Explain the term simplex, half-duplex and full-duplex used in communication dialog mode

Simplex

In simplex operation, a network cable or communications channel can only send information in one direction; it's a “one-way street”. A good example would be your keyboard to your CPU. The CPU never needs to send characters to the keyboard but the keyboard always sends characters to the CPU. In many cases, Computers almost always send characters to printers, but printers usually never send characters to computers (there are exceptions, some printers do talk back). Simplex requires only one lane (in the case of serial).

Half-Duplex

Technologies that employ half-duplex operation are capable of sending information in both directions between two nodes, but only one direction or the other can be utilized at a time. This is a fairly common mode of operation when there is only a single network medium (cable, radio frequency and so forth) between devices. The only advantage that Half-Duplex would have is the single lane or single track is cheaper then the double lane or double track.

For example, in conventional Ethernet networks, any device can transmit, but only one may do so at a time. 

Full-Duplex

In full-duplex operation, a connection between two devices is capable of sending data in both directions simultaneously. Full-duplex channels can be constructed either as a pair of simplex links (as described above) or using one channel designed to permit bidirectional simultaneous transmissions. A full-duplex link can only connect two devices, so many such links are required if multiple devices are to be connected together.

The three main characteristics of analogue signals are,

• 
  Amplitude
  

• 
  Light Switches: Either ON or OFF
  
• 
  Doors: Either OPEN or CLOSED
  

While bandwidth is used to describe network speeds, it does not measure how fast bits of data move from one location to another. Since data packets travel over electronic or fiber-optic cables, the speed of each bit transferred is negligible. Instead, bandwidth measures how much data can flow through a specific connection at one time.

Concentrators are also used in local-area networks (LANs) to combine transmissions from a cluster of nodes. In this case, the concentrator is often called a hub or MAU.

In parallel transmission, multiple bits (usually 8 bits or a byte/character) are sent simultaneously on different channels (wires, frequency channels) within the same cable, or radio path, and synchronized to a clock. Parallel devices have a wider data bus than serial devices and can therefore transfer data in words of one or more bytes at a time. As a result, there is a speedup in parallel transmission bit rate over serial transmission bit rate. However, this speedup is a tradeoff versus cost since multiple wires cost more than a single wire, and as a parallel cable gets longer, the synchronization timing between multiple channels becomes more sensitive to distance. The timing for parallel transmission is provided by a constant clocking signal sent over a separate wire within the parallel cable; thus parallel transmission is considered synchronous.

In serial transmission, bits are sent sequentially on the same channel (wire) which reduces costs for wire but also slows the speed of transmission. Also, for serial transmission, some overhead time is needed since bits must be assembled and sent as a unit and then disassembled at the receiver.

Serial transmission can be either synchronous or asynchronous. In synchronous transmission, groups of bits are combined into frames and frames are sent continuously with or without data to be transmitted. In asynchronous transmission, groups of bits are sent as independent units with start/stop flags and no data link synchronization, to allow for arbitrary size gaps between frames. However, start/stop bits maintain physical bit level synchronization once detected.


Explain the term synchronous and asynchronous transmission
The term synchronous is used to describe a continuous and consistent timed transfer of data blocks.

Synchronous data transmission is a data transfer method in which a continuous stream of data signals is accompanied by timing signals (generated by an electronic clock) to ensure that the transmitter and the receiver are in step (synchronized) with one another. The data is sent in blocks (called frames or packets) spaced by fixed time intervals.

Synchronous transmission modes are used when large amounts of data must be transferred very quickly from one location to the other

asynchronous transmission works in spurts and must insert a start bit before each data character and a stop bit at its termination to inform the receiver where it begins and ends.

• 
  A HUB is a device for connecting multiple ethernet devices together & making them act as single
  
• 
  It does not manage any network traffic
  
• 
  It is just a BROADCAST device
  

• 
  reduces the number of collision domains 
  
• 
  connects LAN segments 
  
• 
  increases the number of collision domains 
  
• 
  filters data before forwarding it to its destination on the network
  

In it's most common configuration, NAT maps all of the private IP addresses on a home network to the single IP address supplied by an Internet Service Provider (ISP). This allows computers on the home LAN to share a single Internet connection. Additionally, it enhances home network security by limiting the access of external computers into the home IP network space.

