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  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

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

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

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 CMP UDP/IP multicasting

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

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

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

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

RMTP – Protocol Description

RMTP - Performance

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

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

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 j filtersi-(j-1) filters f (l) f (r) Node v T (v, i, p) Lowest Tight Ancestor, P f (p) The node has a filter The node does not have a filter i filters, max