High availability and failover in UCMA 5.0

Applies to: Skype for Business 2015

This topic discusses the APIs in Microsoft Unified Communications Managed API 5.0 that are associated with High Availability and Failover.

SipEndpoint class

The following are members of the SipEndpoint class. When a SIP NOTIFY message is received with USC unavailable, the RegistrationStateChanged event is raised. In the associated RegistrationStateChangedEventArgs object, the Reason property is set to None (a value of the RegistrationTransitionReason enumeration) and the UserServicesState property is set to Unavailable (a value of the ServiceState enumeration).

When the registration is subsequently healed by means of a registration refresh, the RegistrationStateChanged event is raised, and the Reason property is set to Refreshed, and UserServicesState property is set to Available. The SipEndpoint class does not expose UserServicesState as a property.

ServiceState enumeration

The values of the ServiceState enumeration represent the state of a service. The enumeration values and their descriptions are shown in the following table.

Value	Description
Unknown	The state of the service is unknown.
Available	The service is available.
Unavailable	The service is unavailable.

RegistrationStateChangedEventArgs class

Three properties of the RegistrationStateChangedEventArgs class are related to high availability and failover. These properties and their descriptions are shown in the following table.

Property	Description
Reason	Gets the reason, if known, for the state transition.
MessageData	Gets the message data containing the message received when a state transition occurs. The value of this property is null when the state transition contains no message data.
UserServicesState	Gets the availability state of the User Services pool.

LocalEndpointStateChangedEventArgs class

Two properties on the LocalEndpointStateChangedEventArgs class are shown in the following table. Most of the Reason values are self-explanatory, but when a SIP NOTIFY message is received, the Reason value is RegistrarNotificationReceived and the Notification value indicates the type of notification.

Property	Description
MessageData	Gets the message received when a state transition occurs. Can be null if the state transition does not contain any message data.
Reason	Gets the reason for the state change, a value in the LocalEndpointStateTransitionReason enumeration.

MessageData property

The MessageData property on the LocalEndpointStateChangedEventArgs class is of type SipMessageData.

Reason property

The Reason property on the LocalEndpointStateChangedEventArgs class can be set to a value in the LocalEndpointStateTransitionReason enumeration. These values are shown in the following table.

Value	Description
None	No SIP NOTIFY message or a SIP NOTIFY message of unknown type.
OwnerDisabledOrRemoved	The user or application endpoint owner has been disabled or removed.
RegistrationRefreshFailed	Registration refresh attempt failed.
RegistrationRefreshSucceeded	Registration was refreshed successfully.
TooManyActiveEndpoints	The number of active endpoints exceeds the limit.

SipSubscription class

There are no public API changes in the SipSubscription class, but there are behavior changes that are triggered only from the UCMA platform. When used as part of the UCMA platform, the retry behavior of SipSubscription objects is optimized to eliminate unnecessary attempts to recover when the User Services pool is unresponsive. When the User Services pool does not respond, a failure to refresh a subscription does not cause a SipSubscription instance to terminate. The UCMA platform triggers this behavior only for subscriptions tied to the User Services pool that the owner is homed on.

LocalOwnerPresence and ContactGroupServices classes

When the User Services pool is offline, LocalOwnerPresence and ContactGroupServices objects change state to WaitingForRetry (see SubscriptionSignalingState) with a TransitionReason value of ServerEvent. In this state, publish operations fail with InvalidOperationException being thrown. Also, if the CurrentState property of the underlying SipSubscription instance changes to Terminated, the CurrentState() property on the LocalOwnerPresence instance changes to WaitingForRetry instead of Idle. When the User Services pool finally recovers, the subscription will be re-established.

RemotePresence class

The home pool subscription of RemotePresence objects is the same as that of LocalOwnerPresence objects.