ough such technologies now frequently sport Ethernet interfaces. Two families of PONs may also be employed at the physical layer. IEEE Ethernet passive optical network (EPON) (clauses 64 and 65 of IEEE 802.3) share much of the standard Ethernet physical layer structure, with modifications (e.g. in the preamble and additional K-codes for forward error correction) and augmentations (such as MultiPoint Control Protocol frames). ITU-T PON flavors (e.g. ITU-T G.989.3) encapsulate Ethernet (and MPLS) in gigabit passive optical network (GPON) encapsulation method (GEM and XGEM) carried in a synchronous bit stream. The physical layer very often avails itself of point-to-point microwave links (either native Ethernet- or TDM-based). An emerging elegant solution (attractive for mobile operators providing their own transport) is integrated access/backhaul (IAB) (described in Section 5.2) wherein the 5G air interface and the backhaul share the same wireless technology. 6.6.5.4 Technology Comparison Any comparison of the pros and cons of the different technologies needs to address the issues of scalability, multiservice support, controlling forwarding behavior, support for slic- ing, resilience, FM, performance monitoring, security, timing, and NFV/MEC, which are discussed in the following subsections. 6.6.5.4.1 Scalability The problem of scalability in the transport network is much less acute than in the mobile network itself, since there is no awareness of individual end users or devices. In most cases the scale should not exceed hundreds of endpoints, including the CSGs and ASGs. 15 PseudoWire 6 Enabling Technologies 6.6.5.4.2 Multiservice Support No transport network is useful if it can't transport the required client traffic types. Ethernet carries a wide variety of traffic types via Ethertype marking, or logical link control (LLC), but does not natively transport TDM, which requires pseudowire extensions (MEF-8). IP carries different traffic types either directly (via the protocol number or "next header" field) or via la