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Push Technology

Push Technology. Humie Leung Annabelle Huo. Introduction. Push technology is a set of technologies used to send information to a client without the client requesting it Push versus Pull

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Push Technology

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  1. Push Technology Humie Leung Annabelle Huo

  2. Introduction • Push technology is a set of technologies used to send information to a client without the client requesting it • Push versus Pull • Pull technology is based on the traditional request/reply model. It requires that users know a priori where and when to look for data. It suffers from transmission latency and duplicate data traffic. • Push technology allows users to get information as soon as it become available and users do not have any knowledge about virtual information servers. This transfer of control from users to providers is a potential problem. • Focus is on Multicast-base push protocols • Multicasting is a 1-to-n form of communication for transmitting packets from one host to a set of member hosts in the same group

  3. Outline • Continuous Multicast Push - CMP • Issues on Push using IP multicasting • Proposed Solutions • Reliable Multicast Protocols - RMTP • Content Based Multicast - CBM

  4. Continuous Multicast Push 1 (1998) • CMP Framework • Requirements for CMP • Problems with using CMP • Proposed solutions 1. P. R. Rodriguez, E. W. Biersack, Continuous Multicast Push of Web Documents over the Internet

  5. CMP UDP/IP multicasting CMP: Framework • CMP • Cyclically deliver a site’s most frequently changing and heavily requested documents on the same multicast address • Based on raw IP multicasting • Reliability is basically achieved through simply repetitive, cyclic transmissions. • Web server • Monitor documents • Transmission • Clients • Subscribe interested information • how to join the multicast group

  6. CMP: Requirements • Multicast Routers • The network connecting is multicast capable for multicast routing and maintaining state information for each active multicast group • Session S ervers (session advertisement) • E.g. map the document’s name (URL) into a multicast address. • Address Assignment Mechanism • Multicast addresses are not assigned to individual hosts, assignments can change dynamically, and addresses sometimes have semantics of their own. • Request Monitoring • The source server needs to check if any client has joined the multicast group corresponding to some objects the server servers. • Congestion Control • UDP/IP multicast only provide multicast connectivity

  7. CMP: Problems and Solutions • Server End • Problem: How to monitor the number of requests for a document at any moment • Solution: Polling the multicast channel periodically for the feedback • Reliability • Forward Error Correction Code (FEC) • Client End • Problem: repeatedly receive the same information or mixed new and old information on a same channel because of the cyclically delivery • Solution: Layered Multicasting

  8. Issues on the Use of IP-Multicast for Push • Advantages • Scalability • Reduce the load on the server • Issues • Need routers to support multicasting • Address assignment mechanism • Reliability • Difficult to specify the recipients • Without concerning about the content or structure of the information being delivered -CBM RMTP

  9. RMTP – Intro and Features • A protocol that uses IP multicasting for the reliable delivery of data from a sender to a group of receivers • Emphasis is on reliability and scalability • Reliability – RMTP compensates for the reliability shortcomings of IP multicasting by monitoring ACKs and NACKs responses from clients • Scalability – (1) independent state information (2) uses a receiver-driven approach (3) groups receivers into local regions • Three main entities: (1) Sender, (2) Receiver and (3) Designated Receiver • Designated Receiver (DR) • assists the sender in processing ACKs and in retransmitting data • Solves the problem of ACK implosion

  10. RMTP – Protocol Description

  11. RMTP – Protocol Description

  12. RMTP – Protocol Description

  13. RMTP – Protocol Description

  14. RMTP - Performance

  15. Content-Based Multicast (CBM)2 • Problem • IP multicast doesn’t concern with the content or structure of the information being delivered. • Solutions • Multiple layers in the same multicast group • Multiple groups corresponding to different information sources • Content-Based Multicast - CBM • Add filters on IP or Application-level Routers 2. R. Shah, R. Jain, F. Anjum, Efficient Dissemination of Personalized Information Using Content-Based Multicast

  16. CBM System Model • An established multicast tree • Filters: A set of software modules • A hierarchical information schema to describe the disseminated information • Filter Criterion • Subscription Algorithm • Matching Algorithm • Filter Placement Algorithm Framework

  17. Lowest Tight Ancestor, P f (p) T (v, i, p) Node v f (l) f (r) j filters i-(j-1) filters The node has a filter The node does not have a filter Filter Placement Algorithm • Objective: Minimizing Total traffic for a given set of subscriptions with K filters, assuming required flow values are provided at each node. If v is a leaf then T(v,i,p)=0 for all p,i Otherwise 0<=j<i T (v, i, p)= min {f (l) + f( r)+min[T(l,,j,l)+T(r,i-j-1,r)], 2f(p)+min[T(l,j,p)+T(r,i-j,p)]} f (v): the information flow into vertex v T(v,i,p): the minimum total traffic in Tree (v) given that up to i filters can be placed in Tree (v) and the Lowest Tight Ancestor of v is p Lowest Ancestor of v : the lowest ancestor of v whose parent has a filter i filters, max

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