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This is a personal recollection on the Move fire on May 13, 1985
In telecommunications, Advanced Data Communication Control Procedures (or Protocol) (ADCCP) is a bit-oriented data link layer protocol developed by the American National Standards Institute. It is functionally equivalent to the ISO High-Level Data Link Control (HDLC) protocol.[1]
Although the ISO and ANSI standards writers coordinated their work, so the differences between the standards are mainly editorial, there is one meaningful difference: ADCCP's definition of the basic subset required to implement balanced asynchronous mode includes the RSET frame, while HDLC makes it optional.[2]
One major difference between the two is the unnumbered (U) format. When extended (7-bit) sequence numbers are used, I and S frames have two-byte control fields. Like early versions of HDLC,[3] ADCCP specifies a 2-byte control field format with the P/F flag duplicated.[4] Later HDLC specifications, in particular ISO/IEC 13239, changed that to specify that U frames have 1-byte control fields in all cases.
| First byte | Second byte | Description | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
| 0 | N(S) | P/F | N(R) | I frame, N(S) is a 3-bit send sequence number | ||||||||||||
| 1 | 0 | type | P/F | N(R) | S frame, N(R) is a 3-bit receive sequence number | |||||||||||
| 1 | 1 | type | P/F | type | U frame | |||||||||||
| 0 | N(S) | P/F | N(R) | Extended I frame, N(S) is a 7-bit sequence number | ||||||||||||
| 1 | 0 | type | —0— | P/F | N(R) | Extended S frame, N(R) is a 7-bit sequence number | ||||||||||
| 1 | 1 | type | P/F | type | P/F | —0— | Extended U frame (ADCCP only) | |||||||||
This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22.Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
High-Level Data Link Control (HDLC) is a communication protocol used for transmitting data between devices in telecommunication and networking. Developed by the International Organization for Standardization (ISO), it is defined in the standard ISO/IEC 13239:2002. HDLC ensures reliable data transfer, allowing one device to understand data sent by another. It can operate with or without a continuous connection between devices, making it versatile for various network configurations. Originally, HDLC was used in multi-device networks, where one device acted as the master and others as slaves, through modes like Normal Response Mode (NRM) and Asynchronous Response Mode (ARM). These modes are now rarely used. Currently, HDLC is primarily employed in point-to-point connections, such as between routers or network interfaces, using a mode called Asynchronous Balanced Mode (ABM).
Synchronous Data Link Control (SDLC) is a computer serial communications protocol first introduced by IBM as part of its Systems Network Architecture (SNA). SDLC is used as layer 2, the data link layer, in the SNA protocol stack. It supports multipoint links as well as error correction. It also runs under the assumption that an SNA header is present after the SDLC header. SDLC was mainly used by IBM mainframe and midrange systems; however, implementations exist on many platforms from many vendors. In the United States and Canada, SDLC can be found in traffic control cabinets. SDLC was released in 1975, based on work done for IBM in the early 1970s. SDLC operates independently on each communications link in the network and can operate on point-to-point multipoint or loop facilities, on switched or dedicated, two-wire or four-wire circuits, and with full-duplex and half-duplex operation. A unique characteristic of SDLC is its ability to mix half-duplex secondary stations with full-duplex primary stations on four-wire circuits, thus reducing the cost of dedicated facilities. This de facto standard has been adopted by ISO as High-Level Data Link Control (HDLC) in 1979 and by ANSI as Advanced Data Communication Control Procedures (ADCCP). The latter standards added features such as the Asynchronous Balanced Mode, frame sizes that did not need to be multiples of bit-octets, but also removed some of the procedures and messages (such as the TEST message). Intel used SDLC as a base protocol for BITBUS, still popular in Europe as fieldbus and included support in several controllers (i8044/i8344, i80152). The 8044 controller is still in production by third-party vendors. Other vendors putting hardware support for SDLC (and the slightly different HDLC) into communication controller chips of the 1980s included Zilog, Motorola, and National Semiconductor. As a result, a wide variety of equipment in the 1980s used it and it was very common in the mainframe-centric corporate networks which were the norm in the 1980s. The most common alternatives for SNA with SDLC were probably DECnet with Digital Data Communications Message Protocol (DDCMP), Burroughs Network Architecture (BNA) with Burroughs Data Link Control (BDLC), and ARPANET with IMPs.
In telecommunications, Advanced Data Communication Control Procedures (or Protocol) (ADCCP) is a bit-oriented data link layer protocol developed by the American National Standards Institute. It is functionally equivalent to the ISO High-Level Data Link Control (HDLC) protocol. Although the ISO and ANSI standards writers coordinated their work, so the differences between the standards are mainly editorial, there is one meaningful difference: ADCCP's definition of the basic subset required to implement balanced asynchronous mode includes the RSET frame, while HDLC makes it optional. One major difference between the two is the unnumbered (U) format. When extended (7-bit) sequence numbers are used, I and S frames have two-byte control fields. Like early versions of HDLC, ADCCP specifies a 2-byte control field format with the P/F flag duplicated. Later HDLC specifications, in particular ISO/IEC 13239, changed that to specify that U frames have 1-byte control fields in all cases.
Link control may refer to: Data link layer, also known as data link control (DLC) High-Level Data Link Control (HDLC) Synchronous Data Link Control (SDLC)
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
