Packed Encoding Rules

Abstract: syntax notation one (ASN.1) describes the data structures of protocol messages. In the open-systems interconnection (OSI) standards, the manner in which the data values are encoded is negotiated at the start of communications. In principle, there can be several different ways to encode the data values. Until recently, however, there was only one OSI-standardized way to do so. This standard was the basic encoding rules (BER) for ASN.1. Almost all OSI application-layer standards have specified their protocol messages in ASN.1, as have several integrated services digital network (ISDN) signaling standards based on OSI protocols. All have mandated use of the BER for their encoding. Many commercial products are also available that encode and decode protocol messages, as specified in ASN.1, to and from BER-encoded bit streams. Experience with the BER has led to criticism of their efficiency, particularly for real-time applications. Thus, there has been a move to standardize alternative encoding schemes that address these efficiency concerns. This paper introduces the alternative encoding schemes and compares them to the BER. The distinguished encoding rules (DER), canonical encoding rules (CER), packed encoding rules (PER), and lightweight encoding rules (LWER) are the alternative encoding schemes discussed.