SRV, which is an abbreviation for Service, is a DNS record, which permits you to use a domain name for a certain service different from a website. By creating a few SRV records, you are able to use the domain with different providers and point it to several servers at once, every single server managing a separate service. You can specify the port number for the connection to each machine, so there won't be any interference. You can also set individual priorities and weight for two records which are used for the exact same service, but forward to different servers for redundancy or load balancing. By having an SRV record you can use your domain address or a subdomain under it for a Voice-Over-IP server, for example, and have the actual software running on various machines with different providers. Which one a client of yours is going to use depends on the priority and weight values that you have set.