&nbsp;&nbsp;&nbsp;considered&nbsp;senders&nbsp;and&nbsp;receivers.&nbsp;&nbsp;One&nbsp;sends&nbsp;data&nbsp;and&nbsp;receives&nbsp;<br />&nbsp;&nbsp;&nbsp;acknowledgments,&nbsp;the&nbsp;other&nbsp;sends&nbsp;acknowledgments&nbsp;and&nbsp;receives&nbsp;data.&nbsp;<br />&nbsp;&nbsp;&nbsp;Most&nbsp;errors&nbsp;cause&nbsp;termination&nbsp;of&nbsp;the&nbsp;connection.&nbsp;&nbsp;An&nbsp;error&nbsp;is&nbsp;<br />&nbsp;&nbsp;&nbsp;signalled&nbsp;by&nbsp;sending&nbsp;an&nbsp;error&nbsp;packet.&nbsp;&nbsp;This&nbsp;packet&nbsp;is&nbsp;not&nbsp;<br />&nbsp;&nbsp;&nbsp;acknowledged,&nbsp;and&nbsp;not&nbsp;retransmitted&nbsp;(i.e.,&nbsp;a&nbsp;TFTP&nbsp;server&nbsp;or&nbsp;user&nbsp;may&nbsp;<br />&nbsp;&nbsp;&nbsp;terminate&nbsp;after&nbsp;sending&nbsp;an&nbsp;error&nbsp;message),&nbsp;so&nbsp;the&nbsp;other&nbsp;end&nbsp;of&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;connection&nbsp;may&nbsp;not&nbsp;get&nbsp;it.&nbsp;&nbsp;Therefore&nbsp;timeouts&nbsp;are&nbsp;used&nbsp;to&nbsp;detect&nbsp;<br />&nbsp;&nbsp;&nbsp;such&nbsp;a&nbsp;termination&nbsp;when&nbsp;the&nbsp;error&nbsp;packet&nbsp;has&nbsp;been&nbsp;lost.&nbsp;&nbsp;Errors&nbsp;are&nbsp;<br />Sollins&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[Page&nbsp;2]&nbsp;<br />&nbsp;<br />RFC&nbsp;1350&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TFTP&nbsp;Revision&nbsp;2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;July&nbsp;1992&nbsp;<br />&nbsp;&nbsp;&nbsp;caused&nbsp;by&nbsp;three&nbsp;types&nbsp;of&nbsp;events:&nbsp;not&nbsp;being&nbsp;able&nbsp;to&nbsp;satisfy&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;request&nbsp;(e.g.,&nbsp;file&nbsp;not&nbsp;found,&nbsp;access&nbsp;violation,&nbsp;or&nbsp;no&nbsp;such&nbsp;user),&nbsp;<br />&nbsp;&nbsp;&nbsp;receiving&nbsp;a&nbsp;packet&nbsp;which&nbsp;cannot&nbsp;be&nbsp;explained&nbsp;by&nbsp;a&nbsp;delay&nbsp;or&nbsp;<br />&nbsp;&nbsp;&nbsp;duplication&nbsp;in&nbsp;the&nbsp;network&nbsp;(e.g.,&nbsp;an&nbsp;incorrectly&nbsp;formed&nbsp;packet),&nbsp;and&nbsp;<br />&nbsp;&nbsp;&nbsp;losing&nbsp;access&nbsp;to&nbsp;a&nbsp;necessary&nbsp;resource&nbsp;(e.g.,&nbsp;disk&nbsp;full&nbsp;or&nbsp;access&nbsp;<br />&nbsp;&nbsp;&nbsp;denied&nbsp;during&nbsp;a&nbsp;transfer).&nbsp;<br />&nbsp;&nbsp;&nbsp;TFTP&nbsp;recognizes&nbsp;only&nbsp;one&nbsp;error&nbsp;condition&nbsp;that&nbsp;does&nbsp;not&nbsp;cause&nbsp;<br />&nbsp;&nbsp;&nbsp;termination,&nbsp;the&nbsp;source&nbsp;port&nbsp;of&nbsp;a&nbsp;received&nbsp;packet&nbsp;being&nbsp;incorrect.