This is the optional PPPoE 'service name' some access concentrators use to route a PPPoE session to a specific service profile on their end, left blank unless the ISP's equipment specifically requires it. Most deployments never touch this field, but a subscriber failing to connect on an access concentrator that enforces service-name matching would need it filled in exactly as the ISP specifies. For example, an ISP requiring the exact string 'internet' here to route sessions correctly would cause connection failures for any subscriber whose field is left blank.