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Communication NetworksUniversity of Kansas EECS 780Preliminaries and Foundations

James P.G. Sterbenz

Department of Electrical Engineering & Computer Science

Information Technology & Telecommunications Research Center

The University of Kansas

jpgs@eecs.ku.edu

https://www.ittc.ku.edu/~jpgs/courses/nets

22 August 2016 KU EECS 780 – Comm Nets – Preliminaries NET-PR-2

Comm. Network PreliminariesPR.1 Network Architecture and Topology

PR.1 Network architecture and topology

PR.2 Performance metrics and style

PR.3 Theoretical foundations and network science

PR.4 Scope of communication

PR.5 Protocols and layering

PR.6 Communication flow diagrams

Network Architecture and TopologyThe Network

• Collection nodes or intermediate systems (IS)

– switches, routers, bridges, etc.

• Interconnected by links that

• Provide connectivity amongend systems (ES) or hosts or terminals– desktops, laptops, servers, telephone handsets, etc.

– note: in some networks nodes may be both ES and IS

• To support distributed applications– e.g. email, Web browsing, peer-to-peer file sharing

Network Architecture and TopologyThe Network

End system

Intermediate system

edge or access switch

core or backbone switch

multihomed

Network Architecture and TopologyHeterogeneous Networks

• Disparate networks are interconnected by gateways– translate data packet formats

– interoperate signalling and control

Network Architecture and TopologyApplication Relationships

• Peer-to-peer

– e.g. telepresence (video-conferencing)

request

response

• Client/server

– e.g. Web browsing

data streams with embedded synchronisation

serverclient

Network Architecture and TopologyGroup Communication Topologies

• Group communication

– communication among participants in a group of nodes

• Topologies

– unicast

– anycast

– k-cast

– multicast

– broadcast

Group Communication TopologiesUnicast

• Unicast– point-to-point

• Anycast– point-to-any in group

• k-cast– point-to-k receivers in group

• Multicast– point-to-multipoint– multipoint-to-multipoint– multipoint-to-point (reverse multicast or Concast)

• Broadcast– point-to-all– broadcast and select multicast

Group Communication TopologiesAnycast

Group Communication Topologiesk-cast

Group Communication TopologiesMulticast: Point-to-Multipoint

Group Communication TopologiesMulticast: Multipoint-to-Multipoint

Group Communication TopologiesConcast: Multipoint-to-Point

Group Communication TopologiesBroadcast

spanning

Group Communication TopologiesMulticast: Broadcast and Select

spanning

Network Architecture and TopologyStar vs. Mesh Topologies

• Star hierarchy

• Centralised control

• Examples– PSTN

– early enterprise nets (SNA)• later became meshes

• Mesh

• Fully distributed control

• Examples

– ARPANET, Internet

– DECnet

• Spanning tree may be overlaid

Comm. Network PreliminariesPR.2 Performance Metrics

PR.3 Theoretical foundations

Performance MetricsStyle and Usage: Variables1

• Proper style in formulæ is important

– sloppy style can lead to ambiguity

– guidelines at physics.nist.gov/cuu/Units/

• Variables, indices, constants, and parameters (scalar)

– italic serif font if single character

• = 3.14159…

• c 3108 m/s speed of light

• ri rate of the ith link

• rij rate of the (i,j)th link

• multiplication is implicit: ab = ab = ab

– never use * for multiplication in typeset documents

– Roman serif font if multiple characters

• RTT round trip time

• warning: RTT = RTT = RT2 RTT

• queuelen queue length

• adjacent multiplication must be explicit, e.g.: a RTT

• in LaTeX math mode declare using \textrm{ …}

• in MathType (MS Equation Editor) change style to “Text”

