Abdo, Mohammed (PhD)Demissie, Abebe2018-07-052023-11-282018-07-052023-11-282008-03http://etd.aau.edu.et/handle/12345678/6586Pe r c e iv e d co nv e r s a t i on a l s pe e c h q ua l i t y i s a n imp o r t a n t me t r i c s in Vo i c e o v e r ip (vo ip) a ppl i c a t i on s . As ip n e two r ks a r e not d e s i gn ed f o r R e a l - t ime a pp l i c a t io ns , t h e n e two rk imp a i rmen t s su c h a s p a ck e t lo s s , J i t t e r a nd d e l a y h a ve a s e ve r e imp a c t on s p e e ch q u a l i t y. Sin c e se cu r i t y h a s b e come a ma j o r c o n c e r n wi t h th e r a p id gr owth o f I nt e r e s t in t h e in t e r n e t , t he th e s i s de a l s wi th t h e s e cur i t y a s p e c t s o f Vo ip s ys t ems an d t h e p e r fo rma n c e ana l ys i s of s e cu r e voip n e two rk s . I t s t r e s s e s o n th e u n de r l yi n g o f vo ip p ro to c ol s l ik e se s s io n in i t i a t i on Pro to c ol (sip) , h.3 2 3 a nd me di a ga t ewa y co nt r ol prot o col (mgcp) . Thi s t h e s i s s t r e s s e s mo r e on i s s u e s r e ga r d in g t h e f i r ewa l l a nd th e P r ob l em f a c ed i n u s i n g i t ’ s f o r vo ip; i t f u r th e r d i s cus s e s t h e r e s ul t s O bt a i n ed wh en s e c ur i t y me c h an i sm a r e a pp l i ed . Thi s th e s i s d e v e lo ps an a l go r i thm o f a n a d ap t iv e me t ho d c od e c S e l e c t io n me ch an i sm whi c h c h an ge s th e v oi c e en co di n g s c h eme in t h e Mid dl e of a n a c t iv e c a l l ba s ed o n t h e n e two rk c on di t io ns . Th e pr op os e d Me c ha ni sm in vo lve s e s t a bl i sh in g a t h r e e -wa y h a n d sh ak e p r o c e s s i n Mid - c a l l t o r e - ne go t i a t e s t a t i on c ap ab i l i t i e s , maki n g the swi t c h a t a D e t e rmin e d s eq u enc e numb e r in a r e a l t ime t r a ns po r t p r ot oc ol (rtp) P a c k e t to sol v e th e p r obl ems an d th en to i n c r e a s e th e pe r f o rman c e of Voip.enVOIPThesis