ing layer, most of the standards are developed in IETF as RFCs (Request for Comments). Since the TNL layer apart from the logical interface definition is to a great extent an implementation topic, candidate solutions can be - and are - reused from IP enterprise networks, fixed residential Internet networks, optical transmission systems, and other transport and networking domains. The low layer split point is a special case also in standardization: it is SO far not defined at the protocol level by 3GPP, but instead there are industry forum standards and the IEEE task force. It also has special demands for capacity and latency. Capacity and Latency 9.2.1 Transport Capacity Upgrades The very first transport question for the 5G system is, how much capacity is needed for the transport network, for the first mile link, and from any hub point upward? Different strategies for dimensioning are used, depending on the amount of infor- mation available, business strategies and targets, with the final result of the method used also in practice double-checked and possibly impacted by the resulting cost of the transport service. Typically, a major upgrade or strategic redesign cycle of the transport network occurs every once in a while, complemented with smaller incremental designs taking place more often. During a major redesign, technology platforms possibly change, while the smaller cycles rather enhance the existing production network with changes of limited 9 Transport scope. Introduction of a new mobile network generation is a trigger to assess the future-proofness of current transport. Overdimensioning is costly and should be avoided; on the other hand, any future capacity upgrade requiring site visits (e.g. for installing higher-bit-rate optical plug- gables) becomes costly, too, especially if the upgrade concerns access links which are numerous. With the introduction of a new system, the traffic volume in the network grows with the penetration rate of the terminals. The take-up can, however, be rapid, as was experience