Lecture 4 - Computer Networks and the Internet

[Queuing Delay] There is a _ for each outbound link at the router.

buffer

[Queuing Delay] If the buffer at the outbound link of the router is full, a new incoming packet will get ___.

dropped

[Queuing Delay] A ___ can happen when multiple senders simultaneously send to one receiver

packet drop

[Queuing Delay] A ___ can happen when a higher transmission rate host sends to a lower transmission rate host, etc.

packet drop

[Queuing Delay] When there is more data flowing in than the router can push out, ___ can occur.

queuing delay

[Queuing Delay] If buffer size is too _ there is not much room for new packets, resulting in a lot of packet loss

small

[Queuing Delay] If buffer size is too _, packets get stuck in ‘traffic jam’ for potentially long periods of time.

large

[Queuing Delay] The sweet spot is when there is just enough _ so that a reasonable number of packet can be queued; if new packets find a full buffer, they will know to take an alternative route, potentially saving time.

buffer

[Throughput] The ___ at any instant is the rate (in bits/second) at which the receiver receives the file

throughput

Provides reliable data transfer, Congestion control, & some security

TCP(Transmission Control Protocol)

Does not include reliable data transfer or congestion control. Very lightweight and fast, however(Good for internet telephony).

UDP(User Datagram Protocol)

The world wide web(WWW) is a ___ running on top of the internet.

network application

World wide web uses the ___ architecture, governed by HTTP(Hypertext Transfer Protocol)

client-server

Consists of objects, such as HTML, JPG image, mp4 video clips

Web Pages

Each object in a web page has an addressable ___.

URL

_ is the base file, and references other objects of web pages.

HTML

Houses web objects. Always on and connected to the internet.

Web Servers

Implements the client side of the HTTP

Web Browsers

[HTTP Status Code] OK

200

[HTTP Status Code] Moved Permanently

301

[HTTP Status Code] Bad Request

400

[HTTP Status Code] Not Found

404

[HTTP Status Code] HTTP version not understood

505

[Queuing Delay] The easiest way to understand queuing delay is to think of a router like a _: packets arrive, but the router can only send them out at a certain rate. If faster than they leave, they have to wait.

checkout line

[Queuing Delay] When a packet reaches a router, the router needs to transmit that packet onto an _, which may already be busy transmitting other packets. The new packets therefore has to wait in the router’s _ which is essentially temporary storage.

outbound link; buffer

[Queuing Delay] New packets arriving to a router have to wait in the router’s _. The waiting time is called _.

buffer; queuing delay

[Queuing Delay] Mental model of Queuing Delay: Packets Arrive → ___ → ___ → Next Device

Router Buffer; Outbound Link

[Queuing Delay] If the ___ can keep up with arriving traffic, there may be little or no queuing. If it cannot keep up, packets begin accumulating.

outbound link

[Queuing Delay] The ___ is temporary memory inside the router where packets wait before they can be transmitted.

buffer

[Queuing Delay] The router sends packets out of the buffer according to the capacity of the ___. There is a buffer for each outbound link at the router.

outbound link

[Queuing Delay] The ___ is not infinitely large. Eventually it can fill up.

buffer

[Queuing Delay] Suppose packets arrive faster than the router can transmit them (arrival: 2Mbps | transmission rate: 1Mbps) resulting in traffic accumulation. Once the buffer is full, there is nowhere to store newly arriving packets. The router therefore _ packets.

drops

[Queuing Delay] A _ is the slowest link along a path that constrains how quickly data can move through the network.

bottleneck

[Queuing Delay] Queuing delay is ___. If very little traffic is arriving a packet may leave immediately. If traffic increases, a newly arriving packet has to wait behind other packets. If the buffer reaches capacity, the packet may be dropped.

variable

[Queuing Delay] If incoming traffic is below transmission capacity (Arrival Rate < Transmission Capacity), the router generally _, resulting in little or no persistent queuing from the rate mismatch.

can keep up

[Queuing Delay] If incoming traffic approaches outgoing capacity (Arrival Rate = Transmission Capacity), the router is _, resulting in possible queues, particularly because real network traffic tends to arrive in bursts.

near its limit

[Queuing Delay] If incoming traffic exceeds outgoing capacity (Arrival Rate > Transmission Capacity), the router _, resulting in a growing queue, where packets can be dropped if buffer fills.

cannot keep up

[Throughput] The actual rate at which data is successfully transferred from a sender to a receiver.

Throughput

[Throughput] The actual data transmission rate from end-to-end.

Throughput

[Throughput] Throughput is decided by the ___ transmission rate between both the server and the client.

minimum

[Throughput] Formula for throughput:

min{R(server), R(client)

[Internet Protocol Stack] The application doesn’t need to understand every router, cable, switch, radio signal, etc. It relies on the lower layers(OSI) to make deliver happen. This concept is called ___.

layering

[Internet Protocol Stack] Layers whose main responsibility is network application/services(HTTP, SMTP)

Application

[Internet Protocol Stack] Layers that handles Process-to-process communication(TCP, UDP)

Transport

[Internet Protocol Stack] Layers that handles host-to-host delivery and routing(IP)

Network

[Internet Protocol Stack] Layer that handles transfer between neighboring network elements (Ethernet, Wi-Fi)

Data Link

[Internet Protocol Stack] Layer transmits individual bits (Electrical, optical, radio signals)

Physical

[Internet Protocol Stack] Sender’s data path

Application → Transport → Network → Data Link → Physical

[Internet Protocol Stack] Receiver’s data path

Physical → Data Link → Network → Transport → Application

[Internet Protocol Stack] The application layer supports ___ applications(Such as HTTP, SMTP)

network

[Internet Protocol Stack] The ___ layer doesn’t concern itself with the physical route through the internet. It passes data to be sent to the transport layer.

application

[Internet Protocol Stack] The process of adding information around data.

