SRV, which is an abbreviation for Service, is a DNS record, which enables you to use a domain for a specific service different from a website. By setting up a few SRV records, you are able to use the domain with different providers and direct it to several servers at once, each and every server handling a different service. You could specify the port number for the connection to every machine, so there will not be any interference. You could also set different priorities and weight for 2 records which are used for the very same service, but direct to different servers for redundancy or load balancing. By having an SRV record you can employ your domain or a subdomain under it for a Voice-Over-IP server, for instance, and have the specific software running on various machines with different companies. Which one a client of yours is going to use will depend on the priority and weight values which you have set.