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{{Short description|Computer networking protocol}}

In [[telecommunications]], '''Advanced Data Communication Control Procedures''' (or '''Protocol''') ('''ADCCP''') is a [[Bit-oriented protocol|bit-oriented]] [[data link layer]] [[Communication protocol|protocol]] developed by the [[American National Standards Institute]]. It is functionally equivalent to the ISO [[High-Level Data Link Control]] (HDLC) protocol.<ref>{{harvnb|Friend|Fike|Baker|Bellamy|1988|p=191}}</ref>

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.<ref>{{harvnb|NBS|1980|p=6|loc=§3.0 ADCCP classes of procedures}}</ref>

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,<ref>{{harvnb|ISO|1984|p=18|loc=§7.4 Extended control field formats}}</ref> ADCCP specifies a 2-byte control field format with the P/F flag duplicated.<ref>{{harvnb|ANSI|1979|p=28|loc=§5.2.2 Extended control field}}</ref> Later HDLC specifications, in particular ISO/IEC 13239, changed that to specify that U frames have 1-byte control fields in all cases.

{| class="wikitable" style="text-align:center"
|+ADCCP control fields
!colspan=8| First byte ||colspan=8| Second byte ||rowspan=2| Description
|-
! 0 || 1 || 2 || 3 || 4 || 5 || 6 || 7
! 0 || 1 || 2 || 3 || 4 || 5 || 6 || 7
|-
| 0 ||colspan=3| N(S) || P/F ||colspan=3| N(R) ||colspan=8 rowspan=3 bgcolor=lightgrey| ||align=left| I frame, N(S) is a 3-bit send sequence number
|-
| 1 || 0 ||colspan=2| type || P/F ||colspan=3| N(R) ||align=left| S frame, N(R) is a 3-bit receive sequence number
|-
| 1 || 1 ||colspan=2| type || P/F ||colspan=3| type ||align=left| U frame
|-
| 0 ||colspan=7| N(S) || P/F ||colspan=7| N(R) ||align=left| Extended I frame, N(S) is a 7-bit sequence number
|-
| 1 || 0 ||colspan=2| type ||colspan=4 bgcolor=lightgrey| —0— || P/F ||colspan=7| N(R) ||align=left| Extended S frame, N(R) is a 7-bit sequence number
|-
| 1 || 1 ||colspan=2| type || P/F ||colspan=3| type || P/F ||colspan=7 bgcolor=lightgrey| —0— ||align=left| Extended U frame (ADCCP only)
|}

==See also==
* [[Data link layer]]
* [[High-Level Data Link Control]]
* [[Self-synchronizing code]]

==References==
{{Reflist}}

*{{cite book
|last1=Friend
|first1=George E.
|first2=John L.
|last2=Fike
|first3=H. Charles
|last3=Baker
|first4=John C.
|last4=Bellamy
|title=Understanding Data Communications
|edition=2nd
|year=1988
|publisher=Howard W. Sams & Company
|location=Indianapolis
|isbn=0-672-27270-9
}}
*{{cite book
|title=Guideline for implementing advanced data communication control procedures (ADCCP)
|publisher=National Bureau of Standards
|date=26 September 1980
|id=FIPS PUB 78
|ref={{harvid|NBS|1980}}
|url=https://archive.org/details/federalinformati78nati
}}
*{{cite book
|title=ISO 4335:1984 Data Communication—High Level Data Link Control Procedures—Consolidation of Elements of Procedures
|ref={{harvid|ISO|1984}}
|url=https://law.resource.org/pub/in/bis/S04/is.11418.2.1986.pdf
|archive-url=https://web.archive.org/web/20190323134103/https://law.resource.org/pub/in/bis/S04/is.11418.2.1986.pdf
|archive-date=23 March 2019
|url-status=live
}} [https://archive.org/details/gov.in.is.11418.2.1986 Alt URL]
*{{cite book
|title=ANSI X3.66-1979: American National Standard for advanced data communication procedures (ADCCP)
|publisher=[[American National Standards Institute]]
|date=9 January 1979
|id=FIPS PUB 71-1980
|url=https://archive.org/details/federalinformati7119nati
|ref={{sfnRef|ANSI|1979}}
}}
* {{FS1037C}}

[[Category:Link protocols]]

Advanced Data Communication Control Procedures - Revision history

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