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 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

CMPUDP/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 DescriptionSender

Router

Receiver

Router Router

Router RouterRouter

Router

Router


Router

Receiver

Router Router

Router RouterRouter

Router

Router

ACK

RMTP – Protocol Description

Sender

Router

Receiver

Router Router

Router RouterRouter

Router

Router

DesignatedReceiver


Router

Receiver

Router Router

Router RouterRouter

Router

Router

DesignatedReceiver

ACK

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 thenT(v,i,p)=0 for all p,iOtherwise 0<=j<iT (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 vT(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 filters i-(j-1) filters

f (l) f (r)

Node vT (v, i, p)

LowestTight

Ancestor, P

f (p)

The node has a filterThe node does not have a filter

i filters, max