A method of operating an access network in order to transmit data over a predetermined twisted metallic pair connection in accordance with a predetermined digital subscriber line protocol of transmission, the access network including an access network modem connected to, or operable to be connected to, the predetermined twisted metallic pair connection which is capable of transmitting and receiving signals over the predetermined twisted metallic pair connection in accordance with the predetermined digital subscriber line protocol of transmission, the method comprising: receiving a deployment indication; identifying at least two deployment factors associated with the received deployment indication including an estimated line length specifying an estimated length of the predetermined twisted metallic pair connection and one or more further deployment factors; determining an estimated data rate specifying an estimated potentially achievable data rate at which the predetermined digital subscriber line protocol of transmission is able to transmit data over the predetermined twisted metallic pair connection, the estimated data rate being determined in dependence upon the identified deployment factors including the estimated line length and the one or more further deployment factors; determining a value for each of one or more configuration parameters associated with the operation of the access network modem connected to, or operable to be connected to, the predetermined twisted metallic pair connection in dependence upon the estimated data rate; deploying a customer premises equipment modem at a customer premises side of the twisted metallic pair, which modem is capable of transmitting and receiving signals over the predetermined twisted metallic pair connection in accordance with the predetermined digital subscriber line protocol of transmission; and operating the access network modem in accordance with the determined value or values of the one or more configuration parameters characterised in that the one or more further deployment factors are one or more modem types and/or types of modem chipsets wherein determining an estimated data rate in dependence upon the identified deployment factors comprises: preliminarily generating a plurality of rate versus reach functions, each of which enables an estimated data rate to be output for any input estimated line length within a predetermined range, for a plurality of different values of the further deployment factors or for different combinations of values of the further deployment factors where there are a plurality of further deployment factors; selecting one of the pre-generated rate versus reach functions in dependence upon the one or more further deployment factor; and using the estimated line length, together with the selected rate versus reach function, to generate an estimated data rate. receiving a deployment indication; identifying at least two deployment factors associated with the received deployment indication including an estimated line length specifying an estimated length of the predetermined twisted metallic pair connection and one or more further deployment factors; determining an estimated data rate specifying an estimated potentially achievable data rate at which the predetermined digital subscriber line protocol of transmission is able to transmit data over the predetermined twisted metallic pair connection, the estimated data rate being determined in dependence upon the identified deployment factors including the estimated line length and the one or more further deployment factors; determining a value for each of one or more configuration parameters associated with the operation of the access network modem connected to, or operable to be connected to, the predetermined twisted metallic pair connection in dependence upon the estimated data rate; deploying a customer premises equipment modem at a customer premises side of the twisted metallic pair, which modem is capable of transmitting and receiving signals over the predetermined twisted metallic pair connection in accordance with the predetermined digital subscriber line protocol of transmission; and operating the access network modem in accordance with the determined value or values of the one or more configuration parameters characterised in that the one or more further deployment factors are one or more modem types and/or types of modem chipsets preliminarily generating a plurality of rate versus reach functions, each of which enables an estimated data rate to be output for any input estimated line length within a predetermined range, for a plurality of different values of the further deployment factors or for different combinations of values of the further deployment factors where there are a plurality of further deployment factors; selecting one of the pre-generated rate versus reach functions in dependence upon the one or more further deployment factor; and using the estimated line length, together with the selected rate versus reach function, to generate an estimated data rate.