Transcript Part I: Introduction

Protocol “Layers”
Networks are complex!
r many “pieces”:
m hosts
m routers
m links of various
media
m applications
m protocols
m hardware,
software
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
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Organization of air travel
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
r a series of steps
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Organization of air travel: a different view
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
Layers: each layer implements a service
m via its own internal-layer actions
m relying on services provided by layer below
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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
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ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
arriving airport
Departing airport
Distributed implementation of layer functionality
intermediate air traffic sites
airplane routing
airplane routing
airplane routing
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Why layering?
Dealing with complex systems:
explicit structure allows identification,
relationship of complex system’s pieces
m layered reference model for discussion
r modularization eases maintenance, updating of
system
m change of implementation of layer’s service
transparent to rest of system
m e.g., change in gate procedure doesn’t affect
rest of system
r layering considered harmful?
r
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Internet protocol stack
r
application: supporting network
applications
m
r
transport: host-host data transfer
m
r
ip, routing protocols
link: data transfer between
neighboring network elements
m
r
tcp, udp
network: routing of datagrams from
source to destination
m
r
ftp, smtp, http
application
transport
network
link
physical
ppp, ethernet
physical: bits “on the wire”
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Layering: logical communication
Each layer:
r distributed
r “entities”
implement
layer functions
at each node
r entities
perform
actions,
exchange
messages with
peers
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
application
transport
network
link
physical
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Layering: logical communication
E.g.: transport
r
r
r
r
r
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
application
transport
transport
network
link
physical
application
transport
network
link
physical
ack
data
network
link
physical
application
transport
network
link
physical
data
application
transport
transport
network
link
physical
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Layering: physical communication
data
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
data
application
transport
network
link
physical
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Protocol layering and data
Each layer takes data from above
r adds header information to create new data unit
r passes new data unit to layer below
source
M
Ht M
Hn Ht M
Hl Hn Ht M
application
transport
network
link
physical
destination
application
Ht
transport
Hn Ht
network
Hl Hn Ht
link
physical
M
message
M
segment
M
M
datagram
frame
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Internet structure: network of networks
roughly hierarchical
r national/international
backbone providers (NBPs)
r
m
m
r
regional ISPs
m
r
e.g. BBN/GTE, Sprint,
AT&T, IBM, UUNet
interconnect (peer) with
each other privately, or at
public Network Access Point
(NAPs)
connect into NBPs
local ISP, company
m
local
ISP
regional ISP
NBP B
NAP
NAP
NBP A
regional ISP
local
ISP
connect into regional ISPs
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National Backbone Provider
e.g. BBN/GTE US backbone network
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Internet History
1961-1972: Early packet-switching principles
r
r
r
r
1961: Kleinrock - queueing
theory shows
effectiveness of packetswitching
1964: Baran - packetswitching in military nets
1967: ARPAnet conceived
by Advanced Reearch
Projects Agency
1969: first ARPAnet node
operational
r
1972:
m ARPAnet demonstrated
publicly
m NCP (Network Control
Protocol) first hosthost protocol
m first e-mail program
m ARPAnet has 15 nodes
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Internet History
1972-1980: Internetworking, new and proprietary nets
r
r
r
r
r
r
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:
m minimalism, autonomy no internal changes
required to
interconnect networks
m best effort service
model
m stateless routers
m decentralized control
define today’s Internet
architecture
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Internet History
1980-1990: new protocols, a proliferation of networks
r
r
r
r
r
1983: deployment of
TCP/IP
1982: smtp e-mail
protocol defined
1983: DNS defined
for name-to-IPaddress translation
1985: ftp protocol
defined
1988: TCP congestion
control
new national networks:
Csnet, BITnet,
NSFnet, Minitel
r 100,000 hosts
connected to
confederation of
networks
r
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Internet History
1990’s: commercialization, the WWW
r
r
r
Early 1990’s: ARPAnet
decomissioned
1991: NSF lifts restrictions
on commercial use of NSFnet
(decommissioned, 1995)
early 1990s: WWW
m hypertext [Bush 1945,
Nelson 1960’s]
m HTML, http: Berners-Lee
m 1994: Mosaic, later
Netscape
m late 1990’s:
commercialization of the
WWW
Late 1990’s:
r
r
r
est. 50 million
computers on Internet
est. 100 million+ users
backbone links runnning
at 1 Gbps
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ATM: Asynchronous Transfer Mode nets
Internet:
r today’s de facto
standard for global
data networking
1980’s:
r telco’s develop ATM:
competing network
standard for carrying
high-speed voice/data
r standards bodies:
m
m
ATM Forum
ITU
ATM principles:
r
small (48 byte payload, 5
byte header) fixed length
cells (like packets)
m
m
r
r
fast switching
small size good for voice
virtual-circuit network:
switches maintain state for
each “call”
well-defined interface
between “network” and
“user” (think of telephone
company)
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ATM layers
r
ATM Adaptation
Layer (AAL):
interface to upper
layers
m
m
r
r
end-system
segmentation/rea
ssembly
ATM Layer: cell
switching
Physical
application
TCP/UDP
IP
AAL
ATM
physical
application
TCP/UDP
IP
AAL
ATM
physical
Where’s the application?
r ATM: lower layer
r functionality only
r IP-over ATM: later
ATM
physical
application
TCP/UDP
IP
AAL
ATM
physical
application
TCP/UDP
IP
AAL
ATM
physical
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Chapter 1: Summary
Covered a “ton” of
material!
r
r
r
r
r
r
r
r
Internet overview
what’s a protocol?
network edge, core,
access network
performance: loss, delay
layering and service
models
backbones, NAPs, ISPs
history
ATM network
You now hopefully have:
r context, overview,
“feel” of networking
r more depth, detail
later in course
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