Computer Network and the Internet Flashcards
(47 cards)
Computer network definition
group of devices that uses common communication protocols over digital interconnections to share resources
Computer network main elements
Node, interconnections
Computer network: problems that brought to their development
Low flexibility of devices
Low exploitation of available computer resources
Computer networks have grown exponentially because
Standardization of protocols
Development of network design methodologies
Tech advancements
Computer network foundation principle
= client-server architecture
client = device that accesses shared resources
server = device that provides services
Computer networks are beneficial because
Allows resource (data + peripheral devices) sharing
Good ratio price-performance
High reliability
Expand incrementally
Computer network requirements
Connectivity
Resource sharing
Reliability
Performance
What does connectivity mean for Computer networks?
Nodes are interconnected through a communication subnetwork
Connectivity: types of nodes
End system:
- Master: manages communication
- Slave: forwards request/receives mex
Intermediate system: connects transmission channels
Connectivity: types of connections and topologies
Point-to-point:
- star
- tree
- ring
- complete mesh
- uncomplete mesh
Multipoint: slave can use channel if authorized by the master
Broadcast:
- Wireless: data travels through air, received by antenna, the broadcast channel has arbitration policies
- Bus
- Ring
Connectivity: a communication subnetwork is composed by
Intermediate Systems (that connect)
Transmission Channels
If the IS connects different subnetworks we talk about routers, if they are in the same subnetworks we talk about switches
Connectivity: the presence of IS forms switched networks: types
Circuit-switched network
- A private connection is opened between the nodes that want to communicate through a virtual path
- Time-based pricing
- Pros: delays only for electromagnetic propagation, no congestion, IS are low cost because don’t have intelligence
- Cons: wait for path search, low use of communication channel
Packet-switched network
- Mex are sent on the channel in limited-size packets. Each IS decides best route to sent the packet for it to reach its destination node
- Volume-based pricing
- Pros: efficient use of transmission channels, error detection and recovery done by IS
- Cons: possible packet lost, IS ar eintelligent so they cost more
Resource sharing operates on the principle of
Multiplexing (multiplexer = circuit that decides which node accesses the channel) and demultiplexing (circuit that sends data received through the channel to its destination)
Method of multiplexing-demultiplexing
Time-Division multiplexing:
- time divided into equal quanta of time, each stream can transmit for a quantum of time
Frequency division multiplexing
- all streams transmit packets on the channel with != frequencies, multiplexer decides priority of packages
Problems with de-multiplexing methods
Inefficient: time/frequency busy even if no packets, hard to add streams
new -> statistical multiplexing: quantum of time given only if the stream has something to transmit
What does reliability mean?
A network must ensure that the correct message arrives
Reliability: categories of fault
Altered bits -> parity bit
Packet loss (node overload, bit-level error, management sw error)
Physical connection/node down (operator’s fault, power down, sw not working)
Performance: influenced by
bandwidth -> P=n_of_bits*time_interval
latency -> time taken for a bit to propagate from one end of the channel to the other, Tprop + Ttrans + Tacc
Tprop
Propagation delay = dist/Vlight
T acc
queuing delay
Ttrans
Time to transmit a datum
Dim/P
size_of_data/bandwidth
L*P
= volume of the channel
= number of bits to send before the first bits reaches its destination
Bidirectional latency =
Round-Trip time
Networking devices
NIC card
Switch
Hub
Repeater
Bridge
Router
gateway
Firewall
