he EU that travel within EU countries. Another example of no-cost roaming is T-Mobile, which offers customers on certain plans no-fee texts, voice, and data usage when they roam in 140 countries internationally. Agreements among carriers are required for every region in which roaming is enabled. Roaming agreements spell out costs, billing, and payment terms. www.TechnicalPDF.com To illustrate the complexity of roaming arrangements, most carriers have agreements with 200 to 250 other carriers. Some carriers use brokers that already have agreements worldwide and share revenue with the broker. Thus, calls made and received while roaming are more expensive than those in the subscriber's home territory; with the additional costs covering the fees imposed by the other network. Once the agreement has been signed and the service tested, roaming is activated. Carriers lease high-speed links to other providers such as AT&T, France Telecom, and Belgacom (in Belgium), all of which have an international presence. These links carry the actual voice and data traffic. Signaling links are also established to perform functions such as the handshake between the handset and the user's home carrier. The handshake verifies that users are legitimate customers of the originating network and have roaming privileges. Gateways are used to translate signaling between handshakes that use incompatible types of Session Initiation Protocol (SIP) links over which the handshake is done. Roaming revenues are shrinking because many customers use Wi-Fi in cafes and hotels when they travel internationally. For more on Wi-Fi international networks see the section "Wi-Fi for Roaming" later in this chapter. MORE EFFICIENT 4TH GENERATION DIGITAL NETWORKS Mobile protocols define how data and voice are carried on cellular networks. For example, 3rd generation (3G) networks carry data and voice separately. However, 4th generation (4G) networks specify that voice and data are to be transmitted on the same spectrum streams. They essentially treat voice as dat