string and charecter array

Strings are const char arrys, they are readonly, cannot be modified
eg:
char *a="hello";
*a='b'; --> Causes runtime errors

Arrays are allocated in user data area and can be modified.
eg:
char a[]="hello";
*a='b';
cout<-->prints bello.

MMS(Multimedia Messaging Service)

MMS(Multimedia Messaging Service) is a non real time message delivery system that intended to provide rich set of content to the subscriber. Content can be images, audio, video or text. It comes under the set of 3G services

The architecure of MMS network would be as shown in the picture

MMS Client :- Mobile equipment that is used by the user to send the MMS

MMS Proxy Relay:- It provides the access to the other messaging components and to the components that stores the message

MMS Server :- Provides the storage of message

EMail Server:- Traditional Internet Mail server

Legacy wireless messaging system:- Existing messaaging systems like SMS and paging.

How MMS works?

MMS Client composes a MMS and submits it to the associcated MMS Proxy relay. Proxy relay resolvs the target target address and forwards the MMS to the target MMS Proxy relay. The target proxy relay saves the MMS in the MMS Server and sends a notification to the target client. Target MMS client retrives the MMS from the MMS Server and notifies the user. Once the user reqests for the rendering of the MMS the MMS client renders the MMS on the terminal

Global System for Mobile(GSM)

GSM is (Global System for Mobile) is a global system from digital mobile communication. It
comes under 2G tehnologies that offers high bit rate voice and limitted data communication. GSM uses a variation of Time Division Multiple Access(TDMA).

SIP

Introduction

SIP offers the possibility of users to start communication and services form any location and for network to identify the users wherever they may be.

•SIP is a Session Initialization Protocol
•SIP is an application layer protocol
•It is a signaling protocol
•SIP is an alternative to H323 protocol – the video conference transmission protocol.
•It establishes, modifies, and terminates media session.

Applications supported by SIP

•Video Conferencing
•Internet telephony
•Distance learning
•Multimedia distribution

Strengths of SIP

•Simplicity
•Scalability
•Extensibility
•Modularity


Five Facets of SIP

•User Location – Where are the end users of the session present?
•User Capabilities- What should be the media of communication and media parameters ?
•User availability – whether the called party is available for a communication?
•Call Setup – Establishing a call.
•Modifying session parameters – Manages the call.

Components in SIP

•User agent server
–Server application that contacts the user when a SIP request is received.
•User agent Client
–Client application that initiates the request
•Proxy server
–Intermediate program that act both as server and client.
•Redirect server
–It does not accepts call or initiates requests. It maps the address to one or more address and returns these address to client
•Location server
–It accepts the register request and offer location services.

Other Protocols that are used with SIP

•RTPàReal time Transport Protocol
•RTSPàReal Time Streaming protocol
•MEGACOàMedia Gateway Access Control Protocol
•SDPàSession description Protocol
•RADIUS/ DIAMETER- Remote Authentication Dial In User Service
•RSVP/YESSIR- Reservation Protocol/Yet another Sender Session Internet Reservations
•LDAPàLightweight Directory Access Protocol

Elf files

ELF means Executable and Linking Format. It is a file format executables, shared libraries, core dumps and object codes. It is now a competitor to other formats like a..out(Assembler Output) and COFF(Common Object File Format) in Unix based operating systems and even in non Unix based operating systems.

Types of Elf files

There are four types of elf types
Executable
It contains code and data that can be executed on a target operating system.
relocatable (.o files)
Created by compilers and assemblers, need to be processed by the linker before running. Relocatable (object) files can be considered as a foundation for creating executables and libraries.
shared object file
It contains information required the static and dynamic linking
core dump file
It is a file that contains the memeory image of the process that was terminated due to errors like memory address violation, illegal instruction, bus errors etc

All these elf types similar is their internal structure but serves purpose