Editing Fiber Distributed Data Interface

{{Short description|Standard for data transmission in a local area network}}
{{Redirect|FDDI|the Indian educational institute|Footwear Design and Development Institute}}
{{Use American English|date=March 2021}}
{{Use mdy dates|date=March 2021}}
[[Image:Sbus-das-fddi.jpg|thumb|Dual-attach FDDI board for [[SBus]]]]
[[File:DEC VAX XMI T2027 DEMFA FDDI Controller.jpg|thumb|Single-attach FDDI controller for [[VAX 6000|XMI]] bus (PHY is on a separate bulkhead module).]]

'''Fiber Distributed Data Interface''' ('''FDDI''') is a standard for [[data transmission]] in a [[local area network]].
It uses [[optical fiber]] as its standard underlying physical medium.

It was also later specified to use [[copper]] cable, in which case it may be called '''CDDI''' (Copper Distributed Data Interface), standardized as '''TP-PMD''' (Twisted-Pair Physical Medium-Dependent), also referred to as TP-DDI (Twisted-Pair Distributed Data Interface).

FDDI was effectively made obsolete in local networks by [[Fast Ethernet]] which offered the same 100&nbsp;Mbit/s speeds, but at a much lower cost and, from 1998 on, by [[Gigabit Ethernet]] due to its speed, even lower cost, and ubiquity.<ref name=":0" />

==Description==
FDDI provides a 100&nbsp;[[Mbit/s]] optical standard for [[data transmission]] in [[local area network]] that can extend in length up to {{convert|200|km|mi|sp=us}}.<ref>ANSI X3.263-1995</ref> Although FDDI logical topology is a ring-based token network, it did not use the IEEE 802.5 [[Token Ring]] [[Communications protocol|protocol]] as its basis; instead, its protocol was derived from the IEEE 802.4 [[token bus]] ''timed token'' protocol. In addition to covering large geographical areas, FDDI local area networks can support thousands of users.  FDDI offers both a Dual-Attached Station (DAS), counter-rotating token ring topology and a Single-Attached Station (SAS), token bus passing ring topology.<ref>{{Cite book |title= FDDI and FDDI-II: architecture, protocols, and performance |author1=Bernhard Albert |author2=Anura P. Jayasumana |publisher= Artech House |year= 1994 |isbn= 978-0-89006-633-1}}</ref>

FDDI, as a product of [[American National Standards Institute]] X3T9.5 (now X3T12), conforms to the [[OSI model|Open Systems Interconnection]] (OSI) model of functional layering using other protocols. The standards process started in the mid 1980s.<ref>{{Cite journal |title= FDDI - A tutorial |author= Floyd Ross |journal=  Communications Magazine |publisher= IEEE Communications Society |doi= 10.1109/MCOM.1986.1093085 |pages= 10–17 |date= May 1986 |volume= 24 |number= 5|s2cid= 6989611 }}</ref>
FDDI-II, a version of FDDI described in 1989, added [[circuit switching|circuit-switched service]] capability to the network so that it could also handle voice and [[video]] signals.<ref>{{Cite book |author= Michael Teener and R. Gvozdanovic |title= &#91;1989&#93; Proceedings. 14th Conference on Local Computer Networks |chapter= FDDI-II operation and architectures |publisher= IEEE |doi= 10.1109/LCN.1989.65243 |isbn= 0-8186-1968-6 |pages= 49–61 |date= October 10, 1989 |s2cid= 29459918 }}</ref> Work started to connect FDDI networks to [[synchronous optical networking]] (SONET) technology.

An FDDI network contains two rings, one as a secondary backup in case the primary ring fails. The primary ring offers up to 100&nbsp;Mbit/s capacity. When a network has no requirement for the secondary ring to do backup, it can also carry data, extending capacity to 200&nbsp;Mbit/s. The single ring can extend the maximum distance; a dual ring can extend {{convert|100|km|mi|abbr=on}}. FDDI had a larger maximum frame size (4,352 bytes) than the standard [[Ethernet]] family, which only supports a maximum frame size of 1,500 bytes,{{efn|[[Jumbo frame]]s can be used to extend Ethernet's maximum frame size to 9,000 bytes or more.}} allowing better effective data rates in some cases.

==Topology==
Designers normally constructed FDDI rings in a [[network topology]] such as a "dual ring of trees". A small number of devices, typically infrastructure devices such as [[router (computing)|router]]s and concentrators rather than host computers, were "dual-attached" to both rings. Host computers then connect as single-attached devices to the routers or concentrators. The dual ring in its most degenerate form simply collapses into a single device. Typically, a computer-room contained the whole dual ring, although some implementations deployed FDDI as a [[metropolitan area network]].<ref>{{Cite journal |title= FDDI-II: A High Speed Integrated Service LAN |author= T. Boston |journal= Sixth European Fibre Optic Communications and Local Area Networks Exposition |publisher= Information Gatekeepers |isbn= 978-1-56851-055-2 |pages= 123–126 |date= June 29, 1988 }} Reprinted in Fiber Optic Metropolitan Area Networks (MANs) 1984-1991</ref>

FDDI requires this network topology because the dual ring actually passes through each connected device and requires each such device to remain continuously operational.
The standard actually allows for optical bypasses, but network engineers consider these unreliable and error-prone. Devices such as workstations and minicomputers that might not come under the control of the network managers are not suitable for connection to the dual ring.

