Csc 450 Test 1

Front 1

What is networking

Back 1

Enable communications between applications on different computers

-web

-peer to peer

-audio/video conferencing

Front 2

Statistical Multiplexing

Back 2

Sharing of network bandwith between users according to the statistics of their demand

-Multiplexing just means sharing

-useful bc users are mostly idle and their traffic is bursty

can use binomial probabilities to determine how much bandwith each user needs

Front 3

Metcalfe's Law

Back 3

The value of a network of N nodes is proportional to N^2

Large networks are relatively more valuable than small ones

Front 4

Application, app, or user

Back 4

Uses the network

Front 5

Host, node, source

Back 5

supports apps (laptop, mobile, desktop)

Front 6

Router, switch, node

Back 6

Relays messages between links (access point, cable/dsl modem)

Front 7

Link, channel

Back 7

Connects nodes (wires, wireless)

Front 8

Full-duplex link

Back 8

<---> or -----

bidirectional link

Front 9

Half-duplex link

Back 9

---> or <---

bidirectional

Front 10

Simplex link

Back 10

--->

unidirectional

Front 11

PAN's scale and example

Back 11

Personal Area Network (ex: Bluetooth)

Scale: Vicinity

Front 12

LAN scale, example

Back 12

Scale: Building

ex: wifi, ethernet

Front 13

MAN scale, example

Back 13

Metropolitan Area Network

Scale: City

Ex: Cable, DSL

Front 14

WAN

Back 14

Wide Area Network

Scale: Country

Ex: Large ISP

Front 15

Network-Application Interfaces`

Back 15

Define how apps use the network

Sockets are widely used in practice

Front 16

Network-Network interfaces

Back 16

Define nodes work together

Traceroute can peek in the network

Front 17

What is Layering?

Back 17

A modular approach to network functionality

ex:

Front 18

Each Instance of a protocol uses only the services of a lower layer. T or F

Back 18

True, also each instance of a protocol talks virtually to its peer using the protocol

Front 19

Examples of protocols

Back 19

TCP, IP, 802.11, Ethernet, http, SSL, DNS, etc

Front 20

Encapsulation

Back 20

The mechanism used to effect protocol layering

-Lower layer wraps higher layer content, adding its own information to make a new message for delivery

-like sending a letter in an envelope, postal service doesn't look inside

Front 21

Disadvantages of Layering

Back 21

Adds overheard

-minor for long messages

Hides information

-sometimes app might care if its running over wired or wireless

Front 22

Protocols (definition)

Back 22

An agreement between parties on how communications should take place

Front 23

OSI 7 Layer Model

Back 23

OSI - open system interconnection

1.Physical: how to transmit bits

2. Data link: how to transmit frames

3. Network: how to route packets

4. Transport: how to send packets end2end

5. Session: how to tie flows together

6. Presentation: byte ordering, security

7. Application: everything else

Front 24

Physical Layer (OSI)

Back 24

How to transmit bits

Front 25

Data Link (OSI)

Back 25

How to transmit Frames

Front 26

Network (OSI)

Back 26

How to route packets

Front 27

Transport (OSI)

Back 27

How to send packets end2end

Front 28

Session (OSI)

Back 28

How to tie flows together

Front 29

Presentation (OSI)

Back 29

Byte ordering, security

Front 30

Application level(OSI)

Back 30

everything not covered by the first 6 layers

Front 31

How many layers of the OSI model does a bridge/switch utilize?

Back 31

2: Physical and Data link

Front 32

How many layers of the OSI model does a router/gateway utilize?

