Transcript Push Technology

Push Technology
Humie Leung
Annabelle Huo
Introduction
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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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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.
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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
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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
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1. P. R. Rodriguez, E. W. Biersack, Continuous Multicast Push of Web Documents over the Internet
CMP: Framework
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CMP
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Web server
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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.
Monitor documents
Transmission
Clients
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Subscribe interested information
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how to join the multicast group
CMP
UDP/IP multicasting
CMP: Requirements
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Multicast Routers
 The network connecting is multicast capable for multicast routing and
maintaining state information for each active multicast group
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Session S ervers (session advertisement)
 E.g. map the document’s name (URL) into a multicast address.
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Address Assignment Mechanism
 Multicast addresses are not assigned to individual hosts, assignments
can change dynamically, and addresses sometimes have semantics of
their own.
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Request Monitoring
 The source server needs to check if any client has joined the multicast
group corresponding to some objects the server servers.
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Congestion Control
 UDP/IP multicast only provide multicast connectivity
CMP: Problems and Solutions
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Server End
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Problem: How to monitor the number of requests for a document at any
moment
 Solution: Polling the multicast channel periodically for the feedback
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Reliability
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Forward Error Correction Code (FEC)
Client End
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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
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Advantages
 Scalability
 Reduce the
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load on the server
Issues
 Need routers to support multicasting
 Address assignment mechanism
 Reliability
 Difficult to specify the recipients
 Without concerning about the content
the information being delivered - CBM
RMTP
or structure of
RMTP – Intro and Features
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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)
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assists the sender in processing ACKs and in retransmitting data
 Solves the problem of ACK implosion
RMTP – Protocol Description
Receiver
Sender
Router
Router
Router
Router
Router
Router
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RMTP – Protocol Description
Receiver
ACK
Sender
Router
Router
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Router
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RMTP – Protocol Description
Receiver
Sender
Router
Router
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Router
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Designated
Receiver
Router
Router
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RMTP – Protocol Description
Receiver
ACK
Sender
Router
Router
Router
Router
Router
Designated
Receiver
Router
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RMTP - Performance
Content-Based Multicast (CBM)2
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Problem
 IP
multicast doesn’t concern with the content or
structure of the information being delivered.
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Solutions
 Multiple
 Multiple
layers in the same multicast group
groups corresponding to different information
sources
 Content-Based Multicast - CBM
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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
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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
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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)=
Lowest
Tight
Ancestor, P
T (v, i, p)
f (p)
Node v
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 (l)
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
f (r)
j filters
i filters,
max
i-(j-1) filters
The node has a filter
The node does not have a filter