Introductory Networking Concepts Introductory Networking Concepts Rudra Dutta CSC 453 - Fall 2013.

Introductory Networking ConceptsIntroductory Networking Concepts

Rudra DuttaCSC 453 - Fall 2013

Copyright Fall 2013, Rudra Dutta, NCSU 2

Digital CommunicationDigital Communication Digital representation of information

– Reduces diverse information to same form– Allows infinite replication– Allows general purpose manipulation (computers)– Allows transmission from one computer to another

Digital communication– Revolution in our times– Created digital economy– Large number of products and services seen as information


Components for CommunicationComponents for Communication Nodes (computers, …) Links Communication primitive


ScalabilityScalability


CooperationCooperation Nodes - endpoint nodes and intermediate nodes Links Communication primitive


ForwardingForwarding Performed by intermediate node

– Process of copying data off one incoming link, on some outgoing link

May be performed at physical layer– (Sub-bitpipe)– Utilize physical phenomena - “Switching”– Electrical circuit, etc.

May be at higher layer– Bits or some organization of bits– “Forwarding”– “Routing” (ambiguity)


The Need for SharingThe Need for Sharing Taking turns “Multiplexing”

– Time division, frequency division


ProtocolsProtocols

“Rule set”, “language” Standards for communication hardware/software Common guidelines for implementations

– Different implementations of same protocol– Standards bodies make protocols

ITU-T, IETF, IEEE– Software manufacturers produce implementations

On = “1” or “0” ?


DelayDelay

Two meanings– How fast can successive bits be put into the pipe?– How long does a bit take to traverse the pipe?

Time

Sender

Receiver“Dis

tanc

e”


ThroughputThroughput

Total number of bits transferred, over given time– Related obviously to the transmission delay– Propagation delay often referred to simply as “delay”

or “latency”– Throughput sometimes referred to as “bandwidth”– “Bandwidth-delay product” - filling the pipe


Software ProtocolsSoftware Protocols Syntax of a message

– what fields does it contain?– in what format?

Semantics of a message– what does a message mean?– for example, not-OK message means receiver got a

corrupted file Actions to take on receipt of a message

– for example, on receiving not-OK message, retransmit the entire file


ISO OSI reference modelISO OSI reference model A set of protocols is open if

– protocol details are publicly available– changes are managed by an organization whose membership

and transactions are open to the public A system that implements open protocols is called an open

system International Organization for Standards (ISO) prescribes a

standard to connect open systems– open system interconnect (OSI)

Has greatly influenced thinking on protocol stacks


The seven layersThe seven layersApplication Top level user of the system

Presentation Resolve platform issues (data representation, possibly encryption)

Session Full-duplex, expedited data delivery, session synchronization

Transport Error control, flow control, multiplexReliability

Network Concatenates links to form end-to-end abstraction

Data Link Control Organizes bit transmissions into frame transmissions (LLC, MAC sublayers)

Physical Moves bits between physically connected end-systems

End-

to-e

ndN

ode-

to-n

ode


Peer ProcessesPeer Processes

End Node Intermediate Node Intermediate Node End Node

DLC DLC

Phy Phy Phy Phy

DLC DLC


Network ComponentsNetwork Components Different network components function at

different layers Embody service at different protocol layers Nomenclature is not very well standardized, and

is changing Mixed, “layer-blurring” devices complicate

matters


DLC

PHY

NET

DLC

PHY

NET

PHY

DLC

PHY

NET

DLC

PHY

NET

A B C D EA

B

C

D

E

Component C in this figure is a wire, or hub.


DLC

PHY

NET

DLC

PHY

NET

DLC

PHY

DLC

PHY

DLC

PHY

NET

DLC

PHY

NET

A B C D EA

B

CD

E

Computer C in this figure is a bridge.(Could be a switch, if dumb component.)


DLC

PHY

NET

DLC

PHY

NET

DLC

PHY

DLC

PHY

DLC

PHY

NET

DLC

PHY

NET

A B C D E

Computer C in this figure is a router, or switch

A

BC D

E

DLC

PHY

NET


DLC

PHY

NET

DLC

PHY

NET

DLC

PHY

DLC

PHY

DLC

PHY

NET

DLC

PHY

NET

A B

C

D E

Computer C in this figure is a router, or switchComputers A, B, D, E are hosts

A

BC D

E

DLC

PHY

NET

TxP

APP

TxP

APP

TxP

APP

TxP

APP


Physical Layer CommunicationPhysical Layer Communication

Digital – concept– Information can be analog or digital

EM waves – analog by definition Analog EM signal can be made to transfer digital data Thus we could (and usually do) have: “Digital interpretation of analog signal representing

digital representation of analog data”

010100…


Propagation MediaPropagation Media Guided

– Twisted pair– Coax cable– Optical fiber

Unguided– Radio (semi-guided follow curvature of earth)– Radio bounced off ionosphere– Fiberless optical (wireless optical)– Communication satellites


Communication in the EM SpectrumCommunication in the EM Spectrum


ModulationModulation A “carrier” wave exists on the medium

– Own amplitude, frequency, phase– Base energy pattern – no information– Analog, of course

A “signal” needs to be transmitted– Time varying; analog, or digital

The value of the signal from instant to instant is used to change the energy pattern of the carrier


The Issue of BitrateThe Issue of Bitrate

Consider simple AM (ASK)– Transmit one of two distinct amplitudes (voltages) transmission

of one bit How soon after can we transmit another bit?

– How fast can transmitter change its state?– How fast can receiver recognize line state?– Appears to limit bit rate, but -

Does not have to be just two states– Why not transmit one of four distinct amplitudes?– Why not more? No limit to bit rate ?! Limited by noise

1 000 01 10 11

Logical Link, Medium AccessLogical Link, Medium Access


25


Layers in a Router/SwitchLayers in a Router/Switch

DLC

PHY

NET

DLC

PHY

DLC

PHY

NET

A R D

DLC

PHY

NET

Forwarding


Software Router OperationSoftware Router Operation Some of L2 and all of L3 protocols are software

processes Exchange of data requires IPC, and blocking

Buffering may be employed between layers– Almost certainly at

higher than the bitpipe layer

Forwarding


Buffering at L3Buffering at L3 Operation of L3 itself may require buffering data

– Store-and-forward Input-buffer-process-buffer-output cycle

– May fall behind Discard data loss

DLC

PHY

NET

DLC

PHY

DLC

PHY

NET

A R D

DLC

PHY

NETForwarding


Overlay NetworkingOverlay Networking Operation of L3 can be performed by L7

– Overlay forwarding – integrate with application logic Receive-process-decide-output cycle

– May fall behind Discard data loss

DLC

PHY

NET

DLC

PHY

DLC

PHY

NET

A D

DLC

PHY

NET

L7 “NET”

TRANSPORTForwarding

Host

TRANSPORT

APP

APPLICATION


Transport LayerTransport Layer First end-to-end layer Functions

– Endpoint abstractionMultiplexing on a host

– “Ports”


Communication EndpointsCommunication Endpoints


Endpoint AccessEndpoint Access Transport software built in two parts

– Host specific part - multiplexes network layer, global context– Application specific part - maintains flow state and provides

network Also provides access point for higher layers (sockets)

SummarySummary Necessary to move bits Break down complex functionality – networking

stack Form packets of bits – PDU Inject packets, forward packets, receive packets API - socket


Introductory Networking Concepts Introductory Networking Concepts Rudra Dutta CSC 453 - Fall 2013.

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