Networks Flashcards
What is a network?
A group of 2 or more devices that are able to communicate with each other
Name 2 Variations of connections.
Connection oriented where there is a open and closed connection e.g. Landline
Connectionless where data is just sent along and we dont know the direction E.g. The postal system. The protocol for connectionless is IP
Name all the topologies and at least 1 advantage and disadvantage
Bus Dis - There are collisions. If 1 node fails the whole network fails
Bus Adv - Quick and easy to set up
Token ring Adv - * All nodes on the network have a chance of transmitting data
* It has good quality service
* There are no collisions
Token ring Dis - * If one node or cable goes down so does the whole network
* Tokens get lost or corrupted
* Difficult to add and delete nodes to/from the ring]
Hierachical topolgy
Star dis - Central point of failure
Nodes can get Isolated
Star adv - Less traffic
Mesh adv - less traffic
Mesh dis - Expensive
Compare the ring and bus topology
Ring has no collisions and poor latency.
Bus has collisions but better latency.
What does CSMA/CD stand for
Carrier Sensor Multi-access collision detection
Describe the steps for CSMA/CD ?
- The algorithm is listening for transmissions of data(Listening for the voltage). Once it cannot hear any more transmissions then you can then start a transmission
- Then it checks if there are collisions if not then it finishes the transmission
- If there is transmission then it transmits data until the maximum packet time(time to deliver data) is reached in order to alert all other nodes that there has been a collision
- Once alerted there is a random back off algorithm that is run so when nodes start transmitting again no 2 nodes transmit at the same time in order to avoid collisions
How do collisions happen ?
When 2 devices try to transmit at the same time.
Go through access and distribution rules?
Access rules follow the CSMA/CD algorithm.
The distribution rules allow traffic to go everywhere but only one packet at a time.
Ethernet devices also follow access and distribution rules
What is POE ?
Stands for power over ethernet. This is when you use thernet cabling to deliver power to some devices connected to the ethernet like the telephone and WAP.
It is useful when you dont have power outlets
What is a gateway used for ?
To access another network beyond your own over the internet
What is octetcs ?
The 4 groupings in the IP address
What are the 2 types of IP ?
Static IP - IP that doesnt change
Dynamic IP - IP allocated from the main part of the domain
How many bits are used for IPv4 and IPv6
IPv4 - 32 bits
Ipv6 - 128 bits
What is the difference between hardware and software ?
Hardware is what physically connects devices in a network.
Software is what enables us to use the hardware for info exchange
What does ISO stand for ?
International Organisation for Standardisation
Why do we need Standardisation ?
So we get effective networks that are compatible and can communicate with each other
What does NIC stand for?
Network Interface Card
Describe the 3 way handshake ?
- Node wants to communicate with server so we send data over and tries to sync with the server
- Once this sync is acknowledged by the server the sequence number of the packet number is incremented and becomes the acknowledgement number
- Then the node gets a new sequence number
- Then when the node gets sent out there is a new sequence number
The previous sync becomes the acknowledgment number but increments
When sending data how do we determine if the location is on the same network or another network?
We use the ARP (Address Resolution Protocol )
How many bits are used for subnet mask fields ?
32 They are used to determine the network and host address
Describe the NIC ?
NIC allows us to communicate across the network
NIC has MAC address
NIC read all broadcast messages
Why go digital ?
Most computer data is digital
Higher data rates
It is easier to switch
Better data rates
What does interoperable mean ?
This means all devices can connect on the network regardless of the operating system.
Name some characteristics of the switched ethernet ?
. Automatically learns source address
. Forwards selectively to the destination
. Supports many ports per switch
. Supports different rates in each port
What is the difference between a switch and a hub ?
The switch operates in store and forward meaning it holds the packet interrogates it and forwards the packet
* Switch checks the header so less time efficient but fewer collsions
* Switch gets a ping return with the IP address
. Switches have a look up table
Hub just takes info in and sends the data straight away. It handles one packet at a time.
. Hub brodcasts data
* Advantage is time efficiency. Disadvantage is increased collision
What are the 2 types of virtual circuits ?
Switched virtual circuit (SVC) and Permanenet virtual circuit (PVC)
Give some characteristics of value added LANS?
. Unlimited distance
High speed and expensive and complex design
Give examples of a switched virtual circuit (SVC)
. Dial up lines
. X.25
. ATM
Give an example of a permanent virtual circuit (PVC)
. Frame relay
. Virtual circuits
. ATM
What is a virtual LAN?
