Cisco Preferred Architecture for Webex Calling — Design Overview

Publisher

Cisco Systems, Inc. (CTG TME)

URL

https://www.cisco.com/c/dam/en/us/td/docs/solutions/CVD/Collaboration/hybrid/AltDesigns/PA-WbxCall.pdf

Published

2025-08

Updated

unknown

Accessed

2026-09-04

HTTP status

200

License

Cisco proprietary documentation, all rights reserved; no-redistribution; short excerpts and locators only

Claims citing this source

• A migration that concentrates many users into a single Webex Calling location served by 1 registration-based Local Gateway can reach the 250 concurrent call ceiling at peak, producing SIP 403 rejections that look like a carrier fault rather than a design limit. inference in context
• A Webex Calling dial plan differentiates destinations bound for the on-premises Unified CM, which are sent as enterprise calls, from all other destinations, which are sent as PSTN calls, over the same trunk or route group. fact in context
• During coexistence a Local Gateway can simultaneously provide PSTN access and an interconnect to the existing on-premises call control, and the on-premises call control may remain in permanent use alongside Webex Calling. fact in context
• A certificate-based Local Gateway trunk supports up to 2000 concurrent calls over the internet, an order of magnitude more than the registration-based model. fact in context
• A location using a Local Gateway is subject to a default scale limit of 250 concurrent calls, which affects how locations should be sized and split; locations using Cloud Connected PSTN are not subject to that limit. fact in context
• Webex Calling does not support wildcard certificates on the Local Gateway, and only certificates carrying the server authentication extended key usage are accepted. fact in context
• Calls exceeding the registration-based Local Gateway concurrency ceiling are rejected by the Webex Calling access session border controller with a SIP 403 Forbidden response. fact in context
• A registration-based Local Gateway is limited to 250 concurrent calls per registering gateway, a ceiling attributed to TLS and TCP signalling performance. fact in context
• Webex Calling ignores the registration expiry value sent by the Local Gateway and enforces a value of 120 seconds, refreshing at approximately half that lifetime. fact in context
• Registration-based Local Gateway signalling is established outbound only from the enterprise to Webex Calling over SIP with TLS, so no inbound firewall rule is required. fact in context
• A maximum of 10000 dial plans may be configured per customer, and each dial plan may hold up to 10000 dial patterns. fact in context
• Changing a location from 1 PSTN type to another is partly self-service, partly a manual migration, and in a small number of combinations unsupported. fact in context
• Exactly 1 PSTN choice can be configured for each Webex Calling location. fact in context
• The PSTN provider used for a call depends only on the originating location of the Webex Calling call; no other attribute of the call affects PSTN selection, not even the called number. fact in context
• Rerouting to another trunk is triggered by SIP responses 401, 470, 480 and 606 when no provisional 18x response preceded them, by all other 4xx responses except 403, 404, 410, 413, 484 and 486, by all 5xx responses, and by a 12 second SIP timeout. fact in context

Cite this source record

APA

WarmTransfer. (n.d.). Cisco Preferred Architecture for Webex Calling — Design Overview. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-pdf-preferred-architecture-webex-calling

BibTeX

@misc{warmtransfer-cisco-pdf-preferred-architecture-webex-calling,
  title  = {Cisco Preferred Architecture for Webex Calling — Design Overview},
  author = {{WarmTransfer}},
  year   = {2025},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-pdf-preferred-architecture-webex-calling},
  note   = {Cisco Systems, Inc. (CTG TME), accessed 2026-09-04}
}