On the Internet side (it's still telecom, right?), ISPs exchange traffic at IXP (Internet Exchange Points). To get free exchange, ISPs generally require a less than 2:1 imbalance in traffic (incoming vs outgoing) and require the ISP wishing to peer to peer at several IXPs. There's some interesting terminology used. In "hot potato" routing, traffic is handed off at the IXP that is closest to the originator of the traffic, requiring the one who is handed the traffic to transport it a longer distance (which increases cost) to the final customer. In "cold potato" routing, the carrier that wants to hand off the traffic hands it off at the IXP closest to the destination so the original carrier carries the traffic for a longer distance and incurs those costs.
They then go on to discuss Content Delivery Networks that deliver content like Netflix. The paper appears to advocate free peering of CDNs regardless of the traffic imbalance if cold potato routing is used. The ISP the content is being handed to only has to carry the traffic a short distance to the customer.
Division of cost of carriage is an OLD problem going back to the 1800s. As part of the General Postal Union, Each country should retain all money it has collected for international postage. The assumption was that there was balance between sending and receiving mail, so complex division of charges was not necessary. The originating country got the postage fee. In the return letter, the other country got the fee. So, today, as with then, we look at traffic imbalance to determine if peering should be free.
Harold