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Two-binary, one-quaternary (2B1Q) is a line code used in the U interface of the Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) and the high-bit-rate digital subscriber line (HDSL). [1] 2B1Q is a four-level pulse-amplitude modulation (PAM-4) scheme without redundancy, mapping two bits (2B) into one quaternary symbol (1Q).
Through the use of 2B1Q encoding, two bits are combined to one symbol, further reducing the symbol rate by a factor of two. For this two-pair 2B1Q variant of HDSL, framing increases the bitrate from 1.544 Mbit/s to 1.568 Mbit/s, resulting in a symbol rate of 392 kilobaud and a Nyquist frequency of 196 kHz.
2B1Q coding is defined in Appendix II of G.961, [9] ANSI T1.601, [7] and Annex A of ETR 080. [8] It can operate at distances up to about 18,000 feet ( 5.5 km ) with loss up to 42 dB . An internal termination impedance of 135 ohms is presented to the line at each end of the U-interface.
Security - information and systems are protected against unauthorized access and disclosure, and damage to the system that could compromise the availability, confidentiality, integrity and privacy of the system. Firewalls; Intrusion detection; Multi-factor authentication; Availability - information and systems are available for operational use.
Trellis-coded pulse-amplitude modulation (TC-PAM) is the modulation format that is used in HDSL2 and G.SHDSL.It is a variant of trellis coded modulation (TCM) which uses a one-dimensional pulse-amplitude modulation (PAM) symbol space, as opposed to a two-dimensional quadrature amplitude modulation (QAM) symbol space. [1]
Early disk drives used very simple encoding schemes, such as RLL (0,1) FM code, followed by RLL (1,3) MFM code which were widely used in hard disk drives until the mid-1980s and are still used in digital optical discs such as CD, DVD, MD, Hi-MD and Blu-ray using EFM and EFMPLus codes. [11]
In some related but distinct contexts, the term AAA has been used to refer to protocol-specific information. For example, Diameter uses the URI scheme AAA, which also stands for "Authentication, Authorization and Accounting", as well as the Diameter-based Protocol AAAS, which stands for "Authentication, Authorization and Accounting with Secure Transport". [4]
IAS 1 sets out the purpose of financial statements as the provision of useful information on the financial position, financial performance and cash flows of an entity, and categorizes the information provided into assets, liabilities, income and expenses, contributions by and distribution to owners, and cash flows.