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30-699: Single density (SD or 1D) describes the first generation of floppy disks that use an iron oxide coating. Floppy drives utilize 300-oersted write heads, FM encoding , and a track width of 0.330 mm (0.0130 in) for a density of 48 tracks-per-inch (tpi) and 5,876 bits-per-inch (bpi). Double density (DD or 2D) doubles capacity over SD by replacing FM encoding with an improved line code , such as modified frequency modulation (MFM), modified modified frequency modulation (M²FM), FM/MFM or group coded recording (GCR). SD ( 1D ) and DD ( 2D ) designations were generally identical to those of 8-inch disks. Quad density (QD or 4D) doubles capacity over DD by narrowing

60-602: A 16 Mbit/s version that ran on unshielded twisted pair cable. IBM launched their own proprietary Token Ring product on October 15, 1985. It ran at 4 Mbit/s , and attachment was possible from IBM PCs, midrange computers and mainframes. It used a convenient star-wired physical topology and ran over shielded twisted-pair cabling. Shortly thereafter it became the basis for the IEEE 802.5 standard. During this time, IBM argued that Token Ring LANs were superior to Ethernet , especially under load, but these claims were debated. In 1988,

90-705: A token passing ring topology , and many teams worldwide began working on their own implementations. At the IBM Zurich Research Laboratory Werner Bux and Hans Müller, in particular, worked on the design and development of IBM's Token Ring technology, while early work at MIT led to the Proteon 10 Mbit/s ProNet-10 Token Ring network in 1981  – the same year that workstation vendor Apollo Computer introduced their proprietary 12 Mbit/s Apollo Token Ring (ATR) network running over 75-ohm RG-6U coaxial cabling . Proteon later evolved

120-538: A 'concentration' configuration by default, but later MAUs also supporting a feature to act as splitters and not concentrators exclusively such as on the IBM 8226. Later IBM would release Controlled Access Units that could support multiple MAU modules known as a Lobe Attachment Module . The CAUs supported features such as Dual-Ring Redundancy for alternate routing in the event of a dead port, modular concentration with LAMs, and multiple interfaces like most later MAUs. This offered

150-418: A Token Ring network is wired as a star , with 'MAUs' in the center, 'arms' out to each station, and the loop going out-and-back through each. A MAU could present in the form of a hub or a switch; since Token Ring had no collisions many MAUs were manufactured as hubs. Although Token Ring runs on LLC , it includes source routing to forward packets beyond the local network. The majority of MAUs are configured in

180-412: A density of 135 tpi and 8,717 bpi. High density (HD) 3½-inch disks switch to a cobalt disk coating, just as with 5¼-inch HD disks. Drives use 700-oersted write heads for a density of 17,434 bpi. Extra-high density (ED) doubles the capacity over HD by using a barium ferrite coating and a special write head that allows the use of perpendicular recording . Triple density (TD) triples

210-430: A disk. High density (HD) improves capacity by utilizing a 96 tpi track density in conjunction with improved cobalt disk coating and stronger 600-oersted write heads, allowing 9,646 bpi to be written. Double density (DD) 3½-inch disks use an iron oxide coating, just as with 5¼-inch DD/QD disks. However, drives utilize stronger 670-oersted write heads and a narrower track width of 0.115 mm (0.0045 in) for

240-463: A more reliable setup and remote management than with an unmanaged MAU hub. Cabling is generally IBM "Type-1", a heavy two-pair 150 ohm shielded twisted pair cable. This was the basic cable for the "IBM Cabling System", a structured cabling system that IBM hoped would be widely adopted. Unique hermaphroditic connectors , referred to as IBM Data Connectors in formal writing or colloquially as Boy George connectors, were used. The connectors have

270-434: A presence or absence of signal level transition in the middle of the bit period, followed by the mandatory level transition at the beginning. The code is insensitive to an inversion of polarity. In various specific applications, this method is also called by various other names, including biphase mark code ( CC ), F2F (frequency/double frequency), Aiken biphase , and conditioned diphase . Differential Manchester encoding

300-436: A shared transmission medium. They differed in their channel access methods . These differences have become immaterial, as modern Ethernet networks consist of switches and point-to-point links operating in full-duplex mode. Token Ring and legacy Ethernet have some notable differences: Stations on a Token Ring LAN are logically organized in a ring topology with data being transmitted sequentially from one ring station to

330-450: A standby monitor. All stations must be capable of becoming an active monitor station if necessary. The active monitor performs a number of ring administration functions. The first function is to operate as the master clock for the ring in order to provide synchronization of the signal for stations on the wire. Another function of the AM is to insert a 24-bit delay into the ring, to ensure that there

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360-545: A start delimiter, an access control octet, and an end delimiter. Used by the sending station to abort transmission. Data frames carry information for upper-layer protocols, while command frames contain control information and have no data for upper-layer protocols. Data and command frames vary in size, depending on the size of the Information field. Frame type – 01 indicates LLC frame IEEE 802.2 (data) and ignore control bits; 00 indicates MAC frame and control bits indicate

390-473: Is a differential encoding technology, using the presence or absence of transitions to indicate logical value . An improvement to Manchester coding which is a special case of binary phase-shift keying , it is not necessary to know the initial polarity of the transmitted message signal, because the information is not represented by the absolute voltage levels but by their transitions. There are two clock ticks per bit period (marked with full and dotted lines in

420-416: Is a physical and data link layer computer networking technology used to build local area networks . It was introduced by IBM in 1984, and standardized in 1989 as IEEE 802.5 . It uses a special three-byte frame called a token that is passed around a logical ring of workstations or servers . This token passing is a channel access method providing fair access for all stations, and eliminating

