A DSPFarm on a router is a pool of DSP resources configured for particular functions (services);

  • MTP
  • Conference Bridge
This DSPFarm needs to register itself (the DSPFarm and resource types) with a call control element. This call control element can be either CUCM or CME. This is done by using the SCCP group configuration and SCCP protocol on the router to register with call control elements, more than one group can be created to register different pools (DSPFarm) resources with many simultaneous call control elements.
The common configuration is for a single group (called ‘ccm group’ in IOS) with an ordered (preference) list of call control elements to register with. All resources in the ccm group are registered with the most preferred call control element. If this call contol element is not available or fails, the next in the ordered list (next preference) is used to register the resources.
So in the case of a router than had DSPFarm resources that registers these with CUCM, where the connection to CUCM fails and if the router is running SRST, the next available call control element (if configured in the list) can be the local router running SRST. The DSPFarm resources then register with this local SRST instance (telephony-service) and therefore provides DSPFarm resources to the SRST service when active. When CUCM is back online, the DSPFarm will de-register with the local telephony-service and register with a more preferred call control element (CUCM).
As the DSPFarm registers with a call control element, it can register locally with SRST, CME and also with non local call control elements such as CUCM and also CME on separate routers therefore meaning a few routers could provide DSPFarm resources to a distributed network of CME routers therefore reducing the overall requirement for DSPs on those distributed routers. Some DSP resources may still be required locally on the distributed routers for PSTN connections (FXO, E1, etc).
Note that the call control element that the DSPFarm registers with must be configured to accept the registration. CUCM has Media Resource configuration and IOS has the telephony-service configuration as the example shows below.
 sdspfarm units 2
 sdspfarm transcode sessions 4
 sdspfarm tag 1 mtpa0ecf9440b88
 sdspfarm tag 2 CFB_BR3_GW
 conference hardware
The following example shows the DSPFarm configuration for registering to one call control element at, more can be added with ‘sccp ccm’ and ‘assocaiate ccm x priority y’ paying attention to the unique call control element identifiers and priorities.
voice-card 0
 dsp services dspfarm
sccp local GigabitEthernet0/0.500
sccp ccm identifier 1 version 7.0
sccp ccm group 1
 bind interface GigabitEthernet0/0.500
 associate ccm 1 priority 1
 associate profile 1 register mtpa0ecf9440b88
 associate profile 2 register CFB_BR3_GW
 keepalive retries 5
dspfarm profile 1 transcode
 codec g729abr8
 codec g729ar8
 codec g711alaw
 codec g711ulaw
 codec g729r8
 maximum sessions 4
 associate application SCCP
dspfarm profile 2 conference
 codec g711ulaw
 maximum sessions 1
 associate application SCCP

Simon Birtles

I have been in the IT sector for over 20 years with a primary focus on solutions around networking architecture & design in Data Center and WAN. I have held two CCIEs (#20221) for over 12 years with many retired certifications with Cisco and Microsoft. I have worked in demanding and critical sectors such as finance, insurance, health care and government providing solutions for architecture, design and problem analysis. I have been coding for as long as I can remember in C/C++ and Python (for most things nowadays). Locations that I work without additional paperwork (incl. post Brexit) are the UK and the EU including Germany, Netherlands, Spain and Belgium.