Editing Media access unit

{{Short description|Token Ring network hub}}
{{redirect|MSAU|the settlement in the Coast Province|Msau}}
{{Distinguish|Medium Attachment Unit}}

[[File:IBM 8228 Multistation Access Unit.JPG|thumb|An IBM 8228 Multistation Access Unit with accompanying Setup Aid]]
[[File:TokenRingLogicalNetwork.svg|thumb|Data flow though a 3-station Token Ring network built using a single MAU]]

A '''media access unit''' ('''MAU'''), also known as a '''multistation access unit''' ('''MAU''' or '''MSAU'''), is a device to attach multiple network stations in a  [[Ring network|ring topology]]  when the cabling is done in a [[Star network|star topology]] as a [[Token Ring]] network, internally wired to connect the stations into a logical ring (generally passive i.e. non-switched and unmanaged; however managed Token Ring MAUs do exist in the form of CAUs, or Controlled Access Units).<ref>http://ps-2.kev009.com/ohlandl/books/TR_Networks_Intro_Planning_Guide_Chpt1.pdf {{Bare URL PDF|date=March 2022}}</ref>

Passive Token Ring was an active IBM networking product in the 1997 time frame, after which it was rapidly displaced by [[switched network]]ing.

==Advantages and disadvantages==

===Passive networking without power===
[[File:8228 setup aid.JPG|thumb|An IBM 8228 Setup Aid opened exposing the battery]]
[[File:8226 relays.JPG|thumb|Relays found on the 8226 MAU circuit board]]
The majority of IBM-implemented (actual) passive Token Ring MAUs operated without the requirement of power; instead the passive MAU used a series of relays that adjusted themselves as data is passed through: this is also why Token Ring generally used relays to terminate disconnected or failed ports. The power-less IBM 8228 Multistation Access Unit requires a special 'Setup Aid' tool to re-align the relays after the unit has been moved which causes them to be in incorrect states: this is accomplished by a 9v battery sending a charge to snap the relays back in a proper state.<ref>{{Cite web|url=http://www.mcamafia.de/mcapage0/8228tool.htm|title = IBM 8228 Setup Aid}}</ref> The advantages of having a MAU operate without power is that they can be placed in areas without outlets, the disadvantage is that they must be primed each time the internal relays experience excessive force. The IBM 8226 MAU, while containing a power jack, primarily uses this for the LEDs: relays are still used inside the unit but do not require priming.<ref>{{cite web |url=ftp://public.dhe.ibm.com/networking/nswww/neteam/998pg/c822602.pdf |archive-url=https://web.archive.org/web/20200616170934/ftp://public.dhe.ibm.com/networking/nswww/neteam/998pg/c822602.pdf |archive-date=2020-06-16 |url-status=dead |title=FTP link |work=public.dhe.ibm.com }}</ref>

===Bandwidth===
In theory, this networking technology supported large geographic areas (with a total ring circumference of several kilometers).  But with the bandwidth shared by all stations, in practice separate networks spanning smaller areas were joined using [[Source route bridging|bridges]].  This bridged network technology was soon displaced by high-bandwidth switched networks.<ref>{{cite web|url=http://www.raleigh.ibm.com/trl/trl0c01.ps |title=Token-Ring Migration to Switched LAN Interconnect — A Technical White Paper |author=IBM |date=1997 |url-status=dead |archiveurl=https://web.archive.org/web/19970111021530/http://www.raleigh.ibm.com/trl/trl0c01.ps |archivedate=January 11, 1997 }}</ref>

==Fault tolerance==
Multistation Access Units contain relays to short out non-operating stations. Multiple MAUs can be connected into a larger ring through their ring in/ring out connectors.<ref>{{foldoc|Media+access+unit}}</ref><ref>{{cite web|url=ftp://service.boulder.ibm.com/networking/nswww/neteam/int_hubs.pdf|title=LAN Hub Sales Guide|author=IBM|archive-url=https://web.archive.org/web/20200616170933/ftp://service.boulder.ibm.com/networking/nswww/neteam/int_hubs.pdf|archive-date=2020-06-16|url-status=dead|date=1997}}</ref>

An MAU is also called a "ring in a box". The loop that used to make up the ring of the token Ring is now integrated into this device. In Token Ring, when a link is broken in the ring, the entire network goes down; however with an MAU, the broken circuit is closed within 1ms; allowing stations on the ring to have their cords unplugged without disabling the entire network.

==See also==
*[[Lobe Attachment Module]]

==References==
{{Reflist}}

==External links==
*{{Commons category-inline|Media access unit}}

[[Category:Networking hardware]]