Cell phone cloning

What is cell phone cloning ?

Introduction and definition :-
Cell phone cloning is copying the identity of one mobile telephone to another  telephone .Usually this is done for the purpose of making fraudulent telephone calls .The bill for the calls go to the legitimate subscriber .This made cloning very popular in areas with large immigrant populations , where the cost to "call home" was very steep . The cloner is also able to make effectively anonymous calls ,which attracts another group of interested users.

History
Cell phone cloning started with Motorola "bag" phones and reached its peak in the mid 90's with a commonly available modification for the Motorola "brick" phones , sch as the Classic, the Ultra Classic , and the Model 8000.

Significance
Cloning involved modifying or replacing the EPROM in the phone with a new chip which would allow you to configure an ESN (Electronic Serial Number) via software. You would also have to change the MIN (Mobile Identification Number).

Benefits
When you had successfully changed the ESN/MIN pair , your phone was an effective clone of the other phone.

Theories/ Speculation
Cloning required access to ESN and MIN pairs. ESN/MSN pairs were discovered in several ways:
Sniffing the cellular network
Thrashing cellular companies or cellular resellers
Hacking cellular companies or cellular resellers
Phone are more difficult to find and newer phones have not bee successfully reverse - engineered.

Cloning has been successfully demonstrated under GSM , but the process is not easy and it currently remain in the realm of serious hobbyists and researchers.

Transport Layer Protocols

Need of Transport Layer
a. The Internet layer provides unreliable , connectionless service - "best effort" network.
b. The underlying layer (internal layer ) provides the connectionless protocol IP .
c. Datagrams may be lost or reordered .
d. Datagrams can be duplicated or delivered after long delays .
Thus , there is a need for a layer , which takes care of end - to - end delivery.

Features of transport layer
i. True end to end layer .
ii. Takes care of process to process delivery.
iii. Acts as a liaison between the application layer and the underlying internetwork details .
iv. Shields the applications  from  the complexities of the internetwork.
v. Provides a "logical communication " between application processes running on different hosts .

For this purpose ,it performs the following duties:
i. Packetizing : Divides the application data into packets to be sent over the internetwork .
ii. Connection Control : Controls the "logical " connection between applications processes on source and destination hosts .
iii. Addressing: The packets have to be given to the correct application in the destination machine . For this purpose ,the transport layer uses port numbers to identify the application .

Types of Transport Protocols
The end to end applications require transport services of different types.
a. Some applications like file transfer ,remote login,etc. require reliable ,full duplex , data transmission .
b. Applications using client -server communication ,internet  telephony etc. do not need reliable communication but the communication has to be done at high speed.
Hence there are two protocols in the transport layer :
i. Connectionless unreliable service - UDP
ii. Reliable byte -stream service - TCP

i. UDP
User Datagram Protocol
UDP is a connectionless
unreliable protocol.
- No connection is established  between the sender and receiver beforehand.
- "Best effort" i.e. UDP segments may be lost or delivered out of order .
It does not provide flow and error control.
The sender and receiver applications are identified by ports .
It does multiplexing at the source and demultiplexing at the receiver to deliver data segments to the correct application.

Why is UDP used ?
In spite of the fact that is connectionless and unreliable , UDP is used because
i.    It is a very simple protocol.
ii.   Requires minimum overhead.
iii.  Communication is much faster.
iv.   Some applications themselves do flow and error control. For them, UDP is ideal.

UDP Datagram
The various fields of the datagram are as follows:
Source Port Number (16 bits): Port number used by process running on source host.
Destination Port Number (16 bits ) : Port number used by process running  on destination host.
Length (16 bits ) : Total length of datagram.
Checksum (16 bits ): Optional field . Used to detect errors.

UDP Applications:
i.  It is used for one off data transfer applications.
ii.  If a process requires request response communication like DNS ,UDP is used.
iii.  Some processes have internal error and  flow control mechanisms. They can use UDP, which will be faster. Example : Trivial File Transfer Protocol (TFTP).
iv.  Used in multimedia applications where a stream of multimedia data has to be sent from the source to the receiver.
v.   TCP does not support multi casting or broadcasting . Hence ,applications requiring multi casting or broadcasting use UDP.
vi.  Used in router updating protocols for updating router tables
vii. It can also be used for reliable data transfer, if reliability is added at the application layer.
viii.  Used in Network  Management Protocols like SNMP for communication between manager and agent processes .