Bypass IDs

Media Bypass works by assigning a unique bypass ID to each location, and each subnet associated with that location automatically inherits the same bypass ID. When a Lync endpoint attempts a call, the subnet of the endpoint is examined. If the bypass ID of the subnet matches the bypass ID of the subnet where the media gateway resides, Media Bypass will be allowed.

The same concept applies for inbound calls from the PSTN. When the media gateway receives a call and sees an endpoint with a matching bypass ID, the audio flows directly to the Lync client. Using the network configuration example in Figure 32.8, the San Francisco, San Jose, and Sacramento sites share a bypass ID because they are not bandwidth constrained. The Mendocino and Healdsburg sites each receive a unique ID because they have WAN bandwidth limitations.

Keep in mind that a unique bypass ID does not necessarily get assigned to each network region or site. Any network region with sites that have no bandwidth policy profile assigned all share the same bypass ID. This is because without a policy applied, it is assumed that all subnets have sufficient bandwidth between each other and Media Bypass can be used from any endpoint to any media gateway.

If a site does have a bandwidth policy profile assigned because WAN bandwidth is limited, a new bypass ID is generated for the site. Users placing calls from within the bandwidth-constrained site are allowed to use Media Bypass to a local media gateway. When users attempt a call to the same gateway from a subnet with a different bypass ID, Media Bypass is not allowed and the audio flows through a Mediation server. Figure 32.11 shows how a user can leverage Media Bypass in a local office, but be forced to send media through a Mediation server in the Chicago office across a constrained WAN link. This is because the bypass ID of the user’s endpoint does not match the bypass ID of the gateway in the Chicago site.

Figure 32.11. Media Bypass behavior with bypass IDs.