Week 1 - Overview Internet Flashcards
Describe briefly the history of the internet?
1972: The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite.
1973: Internet - Robert Metcaffe’s phD Thesis proposes the Ethernet which is still used for LAN, MAN, and WAN.
1983: Formalised use of TCP/IP and DNS in the Ethernet
1988: TCP Congestion control added
1992: The World Wide Web developed by Tim Berners Lee in CERN becomes available to everyone.
2000s: Javascript
2007: Cellular
Today: Mostly video streaming on the network - content distribution networks (CDNs)
What were some of the design philosophy and principles of the internet?
Designed for minimalism, autonomy - no internal changes required to interconnect more, best effort model, stateless routers, decentralized control.
End-To-End argument: important functions left to the end systems. This allowed for fate-sharing which means that functionality only breaks in the end system which would make the comms useless anyway.
Briefly describe LAN, MAN, WAN, PAN
Local Area Network:
Connects computers physically close (<1 mile)
- high speed
- multi-access
Technologies:
- ethernet, token ring
Data Center Networks
Metropolitan Area Network
Between LAN and WAN
- Campus networks
Technologies:
- Microwave
- Optical
Wide Area Network
Connects far apart
- Higher Delay than Lan
- Less Reliable
Technologies
- Telephone lines
- Satellite comms
- Ethernet
Personal Area Network
A niche market but growing. Mostly dominated by bluetooth but new low wifi technologies may change things. Energy is critical.
Technologies:
- Healthcare and Internet of Things
What are the four addressing methods?
Unicast: one destination
Broadcast: all hosts in a network
Multicast: all members of a group
Anycast: sent to closest member of a group
What are the quality of service metrics?
Throughput: Measured in bits/s
Packet loss: congestion in the network, link failures, queueing policies
Delay: packet end to end delay - example: financial services
What are the types of delay?
Propagation delay:
- Dominated by speed of light on fibre (210km per milisecond)
Queueing Delay:
- Each link has a queue. Overloaded links can have delays.
Processing Delay:
- Router, wireless points, end hosts take time to analyse the packet
Packetization delay:
- Time to acquire the data to be sent i.e. voice to be encoded
Transmission delay:
- Determined by data rate links. 1mbps link takes 10ms to send 10000 bit packet.
What is a connection-oriented service?
Uses circuits.
1. A single path is first established for each new connection
2. The network guarantees that data are delivered in order.
3. No loss or duplication.
4. Any issues and connection breaks.
5. Bandwith can be guaranteed on setup.
Examples: cellular networks
What is a connectionless service?
Uses datagrams (frames)
1. Each datagram is independently routed.
2. Each datagram includes a destination address.
3. No guarantee that the datagram is delivered in order.
4. No guarantee that not lost or duplicated.
5. No setup required
6. Best effort delivery
7. Resources shared, little waste of bandwith
Examples: internet
What is the OSI Reference Model?
Created during the deployment of the internet. Published in 1984 by ISO. Consists of: reference model organizing networking functions in 7 layers and a set of specific protocols for each layer (never really deployed but with very interesting ideas.
What are the 7 layers of the OSI protocol?
- Physical Layer:
- Transmits raw bits over a comms channel. - Datalink Layer:
- Ethernet Frame with mac address source/destination, ether type, the data itself and the checksum bytes - Network Layer
- Path selection between end-systems (routing), subnet flow control, fragmentation and reassembly, translation between network types. - Transport Layer
- provides virtual end-to-end links between peer processes. end-to-end flow control/congestion control. Reliable comms. - The session layer
- Dialog control (keep track of whose turn it is to transmit), token mangement (preventing both parties from attempting the same critical operations), synchronization (checkpointing long transmissions to allow time to pick it up from where they left in the event of a crash and recovery). Usually implemented by the application itself. - Presentaiton layer
- Data encryption, compression, conversion (many protocol suites don’t include a presentation layer). - Application Layer
- Anything not provided by any of the other layers (HTTP for the WWW -> used to get web browsers to get web pages from servers).
What is CSMA/CD?
Carrier Sense Multiple Access with Collision Detection
1. Computers sense the medium to check if anybody is transmitting. If not, they start sending.
2. While sending they check if the wave is changed. if it does, then a collision is detected. The computer waits a random amount of time and then retransmits again.
How can the data link layer correct for errors?
Error correcting codes:
- Hamming codes
- Binary convolutional codes
- Reed-salomon codes
- Low-density parity check codes
Error detecting codes:
- Parity
- Checksum
- Cyclic Redundancy Code
What technologies are used to connect networks?
Repeater (physical layer)
- Copies bits from one part of the same network to another - doesn’t look at any bits just regenerates - allows extension of network beyond physical length limitations. Another example of this is a hub (like a service bus) where there’s multi access).
Bridge (data link layer)
- Copies bits from one part of the network to a different one. Can be selective and copy selective frames.
Router (network layer)
- Transfers packets form one network to another. Make decisions about what route a packet should take (looks at network headers).
Gateway (network layer and above)
