http://www.rfc-editor.org/rfc/rfc5993.txt
RFC 5993: RTP Payload Format for Global System for Mobile Communications Half Rate (GSM-HR), X. Duan, S. Wang, M. Westerlund, K. Hellwig, I. Johansson2010-10-01T23:00:00-00:00This document specifies the payload format for packetization of Global System for Mobile Communications Half Rate (GSM-HR) speech codec data into the Real-time Transport Protocol (RTP). The payload format supports transmission of multiple frames per payload and packet loss robustness methods using redundancy. [STANDARDS-TRACK]