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 creating a number of SRV records, you can use the domain name with different companies and point it to several servers at a time, each and every server handling a separate service. You'll be able to specify the port number for the connection to every machine, so there won't be any interference. You can even set individual priorities and weight for two records which are used for the exact same service, but direct to different servers for redundancy or load balancing. With an SRV record you can use your domain or a subdomain under it for a Voice-Over-IP server, for example, and have the actual software running on a number of machines with different companies. Which one a customer of yours will use will depend on the priority and weight values you have set.