Octet Encoding Rules

The Octet Encoding Rules (OER) are the fastest ASN.1 encoding rules.

OER, like PER, produces compact encodings by taking advantage of information present in the ASN.1 schema to limit the amount of information included in each encoded message. However, in contrast to PER, OER favors encoding/decoding speed and ease of implementation over compactness of the encodings. Unlike PER Aligned, OER is completely octet-oriented. Whereas in PER Aligned a fixed-size encoding occupying less than 8 bits may begin at any bit position within an octet and may end at any bit position within the same or another octet, in OER the encoding of every possible value of every ASN.1 type occupies a whole number of octets, and all the fields of the encoding are octet-aligned.

There are two versions of OER: Basic OER and Canonical OER. In Canonical OER, each possible value of a type is encoded in exactly one way. In Basic OER, in some cases there are two or more slightly different ways to encode the same value.

OER is used in Intelligent Transportation protocols and is highly suited for any protocol for which the speed of encoding/decoding is essential.

Example

Related Topics

• Packed Encoding Rules
• OER Implementation

---