 to access voicemail messages within e-mail inboxes. Billing databases called Policy and Charging Rule Function (PCRF) data- bases keep specific information on contract terms for each subscriber. The Packet Data Network (PDN) transmits usage records to the PCRF, which is connected to billing software. Connecting Cell Sites and Core Networks In addition to managing vast amounts of cellular traffic, carriers operate large landline networks between their cell sites and their IP core. The links between cell sites and equipment in their core are referred to as backhaul. Backhaul is also referred to as the transport network. Traffic from many sites is backhauled to a central location-the operator's core network. This network transports signals between base stations and core networks. Transport networks consist of links to mobile switches and other net- works. From the core, traffic is sent to the operator's mobile central office switch, the The Streamlined Infrastructure of Long-Term Evolution Architecture Internet, or another public data network. Depending on the amount of traffic, backhaul networks use the following: T1/E1 (1.54Mbps/2.05Mbps) on copper cabling Microwave (a Wireless Transmission Service at T1/E1) or T3/E3 (44Mbps/34.4Mbps) or Carrier Ethernet at speeds up to 1Gbps Gigabit Ethernet and Multi-Protocol Label Switching (MPLS) (multiple 10Gbps streams with MPLS-enabled QoS capabilities) on fiber-optic cabling A backhaul network comprises the following: The access that connects cell sites in the same area together, before base sta- tion traffic is aggregated and transmitted to the core Aggregation networks that merge traffic from many cell sites and transmit it to the core network, as shown in Figure 7-6 Aggregation network network Access networks MME = Mobility Management Entity SGW = Serving Gateway Controllers for 2G and 3G services also are located in the core. Figure 7-6 The aggregation network consolidates traffic from multiple cells before sending it to the core. Mobile and Wi-Fi Networks Traditional