– Roman serif font if multiple characters

– may use fixed-width or sans-serif font for variables

• cwnd TCP congestion window

• init_val initialisation value

• conlsolas (Windows) or Monaco (Mac) are better than courier

• multiplication must be explicit

Performance MetricsGreek Letters

Name Lower Capital Name Lower Capital

alpha α Α nu ν Ν

beta β ϐ Β xi ξ Ξ

gamma γ Γ omicron ο Ο

delta δ Δ pi π Π

epsilon 0 ε Ε rho ρ Ρ

zeta ζ Ζ sigma σ ς Σ

eta η Η tau τ Τ

theta θ Θ upsilon υ Υ

iota ι Ι phi φ Φ

kappa κ Κ chi χ Χ

lambda λ Λ psi ψ Ψ

mu μ Μ omega ω Ω

ι, ο, υ, capitals identical to Latin rarely used digamma Ϝ F

Performance MetricsStyle and Usage: Attributes

• Attributes

– Roman font even if single character

• dq delay due to queuing: note q is not an index

• dq delay due to queuing: note q is not an exponent

• explicitly declare in LaTeX math mode or MathType

Performance MetricsStyle and Usage: Num., Delimiters, Operators

• Numerals, delimiters, operators, numerals in Roman

– never italic

– e.g. z = 4 (x + y) not z = 4 (x + y)

– e.g. i di not i di

– LaTeX math mode and MathType do it properly

– be selective when selecting inline PowerPoint or Word style

• Do not use hyphen for subtraction

– en-dash approximation but does not perfectly vertically align

– e.g.: a = b – c not a = b - c

Performance MetricsStyle and Usage: Functions

• Functions: similar rules to variables

– italic font if single character

• f (x) function f applied to x

– roman font if multiple characters

• max(x) maximum value of x

Performance MetricsUnit Multipliers

SI decimal EIC binary

10–1 d deci 101 da deka

10–2 c centi 102 h hecto

10–3 m milli 103 k kilo 210 Ki kibi

10–6 micro 106 M Mega 220 Mi mebi

10–9 n nano 109 G Giga 230 Gi gibi

10–12 p pico 1012 T Tera 240 Ti tebi

10–15 f femto 1015 P Peta 250 Pi pebi

10–18 a atto 1018 E Exa 260 Ei exbi

10–21 z zepto 1021 Z Zetta typically used for disk storage

10–24 y yocto 1024 Y Yotta in networking K = 1024 = 210

m, , n, k, M, G, T, P are essential for networking and must be memorised

Performance MetricsStyle and Usage: Unites and Prefixes

• Units and prefixes

– Roman font

• s microseconds

– always insert space between number and unit

• e.g. 4 m/s not 4m/s

– use solidus or exponent for division rather than “p” (“per”)

• e.g. 2.4 Gb/s or 2.4 Gbs-1 not 2.4 Gbps

– optionally use square brackets for unit dimensions

• e.g. 3.25 [m/s]

– data unit conventions

• b for bit, B for Byte

• k prefix for 103, K prefix for 1024

Performance MetricsStyle and Usage: Plain Text1

• Plain text style

– frequently necessary to put formulæ in plain text, e.g. email

– no standard, but generally combination of C and LaTeX

Performance MetricsStyle and Usage: Plain Text2

• Operators* for explicit multiplication, e.g. a*b = ab

^ for exponentiation, e.g. e^x = ex

• Variables_ for subscripts, e.g. x_i = xi

^ for superscripts, e.g. x^i = xi

• Scientific notation* and ^, e.g. 3*10^-5 = 3.510–5

• Greek letters• spell out, e.g. 3*pi = 3

• u for micro () prefix if unambiguous, e.g. 50 us = 50 s

Performance MetricsDelay and Bandwidth

• Delay or latency

D end-to-end

d per hop

– jitter is delay variance

• Bandwidth or data rate

B or R aggregate

b or r per flow

– not channel capacity (bandwidth in EE sense)

• Bandwidth-×-delay product

– number of bits in flight on a high-speed path

b [bits/sec] × d [sec] = [bits]

