ic. The Iur traffic can be assumed here to be, for example, 1-2% of the total I traffic. This assumption depends heavily on the network plan and parameters, as explained later. In this case, the total I traffic is I-cs + Iu-ps = 42.9 Mbps + 292.3 Mbps = 335 Mbps Thus, the total Iur traffic = 2% of 335.2 Mbps = 6.704 Mbps 3.7 Topology Planning After individual link planning is done, the next step is to define the topology of the network. The topology is not only important from the perspective of defining the BOQ (bill of quantity) but also the performance of the network. Now consider the site location shown in Figure 3.60. When the sites are connected directly to the BSC, the topology is called 'point-to-point' topology. This topology is easy to plan and implement. However, the capacity is not fully utilised. If all the sites need only 0.5E1s, then the rest of the link capacity is wasted. Apart from this the protection is expensive as the usual protection that is used is equipment diversity. This topology is usually used for sites that cannot be incorporated into any of the topologies (discussed next). Topology Planning Figure 3.61 Chain topology Chain topology (shown in Figure 3.61) is an extension of the point-to-point topology. In this topology, only some of the sites are connected directly to the BSC. These are the sites that are either very near to the BSC or do not have a possible connection to other neighbouring sites. The advantage of this topology is that the possibility of utilising the link capacity increases further. Sometimes transmission nodes are connected to the BSC using this technology. These transmission nodes basically act as digital multiplexers that groom the traffic of far-away locations and transfer it to the BSC. The major disad- vantage of this topology is that if the first hop or site towards the BSC and/or the transmission node and/or the links is connected to the BSC, a large amount of traffic would be lost, resulting in loss of revenues. In thus figure, if the last sites of the two ch