Networkscanbeinterconnectedbydifferentdevicesinthephysicallayernetworkscanbeconnectedby()_orhubs.whichjustmovethebitsfromonenetworktoanidenticalnetwork.Onelayerupwefindbridgesandswitcheswhichoperateatdatalinklayer.Theycanaccept()examinetheMACaddressandforwardtheframestoadifferentnetworkwhiledoingminorprotocoltranslationintheprocessinmenetworklayer,wehaveroutersthatcanconnecttwonetworks,Iftwonetworkshave()networklayer,theroutermaybeabletotranslatebetweenthepackerformats.Inthetransportlayerwefindtransportgateway,whichcaninterfacebetweentwotransportconnectionsFinally,intheapplicationlayer,applicationgatewaystranslatemessage(请作答此空).Asanexample,gatewaysbetweenInternete-mailandX.400e-mailmust()thee-mailmessageandchangevariousheaderfields.
A.syntax B.semantics C.language D.format正确答案B
