Group 4 Protocols


Group 4 Protocols refer to a set of standards developed by International Telegraph and Telephone Consultative Committee (CCITT) for fax transmissions across digital lines, particularly integrated services digital network (ISDN). They were designed to send and receive high-quality faxes at a quick pace, even up to near-real-time transmission. However, these protocols are no longer widely used, as they have been largely replaced by more efficient Internet-based solutions.


Group 4 Protocols can be phonetically transcribed as: /ˈgruːp fɔːr ˈproʊtəˌkɔːlz/.

Key Takeaways

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  1. Group 4 Protocols are primarily designated for the use in sending facsimile transmissions over IP networks. They are highly reliable and efficient for transmitting facsimile data.
  2. They work on the basis of store-and-forward technology. Meaning, they save the entire data before it’s sent which makes it possible to make sure all the data is correct before it’s sent to its destination.
  3. The protocols ensure the efficient compression of data which results in faster transmission times and reduced network costs.



Group 4 Protocols, also known as Class 4 protocols, are a significant aspect of technology primarily due to the crucial role they play in the world of fax transmission over telecommunication networks. These protocols are standards created by the International Telecommunication Union (ITU), specifically dedicated to sending and receiving fax messages over Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN). The protocols ensure smooth interoperability between different manufacturers’ fax machines, contributing to a reliable and efficient transmission of data. The use of Group 4 Protocols paved the way for quicker and higher quality fax transmissions, driving productivity and information exchange in various sectors from business to healthcare.


Group 4 Protocols, part of the International Telecommunications Union Telecommunication Standardization Sector (ITU-T), mainly serve the purpose of facilitating the transmission of facsimile documents over Integrated Services Digital Network (ISDN) and Public Switched Telephone Network (PSTN). These protocols act as a roadmap by setting forth the standards that govern how data, specifically in facsimile form, should be processed, transmitted, and received. The development and implementation of these protocols have essentially streamlined the process for sending images, documents, and other fax materials between two different points over digital networks. The use of Group 4 protocols has paved the way for a more efficient, secure and faster transmission of facsimile data over networks, moving away from the analog method. This irreversible shift from analog to digital has resulted in reduced distortion, enhanced clarity, and improved speed. Moreover, these protocols have contributed significantly to the growth and evolution of communication in a number of industrial and business settings, enabling rapid data transmission that is integral to day-to-day operations. Even though their use is currently being overshadowed by the prevalence of Internet-based communication methods, Group 4 protocols have left an indelible mark in the history and evolution of facsimile transmissions.


Group 4 Protocols, also known as G4 Protocol, are primarily associated with fax transmission over Integrated Services Digital Network (ISDN) connections. Here are three real-world examples:1. Fax Machines: Traditional fax machines employed Group 3 protocols. However, with the advent of ISDN lines, fax transmission evolved to Group 4 protocols which provided faster fax transmissions. 2. Multi-function Printers: Modern multi-function printers (those that print, copy, scan, and fax) might use G4 protocols when sending faxes over ISDN.3. Telecommunications Industry: Group 4 protocols are used in the telecommunication sectors where ISDN connections are prevalent. For instance, in network systems that transmit data like faxes over Packet Switched Telephone Networks (PSTNs) or Digital Subscriber Line (DSL).Please note that G4 fax has been largely superseded in many parts of the world due to the demise of ISDN connections as businesses move towards IP-based connections.

Frequently Asked Questions(FAQ)

Q: What are Group 4 Protocols?A: Group 4 Protocols are a set of standards used in transmitting fax data across telephone lines. They are used primarily within the ITU-T T.6 compression standard, which reduces the amount of data necessary to transmit a page of text.Q: What organizations developed the Group 4 Protocols?A: The Group 4 Protocols were developed by ITU-T (International Telecommunication Union – Telecommunication Standardization Sector) Q: What is the significance of Group 4 Protocols?A: Group 4 Protocols are significant because they increase the efficiency of transmitting fax data over telephone lines, paving the way for speedier and more reliable faxing services.Q: What is the relationship between Group 4 Protocols and T.6 compression standard?A: The Group 4 Protocols are a vital part of the T.6 compression standard employed in fax machines. They facilitate the compression of data, which reduces the amount of data to be transmitted.Q: Are Group 4 Protocols still relevant today?A: While faxing may not be as prevalent as it once was due to the advent of digital communication methods, Group 4 Protocols continue to be relevant in fields where faxing is employed, such as healthcare and legal sectors.Q: Can Group 4 Protocols be used over IP networks?A: Group 4 Protocols are designed for telephone lines. For them to be used over IP networks, an additional protocol such as T.38 (known as the Fax over IP protocol) may be necessary. Q: How does Group 4 Protocols affect fax transmission speed?A: The Group 4 Protocols work to increase the speed of fax transmission by compressing the data. Rather than sending every bit of information individually, these protocols allow machines to transmit chunks of information at a time, thereby increasing speed.Q: How different/similar are Group 4 Protocols from/to Group 3 Protocols?A: Group 4 Protocols are an improved version of Group 3 Protocols, offering faster transmission rates and better compression algorithms. However, they require a dedicated digital line for transmission, unlike Group 3 Protocols, which can work over standard telephone lines.

Related Tech Terms

  • Facsimile Communications
  • ITU-T T.6
  • Image Compression
  • Scanned Document Transmission
  • Error Correction Modes

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