgi-bin/Support/DSP/cisco_prodsel.pl

Correct Answer by dprakken1 about 8 years 5 months ago

Same thing - Packet Voice DSP Module (PVDM). Basically needed for terminating analog calls and transcoding between different codecs. Use the Cisco DSP calculator tool to size the PVBM needed.


Dave

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Jonathan Schulenberg Sat, 12/06/2008 - 06:37
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    2017 IP Telephony

SRST is a software feature of IOS. You must be on have "IP Voice" or higher to have access to it: http://cisco.com/en/US/products/sw/iosswrel/ps5460/index.html


On a 3845, up to 720 phones can fall back to it if you are using traditional SRST. If you use CME SRST which includes more functionality to the users as the CME call agent is online, you are limited to 240 phones.


The only requirements surround the appropriate level of DRAM and flash memory to run the IOS code you choose. Other hardware components like DSPs aren't a requirement of SRST directly but could be used by the CME SRST call agent to provide users supplementary features during fallback if you wanted.



http://www.cisco.com/en/US/products/sw/voicesw/ps2169/tsd_products_support_series_home.html

anasubra_2 Sat, 12/06/2008 - 08:18
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Hi J.schulenberg,


Thats really good information and so inorder to run SRST on a Cisco 3845 router,we don't need to have any DSPs(PVDM).I hope inorder to have IP voice and run SRST on the Cisco 3845 we need to have license right ?..Kindly confirm


Thank you very much


Regards

Anantha Subramanian Natarajan

mikram Sat, 12/06/2008 - 10:20
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Hi

You need PVDMs to terminate PCM calls into VOIP. You need it for codec such as G729 etc, Also you need for conference. There is DSP calculator at CCO.


Cheers

Ikram

anasubra_2 Sat, 12/06/2008 - 13:05
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Hi Ikram,


Thank you ...I have a basic doubt now,is DSP is different from PVDM ?


Thanks


Regards

Anantha Subramanian Natarajan

Correct Answer
dprakken1 Sat, 12/06/2008 - 20:14
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Same thing - Packet Voice DSP Module (PVDM). Basically needed for terminating analog calls and transcoding between different codecs. Use the Cisco DSP calculator tool to size the PVBM needed.


Dave

anasubra_2 Sun, 12/07/2008 - 06:22
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Hi Dave,


Thank you for the clarification.


Regards

Anantha Subramanian Natarajan

dprakken1 Sat, 12/06/2008 - 20:14
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Same thing - Packet Voice DSP Module (PVDM). Basically needed for terminating analog calls and transcoding between different codecs. Use the Cisco DSP calculator tool to size the PVBM needed.


Dave

dprakken1 Sat, 12/06/2008 - 20:14
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Same thing - Packet Voice DSP Module (PVDM). Basically needed for terminating analog calls and transcoding between different codecs. Use the Cisco DSP calculator tool to size the PVBM needed.


Dave

Correct Answer
Nicholas Matthews Fri, 12/12/2008 - 12:05
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For an SRST router you will technically only need DSPs (PVDM) if you have an analog connection.


Generally, you will have an analog port for SRST so that phones can dial out of the system, but all you wish to have is intra-system DN reachability, you wouldn't use DSPs.


If this helps clear up the question at all.


Use the DSP calculator to figure out your DSP situation:

http://www.cisco.com/cgi-bin/Support/DSP/cisco_prodsel.pl

anasubra_2 Fri, 12/12/2008 - 12:32
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Hi nicmatth,


The explanation clarifies the question. Thank you very much


Regards

Anantha Subramanian Natarajan

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