Computer Network Unit 1 q what are the topologies in computer n/w ?

Q 7. What is bit stuffing?
Ans: Bit stuffing is the insertion of one or more bits into a transmission unit as a way to provide signaling information to a receiver. The receiver knows how to detect and remove or disregard the stuffed bits.


Q 8. Name the protocols used in signaling channel of the mobile phones ?
Ans: The protocol used in moile phones is GSM.
GSM

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  GSM stands for Global System for Mobile Communication and is an open, digital cellular technology used for transmitting mobile voice and data services.
  
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  The GSM emerged from the idea of cell-based mobile radio systems at Bell Laboratories in the early 1970s.
  
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  The GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard.
  
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  The GSM standard is the most widely accepted standard and is implemented globally.
  
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  The GSM is a circuit-switched system that divides each 200kHz channel into eight 25kHz time-slots. GSM operates in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US.
  
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  The GSM is owning a market share of more than 70 percent of the world's digital cellular subscribers.
  

Why GSM?

The GSM study group aimed to provide the followings through the GSM:

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  Improved spectrum efficiency.
  
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  International roaming.
  
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  Low-cost mobile sets and base stations (BSs)
  
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  High-quality speech
  
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  Compatibility with Integrated Services Digital Network (ISDN) and other telephone company services.
  
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  Support for new services.
  

GSM network areas:

In a GSM network, the following areas are defined:

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  Cell: Cell is the basic service area: one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell.
  
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  Location Area: A group of cells form a Location Area. This is the area that is paged when a subscriber gets an incoming call. Each Location Area is assigned a Location Area Identity (LAI). Each Location Area is served by one or more BSCs.
  
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