network protocols handbook.pdf

194Protocols GuideWAN - Other WAN Protocols• The RECEIVE READY (RR) packet is used to sendseparate acknowledgments where there is no reversetraffic. The ppp field (three first bits of the typefield) tells which packet is expected next.• The RECEIVE NOT READY (RNR) packet allows aDTE to tell the other side to stop sending packets toit for a while.• The REJECT packet allows a DTE to request retransmissionof a series of packets. The ppp field gives thefirst sequence number desired.• The RESET and RESTART packets are used to recoverfrom varying degrees of trouble. Both are acknowledgedby RESET CONFIRMATION and RE-START CONFIRMATION respectively.• The DIAGNOSTIC packet is also provided, to allowthe network to inform the user of problems.3. The format of the data packet is as follows:1 2 4 8 16 23 24 31 32bitGroupChannelQ D ModuloPiggybackData (Variable)M sequence CRelated protocolsLAPB, X.25, Frame Relay, HDLC, ISDN, LLC, LAPDSponsor SourceX.25 protocol stack is defined by ISO (http://www.iso.org) andITU-T (http://www.itu.org)Referencehttp://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/x25.htmX.25 Overviewhttp://www2.rad.com/networks/1996/x25/x25.htmX.25 Protocols