What Is Group 4 Protocols?
Group 4 is a fax protocol that allows you to send and receive documents those which are at up to 400 dpi resolution. It is designed for use with ISDN, or integrated services in a digital network, a particular type of phone line with data and voice capabilities. Group 4 protocols are a protocol suite used to send fax documents over ISDN networks supporting images up to 400 dpi resolution. It is designed for FAX transmissions between ISDN 64 kbps systems and for using protocols. Group 4 was developed by the International Telecommunication Union (ITU) in 1992 and was approved as an international standard in 1993. The ITU-T recommendation T.30 provides a benchmark for Group 4 facsimile machines, which supports transfer rates of up to 2.4 Mbit/s with the capability to transmit images up to 400 dpi resolution. The group 4 protocol suite consists of three layers: Layer 1 - The data link layer, which provides error correction, flow control and synchronization between two modems; Layer 2 - The network layer which handles packet switching; and Layer 3 - The presentation layer, which provides error correction, flow control and synchronization between two modems; Group 4 encoding is the new hotness in the world of document imaging. It's all about getting down to business: it's half the size of Group 3 and does all the same things—but faster. Group 4 encoding is a bit more complicated than Group 3 but still accessible for anyone to use. It was designed for use on data networks and doesn't have any sync codes built in for error detection because they're not used as often for image transfers. Group 4's protocol is identical to MMR; both use the same algorithm and achieve comparable compression results.
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