Prerequisites and limitations

Media optimization is supported across desk phones (excluding DECT & ATA devices), Webex, and the Local Gateway solution. When you make calls within your organization, between supported devices, the media for your call flows directly between the devices whenever possible. This provides lower latency and better quality.

Please see What's New in Webex Calling for global enablement dates.

  • By default, media optimization is enabled on the desk phone devices and Webex and, usually, doesn’t require specified configuration.

  • For Local Gateway, media optimization can be enabled with the command STUN usage lite, which is reviewed in Register Local Gateway to Webex Calling

    STUN (Session Traversal Utilities for NAT) is a standardized set of methods, including a network protocol, for traversal of network address translator gateways in applications of real-time voice, video, messaging, and other interactive communications.

  • The Local Gateway (CUBE) supports ICE-lite. There are several restrictions to ICE support on the CUBE. Please see details about ICE-lite support on CUBE.

  • Media optimization support on Local Gateway requires a minimum CUBE software version of 17.3 or 16.12.5.

  • Media optimization with a Local Gateway requires network reachability between the device and the Local Gateway. This can be achieved by either:

    • Assigning a public IP address to the Local Gateway.

    • Ensuring that the Local Gateway host address is accessible to a device within the same network as the Local Gateway.

  • In order to route calls, signaling data is sent to the Webex Calling cloud. An active internet connection is always required to make Webex Calling calls. However, media makes up the majority of traffic for a call.

  • Calls can only be optimized within a single organization. For interorganization calls, media must flow via the PSTN for regulatory reasons.

  • If Call Recording is enabled, media for recorded calls is routed to the cloud and are not optimized.

ICE (Media optimization) and Call Recording are both features that independently introduce a small audio delay at the beginning of the call and when used together the audio delay is slightly longer and more noticeable to customers.

Phases of Webex Calling media optimization

Media optimization uses Interactive Connectivity Establishment (ICE) to discover optimized media paths.

This happens in the following phases:

  1. Candidate discovery

    When a call is made, an endpoint must first discover a list of addresses where it can receive media. These addresses, or candidates, include an endpoint’s local address, and a server reflexive address that can be used to contact the endpoint through a NAT. The server reflexive address is determined by querying a STUN server in the Webex Calling cloud.

  2. Candidate exchange

    In this phase, endpoints exchange the list of candidate addresses that are collected in Candidate discovery using SIP.

  3. Connectivity checks

    Endpoints test the candidate addresses exchanged in Candidate exchange to determine the best media path between two devices.

  4. Media path optimization

    Using a re-invite, the endpoints now begin to send media through the optimized path.