SRV, which is an abbreviation for Service, is a DNS record, which allows you to use a domain name for a certain service different from a site. By setting up a couple of SRV records, you can use the domain name with different companies and forward it to several servers at the same time, each server managing a different service. You'll be able to specify the port number for the connection to every single machine, so there will not be any interference. You could also set individual priorities and weight for two records which are used for the very same service, but direct to different servers for redundancy or load balancing. With an SRV record you can employ your domain or a subdomain under it for a Voice-Over-IP server, for example, and have the actual software running on several machines with different providers. Which one a customer of yours will use will depend on the priority and weight values you have set.