450-407: Is always sufficient buffering in the ring for the token to circulate. A third function for the AM is to ensure that exactly one token circulates whenever there is no frame being transmitted, and to detect a broken ring. Lastly, the AM is responsible for removing circulating frames from the ring. Token Ring stations must go through a 5-phase ring insertion process before being allowed to participate in

480-484: The ISO/IEC 7811 standard. Differential Manchester encoding is also the original modulation method used for single-density floppy disks , followed by double-density modified frequency modulation (MFM). [REDACTED]  This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from the original on 2022-01-22. IEEE 802.5 Token Ring

510-469: The collisions of contention -based access methods. Token Ring was a successful technology, particularly in corporate environments, but was gradually eclipsed by the later versions of Ethernet . Gigabit Token Ring was standardized in 2001. A wide range of different local area network technologies were developed in the early 1970s, of which one, the Cambridge Ring , had demonstrated the potential of

540-472: The Token Ring priority MAC, eight priority levels, 0–7, are used. When the station wishing to transmit receives a token or data frame with a priority less than or equal to the station's requested priority, it sets the priority bits to its desired priority. The station does not immediately transmit; the token circulates around the medium until it returns to the station. Upon sending and receiving its own data frame,

570-425: The above conditions take place and a station decides that a new monitor is needed, it will transmit a claim token frame, announcing that it wants to become the new monitor. If that token returns to the sender, it is OK for it to become the monitor. If some other station tries to become the monitor at the same time then the station with the highest MAC address will win the election process. Every other station becomes

600-401: The capacity over ED by tripling the track density and improving other parameters. The drives used longitudinal recording . Differential Manchester encoding Differential Manchester encoding ( DM ) is a line code in digital frequency modulation in which data and clock signals are combined to form a single two-level self- synchronizing data stream . Each data bit is encoded by

630-468: The disadvantage of being quite bulky, requiring at least 3 cm × 3 cm (1.2 in × 1.2 in) panel space, and being relatively fragile. The advantages of the connectors being that they are genderless and have superior shielding over standard unshielded 8P8C. Connectors at the computer were usually DE-9 female. Several other types of cable existed such as type 2, and type 3 cable. In later implementations of Token Ring, Cat 4 cabling

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660-594: The expense of doubling the clock frequency of the encoded data stream. Differential Manchester encoding is specified in the IEEE 802.5 standard for Token Ring local area networks, and is used for many other applications, including magnetic and optical storage. As Biphase Mark Code (BMC), it is used in AES3 , S/PDIF , SMPTE time code , USB PD , xDSL and DALI . Many magnetic stripe cards also use BMC encoding, often called F2F (frequency/double frequency) or Aiken Biphase, according to

690-473: The faster 16 Mbit/s Token Ring was standardized by the 802.5 working group. An increase to 100 Mbit/s was standardized and marketed during the wane of Token Ring's existence and was never widely used. While a 1000 Mbit/s standard was approved in 2001, no products were ever brought to market and standards activity came to a standstill as Fast Ethernet and Gigabit Ethernet dominated the local area networking market. Early Ethernet and Token Ring both used

720-458: The figure). At every second clock tick, marked with a dotted line, there is a potential level transition conditional on the data. At the other ticks, the line state changes unconditionally to ease clock recovery. One version of the code makes a transition for 0 and no transition for 1; the other makes a transition for 1 and no transition for 0. Differential Manchester encoding has the following advantages: These positive features are achieved at

750-500: The next with a control token circulating around the ring controlling access. Similar token passing mechanisms are used by ARCNET , token bus , 100VG-AnyLAN (802.12) and FDDI , and they have theoretical advantages over the CSMA/CD of early Ethernet. A Token Ring network can be modeled as a polling system where a single server provides service to queues in a cyclic order. The data transmission process goes as follows: Physically,

780-455: The ring network. If any of these phases fail, the Token Ring station will not insert into the ring and the Token Ring driver may report an error. In some applications there is an advantage to being able to designate one station having a higher priority. Token Ring specifies an optional scheme of this sort, as does the CAN Bus , (widely used in automotive applications) – but Ethernet does not. In

810-597: The station downgrades the token priority back to the original priority. Here are the following eight access priority and traffic types for devices that support 802.1Q and 802.1p : Bridging solutions for Token Ring and Ethernet networks included the AT&;T StarWAN 10:4 Bridge, the IBM 8209 LAN Bridge and the Microcom LAN Bridge. Alternative connection solutions incorporated a router that could be configured to dynamically filter traffic, protocols and interfaces, such as

840-417: The type of MAC control frame A = 1, Address recognized C = 1, Frame copied Every station in a Token Ring network is either an active monitor (AM) or standby monitor (SM) station. There can be only one active monitor on a ring at a time. The active monitor is chosen through an election or monitor contention process. The monitor contention process is initiated when the following happens: When any of

870-478: The width of tracks to 0.160 mm (0.0063 in) for a density of 96 tpi. Some manufacturers ( Micropolis , Tandon , Micro Peripherals (MPI), Teac ) used a track density of 100 tpi for quad-density drives, which were incompatible with 96 tpi models. The Commodore 8050 and 8250 are rare instances of drives that used 375 kbit/s GCR code instead of the usual 250 kbit/s double-density format and they could store roughly 500 kilobytes on one side of

900-474: Was also supported, so 8P8C (RJ45) connectors were used on both of the MAUs, CAUs and NICs; with many of the network cards supporting both 8P8C and DE-9 for backwards compatibility. When no station is sending a frame, a special token frame circles the loop. This special token frame is repeated from station to station until arriving at a station that needs to send data. Tokens are three octets in length and consist of

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