Computer)Networks) - cs.uh.edugnawali/courses/cosc6377-f11/cosc6377-f11-l11.… ·...
Transcript of Computer)Networks) - cs.uh.edugnawali/courses/cosc6377-f11/cosc6377-f11-l11.… ·...
Computer Networks COSC 6377
Lecture 11 Fall 2011
October 3, 2011
Announcements
• Some people sent feedback, conAnue to send them
• Exam1 will be returned on Wednesday • Project1 due on Wednesday
Unicast
D E F A B C
MulAcast
D E F A B C
IP MulAcast Model
• Groups – Nodes subscribe to a group – Messages are directed to a group
Group Management Using IGMP
D E F A B C
R1 R2
• Hosts subscribe • Maintainance – Polling by routers – Response Suppression
How many poll and response messages per group?
DVMRP
• Flood • Prune
D E F A B C
• How do we discover new nodes?
PIM
S1
RP
S2
• Shared tree • Rendez-‐Vous point • Switch to
source-‐specific trees • Where is RP?
Challenges
• Billing – Who to charge? – How many users?
• Secure broadcast • Address space • Scaling
EXPRESS
• Channel Model – (S,E)
• Subscriber subscribes to (S,E) • Sender S sends to (S,E)
EXPRESS Service
• Channel Model – (S,E)
• At source – Count = CountQuery(channel,countId,Ameout) – channelKey(channel, K(S,E))
• Subscriber – result = newSubscripAon(channel, [K(S,E)]) – count(channel, countId, count)
EXPRESS Advantages
• 2^24 channels per host – 232.0.0.0/8
• Source has exclusive transmission access to the channel
• CounAng operaAons available – Can be used for accounAng
• Subscriber can be selecAve • ISP’s know who to bill
ECMP
• Maintain the distribuAon tree • Count
• Flood the network with CountQuery • Subscribers respond with Count
• How can we use Count for – SubscripAon – VoAng
CountQuery RouAng
• Forward the message to downstream routers
• At each hop, set Ameout – Decrement by k * RTT to the upstream router
A
B
C D E
DistribuAon Tree Maintenance
• Subscribe with unsoliciated Count(ch,countId,1)
• Keepalive – TCP or UDP
• Unsubscribe with Count(ch,countId, 0) • Discovery with CountQuery(neighbors)
MulA-‐source MulAcast
• Example – Video conferencing applicaAon
• Almost single-‐source mulAcast applicaAon – Distance learning
• Session Relay
SR
C D E
F
S1 S2
(SR,E) (SR,E)
(SR,E)
(SR,E)
SR comparisons
• PIM-‐SM – Switch from rendez-‐vous to source-‐specific tree
• Why SR? – ApplicaAon control over Relay placement – Not much worse than shared tree
Cost and Overhead
• Price for router components – Memory, CPU
• State maintenance Overhead – Refresh state – TCP helps
ProacAve CounAng
• Send updated count if it is outside the tolerance