reliable multicast

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Information about reliable multicast

Published on October 3, 2007

Author: Kestrel


Reliable Multicast Transport for Distributed Middleware:  Reliable Multicast Transport for Distributed Middleware Gidon Gershinsky IBM Haifa Research Lab Talk outline:  Talk outline IP multicast overview IETF Market adoption Our work IP Multicast:  IP Multicast Deering’s PhD, 1988 RFC1112 “Host extensions for IP multicast”, 1989 D class of IP addresses: – Administratively scoped multicast (RFC 2365) - IP, UDP. Win*, Unix, Linux, AS. Java (UDP). Ethernet, TokenRing, FDDI. Satellite. Cisco and Nortel routers. “Without a doubt, multicast has become a hot topic“ “Next year is the year of multicast”. IP to Ethernet:  IP to Ethernet Ethernet multicast: 23 low-order bits of IP multicast address are placed to 01.00.5E.00.00.00 Switching:  Switching Switches: default “on” CGMP (Cisco Group Management Protocol) Must be configured on both routers and Layer 2 switches. Receiver: IGMP “join” to router. Router: CGMP join to switch. IGMP snooping Eavesdrop on Layer 3 IGMP messages. Must examine every multicast packet – not suitable for low-end switches. Can require dedicated h/w circuits. Routing:  Routing Routers: default “off” Dense mode: flood and prune Reverse Path Forwarding (RPF) PIM-DM, DVMRM Dense mode: explicit topology MOSPF Sparse mode: rendezvous points PIM-SM Cisco: PIM-DM, PIM-SM IGMP: v2 – active leave, v3 – ssm (s,g) PIM-SM:  PIM-SM Reliable Multicast:  Reliable Multicast "no single reliable multicast protocol will likely meet the needs of all applications" RFC 2357 Transport characteristics Reliability Real-time delivery Number of transmitters Late joins Network topology Reliability - protocol families (RFC 3048): Negative Acknowledgment (NACK) Tree-based ACK Asynchronous Layered Coding (ALC) Router assist Reliable Multicast:  Reliable Multicast Bulk Data Corporate data, server cache replication, software distribution Files, large memory segments Static Full reliability, no real-time, one sender Streaming Data Stock quotes, news, video, audio Messages, v/a formats Dynamic Full-to-none reliability reqs, varying real-time reqs, one/few sender(s) Collaborative Whiteboard interaction, multimedia conference Short messages, v/a formats Dynamic and/or static Full-to-moderate reliability reqs, moderate real-time reqs, many senders IETF RMT WG:  IETF RMT WG No standard protocol defined. “Building Blocks” (RFC 2887) for One-to-many bulk-data transfer (RFC 3048) Nack-oriented reliable multicast (Draft) Tree-ACK (TRACK) reliable multicast (Draft) Layered-coding transport (Draft) Generic Router Assist (Draft) Forward Error Correction (Draft) Tree Auto-Configuration (Draft) IETF WGs:  IETF WGs Multicast-Address Allocation (malloc) Multicast Security (msec) Group key management Subset-Difference (Dalit Naor, IBM Haifa) Source-Specific Multicast (ssm) (source IP, mcast group) Protocol- Independent Multicast (PIM) Inter-Domain Multicast Routing (idmr) DVMRP Nack-based reliability:  Nack-based reliability PGM protocol, Experimental RFC 3208 Packet stream; transmission window Nack suppression Exponential t = T/L*ln(x*(exp(L)-1)*(T/L)) Dependent on gap size Designated local repairers (DLR) Network Elements Additional Nack suppression Repair data filtering Cisco router support Erasure codes:  Erasure codes a.k.a Forward Error Correction Salomon-Reed codes: Improve scalability by reducing (Nack) feedback traffic. k packets -> k+n packets. Streaming data Proactive encoding Reactive encoding “Tornado codes”: k packets -> infinite number Content distribution. No backlink. Congestion Control:  Congestion Control Datagram (IP or UDP) traffic is unfair to self-managed data streams (inc TCP). No standard. Feedback from end-points (receivers) and network elements. Nack suppression. TCP-friendly CC: Rate ~ mtu/(rtt*sqrt(loss)) TCP-like window slide, ACKer selection. Worst-throughput. “Crying-baby” problem. Layered Architecture:  Layered Architecture Same (or multi-layer) data - to a number of multicast groups. Possibly no feedback Static layer scheme Base group, r0. r1=r0*k, r2=r0*k^2, etc Time slots Leave if packet lost Join new if zero loss and trigger set Receiver-driven congestion control Equation-based reception rate, RTT measured by e.g. the time required to join. Dynamic layer scheme:  Dynamic layer scheme “Wave and Equation Based Rate Control, WEBRC” Leave latency (IGMP v1 + leave propagation) G groups, A – active, G-A - quiescent. r(G)=0, r(G-1)=0,…,r(A+1)=0,r(A),r(A-1),…,r(1) Group j, timeslot t, rate is r(((j-t-1) mod G)+1) Always join the base group. Must leave quiescent wave groups. Marketplace:  Marketplace Enterprise “Middleware”. No use in public internet domain, private customers. Messaging (JMS and like) Tibco: Rendezvous “reliable broadcast” or multicast 60-second limit, probably Nack mechanism Routing daemons: subnet and wide-area Talarian: PGM implementation Pro/re-active FEC Network elements: Host implementation Bought by Tibco 01/2002 110m$ Marketplace:  Marketplace Messaging (cont) Microsoft: PGM for MSMQ SoftWired Proprietary protocol (nack-based) JMS Automatic assignment of topics to mcast groups Positive ACK for “epoch” Scalable to ~100 Fiorano Proprietary protocol (nack-based) Uses standard mcast-routers Uses one multicast group only Marketplace:  Marketplace Content (bulk data) delivery Digital Fountain FEC (Tornado-style erasure codes) Useful for unicast streams as well, e.g. on long distance links Bandwiz Proprietary patented FEC algorithm Cluster synchronization (Horus-style) BEA (WebLogic server cluster) Software replication Symantec “Norton Ghost Tool” Multimedia real-time streams IBM Haifa:  IBM Haifa Enterprise middleware environment NACK, FEC reliability mechanisms Security Congestion control Message streams, bulk data (files) delivery Burst suppression:  Burst suppression small messages at extreme rates (Nagle-like algorithm) P = A + B*Size. Cisco 2500 Router: Hub-centric distribution:  Hub-centric distribution Message stream concatenation Extreme storage demands Reliability definition B = T*Rate; Tmin depends on Loss, Nrec Persistence SSD technologies Topic mapping to groups:  Topic mapping to groups Limited number of multicast groups Ti1,..,Tin(i) -> Gi, i=1,…,Ng Sk subscribes to {T}. Will get {T} and {Tr} Perform mapping taking into account: Topic load Network topology Receiver characteristics, interest correlation Dynamic re-mapping as congestion control tool Publications:  Publications Patent on Nack suppression (filed) Patent on Multidocument multicasting (filed) Patent on Multicast Caching (filed) Paper on Networked Group Communication (to be submitted)

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