of peering agreements, there was an understanding that peers were equals. Newer agreements often call for charges to be applied when traffic levels exceed what was agreed to in negotiations. The most obvious benefit of peering is that because two parties agree to work with one another, and therefore exchange information about the engineering and performance of their networks, the overall performance of the network is increased, including better availability, the ability to administer service-level agreements (SLAs), and the ability to provide greater security. Major backbone providers are very selective about international peering, where expensive international private- line circuits are used to exchange international routes. Buying transit provides the same benefits as peering, but at a higher price. Exchanging traffic between top-tier providers basically means better performance and involves fewer routers. Again, these types of arrangements are critical to seeing the evolution and growth in IP telephony, VoIP, IPTV, interactive gaming, and the expanding varieties of multi- media applications. One problem with peering is that it can be limited. Under peering arrange- ments, ISPs often can have access only to each other's networks. In other words, I'll agree to work with you, but you can work only with me; I don't want you working with anyone else. Exclusivity demands sometimes arise. IP QoS IP QoS QoS is one of the most important issues in networks in general, and particularly SO in the Internet and other IP networks. QoS deals with the strict management of traf- fic such that guarantees can be made and SLAs between customers and service pro- viders can be observed. In the case of packet switching, QoS basically guarantees that a packet will travel successfully between any two points. QoS is also of concern in circuit-switched networks, such as the PSTN, where the demands of real-time voice impose conditions that need to be tightly controlled, including availability, latency, and control of noise. In packet-swit