This paper describes the problems of identifying effective sales channels for services working with a call center. The solution is presented in the form of a multi-level model of sales channels that works with call tracking with a limited number of phone numbers. This approach can be applied in services of small and medium-sized businesses, which cannot afford a large number of phone numbers for call tracking.

Keywords: sales channel, contextual advertising, call tracking, call center, marketing, Yandex Direct, Google AdWords