e. Backhaul-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 networks. From the core, traffic is sent to the operator's mobile central office switch, the Internet, or another public data network. See Figure 7-5 for an example of backhaul links. Depending on the amount of traffic, backhaul networks use the following: Microwave (a Wireless Transmission Service at 44Mbps/34.4Mbps) or wireless Carrier Ethernet at speeds up to 40Gbps www.TechnicalPDF.com Fiber-optic cabling transmitting Gigabit Ethernet traffic Gigabit Ethernet and Multi-Protocol Label Switching (MPLS) (multiple 100Gbps streams with MPLS-enabled QoS capabilities) on fiber-optic cabling Provider's Data Backhaul Center with Core Functions* *Billing, tracking devices, tracking outages, signalling Figure 7-5 The aggregation backhaul network consolidates traffic from multiple cells and sends it to the core. A backhaul network is made up of traffic from cell sites that is aggregated and transmitted to the core. www.TechnicalPDF.com In the United States, most providers have upgraded much of their backhaul network to fiber. In areas of the country and worldwide where fiber is not already installed, backhaul traffic is carried by microwave and other higher-capacity wireless technologies. The higher costs for fiber are viable because more traffic is carried on these links. Fiber is likely to be more readily available in aggregation networks where carriers have previously laid fiber that often has spare capacity. In many instances, the landline divisions of mobile carri