Chapter 1 Network [Kurose]

network edge

hosts, access network, physical media

network core

packet/circuit switching, internet structure

devices connected to the internet

hosts or end systems

packet switches

forward packets (chunks of data)

routers and switches

communication links

fiber, copper, radio, satellite

networks

collection of devices, routers, links managed by an organization

the internet is a _

a network of networks; interconnected ISPs

What are the internet standards?

RFC and IETF

RFC

Request for Comments

IETF

Internet Engineering Task Force - develops and promotes voluntary Internet standards and protocols

"Service" View of the Internet

infrastructure that provides services to applications by providing programming interface to distributed applications

network protocols

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

"Nuts and Bolts" View of the Internet

a collection of computing devices and packet switches interconnected by links; a network or networks

Access Network

connects the edge device to the router/ larger internet

What are the three different types of access networks?

residential, institutional, mobile access networks

Frequency Division Multiplexing (FDM)

different channels transmitted in different frequency bands; used for cable accessing networks

cable access network

HFC (hybrid fiber coax) - asymmetric; network of cable, fiber attaches home to ISP router and home shares access network to cable headend

Digital Subscriber Line (DSL)

A type of Internet connection that uses phone lines but transmits signals digitally across an always-open connection.

wireless access network

access point gives network access

Enterprise Access Networks (Ethernet)

typically used in companies, universities, etc; has multiple routers

hosts sending function

takes application message, breaks into smaller chunks called packets, transmits packet into access network at a certain bandwidth or transmission rate r

bit

propagates between transmitter and receiver pair

physical link in physical media

lies between transmitter and receiver

Guided Physical Media

signals propagate in solid media: fiber,copper

unguided physical media

signals propagate freely such as radio signals

Twisted Pair (TP)

two insulated copper wires

coaxial wire

bidirectional

Wireless LAN (WLAN)

A type of LAN that does not use wires or cables to create connections, but instead transmits data over radio or infrared waves; WIFI

fiber optic cable

high transmission rate and low bit error rate

packet-switching

hosts break application layer messages into packets and forwards them from router across links on path from source destination

What type of action is forwarding [switching]?

local action: move arriving packets from router's input link to appropriate router output link

What type of action is routing?

global action: determines source-destination paths taken by packets

packet transmission delay

takes L/R seconds to transmit L-bit packet into link at R bps

store and forward

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

queueing in packet switching

queue of packets waiting for transmission over output link

When does queueing occur in packet switching?

when work arrives faster than it can be serviced

packet queuing and loss

if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time packets will queue, waiting to be transmitted on output link, packets can be dropped/lost if memory (buffer) in router fills up (i.e too long a queue)

circuit switching

end-end resources allocated to, reserved for call between source and destination; link capacity reserved for call [no sharing]

cons of circuit switching

unused bandwidth is lost if no calls

Frequency Division Multiplexing (FDM)

each call allocated to its own band, can transmit at max rate of the narrow band

Time Division Multiplexing (TDM)

Time divided into slots. Each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time slot(s)

when is packet switching ideal?

great for burst data [ sometimes data available to send but not always], resource sharing

How to connect millions of access ISPs?

instead connecting them together connect them to global transmit ISP

How to connect global ISPs together?

via internet exchange points or peering link

What are tier 1 ISPs?

commercial ISPs that provide national and international coverage [at&t,sprint]

What are content network providers?

private network that connects its data center to internet often by bypassing tier-1 and regional ISPs [google,facebook]

Point of Presence (POP)

a local connection to a wide area network

How do packet delay and loss occur?

packets queue in router buffers, waiting for turn for transmission causing queue length to grow when arrival rate to link exceeds output link capacity; packet loss occurs when memory to hold queued packets fills up

What are the four sources for packet delay?

nodal processing, queueing delay, transmission delay, propagation delay

nodal processing

check bit errors, determine output link

queueing delay

time waiting at output link for transmission, depends on congestion level of router

transmission delay

the amount of time required to push all of the packet's bits into the link (L/R)

propagation delay

length of physical link over propagation speed

trace route programs

provides delay measurement from source to router along end-end internet path towards destination

How does trace route work?

sends 3 packets that will reach router on path towards destination, router will return packets to sender, sender measures time interval between transmission and reply

What do the stars on trace route represent?

means no response (probe lost, router not replying)

What is the bottleneck link?

link on end-end path that constrains end-end throughput

layers

each layer implements a service via its own internal layer actions or by relying on services provided by layers below

What are the pros to layered architecture?

shows relationship of system pieces to use as a reference model and modularization eases maintenance, updating of system [change in one area wont affect another]

What are the five layers of internet?

application, transport, network, link, physical [top-down]

application layer

exchanges messages to implement some application service using services of layer below; supporting network applications [HTTP,IMAP,SMTP,DNS]

transport layer

protocol transfers M from one process to another by encapsulating message with a header to create a segment; process-process data transfer [TCP,UDP]

network layer

transfers transport-layer segment from one host to another by encapsulating previous transport segment with a new header; routing of datagrams from source to destination [IP, routing protocols]

link layer

adds a header to message and its called a frame; data transfer between network device [ethernet, wifi]

physical layer

bits on the wire

What happens moving down layers?

headers are added to message called encapsulation

What happens moving up a stack?

headers are read and removed

packet sniffing

an attack by a network interface that reads and records all packets passing by (for example passwords)

IP spoofing

injection of packet with false source address [fake packets]

denial of service [DOS]

attackers make resources [server, bandwidth] unavailable to legitimate traffic by overwhelming resource with fake traffic by sending packets to target from compromised hosts

What is the defense for spoofing?

authentication: proving you are user such as cellular networks provides hardware identity via SIM card

What is the defense for sniffing

?

confidentiality: via encryption [hiding packets]

What is the defense for DOS?

access restrictions: password-protected VPNs

What are integrity checks?

digital signatures that prevent/detect tampering of data

firewalls

specialized middle boxes in access and core networks that are off by default that filter incoming packets to restrict senders, receivers, applications and they also detect and react to DOS attacks

internet working principles

-minimalism, autonomy: no internal changes required to interconnect networks

-best-effort service model

-stateless routing

-decentralized control

protocols

define format, order of msgs sent and received among network, and actions taken on msg transmission, receipt

How to connect end systems to edge router?

-residential access nets

-institutional access networks (school, company)

-mobile access networks

throughput

rate at which bits transferred between sender and receiver

scenario of throughput

larger pipe needed at network core because more traffic through to avoid bottleneck situation

ISO/OSI reference model

Application

Presentation

Session

Transport

Network

Link

Physical

presentation layer OSI

encryption, compression

Session (OSI)

synchronization, checkpointing

What happened to the two layers in the OSI model?

they are now included in the application layer