Classification of Data-Delivery Mechanisms in mobile computing

Data Dissemination and Broadcasting Systems:

Classification of Data-Delivery Mechanisms:

·         Push-based mechanisms (publish–subscribe mode)

·         Pull-based mechanisms (on-demand mode)

·         Hybrid mechanisms (hybrid mod

                      

Push-based Mechanisms:

·         Server pushes data records from a set of distributed computing systems

·         Examples of distributed computing systems advertisers or generators of traffic congestion, weather reports, stock quotes, and news report

A server or computing system pushing the data records from a set of distributed systems:

Publish–subscribe mode

• In which the data pushed as per the subscription for a push service by a user

Pushing Algorithm:

Select a structure of data records to be pushed

• An algorithm provides an adaptable multi-level mechanism that permits data items to be pushed uniformly or none uniformly after structuring them according to their relative importance

Data pushed at selected time intervals using an adaptive algorithm

• Pushing only once saves bandwidth

• However, pushing at periodic intervals important because it provides the devices that were disconnected at the time of previous push with a chance to cache the data when it is pushed again

3.      Bandwidths adapted for downlink (for pushes) using an algorithm

4. The same fixed periods can be used for pushing all records but usually higher bandwidth is allocated to records having higher number of subscribers or to those with higher access probabilities

5. A mechanism also adopted to stop pushes when a device is handed over to another cell

Advantage of push-based mechanisms

• Enable broadcast of data services to multiple devices

• Server is not interrupted frequently by requests from the mobile devices

• Best option for the server as they prevent server overload, which may occur due to flooding of device requests

Disadvantage of push-based mechanisms

• Dissemination of unsolicited, irrelevant, or out-of-context data

• User may not be interested in the disseminated data and may be inconvenienced

Pull-based Mechanisms:

User-device or computing system pulls the data records from the service provider’s application database server or from a set of distributed computing systems

On-demand mode from a set of distributed computing systems, music album server, ring tones server, video clips server, or bank account activity server

·         Records pulled and selective response to demand

·         Server transmits data packets as response selectively

·         After client-authentication, verification, or subscription account check

Pulling Bandwidth:

1. Used for the uplink channel depends upon the number of pull requests

• Assume that an uplink bandwidth of 19.2 kbps and service provider’s application distribution system server accept 384 kbps

• Then only 20 pull requests can be used at 19.2 kbps

• Number of pull requests is larger, the link channel bandwidth lowered to 9.8 kbps or 4.8 kbps

• Similarly, the service provider’s application distribution system adapting to the bandwidth required for serving the requests (downlink) in case the server is unable to deliver the response in a reasonable period

2. Threshold limits the number of pull requests in a given period of time

• Controls the number of server interruptions

3. A mechanism adopted to prevent access when handed over to another cell.

• On device handoff, the subscription cancelled or passed on to the new service provider system

Advantage of Pull-based mechanisms:

·         No unsolicited or irrelevant data arrives at the device

·         Relevant data disseminated only when the user asks for it

·         Best option when the server has very little contention and is able to respond to many device requests within expected time intervals

Disadvantage of Pull-based mechanisms:

·         Server faces frequent interruptions and queues of requests at the server may cause congestion in cases of sudden rise in demand for certain data records)

·         The energy and bandwidth required for On-demand mode when sending the requests for hot items and temporal records (records changing with time) large

·         The number of server interruptions and uplink bandwidth requirement may increase a thousand times in the pull mode for hot records (e.g. World cup football score)

·         A large number of devices making requests to the service provider choke the network

·         The server is flooded with interruptions