Software that gives the appearance of a physical connection. E.g a VPN
Give some other names for data
Packets or frames or cells
. Packet and frames are of variable length. This means they require software processing which limits the data processing e.g. X.25
What data is fixed length?
Cells. They are processed in hardware meaning higher data rates
What is an alternative to X.25?
Frame relay
What is x.25 ?
X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks
Compare x.25 and frame relay
X. 25 is worldwide but frame relay is only in countries with fibre optic infrastructure
X.25 uses virtual circuits to establish connections between devices, which means a dedicated connection is created for data transmission. Frame Relay, on the other hand, uses virtual circuits as well but is more focused on efficient data transmission without error checking.
In summary, X.25 is an older, slower, and more reliable protocol, whereas Frame Relay is a faster and more efficient protocol. X.25 focused on error detection and correction, while Frame Relay prioritized speed and efficiency.
What is a protocol?
A protocol is a set of instructions for how devices should communicate in a network
What is a packet?
A packet is a unit or package of data sent across a network.
Describe the makeup of a packet
Header - This conatins the recipeint and sender address. It also has coding to handle transmission errors. It also contains the time the packet has to live
Payload - The actual data being transported
The trailer - Contains error checking stuff like checksum
What does UDP stand for?
User datagram protocol
What does TCP/IP stand for?
Transmission Control protocol / Internet Protocol
How are packets sent across a network using TCP/IP?
1.) Data is split into packets by the IP part of TCP/IP and is given header info. (The IP part also determines how much data can fit into a single packet)
2. ) Using the header info the routers determine the best path for each packet to be sent along.
3. ) Once the packet has reached its final destination the TCP part reassembles packets and checks their integrity. If any packets are missing or damaged it requests that those packets are resent.
Describe UDP?
Works like a connectionless network meaning when it gets data it just sends it regardless of whether you can receive it or not
. It is an alternative to TCP, it has a poorer quality of service but is faster.
Compare UDP and TCP
. UDP is connectionless TCP is connection-oriented
. TCP is used for reliable transport UDP is used for unreliable transport
. UDP is also used for broadcasts and real time
Describe how data is sent using layers
. If the destination is local the node can communicate directly else use a gateway
. Once the packet is prepared it’s passed to the network layer.
. The network access layer transmits the packet to the connection media
Describe receiving data using layers
. When the packets received they are checked for corruption and the correct address
. If all is good the network access layer extracts the data and passes it to the correct protocol
What is OSI reference model?
Enables better compatibility and interoperability between network technologies
What is the acronym for the OSI reference model ?
Please Do Not throw Salami Pizza Away
What are the 7 layers of the OSI reference model?
. Physical
. Data link
. Network
. Transport
. Session
. Presentation
. Application
Describe the physical layer ?
Deals with the physical characteristics of hardware e.g. Voltage levels, timing of voltage, changes and physical data rates
Describe the data link layer ?
Deals with transmission across the media
Can provide reliable transit of data across a physical link by using the MAC address
Describe the network layer?
Defines end-to-end delivery of packets and makes use of routers.
Describe the transportation layer
Regulates info flow to ensure end-to-end connectivity between host applications is reliable and accurate
Breaks data at the host then reassembles it at the recipient end
Makes use of TCP and UDP
Describe the session layer
Defines how to start control and end conversations between applications
It synchronizes dialogue between 2 hosts’ presentation layer and manages their exchange
Describe the presentation layer?
Ensures that the application layer of one system sent out is readable by the application layer of another system
Describe the application layer
Provides network services to the users applications
It synchronizes and establishes agreement on procedures for error recovery and control of data integrity
Describe layered protocol envelopes
Protocol info is used as an envelope at each layer.
Protocol is added and removed at each layer
What things should you consider when choosing cabling media?
. Bandwidth
. Electrical interference
. Cable length
. Cost
. Environment
Name some wireless approaches?
. Satellite communication
. Radar
. Cellular communication
. GPS
. Wi-Fi
. Bluetooth
. Radio Frequency Identification (RFID)
Name some wired approaches.
. Twisted pair cabling
. Coaxial cabling
. Fibre optic cabling
Give some info on unshielded twisted pair?
. Least expensive
. Can go up to 100m
. Cat 6 is the latest form of unshielded twisted pair
. Token ring makes use of this