RAN application, is what is called an asynchronous network, meaning that the nodes do not need to share a common frequency for the network itself to work-instead, each node can operate up to 50 ppm more off nominal, allowing low-cost crystals to be used in equipment. This also means that there is not any guaranteed relationship between the frequency that was used to clock the datastream into a switch and that which is used to clock it out, as shown in Fig. 8-9. Most Ethernet switches use a store-and-forward strategy that means they will wait for a complete 276 Open Radio Access Network (O-RAN) Systems Architecture and Design Clock and Recovery Clock Embedded clock flows from Tx to Rx FIGURE 8-8 Asynchronous Ethernet clocking. Rx Port Tx Port Rx Port Tx Port No requirement for these Elastic buffer handles frequencies to match rate mismatch FIGURE 8-9 Ethernet rate mismatch. data frame to be received before starting to send it out. This allows for the potential differ- ence in transmitting and receiving rate without data loss. However, there is nothing in the Ethernet standards that specify where the transmit clock comes from-just what error it is allowed to have. Specifically, there is nothing stopping one from taking the clock that the receiver recovers from the incoming datastream, cleaning it up with a bit of filtering, and using that as the transmit clock. This allows a frequency to propa- gated across the network, from the master, through a number of switches and finally to the slave nodes, as shown in Fig. 8-10. This is the technique used by Synchronous Ethernet, though more commonly abbreviated to SyncE, which is defined by ITU-T in the recommendations (standards) G.8262 (timing characteristics of a synchronous equipment slave clock) and G.8262.1 (timing characteristics of an enhanced synchronous equipment slave clock). As the titles suggest, G.8262.1 deals with an improved, second generation, version of Synchronous Ethernet. Note that ITU-T uses the term "clock" to refer to a piece of equipment, or a funct