Download Lossless compression of G.711 pulse code modulation

Draft new Recommendation ITU-T G.711.0 (ex G.711-LLC)
Lossless compression of G.711 pulse code modulation
AAP Summary
ITU-T Recommendation G.711 is the benchmark standard for narrowband PSTN/GSTN telephony
encoding and has been so for many decades. Owing to its proven voice quality, ubiquity and utility,
G.711 continues to enjoy widespread use in today’s newer packet-based networks – even when
neither endpoint interfaces to a telephony network.
The rationale for continued use of G.711 over newer and more bandwidth-efficient coders is varied
according to use cases and can include: the desire to attain highest telephony voice quality, to
provide highest available linearity for effective network echo canceller/suppressor applications, to
provide for highest possible FAX/modem connect speeds, and the need for improved interworking
with accessibility devices (e.g., text telephony). Many of these use cases require G.711 without the
use of silence suppression.
To address these needs, G.711.0 (ex G.711-LLC) defines a lossless and stateless compression for
G.711 packet payloads typically used in IP networks. The stateless design does not allow for error
propagation, as the original G.711 payload can be recreated using only data contained in the
compressed payload. The lossless design allows for G.711.0 compression and decompression to be
applied multiple times on an end-to-end connection (multiple self-transcodings) with no
degradation of voice/audio quality.
G.711.0 may be used as a traditional codec with its use negotiated end-to-end. However, its lossless
and stateless design also allows its use as a compression mechanism on any link (or combination of
links) where G.711 has been negotiated end-to-end. In this case, explicit use of G.711.0 on any
intermediate link need not be signaled to or negotiated by the end systems.
G.711.0 accommodates both G.711 coding laws (µ-law and A-law) and frame lengths typically
used in IP networks (40, 80, 160, 240 and 320 samples). It is lossless for all possible G.711 packet
payloads.
G.711.0 has been designed to have low complexity (1.0 WMOPS average, less than 1.7 WMOPS
worst case) and low memory footprint (less than 5k octets RAM, 5k octets ROM, and 3.6k basic
operations) while effectively compressing the dominant use-case of G.711 encoding of zero-mean
acoustic signals (e.g., speech and audio).
The G.711.0 codec has been characterized to provide over 50% average compression in typical
service provider environments and over 65% in typical office environments. Overall compression is
primarily a function of the signal type and level, background noise level, and encoding law (µ-law
or A-law).
ITU-T G.711.0 contains as electronic attachments a reference ANSI-C source code and the
associated test vectors.