When an end user wants to determine another user's availability (his presence information), he or she requests that information. The request identifies the target user by the unique URI. Once the PA receives the request, it generates a response, such as "online, but needs coffee."
The PA then authenticates the subscription requester and authorizes the user's permission for the subscriber to receive presence information--this is what occurs when AOL Instant Messenger and other Internet IM services ask whether you want another user to know if you're online.
The PA sends the subscriber a SIP "200 OK" response if it's authorized to send the subscriber the user's presence information, or a SIP "202 Pending" response if it's not.
A PA must authenticate all SUBSCRIBE requests using digest authentication or another method outlined in RFC 3261. So when the user and subscriber are in the same domain, all subscribers will have shared secrets with the PA for authentication purposes. You get secure authentication when you combine digest authentication with TLS (Transport Layer Security).
Alternatively, in multiple domain settings where subscriptions and notifications traverse internetworks, authentication is established by trust relationships between proxy servers and PAs using TLS. (S/MIME also is used for user-to-user or peer-to-peer authentication to establish the identity of potential subscribers).
Subsea cable alternatives can provide a level of comfort for those concerned about disruptions. Realistically, they will continue to play a small, but critical role in the short term.
Maintaining existing network infrastructures often incurs huge technical debt before newer technologies are adopted over time.
Amid ongoing regional uncertainties, telecom infrastructure in the Middle East has expand to include terrestrial low-latency network infrastructure, which offers resilience and agility in navigating political complexities without relying solely on undersea networks.
