A method of generating summarised network topology parameters of a communications network domain comprising a plurality of network nodes (12, 14, 16) and a plurality of interconnecting network domain paths, the method comprising: identifying a plurality of network nodes configured to interface with one or more other network domains as summarized nodes; identifying each available network domain path between each pair of the summarized nodes within the network domain, at least one said network domain path between each said pair of summarized nodes comprising at least one other network node and respective interconnecting links; and generating summarised network topology parameters for each said pair of summarized nodes, each summarised network topology parameter being dependent on a respective transmission parameter of the said available network domain paths; wherein, where there are a plurality of available network domain paths between a said pair of summarized nodes, the method further comprises the steps of: determining whether a transmission parameter of a first said path would allow the path to be bundled with another said path; comparing any such transmission parameter with the or each transmission parameter of any previously determined paths to determine whether there exists a previously determined path which has a matching transmission parameter; and, if a matching transmission parameter is found, adding the bandwidth of the first path to the bandwidth of the said other path to form a bundled path and comparing the bandwidth of each interconnecting link of the bundled path with a maximum available bandwidth of said interconnecting link, and if the bandwidth of said interconnecting link is greater than its maximum available bandwidth, reducing a bandwidth of one of the first path and the said other path such that the bandwidth of said interconnecting link is not greater than its maximum available bandwidth; wherein the method further comprises advertising said summarised network topology parameters to another network domain. identifying a plurality of network nodes configured to interface with one or more other network domains as summarized nodes; identifying each available network domain path between each pair of the summarized nodes within the network domain, at least one said network domain path between each said pair of summarized nodes comprising at least one other network node and respective interconnecting links; and generating summarised network topology parameters for each said pair of summarized nodes, each summarised network topology parameter being dependent on a respective transmission parameter of the said available network domain paths; wherein, where there are a plurality of available network domain paths between a said pair of summarized nodes, the method further comprises the steps of: determining whether a transmission parameter of a first said path would allow the path to be bundled with another said path; comparing any such transmission parameter with the or each transmission parameter of any previously determined paths to determine whether there exists a previously determined path which has a matching transmission parameter; and, if a matching transmission parameter is found, adding the bandwidth of the first path to the bandwidth of the said other path to form a bundled path and comparing the bandwidth of each interconnecting link of the bundled path with a maximum available bandwidth of said interconnecting link, and if the bandwidth of said interconnecting link is greater than its maximum available bandwidth, reducing a bandwidth of one of the first path and the said other path such that the bandwidth of said interconnecting link is not greater than its maximum available bandwidth; determining whether a transmission parameter of a first said path would allow the path to be bundled with another said path; comparing any such transmission parameter with the or each transmission parameter of any previously determined paths to determine whether there exists a previously determined path which has a matching transmission parameter; and, if a matching transmission parameter is found, adding the bandwidth of the first path to the bandwidth of the said other path to form a bundled path and comparing the bandwidth of each interconnecting link of the bundled path with a maximum available bandwidth of said interconnecting link, and if the bandwidth of said interconnecting link is greater than its maximum available bandwidth, reducing a bandwidth of one of the first path and the said other path such that the bandwidth of said interconnecting link is not greater than its maximum available bandwidth; wherein the method further comprises advertising said summarised network topology parameters to another network domain.