As an alternative to using a dual-attached connection, a workstation can obtain the same degree of [[Resilience (network)|resilience]] through a dual-homed connection made simultaneously to two separate devices in the same FDDI ring. One of the connections becomes active while the other one is automatically blocked. If the first connection fails, the backup link takes over with no perceptible delay.<ref>{{foldoc|Fiber+Distributed+Data+Interface}}</ref>
{{IPstack}}

== Frame format ==
{| class="wikitable"
|+ FDDI data frame format<ref>{{cite web |author=Wolfgang Schulte |title=Fiber Distributed Data Interface |url=https://wwwlehre.dhbw-stuttgart.de/~schulte/htme/55773.htm |access-date=2021-04-20}}</ref>
|-
! Preamble, PA
| 16 bits
|-
! Start delimiter, SD
| 8 bits
|-
! Frame control, FC
| 8 bits
|-
! Destination address, DA
| 48 bits
|-
! Source address, SA
| 48 bits
|-
! Protocol (or packet) data unit, PDU
| Up to 4478 × 8 bits
|-
! Frame check sequence, FCS
| 32 bits
|-
! End delimiter/frame status, ED/FS
| 16 bits
|}

The frame check sequence uses the same [[cyclic redundancy check]] as [[Token Ring]] and [[Ethernet]].

The [[Internet Engineering Task Force]] defined a standard for transmission of the [[Internet Protocol]] (which would be the protocol data unit in this case) over FDDI. It was first proposed in June 1989<ref>{{Cite journal |title= A Proposed Standard for the Transmission of IP Datagrams over FDDI Networks |journal= RFC 1103 |author= Dave Katz  |publisher= IETF |date= June 1989 |doi= 10.17487/RFC1103 |url= http://tools.ietf.org/html/rfc1103 |access-date= August 15, 2013 |doi-access= free }}</ref> and revised in 1990.<ref name="rfc">{{Cite journal |title= A Proposed Standard for the Transmission of IP Datagrams over FDDI Networks |journal= RFC 1183 |author= Dave Katz  |publisher= IETF |date= June 1989 |doi= 10.17487/RFC1188 |url= http://tools.ietf.org/html/rfc1188 |access-date= August 15, 2013 |doi-access= free }}</ref> Some aspects of the protocol were compatible with the [[IEEE 802.2]] standard for [[logical link control]]. For example, the 48-bit [[MAC address]]es that became popular with the Ethernet family. Thus other protocols such as the [[Address Resolution Protocol]] (ARP) could be common as well.<ref name="rfc" />

==Deployment==
FDDI was considered an attractive campus [[backbone network]] technology in the early to mid 1990s since existing Ethernet networks only offered 10&nbsp;Mbit/s data rates and Token Ring networks only offered 4&nbsp;Mbit/s or 16&nbsp;Mbit/s rates. Thus it was a relatively high-speed choice of that era, with speeds such as 100&nbsp;Mbit/s.
By 1994, vendors included [[Cisco Systems]], [[National Semiconductor]], Network Peripherals, SysKonnect (acquired by [[Marvell Technology Group]]), and [[3Com]].<ref>{{Cite news |title= Wading Through Plethora of Options Poses Challenge for Life on the Fast LAN |work= Network World |pages= 41, 44, 46–49 |author= Mark Miller |date= March 21, 1994 |url= https://books.google.com/books?id=eA0EAAAAMBAJ&pg=PA47 |access-date= August 15, 2013 }}</ref>

FDDI installations have largely been replaced by Ethernet deployments.<ref name=":0">{{Cite book |title= Optical Fiber Communication: Principles and Systems |pages= 241–249 |author=A. Selvarajan |author2=Subrat Kar |author3=T. Srinivas |publisher= Tata McGraw-Hill Education |year=2003 |url= https://books.google.com/books?id=uyBSO4hf6DYC&pg=PA241 |isbn= 978-1-259-08220-7 }}</ref>

==Standards==
FDDI standards included:<ref>{{Cite web |title= fiber distributed data interface (FDDI) |url= http://www.its.bldrdoc.gov/fs-1037/dir-015/_2208.htm |date= August 7, 1996 |work= Telecommunications: Glossary of Telecommunication Terms, Federal Standard 1037C |publisher= National Communications System of the US Department of Defense |access-date= August 15, 2013 |archive-url= https://web.archive.org/web/20160304113113/http://www.its.bldrdoc.gov/fs-1037/dir-015/_2208.htm |archive-date= March 4, 2016 }}</ref>
* ANSI X3.139-1987, Media Access Control (MAC) — also ISO 9314-2
* ANSI X3.148-1988, Physical Layer Protocol (PHY) — also ISO 9314-1
* ANSI X3.166-1989, Physical Medium Dependent (PMD) — also ISO 9314-3
* ANSI X3.184-1993, Single Mode Fiber Physical Medium Dependent (SMF-PMD) — also ISO 9314-4
* ANSI X3.229-1994, Station Management (SMT) — also ISO 9314-6
* ANSI X3.263-1995, Twisted Pair Physical Medium Dependent (TP-PMD)

==Notes==
{{Notelist}}

==References==
{{Reflist}}

{{ISO standards}}
{{Authority control}}

[[Category:Computer network technology]]
[[Category:Local area networks]]
[[Category:Link protocols]]
[[Category:ISO standards]]