Prezentare Licen TCP: Studiul mecanismelor pentru evitarea congestiei

Prezentare Licen TCP: Studiul mecanismelor pentru evitarea congestiei

Prezentare Licen TCP: Studiul mecanismelor pentru evitarea congestiei n reea Coordonator tiinific: Sl. Dr. Ing. erban OBREJA Student: Enis TONA Cuprinsul acestei prezentri

Introducere Protocolul de internet (IP) TCP/IP(Protocolul de control al trasmisiei) Arhitectura TCP/IP Conexiunea TCP i politici de trasmisie Algoritmi ultilizai de TCP Versiunile pentru evitarea congestiilor TCP Tahoe i TCP Reno Concluzii Introducere

Prezentarea studiul mecanismelor pentru evitarea congestiilor: Studiul Protocolul de trasmisie TCP/IP Studiul algoritmilor pentru evitarea congestiei Comparaia versiunilor de evitaterea congestiilor Comparaia TCP Tahoe i TCP Reno n mod

teoretic i practic Implementarea TCP Tahoe i TCP Reno, studierea parametrilor Folosirea unei simulator NS2 i reprezentarea grafic Internet Protocol (IP) Funcia protocolului IP (Modul de trasmitere al

pachetelor) Adresa IP (Adresa IP surs Adresa IP destinaie) Versiunea protocolului IP (IPv4-IPv6) Antetul IP

Protocolul de control al trasmisie(TCP) Noiuni generale Formatul pachetelor TCP Arhitectura TCP/IP Arhitectura TCP/IP Nivelul Aplicaie (FTP, HTTP, DNS, NFS) Nivelul Transport (TCP, UDP) Nivelul Internet (IP, ICMP, RIP) Nivel de reea (Ethernet, FDDI, PPP)

Conexiunea TCP si Politici de trasmisie Modelul Serviciului TCP Conexiunea TCP (Numrul de porturi) Stabilirea conexiunii TCP ntreruperea conexiunii TCP Politici de transmisie TCP Managmentul timerelor TCP

Algoritmi ultilizati de TCP Sunt folosii 4 algoritmi Slow Start (cretere exponenial) Congestion Avoidance (cresterea liniar) Fast Retrasmit (Dupa primirea a 3 ACK duplicate se retrasmite pachetul) Fast Recovery (CWND>SSTreshHold)

Versiunile pentru evitarea congestilor Tahoe (Slow Start, Congestion Avoidance, Fast Retrasmit) (Folosete baza de la Tahoe + algoritmul de Fast Recovery) Reno New Reno (Folosete baza de la Reno, se deosebete prin

faptul c poate detecta pierderi de pachete multiple) Sack (Reno + detecia pachetelor multiple i retransmisia a mai mult de un pachet pierdut per RTT ) Vegas (Folosete aceiai algoritmi ca i Reno dar n mod diferit) TCP Tahoe TCP Tahoe

Slow Start (CWND(t+1) = 2 * CWND(t) ) SSThresHold = AWS (Valorea iniial de prag) SSThresHold = CWND/2 cnd TCP detecteaz un pachet pierdut TCP Tahoe Congestion Avoidance CWND > SSTreshHold

Incrementarea CWND cu MSS2/CWND CWND/2 - detecteaz un pachet pierdut CWND = 1 * MSS cnd ncepe slow start TCP Tahoe Fast Retrasmit Dupa primirea 3 ACK duplicate Se retrasmite pachetul pierdut fr s atepte expirarea Timerului TCP Tahoe

Demonstraie TCP Tahoe TCP Tahoe Reprezentarea grafic pentru TCP Tahoe Dimensiunea pachetului de 800 Bytes, valorea de prag (SSTreshHold=1 7)

Dimensiunea pachetului de 550 Bytes,valorea de prag SSTreshHold=2 2 TCP Reno Diferena ntre Tahoe

i Reno este numrul de algoritmi pe care i folosesc. TCP Reno folosete n plus algoritmul de Fast Recovery Cnd recepioneaz 3 ACK duplicate SSTresh = CWND / 2 CWND = SSThresh + 3 * MSS

i se intr n faza de Congestion Avoidance TCP Reno Reprezentarea grafic pentru TCP Reno Dimensiunea pachetului de 800 Bytes (SSTreshHold=17) Dimensiunea

pachetului de 550 Bytes (SSTreshHold=22) Concluzii n urma simulrilor am observat performane mai bune la capitolul de evitare a congestiei fa de TCP Tahoe prin faptul c TCP Reno nu aplic reduceri drastice ale dimensiunii ferestrei de

congestie dup pierderea unui pachet ci continu n modul Congestion Avoidance meninnd astfel o rat de transmisie a pachetelor per total mult mai mare dect n cazul folosirii versiunii TCP Tahoe. Final V mulumesc pentru atenia acordat!

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