ans- missions that are not time critical. Frame preemption is linked with another standard, IEEE 802.3br, "Specification and Management Parameters for Interspersing Express Traffic," which allows split- ting longer frames into smaller fragments when sharing a single physical link. This feature allows the interface to temporarily interrupt the transmission of a long frame and send out a time-critical express frame before resuming transmission of the long frame. The interrupted frame is reas- sembled at the other end of the link (so both ends of the link need to support this feature). Of course, this technique helps to reduce latency, especially where short, highly time-critical traffic is mixed with traffic using very long (jumbo) frames. As traffic interface speeds increase, the posit- ive gain from frame preemption and express interleaving tends to reduce because even jumbo frames transmit quickly at higher speeds (consider 1 GE versus 100 GE). In the 5G RAN, meeting deterministic jitter and latency requirements of the packet-based front-haul network is quite a challenge. For now, just know that front-haul is the name given to the transport network that delivers traffic over the last mile to the cell sites at the very edge of the mobile net- work. front-haul is covered in much more detail in several of the following chapters. For now, just understand that 5G has strict requirements for devices to support low latency and low PDV when used to build RAN front-haul networks. The TSN profile standard, IEEE 802.1CM, was defined to provide recommendations and specifica- tions of TSN and timing techniques to use in front-haul deployments based on Ethernet bridges. As discussed in the preceding section, another factor is that 5G Releases 15 and 16 define time-sensit- ive use cases for mobile, which further adds to the push for deterministic, low-latency transport net- works. Please refer to Chapter 10 for more details on the 5G front-haul network and timing and latency requirements for it. In summary, TSN builds foundati