The ITU-T Recommendation for X.25 packet-mode services over ISDN. See also ISDN and X.25.
"X.31." YourDictionary, n.d. Web. 22 June 2018. <http://www.yourdictionary.com/x-31>.
X.31. (n.d.). Retrieved June 22nd, 2018, from http://www.yourdictionary.com/x-31
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