&nbsp;<br />&nbsp;&nbsp;&nbsp;In&nbsp;this&nbsp;case,&nbsp;an&nbsp;error&nbsp;packet&nbsp;is&nbsp;sent&nbsp;to&nbsp;the&nbsp;originating&nbsp;host.&nbsp;<br />&nbsp;&nbsp;&nbsp;This&nbsp;protocol&nbsp;is&nbsp;very&nbsp;restrictive,&nbsp;in&nbsp;order&nbsp;to&nbsp;simplify&nbsp;<br />&nbsp;&nbsp;&nbsp;implementation.&nbsp;&nbsp;For&nbsp;example,&nbsp;the&nbsp;fixed&nbsp;length&nbsp;blocks&nbsp;make&nbsp;allocation&nbsp;<br />&nbsp;&nbsp;&nbsp;straight&nbsp;forward,&nbsp;and&nbsp;the&nbsp;lock&nbsp;step&nbsp;acknowledgement&nbsp;provides&nbsp;flow&nbsp;<br />&nbsp;&nbsp;&nbsp;control&nbsp;and&nbsp;eliminates&nbsp;the&nbsp;need&nbsp;to&nbsp;reorder&nbsp;incoming&nbsp;data&nbsp;packets.&nbsp;<br />3.&nbsp;Relation&nbsp;to&nbsp;other&nbsp;Protocols&nbsp;<br />&nbsp;&nbsp;&nbsp;As&nbsp;mentioned&nbsp;TFTP&nbsp;is&nbsp;designed&nbsp;to&nbsp;be&nbsp;implemented&nbsp;on&nbsp;top&nbsp;of&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;Datagram&nbsp;protocol&nbsp;(UDP).&nbsp;&nbsp;Since&nbsp;Datagram&nbsp;is&nbsp;implemented&nbsp;on&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;Internet&nbsp;protocol,&nbsp;packets&nbsp;will&nbsp;have&nbsp;an&nbsp;Internet&nbsp;header,&nbsp;a&nbsp;Datagram&nbsp;<br />&nbsp;&nbsp;&nbsp;header,&nbsp;and&nbsp;a&nbsp;TFTP&nbsp;header.&nbsp;&nbsp;Additionally,&nbsp;the&nbsp;packets&nbsp;may&nbsp;have&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;header&nbsp;(LNI,&nbsp;ARPA&nbsp;header,&nbsp;etc.)&nbsp;&nbsp;to&nbsp;allow&nbsp;them&nbsp;through&nbsp;the&nbsp;local&nbsp;<br />&nbsp;&nbsp;&nbsp;transport&nbsp;medium.&nbsp;&nbsp;As&nbsp;shown&nbsp;in&nbsp;Figure&nbsp;3-1,&nbsp;the&nbsp;order&nbsp;of&nbsp;the&nbsp;contents&nbsp;<br />&nbsp;&nbsp;&nbsp;of&nbsp;a&nbsp;packet&nbsp;will&nbsp;be:&nbsp;local&nbsp;medium&nbsp;header,&nbsp;if&nbsp;used,&nbsp;Internet&nbsp;header,&nbsp;<br />&nbsp;&nbsp;&nbsp;Datagram&nbsp;header,&nbsp;TFTP&nbsp;header,&nbsp;followed&nbsp;by&nbsp;the&nbsp;remainder&nbsp;of&nbsp;the&nbsp;TFTP&nbsp;<br />&nbsp;&nbsp;&nbsp;packet.&nbsp;&nbsp;(This&nbsp;may&nbsp;or&nbsp;may&nbsp;not&nbsp;be&nbsp;data&nbsp;depending&nbsp;on&nbsp;the&nbsp;type&nbsp;of&nbsp;packet&nbsp;<br />&nbsp;&nbsp;&nbsp;as&nbsp;specified&nbsp;in&nbsp;the&nbsp;TFTP&nbsp;header.)&nbsp;&nbsp;TFTP&nbsp;does&nbsp;not&nbsp;specify&nbsp;any&nbsp;of&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;values&nbsp;in&nbsp;the&nbsp;Internet&nbsp;header.