While stocks are bought and sold on exchanges, bonds traditionally have been traded over the phone between large banks and brokers. Over the past two decades several brokerage, financial-technology and other firms have launched venues for electronic bond trading that they say offer more transparency about prices and an easier way for buyers and sellers to connect. Those efforts have helped move a small but growing share of transactions to the new marketplaces. Kevin McPartland, head of market-structure research at consulting firm Greenwich Associates, estimates that electronic bond trading could represent as much as 30% of overall trading in the next few years, up from about 20% today.

http://www.wsj.com/articles/ice-to-buy-interactive-data-for-5-2-billion-1445868128