Back 32

3: Physical, data link, network

Front 33

Internet Reference Model

Back 33

A four layer model based on experience; omits some OSI layers and uses IP as the network layer

Front 34

Link Layer in Internet Reference Model and corresponding OSI layers

Back 34

OSI IRM

1,2 Physical & Link Link - send frames

3 Network Internet - send packets over multiple networks

4 Transport Transport end2end data delivery

7 Application Application - programs that use network service

Front 35

Application Layer (IRM)

Back 35

Programs that use network service
FTP/HTTP/SMTP/DNS

Front 36

Transport Layer (IRM)

Back 36

Provides end2end data delivery

UDP/TCP

Front 37

Internet Layer (IRM)

Back 37

Send packets over multiple networks

IP

Front 38

Link Layer (IRM)

Back 38

Send frames over a link

Ethernet/3G/802.11/etc

Front 39

What units of data does the Application Layer use

Back 39

Message

Front 40

What units of data does the Transport Layer use

Back 40

Segment

Front 41

What units of data does the Network Layer use

Back 41

Packets

Front 42

What units of data does the Link layer use

Back 42

Frame

Front 43

What units of data does the Physical Layer use

Back 43

Bit

Front 44

ARQ

Back 44

Automatic Repeat request used for reliability; server is stateless for dns protocol

Front 45

HTTP

Back 45

HyperText Transfer Protocol

basis for fetching web pages

Front 46

Steps for fetching a web page with HTTP

Back 46

Front 47

What is the difference between a static and dynamic web page

Back 47

Static - web page is just a file's contents: ex: image

Dynamic- the result of a program execution

ex: javascript on client, php on server, or both

Front 48

(HTTP commands) GET

Back 48

Read a Web Page

Front 49

(HTTP commands)
HEAD

Back 49

Read a web page's header

Front 50

(HTTP commands)

POST

Back 50

Append to a web page

Front 51

(HTTP commands)

PUT

Back 51

Store a web page

Front 52

(HTTP commands)

DELETE

Back 52

Remove the Web PAge

Front 53

(HTTP commands)

TRACE

Back 53

Echo the incoming request

Front 54

(HTTP commands)

CONNECT

Back 54

connect through a proxy

Front 55

(HTTP commands)

OPTIONS

Back 55

Query options for a page

Front 56

(HTTP Codes)

1xx

Back 56

Information
EX: 100 = server agrees to handle client's request

Front 57

(HTTP Codes)

2xx

Back 57

Success

200 = request succeeded; 204 = no content present

Front 58

(HTTP Codes)

3xx

Back 58

Redirection

301 = page moved; 304 = cached page still valid

Front 59

(HTTP Codes)

4xx

Back 59

Client Error

403 = forbidden page; 404 = page not found

Front 60

(HTTP Codes)

5xx

Back 60

Server Error

500 = internal server error

503 = try again later

Front 61

PLT

Back 61

Page Load Time
-key measure of web performance

-Depends on many factors

-Structure of page/content

-HTTP (and TCP) protocol

-Network RTT and bandwith

Front 62

how many TCP connections did HTTP/1.0 use to fetch one web resource

Back 62

1 each, it made HTTP very easy to build but gave poor PLT

Front 63

What are some ways to reduce PLT

Back 63

Reduce content size for transfer (smaller images, gzip)

Change HTTP to make better use of available bandwith

Change HTTP to avoid repeated transfers of the same content (caching, proxies)

Move content closer to client (CDNs)

Front 64

What is a parallel connection

Back 64

A browser runs multiple HTTP instances in parallel.

Server is unchanged bc it already handles concurrent requests for many clients

This helps because http wasn't using networking much so parallel connections aren't slowed much. pulls in completion time of last fetch

Front 65

What is a persistent connection

Back 65

Make 1 TCP connection to 1 server and use it for multiple HTTP requests

Front 66

Compare and Contrast Persistent and Parallel connections

Back 66

1 is http 1.0
2 is parallel

3 is persistent

parallel has multiple TCP connections to a server

persistent pipelines multiple requests through 1 TCP connection

Front 67

What are CDNs

Back 67

Content Delivery Networks

Efficiently distributes popular content; creates a replica closer to consumers to deliver faster

Front 68

Zipf's Law

Back 68

Few popular items, many unpopular; both matter.

Front 69

How to place content near clients?

Back 69

User browser/proxy caches

place replicas across internet for use by all nearby clients

-done by clever use of DNS

Front 70

What is a waterfall diagram?

Back 70

Shows progression of the page load

Front 71

What is SPDY?

