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55 Cards in this Set
- Front
- Back
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List the "nuts and bolts" of the internet |
Hosts = end systems Running network apps Communication Links Packet Switches (routers and switches) |
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Internet: _______ of ________; interconnected _____ |
network of networks; interconnected ISPs |
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Protocols control _______________________ |
Controls sending and receiving of messages (e.g. TCP, IP, HTTP) |
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Internet standards |
RFC: Request for comments IETF: Internet Engineering Task Force |
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What is the internet from a service view? |
Infrastructure that provides services to applications: Web, VoIP, email, games, social-networks.
Provides programming interface to apps: -hooks that allow sending and receiving app programs to "connect" to Internet -provides service options, analogous to postal service |
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What is a protcol? |
A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event. |
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Network Edge |
-Hosts: Clients and servers -Servers often in data centers |
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Access networks |
The network that physically connects an end |
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Network Core |
-interconnected routers -network of networks |
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How to connect end systems to edge router? |
-Residential access nets -Institutional access networks -Mobile access networks |
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Frequency division multiplexing (FDM) |
Different channels transmitted in different frequency bands |
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Shared wireless access network connects _______ to _______ |
end systems to router |
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Host sending packets of data function: |
-takes application message -breaks into smaller chunks, known as packets, of length L bits -transmits packet into access network at transmission rate R -link transmission rate aka link capacity, or bandwidth |
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Packet transmission delay = |
Time needed to transmit L-bit packet into link = L (bits) / R (bits/sec) |
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Bit |
propagates between transmitter/receiver pairs |
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Physical link |
What lies between transmitter and receiver |
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Guided media |
Signals propagate in solid media: copper, fiber, coax |
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Unguided media |
Signals propagate freely: radio |
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Twisted Pair (TP) |
two insulated copper wires |
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Coaxial Cable |
-2 concentric copper conductors -bidirectional -broadband: -multiple channels on cable -HFC |
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Fiber optic cable |
-glass fiber carrying light pulses, each pulse a bit -high-speed operation -low error rate: -repeaters spaced far apart -immune to electromagnetic noise |
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Radio |
-signal carried in electromagnetic spectrum -no physics "wire" -bidirectional -propagation environment effects: -reflects -obstruction of objects -interference |
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Radio Link Types |
-terrestrial microwave -LAN (WiFi) -wide-area (cellular) -satellite |
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Packet Switching |
Hosts break application layer messages into packets: -forward packets from one router to next, across links on path from source to destination -each packet transmitted at full link capacity |
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Store and foreward |
Entire packet must arrive at router before it can be transmitted on next link |
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Queuing and Loss |
If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: -packets will queue, wait to be transmitted on link -packets can be dropped (lost) if memory (buffer) fills up |
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Routing |
Determines source-destination route taken by packets: -routing algorithms |
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Forwarding |
Move packets from router's input to appropriate router output |
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Circuit Switching |
Dedicated resources: no sharing Circuit segment idle if not used by call Commonly used in traditional telephone networks |
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What are the different paradigms that can be used in the network core to transfer data? which one is used in the internet? Explain the main difference between the two. |
The two different paradigms are packet switching and circuit switching. The current internet uses packet switching because of the high amount of users it has to service. The main difference between these paradigms is that circuit switching reserves lines for communication. This ensures the user using this line will have a stable connection. In packet switching, resources are shared (no lines reserved). This is usually sufficient because users aren't accessing the network 100% of the time. |
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Packet switching is great for _______ data |
bursty |
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End systems connect to internet via _____________ |
access ISPs |
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Access ISPs must be ________________ so that any 2 hosts can send packets to each other |
interconnected |
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Evolution of the network of networks was driven by ____________ and _______________ |
economics and national policies |
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Time-division multiplexing (TDM) |
Time is divided into frames of fixed duration, and each frame is divided into a fixed number of time slots. |
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The internet, the network of networks, contains |
access ISP, regional ISPs, tier1 ISPs, internet exchange points (IXPs), content provider networks |
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Types of delays |
Processing Delay Queuing Delay Transmission Delay Propagation Delay |
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Processing Delay |
-The time required to examine the packet’s header and determine where to direct the packet
-Includes the time needed to check for bit-level errors in the packet that occurred in transmitting the packet’s bits from the upstream node to the router |
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Queuing Delay |
-The waiting time for a packet to be transmitted onto the link.
-The length of the queuing delay of a specific packet will depend on the number of earlier-arriving packets that are queued and waiting for transmission onto the link. |
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Transmission Delay |
Assuming first come first server, the packet can only be transmitted after all the packets that have arrived before it have been transmitted.
So the transmission rate can be denoted as the length of packet L (bits) divided by the rate of transmission R (bits/sec) = L / R |
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Propagation Delay |
Once a bit is pushed into a link, it needs to propagate to the next router.
The time required to propagate from the beginning of the link to the next router is the propagation delay. The bit propagates at the propagation speed of the link.
The propagation delay is the distance d between two routers divided by the propagation speed s. d / s |
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Queuing Delay: L: Packet length (bits) a: average packet arrival rate La/R ~ 0 = _______________ La/R -> 1 = ________________ La/R -> 1 = ________________ |
La/R ~ 0 = Avg queuing delay small La/R -> 1 = Avg queuing delay large La/R > 1 = Avg delay infinite |
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traceroute program |
provides delay measurement from source to router along end-end internet path towards destination |
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Packet Loss |
Queue preceding link in buffer has finite capacity, so any packets arriving to a full queue will be dropped (lost). Lost packet may be re-transmitted by previous node, by source end system, or not at all. |
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Throughput |
Rate (bits/time unit) at which bits transferred between sender/receiver: -instantaneous: rate at given point in time -average: rate over longer period of time |
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Bottleneck link |
link on end-end path that constrains end-end throughput |
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Layers |
Each layer implements a service: -via its own internal-layer actions -relying on services provided by layer below
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Why layering? |
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Internet protocol stack |
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ISO/OSI Reference model |
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Malware can get in host from: |
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spyware malware |
can record keystrokes, web sites visited, and upload info to collection site |
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Denial of Service (DoS) |
Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overshelming resource with bogus traffic |
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Packet sniffing |
Broadcast media (shared ethernet, wireless) Promiscuous network interface reads/records all packets passing by |
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IP spoofing |
Send packet with false source address |
