Reliable and Application Layer Multicast Ghislaine Amrani - PowerPoint PPT Presentation

Reliable and Application Layer Multicast Ghislaine Amrani 9/11/2006 1

Agenda [ [ Agenda I) Introduction Introduction g What is Multicast ? g What are the applications of Multicast ? g How does it works ? II) Reliable Reliable Multicast Multicast g Definition g Techniques III) Application layer Multicast Application layer Multicast IV) Conclusion Conclusion Reliable and Application layer Multicast 2/19 9/11/2006

I) Introduction -What is Multicast [ [ and applications Introduction -How does it works II)Reliable Multicast III) Application Layer Multicast g What is Multicast ? g Multicast is the simultaneous delivery of one copy of the information to a group of receivers who wants to have it. g Advantages : g Bandwidth is conserved on shared links : only one copy of each packet is sent on each link. g Unlimited number of participants. g Not limited to one single LAN (like broadcast) � Multicast routing g What are the applications of Multicast ? g Video and audio streaming g Video conference g Internet games g … Reliable and Application layer Multicast 3/19 9/11/2006

I) Introduction -What is Multicast [ [ and applications Introduction - How does it works II)Reliable Multicast III) Application Layer Multicast g How does it works ? g Multicast uses a different kind of IP adresse : Class D R3 (224.0.0.0 – 239.255.255.255). g One address is assigned to group of receivers instead of one address to a single receiver (unicast) R1 R2 g When a host joins a group, it notifies Sender the nearest multicast subnet router of its presence in the group using IGMP protocol. Reliable and Application layer Multicast 4/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Definition Utilization Challenge Techniques III) Application Layer Multicast g Definition g Reliable multicast is a mechanism by which multicast data from a sender is guaranteed to reach the receivers at some time. g Multicast application requires a Reliable Multicast protocol on top of IP Multicast : g MFTP (Multicast File Transfer Protocol) g SRM (Scalable Reliable Multicast) for video conferences g … g The Reliable Multicast protocol informs the upper-layer about the failure or error-free of the delivery. Reliable and Application layer Multicast 5/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Use Utilization Challenge Techniques III) Application Multi- Multi -Point Applications Point Applications Layer Multicast Delay- -sensitive sensitive Delay Real time Real time Streaming media Streaming media Streaming data Streaming data Ex : Multi-payer Internet games, on-line trading… Interactive Interactive Non- Non -interactive interactive Ex : Video conferencing Ex : Internet TV… We have to be sure that packets Information content is not drastically reduced will reach the destination if loss occur � no need for Reliable Multicast � Need for Reliable Multicast Reliable and Application layer Multicast 6/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Challenges Utilization Challenge Techniques III) Application Layer Multicast g Challenges : g Feedback implosion g Feedback implosion : where feedback from all receivers can saturate the source and the link close to the source. ACK ACK ACK Receivers Sender ACK K ACK C A ACK A C K … g “ g “Crying baby Crying baby” ” : where fee receivers have a high packet loss and slow down the whole multicast process by repeating transmissions. Reliable and Application layer Multicast 7/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g Techniques : g SCE : Single-Connection Emulation g NAK-based loss reporting g Distributed loss recovery g Router-assisted loss recovery g FEC (Forward Error Correction) -based Reliable and Application layer Multicast 8/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g SCE : Single g SCE : Single- -Connection Emulation Connection Emulation g Also called ACK-based loss reporting g The simplest Reliable Multicast protocol g The sender establish a TCP session with every receiver : g He sends data via IP Multicast g He receives ACKs from receivers via IP unicast g Work very well with small groups but has a bad scalability g Risks of implosion if senders send their ACKs at the same time and “Crying baby” Reliable and Application layer Multicast 9/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g Nak g Nak- -based loss reporting based loss reporting Sender Sender g Receivers are responsible for detecting losses (by cheking the sequence number) : g They send NAK (negative acknowledgement) to the sender NAK g They request retransmissions for themselves. 14 g NAK-based Vs ACK-based : g generates less acknowledgement traffic 12 g better throughput � Better reliability than ACK-based 11 g Problem : NAK implosion Receiver Receiver Reliable and Application layer Multicast 10/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g Distributed loss Recovery g Distributed loss Recovery g Uses multiple retransmitters to repair the packet loss of nearby group member. g Advantages : g Speeds up loss recovery process g Prevents the source from overload g Supposed to solve scalability problems g It must decides : g Who should retransmit g Who is close to me and to whom I should send the NAK Reliable and Application layer Multicast 11/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g Two classes of distributed recovery techniques : g Global recovery with duplicate avoidance (no explicit retransmitter) Source g Any receiver may retransmit the packet g RTT (round trip time) to avoid duplicate retransmission and prevent feedback implosion DR2 g Reduce duplicate NAK but can’t avoid them completely Router g Tree-based local recovery (explicit retransmitter designed) : DR1 g Receivers close to each other form a subgroup and elect a DR g Only DR receive NAK and retransmit packets. g Fusion tree = hierarchy of subgroups g When fusion tree is built, three ways to recover losses : g Multicast with duplicate avoidance g Cascaded unicast g Hybrid Receivers of subgroup 1 Reliable and Application layer Multicast 12/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g Router assisted recovery g Router assisted recovery g Adds router support for fast and efficient recovery g Break with the established end-to-end principle : g Intermediate router examine the header g It takes action : repair packet and forward it only to the host who requested it g � reducing data redundancy g Example of protocols : g LMS (Light-weight Multicast) g PGM (Pragmatic General Multicast) g … g New idea : require new hardware or at least new firmware Reliable and Application layer Multicast 13/19 9/11/2006

I) Introduction II)Reliable [ [ Multicast Definition Reliable Multicast - Techniques Utilization Challenge Techniques III) Application Layer Multicast g FEC Sender g FEC- -based recovery based recovery g Restores erased packets using FEC packets. g + : Utilization of NAKs avoided : g Little or no feedback implosion Receiver g No crying baby problem g - : Increase latency 1) We have k packets of data 2) Operation of FEC erasure correction adds n-k FEC packets � so the sender sends k+(n-k) = n packets 3) If loss occurs the receiver can reconstruct the original message if the loss is < to n-k lost packets Reliable and Application layer Multicast 14/19 9/11/2006

I) Introduction II)Reliable Multicast [ [ Application Layer Multicast – WHAT ? III) Application Layer Multicast What is it ? Advantages Aspects g IP Multicast : data packets replicated at routers g Application-layer Multicast : data packets replicated at end hosts. g Overlay Network of intelligent node capable of receiving and sending data to multiple downstream peers via TCP Unicast. g Applications : Live Streaming, Internet TV / Radio… Reliable and Application layer Multicast 15/19 9/11/2006

I) Introduction II)Reliable Multicast [ [ Application Layer Multicast – WHY ? III) Application Layer Multicast What is it ? Advantages Aspects g Effective transport g Builds multicast transport on top of a the unicast transport g One to many reliability (IP Multicast) � Multiple one to one reliability solved by TCP (Application Layer Multicast) g Easy deployment g Not all networks support IP Multicast but all support IP Unicast. g Application layer multicast is bundled with the application g No additional routing state required in the routers g Asynchronous Delivery g Node can store the data and deliver it to the receiver when he’s ready g Versatility g Intelligent adaptation from sender to receiver Reliable and Application layer Multicast 16/19 9/11/2006