introduction to networks in biomedical eng

8/13/2019 Introduction to Networks in Biomedical Eng

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Fundamentals in Networks


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Fundamental Computer Networks Concepts

In the world of computers, networking is the practice

of linking two or more computing devices together forthe purpose of sharing data, resources, andinformation.

Networks are built with a combination of computerhardware and computer software. Simply, more thanone computer interconnected through a communicationmedium for information interchange is called acomputer network.

Networks may be classified according to a wide varietyof characteristics, such as the medium used totransport the data, communications protocol used,scale, topology, and organizational scope.


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Networking History

DARPA:The Defense Advanced Research Projects Agency is an agency

of the United States Department of Defense (DoD) responsible for the

development of new technologies for use by the military. DARPA has

been responsible for funding the development of many technologieswhich have had a major effect on the world, including computer

networking.

packet switching: Refers to protocols in which messages are divided

into packets before they are sent. that are typically routed from source to

destination using network switches and routers. Each packet contains

address information that identifies the sending computer and intended

recipient. Using these addresses, network switches and routers determine

how best to transfer the packet between hops (a hop represents oneportion of the path between source and destination ) on the path to its

destination.

ARPAnet: The Advanced Research Projects Agency

Network was the world's first operational packet switching

network and the progenitor of what was to become the global

Internet. The initial purpose was to communicate with and

share computer resources among mainly scientific users at

the connected institutions. ARPANET took advantage of the

new idea of sending information in small units called packets.

ALOHA: Aboriginal Lands of Hawaiian Ancestry. Its

purpose was to link the University mainframe computer to

client computers located on outer islands at University

campuses. ALOHAnet became operational in June, 1971,

providing the first public demonstration of a wireless packet

data network.

TCP/IP: (Transmission Control Protocol/Internet Protocol).

is the basic communication language or protocol of the

Internet. It can also be used as a communications protocol in

a private network (either an intranet or an extranet). When

you are set up with direct access to the Internet, your

computer is provided with a copy of the TCP/IP program just

as every other computer that you may send messages to or get

information from also has a copy of TCP/IP. The difference isthat TCP is responsible for the data delivery of a packet and

IP is responsible for the logical addressing. In other words, IP

obtains the address and TCP guarantees delivery of data to

that address.

ISO Model: Open Systems Interconnection (OSI) model.

Consisting of seven layers to describe networked systems.

each element provides a set of services to the layer above.


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Networking History, cont.


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Networks are complex!

many pieces:

hosts

routers

links of various media applications

protocols

hardware, software

host: A computer that acts as a source

of information or signals. The term

can refer to any computer, from a

centralized mainframe to a server to a

client PC (user's machine). In a

network, clients and servers are hostsbecause they are both sources of

information in contrast to network

devices, such as routers and switches,

which are responsible only for

d

irecting traffic.router: A hardware device designed to take

incoming packets, analyzing the packets and thendirecting them to the appropriate locations, moving

the packets to another network, converting the

packets to be moved across a different network

interface, dropping the packets, or performing any

other number of other actions.


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protocolsIn computer protocols means a set of rules, a communication language or set

of standards between two or more computing devices. Protocols exist at theseveral levels of the OSI (open system interconnectivity) layers model. In the

telecommunication system, there are one more protocols at each layer of the

telephone exchange. On the internet, there is a suite of the protocols known as

TCP/IP protocols that are consisting of transmission control protocol, internet

protocol, file transfer protocol, dynamic host configuration protocol, Bordergateway protocol (which makes core routing decisions on the Internet ) and a

number of other protocols.

Protocols Properties

Different protocols perform different functions so it is difficult to generalize the properties ofthe protocols. There are some basic properties of most of the protocols.

Detection of the physical (wired or wireless connection)

How to format a message.

How to send and receive a message.

Negotiation of the various connections

Correction of the corrupted or improperly formatted messages. Termination of the session.


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Introduction: roadmap

1.1 What isthe Internet?

1.2Network edge

1.3Network core

1.4 Network access and physical media

1.5Protocol layers, service models


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Whats the Internet? millions of connected computing devices: called hosts,end

systems, or nodes (Hardware Devices) PCs, workstations, servers PDAs, phones, toasters

hosts run network applications communication links

fiber, copper, radio, satellite transmission rate = bandwidth Measured inbits/second

End systems are not usually connected through direct links (point-to-point) but rather indirectly through Packet switches

Packet switches have two famous forms: Routers and link-layer switches:forward packets (chunks of data)

through the network Main working principle: takes packets arriving on one of the incoming

communication links and forward that packet into one of the outgoinglinks.


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Whats the Internet?

Route (path): the sequenceof communication links andpacket switches traversedby a packet

End systems access theInternet through ISP Each ISP is a network of

packet switches andcommunication links

local ISP

companynetwork

regional ISP

router workstation

servermobile


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Whats the Internet?

protocolscontrol sending &receiving of msgs. e.g., TCP, IP, HTTP, FTP, PPP

Protocols are the software partof the Internet

Internet standards define whateach and every protocol does IEEE: for network links

Internet: network of networks public Internet versus private

intranet

local ISP

companynetwork

regional ISP

router workstation

servermobile


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Whats a protocol?

human protocols: whats the time?