Encapsulation

[Internet Protocol Stack] Handles process-to-process data transfer. Helps get data to the correct process/application running on that host.

Transport Layer

[Internet Protocol Stack] When the transport layer encapsulates data, it adds what is called a ___ to the data.

segment

[Internet Protocol Stack] When the network layer encapsulates fata, it adds what is called a ___ to the data.

datagram

[Internet Protocol Stack] The ___ layer is primarily concerned with getting the datagram from the source host to the destination host.

network

[Internet Protocol Stack] ___ examine network-layer information to determine where the datagram should go next.

Routers

[Internet Protocol Stack] Major protocol associated with the network layer.

IP(Internet Protocol)

[Internet Protocol Stack] When the data link layer encapsulates data, it adds what is called a ___ to the data.

frame

[Internet Protocol Stack] The ___ layer is concerned with transferring data between neighboring network elements.

data link

[Internet Protocol Stack] This layer doesn’t encapsulate/add another header to data.

Physical

[Internet Protocol Stack] Job is to transmit bits representing the frame across the physical medium. This layer is ultimately responsible for getting the 1s and 0s physically from one device to the other.

Physical Layer

[Application Layer] At the ___ layer, an application essentially says: “I have data that needs to reach another application, and these are the communication properties I need.” - The lower layers handle the implementation

Application Layer

[Application Layer] The application layer sits directly above the ___. Therefore, applications request communication services from it.

transport layer

[Application Layer] When an application can function across a range of throughput levels, although more throughput generally improves performance is called ___.

Elastic

[Application Layer] When an application performance can adapt to available throughput, it is ___.

elastic

[Application Layer] Initiates communication.

Client

[Application Layer] The server waits to be contacted and provides a service.

Server

[Application Layer] When clients dont necessarily communicate with each other, and individually communicates with the server.

Client-Server Architecture

[Application Layer] When end hosts can communicate directly with one another. Rather than relying entirely on one dedicated central server to providing the actual data, peers can exchange data among themselves.

Peer-toPeer(P2P)

[Application Layer] In P2P a peer can behave somewhat like both a ___ and ___ as it can download pieces from other peers and upload prices to other peers.

client; server

[Application Layer] [Client-Server or P2P] Dedicated server plays a central role.

Client-Server

[Application Layer] [Client-Server or P2P] Peers communicate directly

Peer-to-Peer(P2P)

[Application Layer] [Client-Server or P2P] Clients contact server

Client-Server

[Application Layer] [Client-Server or P2P] Peers contact other peers

Peer-to-Peer(P2P)

[Application Layer] [Client-Server or P2P] Server usually always available.

Client-Server

[Application Layer] [Client-Server or P2P] Peers may come and go

Peer-to-Peer(P2P)

[Application Layer] [Client-Server or P2P] Centralized service model

Client-Server

[Application Layer] [Client-Server or P2P] More distributed model

Peer-to-Peer

[Application Layer] A ___ is essentially an interface through which an application process sends data to and receives data from the transport layer; forms the boundary between the application process and transport-layer services.

socket

[Application Layer] A programmer writes the application’s behavior, but doesn’t generally implement TCO, IP, Ethernet drivers etc. from scratch for every application. The ___ provides the networking stack. The application interacts with that networking functionality through the ___ interface.

operating system; socket

[TCP vs. UDP] ___ establishes a connection.

TCP

[TCP vs. UDP] Does not establish a connection.

UDP

[TCP vs. UDP] Provides reliable, ordered delivery

TCP

[TCP vs. UDP] Does not guarantee delivery

UDP

[TCP vs. UDP] Performs congestion control.

TCP

[TCP vs. UDP] Does not perform congestion control

UDP

[TCP vs. UDP] More transport-layer control and reliability

TCP

[TCP vs. UDP] Less overhead and lower protocol complexity.

UDP

[TCP vs. UDP] TCP/UDP protocols lie within the ___ layer

transport

[Three-Way Handshake] TCP control flag used when establishing the connection and synchronizing initial sequence-nymber state

SYN

[Three-Way Handshake] TCP control flag that indicates that previously received TCP information/data is being acknowledged.

ACK

[Three-Way Handshake] approximately the amount of time required for information to travel (Client → Server → Client)

Round-Trip Time

[Non-Persistent Connections] With non-persistent HTTP, every object(HTML file, image, CSS file, Javascript file etc) retrieved from the server requires a separate ___ connection.

TCP

[Non-Persistent Connections] An ___ is an individual resource needed by the webpage, such as an HTML file, image, CSS file, or JavaScript file.

object

[Non-Persistent Connections] HTTP/1.0 → primarily ___.

non-persistent

[Non-Persistent Connections] HTTP/1.1 → ___ by default.

persistent connection

[Web Cache] A way to make web access faster while reducing the amount of traffic that has to travel across slower or more congested parts of the Internet.

Web Cache

[Web Cache] a system that temporarily stores copies of web objects that users have previously requested.

Web Cache