ks. The main advantage is that traffic passing through an exchange usually isn't billed any party, whereas connection to an upstream provider would be billed by that upstream provider. Also, because IXPs are usually in the same city, latencies are reduced because the traffic doesn't have to travel to another city or, potentially, continent. Finally, there is a speed advantage, SO an ISP can avoid the high cost of Chapter 8 The Internet and IP Infrastructures long-distance leased lines, which may limit its available bandwidth due to the costs, whereas a connection to a local IXP might allow limitless data transfer, improving the bandwidth between adjacent ISPs. A common IXP is composed of one or more switches to which the various ISPs connect. During the 1990s, ATM switches were the most popular type of switch, but today Ethernet switches are increasingly being employed, with the ports used by the different ISPs ranging from 10Mbps to 100Mbps for smaller ISPs to 1Gbps or 10Gbps for larger providers. The costs for operating an IXP are generally shared by all the participating ISPs, with each member paying a monthly fee, depending on the speed of its port or the amount of traffic it offers. (A good source of informa- tion showing all the IXPs around the world is www.ep.net.) Peering Agreements An alternative to IXPs is the use of private peering agreements. In a peering solu- tion, operators agree to exchange with one another the same amount of traffic over high-speed lines between their routers SO that users on one network can reach addresses on the other. This type of agreement bypasses public congestion points, such as IXPs. It is called peering because there is an assumption that the parties are equal, or peers, in that they have an equal amount of traffic to exchange. This is an important point because it makes a difference in how money is exchanged. People are studying this issue to determine whether a regulatory mechanism is needed or whether market forces will drive it. In general, with the first generation 