n pplctn lyr s n bstrctn lyr tht spcfs th shrd cmmnctn prtcls nd ntrfc mthds sd by hsts n cmmnctns ntwrk. n pplctn lyr bstrctn s spcfd n bth th ntrnt Prtcl St (TCP/P) nd th S mdl. lthgh bth mdls s th sm trm fr thr rspctv hghst-lvl lyr, th dtld dfntns nd prpss r dffrnt.