Data Communications Networking Devices - 4th Ed.pdf

4.3 INTELLIGENT MODEMS ________________________________________________________ 451The Link Management PDU is used to implement MNP Class 6 and Class 10functions. Thus, this PDU would be used to direct a change in the operating rate ofa modem during a communications session.The last PDU presently de®ned, Link Management Acknowledgement, acknowledgesreceipt of a Link Management PDU. Thus the LMA PDU wouldinclude the SSN of the LMA being acknowledged.MNP sessionAn MNP session involves the exchange of PDUs as illustrated by the time chart inFigure 4.54. Communication is initiated when one modem transmits a LinkRequest PDU. The receiving modem responds with its own Link Request PDUpermitting the two to agree upon a set of operating parameters when the originatorreturns its Link Acknowledgement PDU. This three-way handshaking process isreferred to as the MNP call establishment process.Once a call is established the originator transmits data using Link TransferPDUs. The receiver acknowledges a speci®c number of Link Transfer PDUs with aLink Acknowledgement PDU, with the number of PDUs based upon negotiationsFigure 4.54Simple MNP session