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?
Organization of air travel
a series of steps
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
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
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
Departing airport
arriving airport
intermediate air traffic sites
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?
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”

Layering: logical communication
Each layer:
distributed
“entities” implement layer functions at each node
entities perform actions, exchange messages with peers
Layering: logical communication
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
transport
transport
Layering: physical communication
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

source
destination
message
segment
datagram
frame
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)
regional ISPs
connect into NBPs
local ISP, company
connect into regional ISPs


NBP A
NBP B
regional ISP
regional ISP
National Backbone Provider
e.g. BBN/GTE US backbone network
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
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
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
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
ATM: Asynchronous Transfer Mode nets
Internet:
today’s de facto standard for global data networking
1980’s:
telco’s develop ATM: competing network standard for carrying high-speed voice/data
standards bodies:
ATM Forum
ITU
ATM principles:
small (48 byte payload, 5 byte header) fixed length cells (like packets)
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)
ATM layers
ATM Adaptation Layer (AAL): interface to upper layers
end-system
segmentation/reassembly
ATM Layer: cell switching
Physical
Chapter 1: Summary
Covered 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
ATM network
You now hopefully have:
context, overview, “feel” of networking
more depth, detail later in course