Reason Header - Local/Remote Resource Availability

Before the introduction of the Reason Header - Local/Remote Resource Availability feature, if there were no resources available on the outgoing TDM side, the IMG 2020 would respond to the incoming SIP network with a 503 Service Unavailable response. The 503 response sent would not give any indication whether the IMG 2020 itself was out of resources or whether the SS7 network was out of resources. With the introduction of this feature, a user can distinguish whether the 503 Service Unavailable response sent to the SIP network was caused due to a lack of resources on the IMG 2020 or lack of resources in the outgoing SS7 network. Refer to the links in the Related Topics section below. 

...