In this tactic, an ISP sells very low cost transit access to the entire peering population at an exchange point. This approach is similar to peering at the exchange point without the overhead of buying and deploying additional hardware, and without establishing and maintaining many relationships at an exchange point.

Note that only the routes announced to the partial transit provider at the exchange are propagated to the customer. While this is not “Peering” by my definition, it is a useful tactic to quickly obtain exchange point routes and it can be very inexpensive for the Partial Transit provider to provide.