SP , ▁which ▁pop s ▁the ▁label ▁from ▁the ▁packet , ▁is ▁called ▁an ▁e gress ▁router . ▁Rou ters ▁in ▁between , ▁which ▁need ▁only ▁swap ▁labels , ▁are ▁called ▁trans it ▁rou ters ▁or ▁label ▁switch ▁rou ters ▁( LS R s ). ▁ ▁Note ▁that ▁L SP s ▁are ▁un id irection al ; ▁they ▁enable ▁a ▁packet ▁to ▁be ▁label ▁switched ▁through ▁the ▁M PL S ▁network ▁from ▁one ▁endpoint ▁to ▁another . ▁Since ▁bid irection al ▁communication ▁is ▁typically ▁desired , ▁the ▁a for ement ioned ▁dynamic ▁signal ing ▁protocol s ▁can ▁set ▁up ▁an ▁L SP ▁in ▁the ▁other ▁direction ▁to ▁compens ate ▁for ▁this . ▁ ▁When ▁protection ▁is ▁considered , ▁L SP s ▁could ▁be ▁categor ized ▁as ▁primary ▁( working ), ▁secondary ▁( back up ) ▁and ▁t ert i ary ▁( L SP ▁of ▁last ▁resort ). ▁As ▁described ▁above , ▁L SP s ▁are ▁normally ▁P 2 P ▁( point ▁to ▁point ). ▁A ▁new ▁concept ▁of ▁L SP s , ▁which ▁are ▁known ▁as ▁P 2 MP ▁( point ▁to ▁multi - point ), ▁was ▁introduced ▁recently . ▁These ▁are ▁mainly ▁used ▁for ▁mult ic ast ing ▁purposes . ▁ ▁Install ing ▁and ▁removing ▁paths ▁ ▁There ▁are ▁two ▁standard ized ▁protocol s ▁for ▁man aging ▁M PL S ▁paths : ▁the ▁Label ▁Distribution ▁Pro tocol ▁( LD P ) ▁and ▁R SV P - TE , ▁an ▁extension ▁of ▁the ▁Resource ▁Res ervation ▁Pro tocol ▁( R SV P )