Push Technology Humie Leung Annabelle Huo Introduction n

Push Technology Humie Leung Annabelle Huo

Introduction n n Push technology is a set of technologies used to send information to a client without the client requesting it Push versus 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. ¨ n n 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 n Issues on Push using IP multicasting n Proposed Solution ¨Reliable Multicast Transport Protocol RMTP n

Continuous Multicast Push n 1 (1998) Comparison of CMP and AMP (Asynchronous Multicast Push 2) CMP Framework n Problems with using CMP and solutions n Issues of the Use of IP Multicast for Push n 1. 2. P. R. Rodriguez, E. W. Biersack, Continuous Multicast Push of Web Documents over the Internet J. Nonnenmacher, E. W. Biersack, Asynchronous Multicast Push: AMP

AMP & CMP: Push Categories Push Non-periodic Unicast Email Lists (Individual unicast messages to multiple clients Multicast Broadcast Asynchronous Multicast Push (AMP) Periodic Unicast Multicast Continuous Multicast Push (CMP) Broadcast

CMP: Framework n 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. ¨ n Web server ¨ ¨ n Monitor documents Transmission Clients ¨ Subscribe interested information n how to join the multicast group CMP UDP/IP multicasting

Server 1. Advertise Information 5. Push Info to G 1 (Eg. 225. 1. 1. 1) 2. Look up services 3. . Return multicast address and port number G 1 G 2 4. . Send IGMP message to tell local router to join the group G 1 IGMP: Internet Group Membership Protocol

CMP: Problems and Solutions n Server End Problem: How to monitor the number of requests for a document at any moment, based on that to decide whether the document is popular or not ¨ Solution: Polling the multicast channel periodically for the feedback but have to avoid the feedback implosion ¨ n Reliability ¨ n 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 n n n Need routers to support multicasting ¨ Tunneling: encapsulate multicast IP packets in Unicast IP packets. MBone the multicast backbone is spammed in this way connecting islands with native multicast support Session Servers or Session Mechanism ¨ Session Description Protocol /Session Announcement Protocol, or use a function to map the document’s URL to the multicast address Assignment Mechanism ¨ Two types of groups: permanent with an permanently assigned address and transient which group gets a multicast address only as long as they have members Difficult to specify the recipients ¨ Host membership is dynamic meaning that hosts can enter and leave a group whenever they wish ¨ The number of hosts in a multicast group is not limited ¨ A host can send multicast datagram to a multicast group without being a member of that group Reliability: UDP is used without any control functions Without concerning about the content or structure of the information being delivered ¨ Multiple groups corresponding to different information sources ¨ Content-Based Multicast 3 Extra content filtering is performed at the interior node of the IP multicast tree 3. R. Shah, R. Jain, F. Anjum, Efficient Dissemination of Personalized Information Using Content-Based Multicast RTMP

RMTP – Intro and Features n n A protocol that uses IP multicasting for the reliable delivery of data from a sender to a group of receivers Emphasis is on (1) reliability (2) scalability (3) heterogeneity Reliability – RMTP compensates for the reliability shortcomings of IP multicasting by monitoring ACKs responses from clients ¨ Scalability – (1) independent state information (2) uses a receiver-driven approach (3) groups receivers into local regions ¨ Heterogeneity – RMTP handles receivers in heterogeneous network environments in an efficient manner ¨

RMTP - Entities n Three main entities: (1) Sender, (2) Receiver and (3) Designated Receiver (DR) ¨ Sender n divides data into fixed-size packets ¨ Receiver n periodically sends ACK packets to sender/DR ¨ DR n assists processing ACKs and in retransmitting data n Alleviates ack-implosion problem n Data Cache - needs to buffer entire data file

RMTP – Protocol Description

RMTP - Performance

Conclusion n CMP - Continuous Multicast Push n RMTP - Reliable Multicast Protocols