Role:

• 
  NAT is a very important aspect of firewall security. It conserves the number of public addresses used within an organization, and it allows for stricter control of access to resources on both sides of the firewall.
  
• 
  NAT can be used to allow selective access to the outside of the network, too. Workstations or other computers requiring special access outside the network can be assigned specific external IPs using NAT, allowing them to communicate with computers and applications that require a unique public IP address. Again, the firewall acts as the intermediary, and can control the session in both directions, restricting port access and protocols.
  

There are two types of ISDN:

• 
  Basic Rate Interface (BRI) -- consists of two 64-Kbps B-channels and one D-channel for transmitting control information.
  
• 
  Primary Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe).
  

ISDN Disadvantages

• 
  The disadvantage of ISDN lines is that it is very costly than the other typical telephone system.
  
• 
  ISDN requires specialized digital devices just like Telephone Company.
  

ISDN Advantages

Frame relay has traditionally provided a cost-effective way for telecommunications companies to transmit data over long distances.

VoIP calls can be made on the Internet using a VoIP service provider and standard computer audio systems. Alternatively, some service providers support VoIP through ordinary telephones that use special adapters to connect to a home computer network. 

• 
  Lab administration
  
• 
  People with disabilities
  
• 
  Point of care testing
  
• 
  Controlling patient data
  

• 
  More efficient learning methods
  
• 
  Ideal for campus wide coverage
  

• 
  Mobile scanners
  
• 
  Direct inventory mgmt.
  

• 
  Product Management
  
• 
  Field based data collection
  

• 
  Mobility
  
• 
  Ease of installation
  
• 
  Cost
  
• 
  Flexibility
  
• 
  Speed
  
• 
  Roaming
  
• 
  Use unlicensed part of radio spectrum
  

• 
  Limited range
  
• 
  Degradation in performance
  
• 
  Interference
  

Features:

• 
  Scalability
  
• 
  Quality of service
  
• 
  Range
  
• 
  Coverage
  

• 
  Speed: Faster than broadband service
  
• 
  Wireless: easier to extend suburban & rural areas
  
• 
  Broad coverage: Much wider coverage than Wi-Fi
  

• 
  Lack of quality
  
• 
  Epxensive network
  
• 
  Bad weather
  
• 
  Power consuming
  

• 
  Range of technology & service level choice for both fixed & wireless broadband operators
  
• 
  Rapidly declining fixed broadband prices
  

1. 
   It possesses the ability of digital treatment and transmission for multiple signals including voice, data and television conference. When transmitting voice, data and television conference, data compression technology has been widely adopted.
   
2. 
   Flexible multi-access mode. The transmission line from primary station to remote small station is called outbound or outroute while the transmission link from small station to primary station is called inbound or inroute.
   
3. 
   Network management system is more and more perfect.
   
4. 
   Abundant network topological structure. Network topological structure of VSAT has three kinds which are star-shaped, meshed and composite. Star-shaped structure mainly applied in data communication must have primary station. Meshed structure mainly applied in voice communication doesn’t have primary station. And composite structure with more complex network management and channel control is available for large website comprehensively transferring multiple sets of information. The selection of network topological structure is mainly based on business demand.
   
5. 
   Compared with other communication ways, VAST system possess the characteristic that communication link cost is not relevant to the distance, thus it is particularly applied to remote areas.
   
6. 
   VSAT system expansion is easier. Use scope and transmission ability of VSAT can be expanded as long as the number of small station is increased and the bandwidth of uplink carrier and downlink carrier is adjusted according to the demand.
   

Network management can be a tedious and time-consuming business for a human administrator. Network virtualization is intended to improve productivity, efficiency, and job satisfaction of the administrator by performing many of these tasks automatically, thereby disguising the true complexity of the network. Files, images, programs, and folders can be centrally managed from a single physical site. Storage media such as hard drives and tape drives can be easily added or reassigned. Storage space can be shared or reallocated among the servers.

• 
  Packet