Performance MetricsNetwork Path Latency

short path

D = di

long path

• Delays sum along a path

– benefit of optimising link directly proportional to contribution

Performance MetricsPath Length and Network Type

– area network– earth orbiting Channel Distance RTT

BW--delay

1 Mb/s 1Gb/s 1 Tb/s

PAN personal RF 10 m 100 ns .05 b 50 b 50 kb

SAN system Cu/Fiber 100 m 1 μs ½ b 500 b 500 kb

LAN local Cu/Fiber/RF 1 km 10 μs 5 b 5 kb 5 Mb

MAN metropolitan Fiber/RF 100 km 1 ms 500 b 500 kb 500 Mb

WAN transcon. wide Fiber 5 000 km 50 ms 25 kb 25 Mb 25 Gb

WAN global wide Fiber 20 000 km 200 ms 100 kb 100 Mb 100 Gb

LEO* low earth RF 21 000 km 25 ms 12 kb 12 Mb 12 Gb

GEO geosynchronous RF/laser 236 000 km 480 ms 240 kb 240 Mb 240 Gb

DSN earth–moon RF/laser 400 000 km 2.5 s 1.2 Mb 1.2 Gb 1.2 Tb

IPN ♂ interplanetary RF/laser55–400106

km6–45 min 1.3 Gb 1.3 Tb 1.3 Pb

IPN ♃ interplanetary RF/laser 109 km 2 hr 3.6 Gb 3.6 Tb 3.6 Pb

IPN ♇ interplanetary RF/laser 1010 km 20 hr 36 Gb 36 Tb 36 Pb* 3000 km footprint

Performance MetricsNetwork Path Bandwidth

bottleneck

R = min(ri)

long path

• Maximum bandwidth limited by bottleneck link

– there is no point in optimising a link that is not a bottleneck

Performance MetricsError and Loss Characteristics

• Error and loss characteristics

– Pr[bit-error]

– burst error (multibit)

– channel fades (e.g. rain)

– episodic link connectivity

– link and node failures

We’ll discuss why these happen later

Comm. Network PreliminariesPR.3 Theoretical Foundations

PR.3 Theoretical foundations and network sciencePR.3.1 Probability, queueing theory, and performance

PR.3.2 Information theoryPR.3.3 Graph theory and network topologyPR.3.4 Game theory and tusslePR.3.5 Control theoryPR.3.6 Fault tolerance and dependabilityPR.3.7 Complex systems

Science of Communication NetsIntroduction

• A number of disciplines are fundament to comm nets

– probability, queueing theory, and performance EECS 86x

– information theory EECS 769

– graph theory and network topology EECS 718

– game theory and tussle

– control theory EECS 444

– fault tolerance and dependability EECS 983

– complex systems

EECS 784 covers many of these

see also [Keshav 2012]

Network ScienceIntroduction

• Network science

– “organized knowledge of networks based on their study using the scientific method” [NRC 2005]

– theory of the interactions of entities organised as nets

– network examples [Newman 2010]

• technological networks (e.g. PSTN, Internet, grid, transport)

• social networks (e.g. genealogy, friendship)

• information networks (e.g. citation nets, Web)

• biological networks (e.g. biochemical, ecological)

• We are primarily interested with

– communication networks (including the Web and social)

Network ScienceScience of Communication Networks

• Fundamental disciplines (e.g.)

– graph theory and flows

– game theory and tussle

– control theory and automata

– fault tolerance and dependability

– queuing theory

Graph TheoryGraph Components

• Model network as a graph

• Vertex | node

• Edge | link

• Vertex | node: v

– switch, Internet router, end system

– represented as

• Edge | link

• Vertex | node: v

– switch, Internet router, end system

– represented as

• Edge | link: ei ={vj, vk}

– ei is joins and is incident to vj and vk

– vj, ↔ vk denotes neighbours such that vj is adjacent to vk

– wired physical link, wireless link association, P2P relationship

– generally undirected | bidirectional link

– may be directed | unidirectional linkbidirectional link

Graph TheoryGraph Definition

• Graph G = (V, E ) is a triple E VV

– set of vertices V(G) = {v0, v1, …} correspond to links

– set of edges E(G) = {e0, e1, …} correspond to nodes

– mapping of ei endpoint pairs {vj, vk} gives net topology

• not the mathematical definition of topology but in common use

• Example

Königsberg graph with multiedges + (self-)loop

– V = {v0, v1, v2, v3}

– E = {e0, e1, e2, e3, e4, e5, e6, e7}

– e0 ,e1 ={v0,v1}, e2,e3 ={v0,v2}, e4 ={v0,v3},

e5={v1,v3}, e6 ={v2,v3}, e7 ={v3,v3}

Graph TheoryGraph Properties

• Structural

– adjacency matrix

– degree distribution

• Connectivity

– how well connected, e.g. clustering coeffecient

• Centrality

– importance of a node or link, e.g. betweenness

Comm. Network PreliminariesPR.4 Scope of Communication

Network ComponentsES vs. IS

• End system (ES)

what is it?

• End system (ES)

– computing system that runs applications (e.g. server)

– may be used by a human user (e.g. client)

• End system (ES)

• Intermediate system (IS)

what is it?

• End system (ES)

– network component used to interconnected distributed ESs

– examples: switches, routers, hubs

• End system (ES)

• Some systems may be both ES and IS

examples?

• End system (ES)

• Some systems may be both ES and IS

– ES may also transit traffic in multihop MANET Lecture MW

– IS may also run applications in active programmable net

Scope of CommunicationE2E vs. HBH Definitions

• Hop-by-hop (HBH)

what is it?

– communication or link between directly attached nodes

– typically IS – IS or ES – IS

– may rarely by ES – ES (no network)

• Edge-to-edge (e2e)

– communication or link between edges of a subnetwork

• End-to-end (E2E)

what is it?

– communication or path between end systems: ES – ES

– typically involves multiple HBH segments

– communication or path between end systems: ES – ES

– typically involves multiple HBH segments

• Application-to-application (A2A)

– communication between applications (similar to E2E)

Scope of CommunicationExamples

End system

Intermediate system

edge or access switch

core or backbone switch

multihomed

HBHEdge2Edge

Comm. Network PreliminariesPR.5 Protocols and Layering

Protocols and ServicesDefinition

What is a protocol?

• Protocol: rules for communication between entities

– message format and sequence

• information transfer (data plane)

• signalling of control information (control plane)

• monitoring and management (management plane)

– definition of actions (state machine)

– message format and sequence

• information transfer (data plane)

• signalling of control information (control plane)

• monitoring and management (management plane)

– definition of actions (state machine)

• Service

– functional primitives provided by layer

• Interface

– service interface to layers above and below

Proper design separates protocols from services

Protocol LayeringProtocol Layering

• Layeringprovidesserviceabstraction– isolate:

protocolscomponentstechnology

• any transport layer over IP

• IP over any link layer

• commodity link layer chip evolution, e.g.– 10BASE-T 100BASE-T 1000BASE-X

802.11b 802.11g

abstraction boundary

peer-peer virtual interaction

services provided

services used

layer n+1

layer n–1

layer n

layer n+1

layer n–1

layer n

Protocol LayeringProtocol Layering

• Layering is useful abstraction– thinking about networking system architecture– organising protocols based on role

2. link3. switch4. end system

end system

link link

network

transport

end system router repeater / bridge

network

transport

Protocol LayeringOSI Model

• ISO 7498: open systems interconnection

• Attempt to formalise needed:– protocol layers and their services

– interfaces between layers

7 application application–application

6 presentation data formatting

5 session dialogue management

4 transport end-to-end

3 network forwarding/routing

2 link hop-by-hop

MAC medium access control

1 physical transmission

• ISO 7498: open systems interconnection

– protocol: rules for communication between entities

• Real implementations– ISO model missed medium access control

– presentation layer• not sensible to standardise

• not necessarily right layer of stack

– session layer• generally not needed for data

• useful for control (e.g. SIP, H.323)

coded LPDU

SPDU TH TT

NH TPDU

LH NPDU LT

SH PPDU

PH PHH

session

transport

presentation

application

network

physical

session

transport

presentation

application

network

physical

network

physical

Send ES Receive ES

Protocol LayeringPerformance Issues

• Layered implementations may perform very poorly

• Inter-layer transfers involve non-trivial overhead

– encapsulation/decapsulation of PDUs

– inter-layer control transfer

• context switching and data copying

– effects of overlapping intra-layer control mechanisms

• Protocol layers should be designed with this in mind

– antithesis of layering to isolate protocols and technology

Protocol LayeringPlanes

• Data plane

role of data plane?

• Data plane

– information transfer

8: social layer social information exchange

7: application layer application-to-application exchange

4: transport layer end-to-end flow

3: network layer forwarded through switch/router

2.5: virtual link layer hop-by-hop over virtual link(concatenation of physical links)

2: link layer hop-by-hop over a link

1: physical layer bits as signals in a medium

Protocol LayeringHybrid Layer/Plane Cube

physical

network

transport

application

data plane

socialL8

virtual linkL2.5

• Data plane

• Control plane

role of control plane?

• Data plane

• Control plane

– signalling to control information transfer, including:

• flow or connection establishment/modification/termination

• error control

• flow and congestion control

– control of network components and organisation, e.g.

• network topology and connectivity

– some control plane layers do not correspond to data plane

5: session layer coördination multiple transport flows

1.5: MAC layer medium access control

physical

network

transport

session

application

data plane control plane

socialL8

virtual linkL2.5

• Data plane

• Control plane

– signalling to control information transfer

– control of network components and organisation

• Management plane

role of management plane?

• Data plane

• Control plane

– signalling to control information transfer

– control of network components and organisation

• Management plane

– monitoring and management of network and its elements

– cuts across all layers and across control/data planes

physical

network

transport

session

application

data plane control plane

management

socialL8

virtual linkL2.5

Protocol LayeringOverlays

• Sometimes reasons to run additional overlay layers

– layer 3 over layer 3

• e.g. IP over ATM

– layer 3 over layer 7

• e.g. P2P addressing and routing for file sharing

• Overlay definition

– layer n over layer m, where n m

– overlay is over an underlay

Protocol LayeringInternet Hourglass

• Internet “hourglass”

• Common network layer: IP

– common addressing essential for seamless interworking

– compatible routing & signalling

• Any transport layer above

– in practice: TCP or UDP

TCP UDP RTP

• Any transport layer above

• Any link layer below

– SONET, 802.n, …

TCP UDP RTP

802.11SONETEnet OTN 802.16HFC

Internet ProtocolsImportant Link and MAC Protocols

Common name Standard Scope Technology

Ethernet IEEE 802.3 LAN/MAN wire, fiber

Token ring IEEE 802.5 LAN wire

WirelessLANWiFi

IEEE 802.11 LAN RF, (IR)

WPAN IEEE 802.15 PAN RF

WirelessMANWiMAX

IEEE 802.16 MAN RF

SONETANSI T1.105ITU G.707

MAN/WANfiber

electronic switch

OTN ITU G.709 MAN/WANfiber

optical switch

IEEE 802 network standards are available from standards.ieee.org/getieee802/portfolio.htmlITU-T standards are available from www.itu.int/publications/sector.aspx?lang=en&sector=2

Internet ProtocolsImportant Network Protocols

Protocol Name Function Status Ref

IP Internet protocoladdressing

datagram forwardingstandard

RFC 0791STD 0005

ICMPInternet control

message protocolsignalling standard

RFC 0792STD 0005

IGMPInternet group

management protocolmulticast signalling

proposed standard

RFC 3376

BGPborder gateway

protocolinterdomain routing

draft standard

RFC 1771

OSPFopen shortest path

routingintradomain routing standard

RFC 2328STD 0054

ISISintermediate system

–intermediate systemintradomain routing

proposed standard

ISO10589(RFC 908)

DNS domain name systemdomain name to IP address

resolutionstandard

RFC 1035STD 0013

RFCs are available from www.rfc-editor.org

Internet ProtocolsImportant Transport Protocols

Protocol Name Function Status Ref

TCPtransmission control

protocolreliable data transfer with

congestion controlstandard

RFC 0793STD 0007

UDPuser datagram

protocolsocket access to unreliable

IP datagramsstandard

RFC 0768STD 0006

RTP real-time protocolstreaming media

(typically over UDP)

standards track

RFC 1889

T/TCP TCP for transactions remote login experimental RFC 1644

RDP reliable data protocolreliable data transfer with

no congestion controlexperimental RFC 0908

SCTPstream control

transmission protocol

signalling

proposed for wireless

proposed standard

RFC 2960

Internet Protocols Important “Application Layer” Protocols

Protocol Name Function/Use Status Ref

HTTPhypertext transfer

protocolWeb browsing

draftstandard

RFC 2616

FTPfile transfer

protocolfile and document transfer standard

RFC 0959STD 0009

Telnet telnet remote login standardRFC 0854STD 0008

SMTPsimple mail transfer

protocolemail relay and delivery standard

RFC 0821STD 0010

POPpost officeprotocol

server mail download standardRFC 1939STD 0053

IMAPinternet message access protocol

server mail accessproposedstandard

RFC 3501

NFS network file system remote access to filesproposedstandard

RFC 3530

RTSPreal-time streaming

protocolcontrol of multimedia

streamingproposedstandard

RFC 2326

Comm. Network PreliminariesPR.6 Communication Flow Diagrams

Communication Flow DiagramsMotivation

• Complex network interactions are hard to understand

• Visualisation technique: communication flow diagram

Communication Flow DiagramsConcepts

• Time and space

Communication Flow DiagramsConcepts: Distance

• Time and space

– distance represented horizontally

d12 d23

Communication Flow DiagramsConcepts: Time

• Time and space

– distance represented horizontally

– time represented vertically

d12 d23

Communication Flow DiagramsConcepts: Bit Propagation

• Bit propagation

how represented?

d12 d23

• Bit propagation

– distance d12 from

node 1 to node 2

– propagation delay tp

how computed?

d12 d23

• Bit propagation

node 1 to node 2

– propagation delaytp [s] =d12 [m] / kc [m/s]

• k constant for

particular medium

• speed of lightc 3108 m/s

d12 d23

• Bit propagation

node 1 to node 2

• k constant for

particular medium

– slope of bit flow

can this vary within a diagram?

d12 d23

• Bit propagation

node 1 to node 2

• k constant for

particular medium

– slope is velocity: only affected by k (k 0.6 for fiber)

• c constant unless you alter the laws of physics

• don’t sketch these with widely varying slopes!

d12 d23

Communication Flow DiagramsConcepts: Packet Transmission

• Packet transmission

– sequence of bitstransmitted on aninterface

– transmission delay tb

how computed?

d12 d23

Communication Flow DiagramsConcepts: Packet Transmission

• Packet transmission

– sequence of bitstransmitted on aninterface

– transmission delaytb [s] = b [b] / r [b/s]

• r rate in bits/sec

• b number of bits

d12 d23

Communication Flow DiagramsConcepts: Packet Propagation

• Packet propagation

how to represent?what shape?

d12 d23

– packet isparallelogram

• width is distance

• thickness ispacket size

d12 d23

total delay?

d12 d23

– total HBH delay:tb + tp

• tb to transmit object

• tp for last bit to propagate

d12 d23

Communication Flow DiagramsConcepts: Multihop Packet Propagation

• Multihop propagation

– processing delayin switches and routers

– forwarding delay

• processing time tf

d12 d23

Communication Flow DiagramsConcepts: Multihop Packet Propagation

• Multihop propagation

– processing delayin switches and routers

– forwarding delay

• processing time tf

– before retransmission

• on next hop

d12 d23

Communication Flow DiagramsConcepts: Signalling Message

• Packets areparallelograms

• Signalling messagesare directed linesegments

d12 d23

SIG-MSG

Communication Flow DiagramsConcepts: Signalling Message

• Packets areparallelograms

• Signalling messagesare directed linesegments

– generally shortwith respect todata(thin parallelogram)

– makes diagrams easier to draw and read

• labelled with message name and parameters

d12 d23

SIG-MSG

Communication Flow DiagramsSummary

• Complex network interactions are hard to understand

• Visualisation technique: communication flow diagram– distance is represented horizontally

– time is represented vertically

– signalling messages are arcs with labels

– packets are parallelograms

– keep slope constant

• It is essential that you are very confident with these!

– you will need to properly draw these on the exams

Communication Flow DiagramsExample: Connection Establishment

• Signalling message exchange

• Signalling message exchange– connection SETUP

– CONNECTion established

CONNECT

• Data transfer

Comm. Network PreliminariesAcknowledgements

Some material in these foils is based on the textbook

• Sterbenz and Touch,High-Speed Networking, A Systematic Approach to High-Bandwidth

Low Latency Communication

Comm. Network PreliminariesFurther Reading

Some material in these foils is based on the textbook

• S. Keshav,Mathematical Foundations of Computer Networking

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