CS 453 Midterm 1

CH 1-3

internet

collection of hardware and software components executing protocols

internet

network of networks

internet

collection of billions of computing devices and packet switches interconnected by links

protocol

define format and order of messages sent and received among network entities, and actions taken on message transmission and receipt

4G cellular LTE

wireless access network, up to 10’s Mbps per device

802.11 WiFi

wireless access network, 10’s to 100’s of Mbps per device

cable access network

wired access network, up to 10’s to 100’s to Mbps downstream per user

Ethernet

wired access network, up to 100’s Gbps per link

digital subscriber line

wired access network, up to 10’s of Mbps downstream per user

fiber optic cable

the physical layer technology that has the highest transmission rate and lowest bit error rate in practice, but most expensive

forwarding

local action of moving arriving packets from router’s input link to appropriate router output link

routing

global action of determining the source-destination paths taken by packets

network edge

consists of hosts, which are clients and servers; this is the transport layer

network core

this consists of interconnected routers, the data plane (which is what’s inside a router), and the control plane (which consists of routing algorithms)

frequency division multiplexing (FDM)

different channels transmitted in different frequency bands

internet service provider (ISP)

connects hosts to Internet

content provider networks

private network that connects its data centers to Internet, often bypassing tier-1 and regional ISPs (e.g. Google, Facebook)

tier-1 commercial ISP

national and international coverage (e.g. Level 3, Sprint, AT&T)

packet-switching

network forwards packets of broken up application-layer messages from one router to the next across links on path from source to destination

packet loss

if arrival rate of packet to link exceeds transmission rate, then the packet will be queues and it can be lost if the memory (buffer) in router fills up

circuit switching

end-end resources allocated to and reserved for call between source and destination during communication; frequency division multiplexing (FDM) and time division multiplexing (TDM) are two approaches for implementation; congestion loss and variable end-end delays are possible because resources are used on demand, not reserved in advance

store-and-forward transmission

entire packet must arrive at router before it can be transmitted on next link

frequency division multiplexing (FDM)

frequencies divided into narrow bands; each call allocated its own band, can transmit at max rate of that narrow band

time division multiplexing (TDM)

time divided into slot; each call allocated periodic slots, can transmit at max rate of wider frequency band only during its time slots

packet delay

delay_nodal = delay_proc + delay_queue + delay_trans + delay_prop

transmission delay

delay_trans = L/R (packet length/link transmission rate)

propagation delay

delay_prop = d/s (length of physical link/propagation speed)

transmission delay

time spent transmitting packets bits into the link

processing delay

time needed to perform an integrity check, lookup packet information in a local table and move the packet from an input link to an output link in a router

queueing delay

time spent waiting in packet buffers for link transmission

propagation delay

time need for bits to physically propagate through the transmission medium from end one of a link to the other

link layer

transfer of data between neighboring network devices (e.g. ethernet, 802.11 (WiFi), PPP); data in frames

application layer

protocols that are part of a distributed network application (e.g. HTTP, IMAP, SMTP, DNS); data in messages

physical layer

transfer of a bit into and out of a transmission media; data in bits

network layer

delivery of datagrams from a source host to a destination host (typically) (e.g. IP, routing protocols); data in datagrams

transport layer

transfer of data between one process and another process (typically on different hosts) (e.g. TCP, UDP); data in segments

encapsulation

taking data from the layer above, adding header fields appropriate for this layer, and then placing the data in the payload field of the “packet” for that layer

encryption

provides confidentiality by encoding contents

access control

limiting use of resources or capabilities to given users

firewall

specialized “middleboxes” filtering or blocking traffic, inspecting packet contents inspections

digital signatures

used to detect tampering/changing of message contents, and to identify the originator of a message

authentication

proving you are who you say you are

1990’s

The WWW starts up (note: the WWW design started at the end of previous decade).

early 1980’s

The Internet Protocol (IP) is standardized in RFC 791

early 1960’s

early studies of packet switching by Baran, Davies, Kleinrock

2010-2020

the number wireless Internet-connected devices surpasses the number of connected wired devices

late 1960’s

first ARPAnet node operational

2000-2010

software-defined networking begins

late 1980’s

congestion control is added to the TCP protocol

1970’s

Internetting: DARPA researchers connect three networks together

packet queueing delay

La/R (packet length * average packet arrival rate / link bandwidth)

traceroute program

a program that provides delay measurement from source to router along end-end Internet path towards destination

throughput

rate at which bits are being sent from sender to receiver

packet sniffer

a passive receiver that records a copy of every packet that flies by, including passwords

IP spoof

injection of packet with false source address

Denial of Service (DoS)

attackers make resources unavailable to legitimate traffic by overwhelming resource with bogus traffic

presentation layer

in OSI/ISO reference model, not in internet protocol stack; allows applications to interpret meaning of data (e.g. encryption, compression, machine-specific conventions)

session layer

in OSI/ISO reference model, not in internet protocol stack; synchronization, checkpointing, recovery of data exchange

client-server paradigm

clients communicate with the always-on server that has a permanent, well-known IP address; often used in data centers due to its ability to handle large amounts of requests; clients communicate with each other through the server

peer-to-peer (P2P) architecture

clients communicate with other clients directly; features self-scalability, meaning new peers can bring new service capacity and demand; P2P applications have client and server processes; peers are intermittently connected and change IP addresses

socket

processes send/receive messages to/from its ____

HTTP Get request message

used by web client to request a web server to send the requested object from the server to the client

HTTP reply

consists of response code and response phrase associated with code

conditional HTTP GET request message

message to allow a server to only send the requested object to the client if this object has changed since the server last sent this object to the client; in other words, if browser doesn’t have up-to-date cached version

enter deep

CDN approach that stores content in access networks, close to clients

DASH

an approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions

an approach where a server divided a video file into chunks that are stored, each encoded at multiple rates; the client plays the video chunk-by-chunk, with each chunk requested at encoding rate that fits the available bandwidth at the time

chunk

a unit of video, each of which may be encoded at multiple different rates, stored in different files

manifest

a file containing the location and encoding rate of files corresponding to video segments in a video

TCP

internet transport protocol service that had reliable transport between sending and receiving process, flow control, congestion control, is connection-oriented, and does not provide timing, minimum throughput guarantee, security

UDP

internet transport protocol service that had unreliable data transfer between sending and receiving process and does not provide reliability, flow control, congestion control, timing, throughput guarantee, security, or connection setup; used when speed is more important

transport layer security (TLS)

provides encrypted TCP connections, data integrity, and end-point authentication

HTTP is “stateless”

when HTTP server maintains no information about past client requests

non-persistent HTTP

HTTP connection where at most one object is sent over open each TCP connection before it is closed

persistent HTTP

HTTP connection where multiple objects can be sent over a single TCP connection between client and that server before the connection is closed

RTT

time for a small packet to travel from client to server and back

POST method

user input sent from client to server in entity body of HTTP request message

HEAD method

requests headers (only) that would be returned if specified URL were requested with an HTTP GET method

GET method

include user data in URL field of HTTP GET request message

PUT method

uploads object to server and completely replaces file that exists at specified URL with content in entity body of POST HTTP request message

cookies

can be used for authorization, shopping carts, recommendations, user session state; they permit sites to learn about you, and tracking ______ allow common identity to be tracked across multiple web sites; doesn’t mean anything in HTTP GET request

web cache

acts as both client and server; reduces response time for client request, reduces traffic on an institution’s access link, and enables “poor” content providers to more effectively deliver content as servers want to be close to clients