 be encoded and decoded by both the transmitting and receiving entity. The RRC proto- col specifies the use for Packed Encoding Rules. ASN.1 tools include parsers that parse human readable definitions of ASN.1 data struc- tures and convert them in computer readable definitions (e.g., C language data structures) as well as APIs to encode and decode to/from serialized bit streams. ASN.1 tools come in open- source and commercial-grade options. DiffServ Since the introduction of the Internet, its use has changed from purely data based to also accommodate voice, video, and time-critical data such as gaming. The early design of the Internet and the TCP/IP protocol did not accommodate the QoS mechanisms needed to sup- port this functionality. Hence, several protocols have been developed to give greater control over QoS in the Internet compared to the original IPv4 (RFC791) and IPv6 (RFC8200) stan- dards. Such mechanisms include Integrated Services, Multiprotocol Label Switching (MPLS), and the Differentiated Services (DiffServ) model. The DiffServ model is the most popular The word "services" defines several characteristics of packet or cell transmission in one direction in a network. Such characteristics can be throughput, delay, jitter, and packet loss. Why do we need differentiated services? Apart from what is explained above (accommo- dation of heterogenous application requirements and user expectations), it also gives the possibility to apply differentiated pricing, which is of course a very interesting feature for an operator. 98 Open Radio Access Network (O-RAN) Systems Architecture and Design In general, for describing QoS, the following functional blocks are used: Classification/marking This is the selection of a packet based on the contents of one or more fields in the header. Policing/shaping. A method of making sure that a traffic source does not transmit on a higher speed than allowed. Shaping the traffic means modifying it in such a way that the source-after shaping-complies with the preagreed traffic requ