Solution Design Guide for Cisco Unified Contact Center Enterprise, Release 15.0(1) - Sizing and Operating Conditions for Reference Designs

Publisher

Cisco Systems

URL

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/icm_enterprise/icm_enterprise_15_0_1/design/guide/ucce_b_ucce_soldg-for-unified-cce-1501/rcct_m_sizing-and-operating-conditions_15_0.html

Published

2025-03-15

Updated

unknown

Accessed

2026-09-25

HTTP status

200

License

Cisco copyright; all rights reserved; no-redistribution; short excerpts and locators only

Source notes citing this source

• Cisco defines average handle time as the mean call duration over a period; it is the sum of handling-time types such as call treatment time for self-service calls or talk time for agent calls. in context
• BHCA (busy hour call attempts) is the total number of calls attempted or received in the contact center during the peak traffic hour or interval. in context
• Worked example: 600 calls in the busy hour averaging 2 minutes each is a busy hour traffic load of 20 erlangs. in context
• Busy hour traffic in erlangs is BHCA multiplied by average handle time in seconds, divided by 3600 (equivalently BHCA times AHT in minutes divided by 60). in context
• Cisco lists the inputs for Erlang calculators as BHCA, average handle time for each resource, service level (percentage answered within x seconds), and the grade of service (percent blockage) wanted for trunks and VRU ports. in context
• The Erlang B model as Cisco describes it assumes random call arrival, and when all trunks or ports are occupied new calls are lost or blocked (busy tone) rather than queued. in context
• Erlang B relates three quantities (busy hour traffic, grade of service and number of ports or lines); given any two, the model calculates the third. in context
• Cisco directs designers to use the Erlang B model to size PSTN trunks, gateway ports and VRU ports. in context
• The Erlang C model as Cisco describes it assumes random call arrival, and when all agents are busy incoming calls are queued rather than blocked. in context
• Cisco lists the Erlang C inputs as the number of calls agents answer in the busy hour (BHCA), average talk time plus wrap-up time, and the delay or service level wanted, given as a percentage of calls answered within a set number of seconds. in context
• The Erlang C model's outputs are the number of agents required, the percentage of calls delayed because no agent is available, and the average queue time. in context
• Cisco directs designers to use the Erlang C model to size agents in contact centers that queue calls before presenting them to agents. in context
• Worked example: 30 calls of 6 minutes each in the busy hour is 180 minutes of traffic, or 3 erlangs. in context
• One erlang is a traffic load equal to 3600 seconds of calls on the same circuit, trunk or port during the busy hour, i.e. enough traffic to keep one circuit busy for one hour. in context
• Cisco describes 1% blockage (P.01) as a typical grade of service for PSTN trunks, noting that other applications may need different grades of service. in context
• Grade of service (percent blockage) is the probability that a resource is busy during the busy hour so that a call is lost or blocked; a grade of service of 0.01 means 1% of busy-hour calls are blocked. in context
• Cisco says the right traffic model depends on three factors: traffic source characteristics (finite or infinite), how lost calls are handled (cleared, held or delayed), and the call arrival pattern (random, smooth or peaked). in context
• Service level is the percentage of offered call volume that is answered within X seconds. in context
• Cisco gives example service level goals of 90% of calls answered in under 10 seconds for sales and 80% of calls answered within 30 seconds for support centers. in context
• Cisco states that the service level goal determines not only the agents needed but also the percentage of queued calls, the average time in queue, and the PSTN trunks and VRU ports needed. in context
• In Cisco's contact center sizing terminology, talk time includes time the caller spends on hold and time spent in consultative conferences. in context
• The agent capacity figures in the Cisco UCCE 15.0(1) reference designs assume up to 30 calls per hour per agent. in context
• Cisco notes that VRU queuing and VRU self-service scenarios each need a different number of VRU ports because each has a different average handle time and possibly a different call load. in context
• Wrap-up (after-call work) time is the time after the caller disconnects that the agent spends completing tasks such as database updates and call documentation. in context

Cite this source record

APA

WarmTransfer. (2025, March 15). Solution Design Guide for Cisco Unified Contact Center Enterprise, Release 15.0(1) - Sizing and Operating Conditions for Reference Designs. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-ucce-1501-sdg-sizing-operating-conditions

BibTeX

@misc{warmtransfer-cisco-ucce-1501-sdg-sizing-operating-conditions,
  title  = {Solution Design Guide for Cisco Unified Contact Center Enterprise, Release 15.0(1) - Sizing and Operating Conditions for Reference Designs},
  author = {{WarmTransfer}},
  year   = {2025},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-ucce-1501-sdg-sizing-operating-conditions},
  note   = {Cisco Systems, accessed 2026-09-25}
}