I have a question

introductions

specific msgs sent

specific actions takenwhen msgs received,

or other events

network protocols: machines communicating

rather than humans

all communication activities

in the Internet aregoverned by protocols

protocols define the formatand order of msgs sent and

received among networkentities, and actions takenon message transmission

and receipt


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Whats a protocol?

a human protocol and a computer network protocol:

Q:Other human protocols?

Hi

Hi

Got thetime?

2:00

TCP connection

requestTCP connectionresponse

Get http://www.awl.com/kurose-ross

time


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Chapter 1: roadmap


1.2 Network edge

1.3Network core




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A closer look at network structure:

network edge: applications and hosts

network core: routers network of networks

access networks,

physical media: communication links connect the edges via

the core


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The network edge:

end systems (hosts): Any device/machine connected at

the edge of network Run (host) application programs

e.g. Web, email

client/server model HW view:

Clints: desktop PC or mobile devices Servers: more powerful machines

SW view: Client program & server program

client requests & receives service

from always-on server e.g. Web browser/server; emailclient/server

peer-peer model: minimal (or no) use of dedicated

servers

e.g. Skype


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Network edge: connection-oriented service

TCP serviceConnectionoriented implies : reliable, in-orderbyte-

stream data transfer ALLdata delivered without

error Achieved through the use

of acknowledgements andretransmissions

Goal:data transfer between endsystems

handshaking:setup (preparefor) data transfer ahead oftime Hello, hello back human protocol set up statein two

communicating hosts Only the end systems are aware

of the connection type.(connection oriented)

TCP - Transmission ControlProtocol Internets connection-oriented

service


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Network edge: connectionless service

Goal:data transferbetween end systems same as before!

NO handshaking

faster UDP- User Datagram

Protocol:

connectionless

unreliable datatransfer

no flow control

no congestion control

Apps using TCP: HTTP (Web), FTP (file

transfer), SMTP

(email)

Apps using UDP: streaming media,

teleconferencing,Internet telephony


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1.2Network edge

1.3 Network core




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Network Topology


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The Network Core

mesh of interconnectedrouters

thefundamentalquestion:how is datatransferred through net? circuit switching:

dedicated circuit percall: telephone net

packet-switching:datasent thru net indiscrete chunks

Illustration of a partial mesh network


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1.1What isthe Internet?

1.2Network edge

1.3Network core




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Access networks and physical media

Q: How to connect endsystems to edge router?

residential access nets

institutional access

networks (school,company)

mobile access networks


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Residential access: point-to-point access

Dialup via modem (voicebandmodem)

up to 56Kbps direct access torouter (often less)

Cant surf and phone at sametime: cant bealways on

ADSL: asymmetric digitalsubscriber line

up to 1 Mbps upstream(today typically < 256 kbps)

up to 8 Mbps downstream(today typically < 1 Mbps)

Residential services often have higher

downstream rates than upstream, while

institutional services are often symmetric.


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Company access: local area networks

company/univ local areanetwork(LAN) connectsend system to edge router

Ethernet:

shared or dedicated linkconnects end systemand router

10 Mbs, 100Mbps,

Gigabit Ethernet


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Wireless access networks

shared wirelessaccess networkconnects end system to router via base station aka access point

wireless LANs (WiFi):

802.11b: 11 Mbps (2.4 GHz ISM) 802.11g: 54 Mbps (2.4 GHz ISM)

802.11a: 54 Mbps (5 GHz ISM)

wider-area wireless access provided by telco operator

3G ~ 384 kbp

WAP/GPRS in Europe

basestation

mobilehosts

router


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Home networks

Typical home network components: ADSL or cable modem

router/firewall

Ethernet

wireless access point

wirelessaccesspoint

wirelesslaptops

router/firewall

cable

modem

to/from

cableheadend

Ethernet


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Physical media: radio

signal carried inelectromagneticspectrum

no physical wire

bidirectional propagation

environment effects: reflection

obstruction by objects interference

Radio link types: WLAN(e.g., Wifi)

2Mbps, 11Mbps, 54 Mbps

wide-area(e.g., cellular)

e.g. 3G: hundreds of kbps satellite

Kbps to 45Mbps channel (ormultiple smaller channels)

270 msec end-end delay

geosynchronous versus lowaltitude


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Internet protocol stack

application:supporting networkapplications FTP, SMTP, HTTP

transport:host-host data transfer

TCP, UDP network:routing of datagrams from

source to destination IP, routing protocols

link:data transfer betweenneighboring network elements PPP, Ethernet

physical:bits on the wire

application

transport

network

link

physical


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Network CommunicationsISOLevel

Service Level

5-7 Applications: HTTP, SMTP, FTP, ..

4 Transport: TCP and UDP

3 Network: IP

for addressing and routing packets1-2 Data Link and Physical Transport:

for detecting and correcting errors

(Ethernet, Wireless,)


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Media Access Control address (MAC address)

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