Distributed Multi-Cluster Call Processing

The distributed multi-cluster call processing model has two or more CUCM clusters. This model is typically used with large organizations that have multiple large sites. A CUCM cluster or CUCME router is provisioned at each site in which local call processing is a requirement. This model is also used for environments where IP WAN links are unreliable or sites are geographically dispersed. The distributed multi-cluster call processing model has the following features: • CUCM H.225 trunks or gatekeeper controlled inter-cluster trunks (ICT) are used to interface with H.323 gatekeeper for inter-site dial plan resolution. • Inter-site calls routed over the IP WAN or PSTN • Inter-site WAN calls are limited by gatekeeper call admission control (CAC) • Compressed audio codecs are normally used over the IP WAN (G.729 or iLBC) • High-bandwidth codecs (G.722 or G.711) are used within the site • Toll bypass and/or tail-end hop off (TEHO) • Multiple gatekeepers (gatekeeper clustering with GUP) should be provisioned to ensure inter-site call routing availability The distributed multi-cluster call processing model does not rely on the availability of bandwidth across the WAN circuits and only sends inter-site call processing over the WAN circuits. Although a G.729 call uses 26.4kbps of bandwidth over Frame-relay or point-to-point protocol (PPP) networks, the H.323 gatekeeper call admission control mechanism calculates the bandwidth usage as 16kbps per call. The calling party site’s CUCM sends an H.323 RAS (registration, administration, and status) ARQ (admission request) to the H.323 gatekeeper with the dialed digits (e.164) and required bandwidth (8kbps for G.729 and 64kbps for G.711). The called CUCM cluster also requests bandwidth from the H.323 gatekeeper zone. One G.729 phone call will require 16kpbs (8kbps + 8kpbs) and one G.711 phone call will require 128kbps (64kbps + 64kbps) of bandwidth. The gatekeeper is responsible for CAC and e.164 to IP Address (CUCM server) resolution. CUCM will route calls between sites by steering inter-site calls to the H.323 gatekeeper as a primary path. The backup call routing path will includes PSTN resources. The route pattern (RP) -> Route List (RL) -> Route Group (RG) call routing hierarchy was described in the call routing blog series posts I made a few months before this blog was written. Check my earlier blog posts for detailed information on distributed multi-cluster call processing model call routing. The next blog post will cover the clustering over the IP WAN call processing model. REFERENCES: CUCM 7.x Solution Reference Network Design (SRND) Guide: http://www.cisco.com/en/US/netsol/ns818/networking_solutions_program_home.html www.cisco.com/go/srnd STST Administration Guide(s) http://www.cisco.com/en/US/docs/voice_ip_comm/cusrst/admin/srst/configuration/guide/srstsa.html