Topic Last Modified: 2011-04-12

This section describes the client sign-in behavior during normal operation and failover. This description does not include all the details of signing in but is intended only to illustrate the general flow when a user signs in to a metropolitan site resiliency topology that is split across geographical sites.

During normal operation, with DNS load balancing deployed, client sign-in with the site resilient topology works basically as it does in any supported topology.

Normal Sign-In Operation

  1. Remote user signs in to Lync 2010. Lync 2010 queries DNS server for its connection endpoint (the Edge Server in this specific instance). The DNS server returns the list of the FQDNs of the Access Edge service on each Edge Server.

  2. The client chooses one of these FQDNs at random and attempts to connect to that Edge Server. This Edge Server may be at either site. If this attempt fails, the client will keep trying different Edge Servers until it succeeds.

  3. Lync 2010 connects by using TLS to one of the Edge Servers.

  4. The Edge Server forwards the request to a Director. The Director may be at either site.

  5. The Director determines the pool where the user is homed and then forwards the request to that pool.

  6. The DNS server again returns the list of Front End Servers in the pool, including those servers at both sites. Each user has an “assigned” list of Front End Servers to which the user’s client is always connected: if the first server on the list for that client is currently unavailable, it tries the next one on the list. It keeps trying until it succeeds. In this example, the request is forwarded to a Front End Server at the North site.

  7. The response is returned to Lync 2010.

Failover Sign-In Operation

The following figures show typical call flow during a user sign-in, in the event that the North site fails. Diagrams have been simplified to highlight the most important aspects of the topology.

The following figure shows the flow for an internal user, with automatic configuration.

The following figure shows the flow for an internal user, with manual configuration.

The following figure shows the flow for an external user.