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Page 1: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

Introduction

Dr. Yingwu Zhu

1

Page 2: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

2

IntroductionGoal: get context,

overview, “feel” of networking

more depth, detail later in course

approach: descriptive use Internet as

example

Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media performance: loss, delay protocol layers, service

models history

Page 3: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

3

What’s the Internet: “nuts and bolts” view

millions of connected computing devices: hosts, end-systems pc’s workstations, servers PDA’s phones, toasters

running network apps communication links

fiber, copper, radio, satellite

routers: forward packets (chunks) of data thru network

local ISP

companynetwork

regional ISP

router workstationserver

mobile

Page 4: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

4

What’s the Internet: “nuts and bolts” view protocols: control sending,

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

Internet: “network of networks” loosely hierarchical public Internet versus private

intranet

Internet standards RFC: Request for comments IETF: Internet Engineering

Task Force

local ISP

companynetwork

regional ISP

router workstationserver

mobile

Page 5: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

5

What’s the Internet: a service view

communication infrastructure enables distributed applications: WWW, email, games, e-

commerce, database., voting,

more?

communication services provided: connectionless connection-oriented

Page 6: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

6

Perspective (I)

Network users: Does the network support the users’ applications Reliability Error-free service Performance: speed of data transfer Even more: security? Privacy?

Network designers: Cost-efficient network design Good utilization of network resources Cost of building the network Types of services to be supported

Page 7: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

7

Perspective (II)

Network providers: Network administration and customer service Maximize Revenue Minimize Operations Expenses Survivability and Resiliency

Page 8: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

8

A closer look at network structure: network edge:

applications and hosts network core:

routers network of networks

access networks, physical media: communication links

Page 9: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

9

Connectivity

We may want a set of hosts (or devices) to be directly connected! WHY ?

We may not always strive for global connectivity! WHY?

Building Blocks to connect at the physical level: links: coax cable, optical fiber... nodes: general-purpose workstations…

(though sometimes very specialized)

Page 10: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

10

Basic Connectivity

Two types of direct connectivity: point-to-point

multiple access

Page 11: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

11

Discussions

If all computers had to be directly connected, networks would be either very limited or expensive and unmanageable!

Question: If n computers were to be completely and directly connected by point-to-point links of cost C, what would be the total cost of the net?

Question: Would it be less expensive to use a multiple-access network? What are the drawbacks and limitations?

Page 12: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

12

Building Blocks

Switches, Routers, Gateways Special network components responsible for

“moving” packets across the network from source to destination.

Network hosts, workstations, etc. they generally represent the source and sink

(destination) of data traffic (packets)

We can recursively build large networks by interconnecting networks via gateways and routers.

Page 13: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

13

An Interconnection Network

Page 14: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

14

What’s a protocol?human protocols: “what’s the time?” “I have a question” introductions

… specific msgs sent… specific actions

taken when msgs received, or other events

network protocols: machines rather than

humans all communication

activity in Internet governed by protocols

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

receipt

Page 15: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

15

What’s a protocol?a human protocol and a computer network protocol:

Q: Other human protocol?

Hi

Hi

Got thetime?2:00

TCP connection req.TCP connectionreply.

Get http://gaia.cs.umass.edu/index.htm

<file>

time

Page 16: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

16

Protocols

Building blocks of a network architecture

Each protocol object has two different interfaces service interface: defines operations on this

protocol peer-to-peer interface: defines messages

exchanged with peer

Term “protocol” is overloaded specification of peer-to-peer interface module that implements this interface

Page 17: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

17

The network edge: end systems (hosts):

run application programs e.g., WWW, email at “edge of network”

client/server model client host requests,

receives service from server e.g., WWW client (browser)/

server; email client/server

peer-peer model: host interaction symmetric e.g.: teleconferencing,

Gnutella, Kazza, BitTorrent

Page 18: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

18

Network edge: connection-oriented service

Goal: data transfer between end sys.

handshaking: setup (prepare for) data transfer ahead of time Hello, hello back

human protocol set up “state” in two

communicating hosts TCP - Transmission

Control Protocol Internet’s connection-

oriented service

TCP service [RFC 793] reliable, in-order byte-

stream data transfer loss: acknowledgements

and retransmissions

flow control: sender won’t overwhelm

receiver

congestion control: senders “slow down

sending rate” when network congested

Page 19: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

19

Network edge: connectionless service

Goal: data transfer between end systems same as before!

UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data

transfer no flow control no congestion

control

App’s using TCP: HTTP (WWW), FTP

(file transfer), Telnet (remote login), SMTP (email)

App’s using UDP: streaming media,

teleconferencing, Internet telephony,

Skype

Page 20: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

20

The Network Core

mesh of interconnected routers

the fundamental question: how is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”

Page 21: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

21

Different Types of Switching

Different Types of Switching: Circuit Switching (telephone network)

• dedicated circuit, sending and receiving bit streams

Packet Switching• store and forward, sending and receiving packets

Message Switching Virtual Circuit Switching Cell Switching (ATM)

What are Packets? Data to be transmitted is divided into

discrete blocks

Page 22: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

22

Network Core: Circuit Switching

End-end resources reserved for “call”

link bandwidth, switch capacity

dedicated resources: no sharing

circuit-like (guaranteed) performance

call setup required

Page 23: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

23

Cost-Effective Resource Sharing Must share (multiplex) network

resources among multiple users.

Common Multiplexing Strategies Time-Division Multiplexing (TDM) Frequency-Division Multiplexing (FDM):

Frequency band bandwidth

Multiplexing multiple logical flows over a single physical link.

Page 24: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

24

Network Core: Circuit Switchingnetwork resources

(e.g., bandwidth) divided into “pieces”

pieces allocated to calls resource piece idle if not

used by owning call (no sharing)

dividing link bandwidth into “pieces” frequency division time division

Page 25: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

25

Network Core: Packet Switching

each end-end data stream divided into packets

user A, B packets share network resources

each packet uses full link bandwidth

resources used as needed,

resource contention: aggregate resource demand

can exceed amount available

congestion: packets queue, wait for link use

store and forward: packets move one hop at a time transmit over link wait turn at next link

Bandwidth division into “pieces”

Dedicated allocationResource reservation

Page 26: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

26

Network Core: Packet Switching

A

B

C10 MbsEthernet

1.5 Mbs

45 Mbs

D E

statistical multiplexing

queue of packetswaiting for output

link

On-demand sharing

Page 27: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

27

Network Core: Packet SwitchingPacket-switching:

store and forward behavior

Page 28: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

28

Packet switching versus circuit switching

1 Mbit link each user:

100Kbps when “active”

active 10% of time

circuit-switching: 10 users

packet switching: with 35 users,

probability > 10 active less than .004

Packet switching allows more users to use network!

N users

1 Mbps link

Page 29: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

29

Packet switching versus circuit switching

Great for bursty data resource sharing no call setup

Excessive congestion: packet delay and loss protocols needed for reliable data transfer,

congestion control Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video apps

still an unsolved problem!

Is packet switching a “slam dunk winner?”

Page 30: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

30

Packet-switched networks: routing Goal: move packets among routers from source

to destination we’ll study several path selection algorithms

datagram network: destination address determines next hop routes may change during session analogy: driving, asking directions

virtual circuit network: each packet carries tag (virtual circuit ID), tag

determines next hop fixed path determined at call setup time, remains fixed

thru call routers maintain per-call state ATM

Page 31: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

31

Access networks and physical media

Q: How to connect end systems to edge router?

residential access nets institutional access

networks (school, company)

mobile access networks

Keep in mind: bandwidth (bits per

second) of access network?

shared or dedicated?

