SRV, which is an abbreviation for Service, is a DNS record, which enables you to employ a domain for a certain service different from a site. By creating a few SRV records, you can use the domain with different providers and point it to several servers at the same time, every single server managing a different service. You are able to specify the port number for the connection to every machine, so there won't be any interference. You could also set different priorities and weight for two records which are employed for the same service, but forward to different servers for redundancy or load balancing. By having an SRV record you can employ your domain name 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 will use depends on the priority and weight values that you've set.