Economical Fixed Wireline Design for a Wireless Network
By Charles C. Zachry, Jr.
Over the past decade Wireless Carriers (WC) have implemented backhaul networks [networks connecting cell sites and trunk circuits to a Mobile Switching Center (MSC)] at such a rapid pace that little thought has been given to their cost or more efficient methods of connection. In many cases DS3 hubs were established at the Serving Wire Center (SWC) for the MSC and DS1 cell site and trunk circuits brought to that hub for SONET connection into their Mobile Switching Office (MSO). In other cases new MSO/MSC locations were established but some wireless carriers simply established inter-MSO (Mobile Switching Office) DS3 circuits for a flash rehoming without ever physically redesigning the Local Exchange Carrier (LEC) network at a later date. In this same period pricing of LEC circuits have seen a substantial decrease as competition for high capacity circuits has increased in many Local Access Transport Areas (LATAs). With many wireless carriers now facing budget constraints and looking for ways to reduce expenses, improved designs with reduced LEC tariffs could greatly assist in that effort.
Design of efficient backhaul networks in each LATA is a function of LEC tariffs as well as the proper placement and efficient loading of DS3s. Twenty-eight DS1s can be accommodated on a DS3. The breakeven point for the installation of a DS3 to carry DS1s on a common route is based on the wireline carrier pricing and circuit mileage.
Most LECs have a common method of pricing circuits whether they are DS1s or DS3s. The elements are as shown in Figure 1 on the following page. Channel terminations are that part of a circuit connecting a customer location, such as a cell site or MSO, to its LEC Serving Wire Center (SWC). This element is usually charged as a fixed price per month regardless of the mileage involved but with some few LECs they are mileage sensitive. The circuit element between SWCs usually has a fixed priced element and a mileage sensitive component. Mileage is determined by using LEC established Vertical and Horizontal coordinates commonly called V&H coordinates for the SWCs involved. Mileage between SWCs is calculated using the following formula:
Distance in miles = square root( ( (V1-V2)**2 + (H1-H2)**2 ) /10 )
Where: V1& H1 are SWC1 coordinates,
V2 & H2 are SWC2 coordinates with
Mileage always rounded up to the
next highest mile.