Page 32: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

32

Residential access: point to point access

Dialup via modem up to 56Kbps direct access

to router (conceptually) ISDN: intergrated services

digital network: 128Kbps all-digital connect to router

ADSL: asymmetric digital subscriber line up to 1 Mbps home-to-

router up to 8 Mbps router-to-

home

Page 33: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

33

Residential access: cable modems HFC: hybrid fiber coax

asymmetric: up to 10Mbps upstream, 1 Mbps downstream

network of cable and fiber attaches homes to ISP router shared access to router

among home issues: congestion,

dimensioning deployment: available

via cable companies, e.g., MediaOne, Comcast

Page 34: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

34

Institutional access: local area networks

company/univ local area network (LAN) connects end system to edge router

Ethernet: shared or dedicated

cable connects end system and router

10 Mbs, 100Mbps, Gigabit Ethernet

deployment: institutions, home LANs soon

Page 35: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

35

Wireless access networks shared wireless

access network connects end system to router

wireless LANs: radio spectrum replaces

wire e.g., Lucent Wavelan 10

Mbps

wider-area wireless access CDPD: wireless access

to ISP router via cellular network (base stations)

basestation

mobilehosts

router

Page 36: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

36

Physical Media

physical link: transmitted data bit propagates across link

guided media: signals propagate in

solid media: copper, fiber

unguided media: signals propagate

freely, e.g., radio

Twisted Pair (TP) two insulated copper

wires Category 3: traditional

phone wires, 10 Mbps ethernet

Category 5 TP: 100Mbps ethernet

Page 37: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

37

Physical Media: coax, fiber

Coaxial cable: wire (signal carrier)

within a wire (shield) baseband: single

channel on cable broadband: multiple

channel on cable

bidirectional common use in

10Mbs Ethernet

Fiber optic cable:glass fiber carrying light

pulseshigh-speed operation:

100Mbps Ethernet high-speed point-to-

point transmission (e.g., 5 Gps)

low error rate

Page 38: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

38

Physical media: radio signal carried in

electromagnetic spectrum

no physical “wire” bidirectional propagation

environment effects: reflection obstruction by objects interference

Radio link types:microwave

e.g. up to 45 Mbps channels

LAN (e.g., waveLAN) 2Mbps, 11Mbps

wide-area (e.g., cellular) e.g. CDPD, 10’s Kbps

satellite up to 50Mbps channel (or

multiple smaller channels) 270 Msec end-end delay geosynchronous versus

LEOS

Page 39: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

39

Different Types of Links

Sometimes you install your own!Category 5 twisted pair 10-100Mbps, 100m50-ohm coax (ThinNet) 10-100Mbps, 200m75-ohm coax (ThickNet) 10-100Mbps, 500mMultimode fiber 100Mbps, 2kmSingle-mode fiber 100-2400Mbps, 40km

Page 40: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

40

Bigger Pipes!

Sometimes leased from the phone company

STS: Synchronous Transport Signal

Service to ask for Bandwidth you getISDN 64 KbpsT1 1.544 MbpsT3 44.736 MbpsSTS-1 51.840 MbpsSTS-3 155.250 MbpsSTS-12 622.080 MbpsSTS-24 1.244160 GbpsSTS-48 2.488320 Gbps

Page 41: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

41

Delay in packet-switched networkspackets experience delay

on end-to-end path four sources of delay at

each hop

nodal processing: check bit errors determine output link

queueing time waiting at output

link for transmission depends on

congestion level of router

A

B

propagation

transmission

nodalprocessing queueing

Page 42: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

42

Delay in packet-switched networksTransmission delay: R=link bandwidth

(bps) L=packet length (bits) time to send bits into

link = L/R

Propagation delay: d = length of physical

link s = propagation speed in

medium (~2x108 m/sec) propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queueing

Note: s and R are very different quantitites!

Page 43: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

43

Bandwidth (throughput)

Amount of data that can be transmitted per time unit

Example: 10Mbps

link versus end-to-end

Notation KB = 210 bytes Mbps = 106 bits per second

Performance

Page 44: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

44

Bandwidth related to “bit width”

Performance

a)

b)

1 second

1 second

Page 45: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

45

Latency (delay) Time it takes to send message from

point A to point B Example: 24 milliseconds (ms) Sometimes interested in in round-trip

time (RTT) Components of latency

Latency = Propagation + Transmit + Queue + Proc.

