9. Fundamentals of Communication and Networking Flashcards
Compare Serial and Parallel Communication.
In a Serial Communication, data is transmitted sequentially bit by bit over a single wire.
In a Parallel Communication groups of bits are sent simultaneously over multiple wires.
Parallel Communication has a limited upper range because the transmitted data is vulnerable to skew (bits arriving out of synch) and crosstalk which can corrupt the data. Whilst the simpler technology of Serial Communication and lack of interference can lead to higher transfer rates.
Compare Synchronous and Asynchronous Transmission.
Synchronous Transmission is where the sender and receiver have a shared timing signal which determines when bits are sent/received. This requires a dedicated connection and is difficult to achieve over long distance.
Asynchronous Transmission is where a start bit indicates when the receiver should start listening for transmitted data. Once the start bit is received, bits will be received at a constant rate until the stop bit is received. The start and stop bits are opposite of one another (0/1 or 1/0).
Define Bit Rate and Baud Rate, how are they related?
Bit Rate is the rate of transfer of data, measured in bits per second.
Baud Rate is the rate of change of the signal transfered over a communication channel.
If the communication channel can transfer more than two signal levels, then potentially more than one bit can be transferred per signal change. For example, if four signal levels can be transferred then 2 bits can be transferred per signal change.
Bit Rate = Baud Rate x #Bits per Signal Change
Define Bandwidth.
Bandwidth is the capacity to transfer data over a communication channel. This is an upper limit on the Bit Rate.
Define Latency.
Latency is the time taken from transmitting data, to it being received.
What is a Protocol?
A Protocol is a set of rules which define how communication happens between two devices.
What is a Network?
A Network consists of Hardware which allows computers and other devices to communicate with one another.
What is the difference between a LAN and a WAN?
A LAN is a Local Area Network, a Network over a small geographical area.
A WAN is a Wide Area Network, a Network over a large geographical area.
What are the characteristics of a Bus Topology Network?
A Bus Topology Network consists of a shared backbone cable over which all connected devices communicate. Transmissions are broadcast on the cable and can be seen by all devices, which is bad for data security. Only a single communication can happen on the cable at any one time, which means Bus Topology Networks decline in performance as more devices are added. If the cable fails the Network stops functioning, a single point of failure. Because only a single device can broadcast at any one time, the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) Protocol is used to manage the use of the shared cable.
What are the characteristics of a Star Topology Network?
A Star Topology Network consists of a central Switch which is connected by cables to each of the devices in the Network. The Switch directs packets of data to the correct device. Each device has its own dedicated cable, and so no collisions can occur and only devices involved in a communication see the packets. Cable failure means that only a single device is removed from the Network. Data can be sent simultaneously between multiple devices. If the switch fails the Network will also fail.
Describe how Client Server Network Applications work?
A Server consists of Software on a device that provides access to a resource. The resource may be files on a disk drive, a database, a printer amongst many other possibilities. In essence a Server provides a service to other computers called Clients. If a computer only runs Server Software then it is a Dedicated Server.
A Client will make a request to a Server which will process the request and create a response.
In Client-Server Network Applications, if the Server fails then the service it provides will stop functioning. Having all the data and Software related to a service on a single computer helps the management of that service.
Describe how Peer-to-Peer Network Applications work?
In Peer-to-Peer Network Applications all the computers involved have an equal level of importance to the maintenance of the service. They may be acting in the role of a Server, a Client, or both at the same time. Resources are spread across all devices in the network. If any one computer is removed from the Network it shouldn’t affect the provision of the service to the other devices.
An example of Peer-to-Peer Networking is Bittorrent where files are distributed across multiple computers. Whilst a computer is downloading a file, it is also uploading the parts of the file it has already downloaded to other computers in the Network.
What is WiFi? What Hardware does a WiFi Network require?
WiFi (Wireless Fidelity) is a technology for wireless Network communication.
Each device on a WiFi Network will require a Wireless Network Adapter. The Network also requires a Wireless Access Point (WAP) to coordinate the traffic in the Network.
What is an SSID?
An SSID is a Service Set IDentifier which is the name of a Wireless Network.
How is Network Security maintained in WiFi Networks?
A Protocol, such as WPA (WiFi Protected Access) or WPA II, require that devices connecting to a Wireless Access Point have the correct password and ensure that traffic is encrypted.
In normal operation the WAP will broadcast it’s SSID (Service Set Identifier), which is the name of the Network, to make it discoverable. If the SSID broadcast is disabled, then only devices which already know about the Network will be able to connect.
A Whitelist is a list of the MAC addresses which are allowed to connect to the Network, this can be used to restrict access to the Network to pre-approved devices.
Describe CSMA/CA with RTS/CTS and how it solves the Hidden Node Problem.
CSMA/CA is Carrier Sense Multiple Access with Collision Avoidance. It is a Protocol for devices sending data over WiFi Networks. The device will listen to see if someone is already sending data, if they are the device will wait for a period of time and try again. If no-one is sending data, then the device will transmit its data.
The Hidden Node Problem is when two devices are far enough from each other that they cannot directly sense whether the other is transmitting. This can lead to collisions, and a slowing of the Network.
RTS (Request to Send)/CTS (Clear to Send) is used to solve this issue. The CSMA/CA Protocol is followed, but instead of immediately transmitting data an RTS is sent to the WiFi Access Point (WAP). The WAP is at the centre of the Network and can see all devices. If the Network is idle the WAP will send a CTS which will cause the sender to transmit its data. If the sender doesn’t receive a CTS it will wait and start the whole process again.
What is the Internet?
The Internet is the physical infrastructure which connects Networks together across the globe.
What is Packet Switching?
Packet Switching is a method for sending data over Networks where messages are split into small Data Packets which are individually Routed across the Network to the destination.
What might you find in a Data Packet?
A Data Packet will consist of a Header, Payload, and sometimes a Trailer. The Payload is the data itself.
The Header will contain:
Sender’s IP Address
Recipient’s IP Address
Protocol
Packet Number
Time To Live
The Trailer may contain a Checksum or other Error Detection information.
What is a Router, and what does it do?
A Router is a piece of Network Hardware which connects two Networks which use the same communication Protocols. A Router forwards a Data Packet into the connected Network identifying the quickest route for it to get to its destination (Routing). Data Packets will be Routed from Router to Router across the Internet (or inside a LAN/WAN) to get to their destination as quickly as possible. Routers takes into account Network Load (traffic) when identifying how to Route a Data Packet to its destination.