Back 71

"speedy"

A set of http improvements

-multiplexed (parallel) HTTP requests on one TCP connection

-Client priorities for parallel requests

-Compressed HTTP headers

-Server push of resources

Basis for an HTTP/2 effort

Front 72

mod_pagespeed

Back 72

an apache server extension that allows the server to "rewrite" (compile) pages to help them load faster.

Rewrites pages 'on the fly' with rules based on best practices

Front 73

TCP/IP Layer Model

Back 73

# Name Encapsulation Units
1. Network Access bits/frames

2. Internet packets

3. Transport segments

4. Application data

Front 74

OSI Layer Model

Back 74

# Name Encapsulation Units

1 Physical bits

2 Data Link frames

3 Network packets

4 Transport Segments

5 Session data

6 Presentation data

7 Application data

Front 75

Socket API

Back 75

simple abstraction to use the network

the network service API used to write all internet applications

part of all major OSes and languages; initially Berkley (unix) ~1983

Front 76

Streams:

Back 76

reliably send a stream of bytes

supported by socket API

Front 77

Datagrams

Back 77

unreliably send separate messages

supported by socket api

Front 78

Sockets (data structure)

Back 78

let apps attach to the local network at different ports

Front 79

Socket API primitives

Back 79

SOCKET, BIND, LISTEN, ACCEPT, CONNECT, SEND, RECEIVE, CLOSE

Front 80

(Sockets)

SOCKET

Back 80

Create a new communication endpoint

Front 81

(Sockets)

BIND

Back 81

associate a local address with a socket

Front 82

(Sockets)

LISTEN

Back 82

announce willingness to accept connctions; give queue size

Front 83

(Sockets)

ACCEPT

Back 83

passively establish an incoming connection

Front 84

(Sockets)

CONNECT

Back 84

actively attempt to establish a connection

Front 85

(Sockets)

SEND

Back 85

send some data over the connection

Front 86

(Sockets)

RECEIVE

Back 86

receive some data from the connection

Front 87

(Sockets)

CLOSE

Back 87

release the connection

Front 88

What is the order for connecting with a socket

Back 88

Front 89

Traceroute

Back 89

Widely used command-line tool that lets hosts peek inside the network

Front 90

What is the purpose of the transport layer?

Back 90

Transport layer provides end-to-end connectivity across the network

Front 91

What are segments?

Back 91

Segements carry application data across the network

Carried within packets within frames

Front 92

What are the differences between TCP and UDP?

Back 92

TCP is full features, UDP is a glorified packet

Front 93

Ports

Back 93

Application process is identified by the tuple:

Ports are 16-bit integers representing local "mailboxes" that a process leases

Servers often bind to "well known ports"

ports higher than 1024 require admin privs

clients often assigned "ephemeral" ports

chosen by OS and used temporarily

Front 94

What kind of apps use UDP

Back 94

Apps that don't want reliability or byte-streams

VoIP (unreliable)

DNS, RPC (message oriented)

DHCP (bootstrapping)

Front 95

is UDP connectionless?

Back 95

Yes,
No handshaking between UDP sender and receiver, each UDP segment handled independently of others

Front 96

Three Way Handshake

Back 96

Used in TCP; opens connection for data in both direction

Each side probes the other with a fresh Initial Sequence Number (ISN)

-sends on a SYNchronize segment

-echo on an ACKnowledgement segment

chosen to be robust even against delayed duplicates

Front 97

Steps of a three way handshake

Back 97

Three steps:
Client sends SYN(x)

Server replies with SYN(y)ACK(x+1)

Client replies with ACK(y+1)

SYN is retransmitted if lost

Front 98

What are the steps of a TCP connection release?

Back 98

Two Steps:
Active sends FIN(x), passive ACKs

Passive sends FIN(y), active ACKs

FINs are retransmitted if lost

Each FIN/ACK closes one direction of data transfer

Front 99

Where should reliability functions be placed on the layer model?

Back 99

Everywhere because it's a key issue, different layers contribute differently.

Front 100

Strategies to handle errors in higher levels of the stack?

Back 100

Detect errors and retrans frames (ARQ automatic repeat request)

Front 101

What's tricky about ARQ?

Back 101

Performance in common case
correctness always

Front 102

w

Back 102

w