t as long as logical (IP) connec- tivity exists between elements, for example, between the gNB and the core. The physical topology becomes interesting in certain cases, like optimizing propagation delay (since the actual cable distance on the signal path matters) and resiliency (since different paths should avoid fate-sharing with each other). 9.1.7 Standards Viewpoint In regard to transport, standardization in 3GPP is concentrated on the definition of the protocol stacks for the logical interfaces of the mobile system, with references to the respective standards of that protocol, with those protocols typically standardized by IETF and IEEE. How connectivity should be arranged between the mobile nodes, with what physical media or with what technology, is not defined by 3GPP, as long as the logical inter- face specification (protocol stack) is met. Since the logical interfaces rely on well-known networking protocols, IPv6, IPv4, and IPsec (IP security suite of protocols), networks, links, and equipment do not need to be mobile network specific. However additional functional requirements may be imposed from synchronization. Figure 9.2 shows the scope of 3GPP work in the transport and networking areas. The division into RNL (Radio Network Layer) and TNL (Transport Network Layer) is shown. Not all relevant standards or forums are included. 9.2 Capacity and Latency N2 N3 GTP-U Radio Network Layer (RNL) Transport Network Layer (TNL) (MP)-BGP IP VPN IS-IS E-VPN IPsed ITU-T IEFF 802 1 IEEE 1588 ITU-T G ETSI NFV IEEE 802.3 IEEE P1914 O-RAN Services Fronthaul CPRI, eCPRI Deliverables Figure 9.2 5G radio and transport standardization. The clear division of standards into RNL and TNL allows RNL to be mostly agnostic to the TNL layer. This makes it simpler to adopt new TNL technologies or otherwise modify TNL behavior. Especially in the area of transport network implementation and solutions for physical media, multiple standardization activities exist, for example, in ITU-T and IEEE, that should be referred to. On the network