Propagation = Distance / SpeedOfLight

Transmit = Size / Bandwidth

Page 46: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

Transmission and Propagation Delays Propagation delay

The propagation delay over a link is the time it takes a bit to travel from on end of the link to the other

= d/s Transmission delay

It is the amount of time it takes to push the packet onto the link

=L/B Total latency over the link

= transmission delay + propagation delay46

Page 47: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

47

Bandwidth v.s. Latency

Consider a standard 6250 bpi magnetic tape that holds 180 Megabytes. A station wagon can easily transport 200 tapes. Suppose the source and destination are an hour’s drive apart.

Calculate the effective throughput: 288000 megabits in 3600 seconds or 80 Mbps

What is the moral of this story ?

Page 48: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

48

Bandwidth v.s. Latency

Never underestimate the bandwidth of a station wagon full of tapes pacing down the highway.

But … What happens to the latency?

Page 49: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

49

The “hard” limit

Speed of light 3.0 x 108 meters/second in a vacuum 2.3 x 108 meters/second in a cable 2.0 x 108 meters/second in a fiber

Notes no queuing delays in direct link bandwidth not relevant if Size = 1 bit process-to-process latency includes

software overhead software overhead can dominate when

Distance is small

Page 50: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

50

Relative importance of bandwidth and latency small message (e.g., 1 byte): 1ms vs. 100ms

dominates 1Mbps vs. 100Mbps large message (e.g., 25 MB): 1Mbps vs.

100Mbps dominates 1ms vs. 100ms

Consider two channels of 1Mbps and 100 Mbps respectively. For a 1 byte message, the available bandwidth is relatively insignificant given a RTT of 1 ms. The transmit delay for each channel is 8 s and 0.08 s, respectively.

Page 51: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

51

Delay x Bandwidth Product

e.g., 100ms RTT and 45Mbps Bandwidth = 560KB of data

We have to view the network as a buffer. This may have interesting consequences: How much data did the sender transmit

before a response can be received?

Bandwidth

Delay

Page 52: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

52

Application Needs bandwidth requirements: burst versus peak

rate jitter: variance in latency (inter-packet gap)

Average Bandwidth Requirement is Not enough: consider a source with an avg. BW-

requirement of 2Mbps. If the application generates 1 Mbit in one second interval and 3Mbit in a second, a channel that can support 2 Mbps max. will have a tough time.

Other Quality of Service (QOS) Parameters: max. and min. delay max. and min. bandwidth demand rates for dynamic increase of demands Cell-Loss Rate

Page 53: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

53

Queueing delay (revisited)

R=link bandwidth (bps) L=packet length (bits) a=average packet

arrival rate

traffic intensity = La/R

La/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R > 1: more “work” arriving than can be serviced,

average delay infinite!

Page 54: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

54

What Goes Wrong in the Network? Different types of Error:

Bit-level errors (electrical interference)• 1 in 106-107 in copper - 1 in 1012 - 1014 in fiber

Packet-level errors (congestion) Link and node failures

How should we deal with these types of error?

What are the consequences of errors?

Page 55: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

55

Other types of problems in the Network?

Messages are delayed Messages are deliver out-of-order Third parties eavesdrop

The key problem is to fill in the gap between what applications expect and what the underlying technology provides.

Page 56: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

56

Protocol “Layers”Networks are

complex! many “pieces”:

hosts routers links of various

media applications protocols hardware,

software

Question: Is there any hope of organizing structure of

network?

Or at least our discussion of networks?

Page 57: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

57

Organization of air travel

a series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Page 58: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

58

Organization of air travel: a different view

Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Page 59: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

59

Layered air travel: services

Counter-to-counter delivery of person+bags

baggage-claim-to-baggage-claim delivery

people transfer: loading gate to arrival gate

runway-to-runway delivery of plane

airplane routing from source to destination

Page 60: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

60

Distributed implementation of layer functionality

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Dep

art

ing

air

port

arr

ivin

g

air

port

intermediate air traffic sites

airplane routing airplane routing

Page 61: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

61

Why layering?

Dealing with complex systems: explicit structure allows identification,

relationship of complex system’s pieces layered reference model for discussion

modularization eases maintenance, updating of system change of implementation of layer’s service

transparent to rest of system e.g., change in gate procedure doesn’t

affect rest of system layering considered harmful?