&nbsp;&nbsp;On&nbsp;the&nbsp;other&nbsp;hand,&nbsp;the&nbsp;source&nbsp;and&nbsp;<br />&nbsp;&nbsp;&nbsp;destination&nbsp;port&nbsp;fields&nbsp;of&nbsp;the&nbsp;Datagram&nbsp;header&nbsp;(its&nbsp;format&nbsp;is&nbsp;given&nbsp;<br />&nbsp;&nbsp;&nbsp;in&nbsp;the&nbsp;appendix)&nbsp;are&nbsp;used&nbsp;by&nbsp;TFTP&nbsp;and&nbsp;the&nbsp;length&nbsp;field&nbsp;reflects&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;size&nbsp;of&nbsp;the&nbsp;TFTP&nbsp;packet.&nbsp;&nbsp;The&nbsp;transfer&nbsp;identifiers&nbsp;(TID's)&nbsp;used&nbsp;by&nbsp;<br />&nbsp;&nbsp;&nbsp;TFTP&nbsp;are&nbsp;passed&nbsp;to&nbsp;the&nbsp;Datagram&nbsp;layer&nbsp;to&nbsp;be&nbsp;used&nbsp;as&nbsp;ports;&nbsp;therefore&nbsp;<br />&nbsp;&nbsp;&nbsp;they&nbsp;must&nbsp;be&nbsp;between&nbsp;0&nbsp;and&nbsp;65,535.&nbsp;&nbsp;The&nbsp;initialization&nbsp;of&nbsp;TID's&nbsp;is&nbsp;<br />&nbsp;&nbsp;&nbsp;discussed&nbsp;in&nbsp;the&nbsp;section&nbsp;on&nbsp;initial&nbsp;connection&nbsp;protocol.&nbsp;<br />&nbsp;&nbsp;&nbsp;The&nbsp;&nbsp;TFTP&nbsp;header&nbsp;consists&nbsp;of&nbsp;a&nbsp;2&nbsp;byte&nbsp;opcode&nbsp;field&nbsp;which&nbsp;indicates&nbsp;<br />&nbsp;&nbsp;&nbsp;the&nbsp;packet's&nbsp;type&nbsp;(e.g.,&nbsp;DATA,&nbsp;ERROR,&nbsp;etc.)&nbsp;&nbsp;These&nbsp;opcodes&nbsp;and&nbsp;&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;formats&nbsp;of&nbsp;&nbsp;the&nbsp;various&nbsp;types&nbsp;of&nbsp;packets&nbsp;are&nbsp;discussed&nbsp;further&nbsp;in&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;section&nbsp;on&nbsp;TFTP&nbsp;packets.&nbsp;<br />Sollins&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[Page&nbsp;3]&nbsp;<br />&nbsp;<br />RFC&nbsp;1350&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TFTP&nbsp;Revision&nbsp;2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;July&nbsp;1992&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;---------------------------------------------------&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;&nbsp;Local&nbsp;Medium&nbsp;&nbsp;|&nbsp;&nbsp;Internet&nbsp;&nbsp;|&nbsp;&nbsp;Datagram&nbsp;&nbsp;|&nbsp;&nbsp;TFTP&nbsp;&nbsp;|&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;---------------------------------------------------&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Figure&nbsp;3-1:&nbsp;Order&nbsp;of&nbsp;Headers&nbsp;<br />4.&nbsp;Initial&nbsp;Connection&nbsp;Protocol&nbsp;<br />&nbsp;&nbsp;&nbsp;A&nbsp;transfer&nbsp;is&nbsp;established&nbsp;by&nbsp;sending&nbsp;a&nbsp;request&nbsp;(WRQ&nbsp;to&nbsp;write&nbsp;onto&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;foreign&nbsp;file&nbsp;system,&nbsp;or&nbsp;RRQ&nbsp;to&nbsp;read&nbsp;from&nbsp;it),&nbsp;and&nbsp;receiving&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;positive&nbsp;reply,&nbsp;an&nbsp;acknowledgment&nbsp;packet&nbsp;for&nbsp;write,&nbsp;or&nbsp;the&nbsp;first&nbsp;data&nbsp;<br />&nbsp;&nbsp;&nbsp;packet&nbsp;for&nbsp;read.&nbsp;&nbsp;In&nbsp;general&nbsp;an&nbsp;acknowledgment&nbsp;packet&nbsp;will&nbsp;contain&nbsp;<br />&nbsp;&nbsp;&nbsp;the&nbsp;block&nbsp;number&nbsp;of&nbsp;the&nbsp;data&nbsp;packet&nbsp;being&nbsp;acknowledged.&nbsp;&nbsp;Each&nbsp;data&nbsp;<br />&nbsp;&nbsp;&nbsp;packet&nbsp;has&nbsp;associated&nbsp;with&nbsp;it&nbsp;a&nbsp;block&nbsp;number;&nbsp;block&nbsp;numbers&nbsp;are&nbsp;<br />&nbsp;&nbsp;&nbsp;consecutive&nbsp;and&nbsp;begin&nbsp;with&nbsp;one.&nbsp;&nbsp;Since&nbsp;the&nbsp;positive&nbsp;response&nbsp;to&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;write&nbsp;request&nbsp;is&nbsp;an&nbsp;acknowledgment&nbsp;packet,&nbsp;in&nbsp;this&nbsp;special&nbsp;case&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;block&nbsp;number&nbsp;will&nbsp;be&nbsp;zero.&nbsp;&nbsp;(Normally,&nbsp;since&nbsp;an&nbsp;acknowledgment&nbsp;packet&nbsp;<br />&nbsp;&nbsp;&nbsp;is&nbsp;acknowledging&nbsp;a&nbsp;data&nbsp;packet,&nbsp;the&nbsp;acknowledgment&nbsp;packet&nbsp;will&nbsp;<br />&nbsp;&nbsp;&nbsp;contain&nbsp;the&nbsp;block&nbsp;number&nbsp;of&nbsp;the&nbsp;data&nbsp;packet&nbsp;being&nbsp;acknowledged.)&nbsp;&nbsp;If&nbsp;<br />&nbsp;&nbsp;&nbsp;the&nbsp;reply&nbsp;is&nbsp;an&nbsp;error&nbsp;packet,&nbsp;then&nbsp;the&nbsp;request&nbsp;has&nbsp;been&nbsp;denied.&nbsp;<br />&nbsp;&nbsp;&nbsp;In&nbsp;order&nbsp;to&nbsp;create&nbsp;a&nbsp;connection,&nbsp;each&nbsp;end&nbsp;of&nbsp;the&nbsp;connection&nbsp;chooses&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;TID&nbsp;for&nbsp;itself,&nbsp;to&nbsp;be&nbsp;used&nbsp;for&nbsp;the&nbsp;duration&nbsp;of&nbsp;that&nbsp;connection.&nbsp;&nbsp;The&nbsp;<br />&nbsp;&nbsp;&nbsp;TID's&nbsp;chosen&nbsp;for&nbsp;a&nbsp;connection&nbsp;should&nbsp;be&nbsp;randomly&nbsp;chosen,&nbsp;so&nbsp;that&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;probability&nbsp;that&nbsp;the&nbsp;same&nbsp;number&nbsp;is&nbsp;chosen&nbsp;twice&nbsp;in&nbsp;immediate&nbsp;<br />&nbsp;&nbsp;&nbsp;succession&nbsp;is&nbsp;very&nbsp;low.&nbsp;&nbsp;Every&nbsp;packet&nbsp;has&nbsp;associated&nbsp;with&nbsp;it&nbsp;the&nbsp;two&nbsp;<br />&nbsp;&nbsp;&nbsp;TID's&nbsp;of&nbsp;the&nbsp;ends&nbsp;of&nbsp;the&nbsp;connection,&nbsp;the&nbsp;source&nbsp;TID&nbsp;and&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;destination&nbsp;TID.&nbsp;&nbsp;These&nbsp;TID's&nbsp;are&nbsp;handed&nbsp;to&nbsp;the&nbsp;supporting&nbsp;UDP&nbsp;(or&nbsp;<br />&nbsp;&nbsp;&nbsp;other&nbsp;datagram&nbsp;protocol)&nbsp;as&nbsp;the&nbsp;source&nbsp;and&nbsp;destination&nbsp;ports.&nbsp;&nbsp;A&nbsp;<br />&nbsp;&nbsp;&nbsp;requesting&nbsp;host&nbsp;chooses&nbsp;its&nbsp;source&nbsp;TID&nbsp;as&nbsp;described&nbsp;above,&nbsp;and&nbsp;sends&nbsp;<br />&nbsp;&nbsp;&nbsp;its&nbsp;initial&nbsp;request&nbsp;to&nbsp;the&nbsp;known&nbsp;TID&nbsp;69&nbsp;decimal&nbsp;(105&nbsp;octal)&nbsp;on&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;serving&nbsp;host.&nbsp;&nbsp;The&nbsp;response&nbsp;to&nbsp;the&nbsp;request,&nbsp;under&nbsp;normal&nbsp;operation,&nbsp;<br />&nbsp;&nbsp;&nbsp;uses&nbsp;a&nbsp;TID&nbsp;chosen&nbsp;by&nbsp;the&nbsp;server&nbsp;as&nbsp;its&nbsp;source&nbsp;TID&nbsp;and&nbsp;the&nbsp;TID&nbsp;chosen&nbsp;<br />&nbsp;&nbsp;&nbsp;for&nbsp;the&nbsp;previous&nbsp;message&nbsp;by&nbsp;the&nbsp;requestor&nbsp;as&nbsp;its&nbsp;destination&nbsp;TID.&nbsp;<br />&nbsp;&nbsp;&nbsp;The&nbsp;two&nbsp;chosen&nbsp;TID's&nbsp;are&nbsp;then&nbsp;used&nbsp;for&nbsp;the&nbsp;remainder&nbsp;of&nbsp;the&nbsp;transfer.&nbsp;<br />&nbsp;&nbsp;&nbsp;As&nbsp;an&nbsp;example,&nbsp;the&nbsp;following&nbsp;shows&nbsp;the&nbsp;steps&nbsp;used&nbsp;to&nbsp;establish&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;connection&nbsp;to&nbsp;write&nbsp;a&nbsp;file.&nbsp;&nbsp;Note&nbsp;that&nbsp;WRQ,&nbsp;ACK,&nbsp;and&nbsp;DATA&nbsp;are&nbsp;the&nbsp;<br />&nbsp;&nbsp;&nbsp;names&nbsp;of&nbsp;the&nbsp;write&nbsp;request,&nbsp;acknowledgment,&nbsp;and&nbsp;data&nbsp;types&nbsp;of&nbsp;packets&nbsp;<br />&nbsp;&nbsp;&nbsp;respectively.&nbsp;&nbsp;The&nbsp;appendix&nbsp;contains&nbsp;a&nbsp;similar&nbsp;example&nbsp;for&nbsp;reading&nbsp;a&nbsp;<br />&nbsp;&nbsp;&nbsp;file.&nbsp;<br />Sollins&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[Page&nbsp;4]&nbsp;<br />&nbsp;<br />RFC&nbsp;1350&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TFTP&nbsp;Revision&nbsp;2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;July&nbsp;1992&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1.&nbsp;Host&nbsp;A&nbsp;sends&nbsp;&nbsp;a&nbsp;&nbsp;&quot;WRQ&quot;&nbsp;&nbsp;to&nbsp;&nbsp;host&nbsp;&nbsp;B&nbsp;&nbsp;with&nbsp;&nbsp;source=&nbsp;&nbsp;A's&nbsp;&nbsp;TID,&nbsp;<br />