SRV, which is an abbreviation for Service, is a DNS record, which allows you to employ a domain for a specific service different from a site. By creating a couple of SRV records, you are able to use the domain name with different companies and direct it to a number of servers at once, each and every server handling a separate service. You are able to specify the port number for the connection to each machine, so there will not be any interference. You could also set different priorities and weight for two records which are used for the same service, but forward to different servers for redundancy or load balancing. Using an SRV record you can use your domain or a subdomain under it for a Voice-Over-IP server, for instance, and have the actual software running on several machines with different companies. Which one a client of yours will use depends on the priority and weight values that you've set.