Page 62: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

62

Internet protocol stack application: supporting network

applications ftp, smtp, http

transport: host-host data transfer tcp, udp

network: routing of datagrams from source to destination ip, routing protocols

link: data transfer between neighboring network elements ppp, ethernet

physical: bits “on the wire”

application

transport

network

link

physical

Page 63: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

63

Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

Each layer: distributed “entities”

implement layer functions at each node

entities perform actions, exchange messages with peers

Page 64: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

64

Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

E.g.: transport take data from

app add addressing,

reliability check info to form “datagram”

send datagram to peer

wait for peer to ack receipt

analogy: post office

data

transport

transport

ack

Page 65: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

65

Layering: physical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

Page 66: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

66

Protocol layering and data

Each layer takes data from above adds header information to create new data unit passes new data unit to layer below

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

datagram

frame

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67

Protocol Data Units

The combination of data from the next higher layer and control information is referred to as PDU. Control Information in the Transport Layer

may include:• Destination Service Access Point (DSAP)• Sequence number• Error-detection code

Page 68: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

68

Internet structure: network of networks

roughly hierarchical national/international

backbone providers (NBPs) e.g. BBN/GTE, Sprint, AT&T,

IBM, UUNet interconnect (peer) with each

other privately, or at public Network Access Point (NAPs) (or switching centers)

regional ISPs connect into NBPs

local ISP, company connect into regional ISPs

NBP A

NBP B

NAP NAP

regional ISP

regional ISP

localISP

localISP

Page 69: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

69

National Backbone Provider

e.g. BBN/GTE US backbone network

Page 70: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

70

Internet History

1961: Kleinrock - queueing theory shows effectiveness of packet-switching

1964: Baran - packet-switching in military nets

1967: ARPAnet conceived by Advanced Reearch Projects Agency

1969: first ARPAnet node operational

1972: ARPAnet

demonstrated publicly NCP (Network Control

Protocol) first host-host protocol

first e-mail program ARPAnet has 15 nodes

1961-1972: Early packet-switching principles

Page 71: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

71

Internet History

1970: ALOHAnet satellite network in Hawaii

1973: Metcalfe’s PhD thesis proposes Ethernet

1974: Cerf and Kahn - architecture for interconnecting networks

late70’s: proprietary architectures: DECnet, SNA, XNA

late 70’s: switching fixed length packets (ATM precursor)

1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles: minimalism, autonomy

- no internal changes required to interconnect networks

best effort service model

stateless routers decentralized control

define today’s Internet architecture

1972-1980: Internetworking, new and proprietary nets

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72

Internet History

1983: deployment of TCP/IP

1982: smtp e-mail protocol defined

1983: DNS defined for name-to-IP-address translation

1985: ftp protocol defined

1988: TCP congestion control

new national networks: Csnet, BITnet, NSFnet, Minitel

100,000 hosts connected to confederation of networks

1980-1990: new protocols, a proliferation of networks

Page 73: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

73

Internet History

Early 1990’s: ARPAnet decomissioned

1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)

early 1990s: WWW hypertext [Bush 1945,

Nelson 1960’s] HTML, http: Berners-Lee 1994: Mosaic, later

Netscape late 1990’s:

commercialization of the WWW

Late 1990’s: est. 50 million

computers on Internet est. 100 million+

users backbone links

runnning at 1 Gbps

1990’s: commercialization, the WWW

Page 74: Introduction Dr. Yingwu Zhu 1. 2 Introduction Goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive

74

SummaryCovered a “ton” of

material! Internet overview what’s a protocol? network edge, core,

access network performance: loss,

delay layering and service

models backbones, NAPs, ISPs history

You now hopefully have:

context, overview, “feel” of networking

more depth, detail later in course


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Design · Tangram Electronic Engineering Co. LTD 339 North Wing, Yingwu Conference Centre No. 6, Hua Yuan Road, Hai Dian District Beijing 100088 P R China Phone: +86(10)62061100 Fax: