Case 6:21-cv-00667-ADA Document 37-7 Filed 03/14/22 Page 1 of 3
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`Exhibit 6
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`Case 6:21-cv-00667-ADA Document 37-7 Filed 03/14/22 Page 2 of 3
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`26 Understanding telecommunications networks
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`the PNO exchange code at Brighton is 75 compared to 34 for the BT exchange. The
`two networks are connected at various POI, usually at the tnmk exchange level in
`BT's network. All calls from BT subscribers destined for a PNO's network are routed
`to the destination exchange via the designated POI. Similarly, calls originating in the
`PNO network are routed to the destination BT exchange via the appropriate POI. As
`Fig. 2.4 shows, there may be a choice of PO Is to use for a call: the routeing either
`staying on the originating network until the last available POI - known as 'far-end
`handover', or interconnecting at the nearest POI - known as 'near-end handover' .
`As an example, let us consider the routeing of a call from the BT subscriber in
`Penzance (01736 89YYYY) to the subscriber on the PNO network in Brighton (01272
`75BBBB). The control system of the BT local exchange in Penzance, on examination
`of the non-local area code 01273, passes the call onto its parent trunk exchange at
`Plymouth. The control system of Plymouth trunk exchange identifies O 12 7 3 as an area
`code parented on Haywards Heath Trunk exchange and switches the call accordingly.
`The Hayward Heath trunk exchange, on recognising 01273, examines the exchange
`code 75 and routes the call to the designated POI for the serving PNO, which in
`this case is a route from the BT trnnk exchange to the Brighton PNO exchange.
`The call is passed to the PNO exchange, the signalling from the control systems
`of Haywards Heath giving the full dialled number (01273 75BBBB), so that the
`call can be completed within the PNO network - in this case directly to the called
`subscriber's line.
`A similar arrangement applies to calls from a PNO to BT's fixed network.
`The flow of calls is measured between the BT trunk exchanges and each of the
`interconnected PNO exchanges so that interconnect conveyance charges can be deter(cid:173)
`mined. Each network operator must pay the receiving operator for the conveyance
`and completion of calls passed over the POI. Normally, this follows the principle of
`a receiving operator charging on a call-minutes basis, according to the amount of
`their network traversed in delivering the call ( either to its subscriber or onto another
`network for completion). The rate of charge for traversing a network depends on
`the type of network involved, the mobile networks being rated higher than a fixed
`network. Like most aspects of interconnect, these call-completion-charge rates are
`usually subject to scrntiny or determination by the national regulator [3].
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`2.3.3 Mobile to mobile via the PSTN
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`Fig. 2.5 illustrates the general situation for calls between two different mobile net(cid:173)
`works in the same country. It is interesting to note that there are two basic scenarios for
`needing such a configuration. The first is a call between a terminal belonging to (i.e.
`registered with a service provider using) mobile network A and a terminal belonging
`to mobile network B. The other is a call between two terminals belonging to mobile
`network A, but the second terminal has moved temporarily onto (i.e. visiting) mobile
`network B - a process known as 'roaming'.
`Although calls between mobile networks in the same country may be delivered
`over direct links between MSCs on their respective networks, generally it is more
`economical to route calls to other mobile operators, as well as the wide range of fixed
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`VOP0009420
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