In most modern switched or hubbed
Ethernet over twisted pair systems, neither the MAU nor the AUI interfaces exist (apart, perhaps as notional entities for the purposes of thinking about layering the interface), and the
category 5 (CAT5) or better cable connects directly into an Ethernet socket on the host or router. For backwards compatibility with equipment which still had external AUI interfaces only, adapter-type MAUs with
10BASE2 or
10BASE-T connectors long remained available after the obsolescence of original vampire-tap MAUs, but even adapter-type MAUs have become very rare as of the 2020s.
Similar equipment
The original Ethernet's successor standard,
Fast Ethernet, introduced division onto
media access control (MAC) and physical (
PHY) layers connected with
media-independent interface (MII). Some early Fast Ethernet hardware had physical external MII connectors, functionally similar to AUI connector, but generally separate adaptors got obsoleted, see above. However, the tradition of using a separate low-level I/O device in networking has continued in fast
optical fiber network interfaces, where the
GBIC,
XENPAK,
XFP, and
enhanced small form-factor pluggable (SFP+) pluggable transceiver modules using the
XAUI interface play a similar role.
Provide the physical means for communication between local network data link entities.
It defines a physical interface that can be implemented independently among different manufacturers of hardware and achieve the intended level of compatibility when interconnected in a common local network.
Provide a communication channel capable of high bandwidth and low bit error ratio performance.
Provide for ease of installation and service.
Provide for high network availability (ability of a station to gain access to the medium and enable the data link connection in a timely fashion).
Enable relatively low-cost implementations.
MAU Characteristics
Enables coupling the Physical Layer Signalling (PLS) by way of the
AUI to the explicit baseband coaxial transmission system.
Supports message traffic at a data rate of 10, 100, or even 1000 Mbit/s.
Provides for driving up to 500m of coaxial trunk cable without the use of a repeater.
Permits the DTE to test the MAU and the medium itself.
Supports system configurations using the
CSMA/CD access mechanism defined with baseband signaling.
Supports bus topology interconnection.
Services provided by MAUs
Transmit.
Receive.
Collision detection and Loop-back functions direct transfer through the MAU.
It removes equipment from the network whenever it continuously transmits for periods significantly longer than required for a maximum-length packet, indicating a possible problem with the
NIC.
Signal quality error test.
The signal quality error test detects silent failures in the circuitry.
Link integrity functions
detects breaks in the wire pairs.
Both Signal quality error test and Link integrity functions assist in fault isolation.
Two modes of operation
Normal mode:
The MAU functions as a direct connection between the baseband medium and the
DTE. Data output from the
DTE is output to the coaxial trunk medium and all data on the coaxial trunk medium is input to the
DTE. This mode is the "normal" mode of operation for the intended message traffic between stations.
Monitor mode or Isolated mode:
The MAU functions as a receive-only connection between the baseband medium and the
DTE. Data output from the
DTE is suppressed and only data on the coaxial trunk medium is input to the
DTE. This mode is for observing message traffic.
MAU functional specifications
Transmit function
The ability to transmit serial data bit streams on the baseband medium from the local
DTE entity and to one or more remote
DTE entities on the same network.
Receive function
The ability to receive serial data bit streams over the baseband medium.
Collision Presence function
The ability to detect the presence of two or more stations concurrent transmissions.
Monitor function (Optional)
The ability to inhibit the normal transmit data stream to the medium at the same time the normal receive function and collision presence function remain operational.
The ability to automatically interrupt the transmit function and inhibit an abnormally long output data stream. It removes equipment from the network whenever it continuously transmits for periods significantly longer than required for a maximum-length packet, indicating a possible problem with the
NIC.