Chapter 1 Introduction
Computer Networks and the Internet
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
What is networking? A network? Hardware? Software
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History: 60’s
Mainframes with terminals Not much more than keyboard and display Character based (display and comms) ASCII and EBCDIC
Is this networking?
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Remote offices
Modem access Telephone company acted as a “cable” Modulator-Demodulator
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Telco
Telco
Actually a series of offices When dialed a connection formed a
physical link
Each connection a switch so switched connection, or circuit-switched
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telephonenetwork
central office
Bandwidth Audio frequencies limited bandwidth Local connections: 9600 or 19.2 bps Early modems 400 baud
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telephonenetwork
central office
10 Million bps!!70’s and Ethernet
Ethernet was developed at Xerox Palo Alto Research Center Incorporated (PARC)
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Coax
Frame basedFrame based
Bridged
Only so many could share the same media
Collisions (CSMA/CD)
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Bridge Bridge
Telco
Connecting offices
Telco began providing high speed connections
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T11.54Mbps
DS0 - 64 k ilobits per secondISDN - Two DS0 lines plus signaling (16 kilobytes per second), or 128 kilobits per secondT1 - 1.544 megabits per second (24 DS0 lines)T3 - 43.232 megabits per second (28 T1s)
80’s UTP and PCs
Unshielded Twisted Pair (UTP) Early 1Mbs but quickly 10Mbps
(now 100 and above) Still shared (hubs)
PCs
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Meanwhile As early as the 60s began investigating
packet switching (vs. physically switched)
First packet switching network The Advanced Research Projects Agency
Network (ARPANET) Funded by the Defense Advanced Research
Projects Agency (DARPA) 1969 contract awarded to
BBN Technologies (originally Bolt, Beranek and Newman)
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Took a decade
Various packet switching protocols vied for dominance
1981 NSF funded creation of a “backbone” 1982 the Internet Protocol Suite (TCP/IP)
was accepted as standard
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Finally the internet
Late 80’s early 90’s ARPANET and
NSFNET decommissioned (commercialized)
ISPs began emerging
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1974: Term Internet first used as shorthand for internetworking
• RFC 675 – Specification of Internet Transmission Control Program, by Vinton Cerf, Yogen Dalal, and Carl Sunshine
1974: Term Internet first used as shorthand for internetworking
• RFC 675 – Specification of Internet Transmission Control Program, by Vinton Cerf, Yogen Dalal, and Carl Sunshine
telephonenetwork Internet
homedial-upmodem
ISPmodem(e.g., AOL)
homePC
central office
Home PCs and Dial-up Modems
You’ve got mail You’ve got mail
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Switched, analog network to the internet service provider
Then packet switched
00’s
Remember hubs and bridges
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Hubs
Bridge
Bridges/Also known as switches
What’s the advantageWhat’s the advantage
Is it really circuit-switch?Is it really circuit-switch?
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What is the internet?
World Wide Web? The hardware? The protocols?
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
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What’s the Internet: “nuts and bolts” view
millions of connected computing devices: hosts = end systems running network apps
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
router
PC
server
wirelesslaptop
cellular handheld
wiredlinks
access points
communication links fiber, copper,
radio, satellite transmission
rate = bandwidth
routers: forward packets (chunks of data)
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Backbone Optical Fiber and bandwidth
OC3 - 155 megabits per second (84 T1s) OC12 - 622 megabits per second (4 OC3s) OC24 - 1.25 gigabits per seconds (2
OC12s) OC48 - 2.5 gigabits per seconds (4 OC12s) OC192 - 9.6 gigabits per second (4 OC48s) OC768 - 9.6 gigabits per second (4
OC192s)
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Institutional networkGlobal ISP
Regional ISP
Introduction: copyright J.F Kurose and K.W. Ross 1-19
What’s the Internet: “nuts and bolts” view Protocols control
sending, receiving of msgs e.g., TCP, IP, HTTP, Skype,
Ethernet
Internet: “network of networks” loosely hierarchical public Internet versus
private intranet
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
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What’s a protocol?a human protocol and a computer network protocol:
Q: Other human protocols?
Hi
Hi
Got thetime?
2:00
TCP connection request
TCP connectionresponseGet http://www.awl.com/kurose-ross
<file>time
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protocols define format, order of msgs sent and
received among network entities, and actions taken on msg transmission, receipt
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Already talked about one protocol
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Shared media
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With packet switched
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Packet comes into a router Which outward bound link should it take?
packetWhich path? Which path?
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A closer look at network structure:
Hosts (and applications): network edge
Access networks, LAN, physical media: wired, wireless communication links
Network core: interconnected
routers network of
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The network edge: end systems (hosts):
run application programs e.g. Web, email at “edge of network”
client/server
peer-peer
client/server model client host requests,
receives service from always-on server
e.g. Web browser/server; email client/serverpeer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype, BitTorrent
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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
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telephonenetwork
DSLmodem
homePC
homephone
Internet
DSLAM
Existing phone line:0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data
splitter
centraloffice
Digital Subscriber Line (DSL)
Also uses existing telephone infrastruture up to 1 Mbps upstream (today typically < 256
kbps) up to 8 Mbps downstream (today typically < 1
Mbps) dedicated physical line to telephone central office
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Introduction: copyright J.F Kurose and K.W. Ross 1-27
Residential access: cable modems Does not use telephone infrastructure
Instead uses cable TV infrastructure Homes share access unlike DSL (dedicated)
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Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
Typically 500 to 5,000 homes
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Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork
server(s)
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Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
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Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork
Channels
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
DATA
DATA
CONTROL
1 2 3 4 5 6 7 8 9
FDM (more shortly):
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ONT
OLT
central office
opticalsplitter
ONT
ONT
opticalfiber
opticalfibers
Internet
Fiber to the Home
Optical links from central office to the home Two competing optical technologies:
Passive Optical network (PON) Active Optical Network (AON)
Much higher Internet rates; fiber also carries television and phone services
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100 Mbps
100 Mbps
100 Mbps1 Gbps
server
Ethernetswitch
Institutionalrouter
To Institution’sISP
Ethernet Internet access
Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into
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Introduction: copyright J.F Kurose and K.W. Ross 1-34
Wireless access networks
shared wireless access network connects end system to router via base station aka “access
point”
wireless LANs: 802.11b/g (WiFi): 11 or 54
Mbps
wider-area wireless access provided by telco operator ~1Mbps over cellular system
(EVDO, HSDPA) next up (?): WiMAX (10’s Mbps)
over wide area
basestation
mobilehosts
router
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Home networks
Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point
wirelessaccess point
wirelesslaptops
router/firewall
cablemodem
to/fromcable
headend
Ethernet
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Wireless is shared medium. As such uses a contention based protocol (CSMA/CD)
Wireless is shared medium. As such uses a contention based protocol (CSMA/CD)
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Physical Media
Bit: propagates betweentransmitter/rcvr pairs
physical link: what lies between transmitter & receiver
guided media: signals propagate in solid
media: copper, fiber, coax
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: 100Mbps Ethernet
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Physical Media: coax, fiber
Coaxial cable: two concentric copper
conductors bidirectional baseband:
single channel on cable legacy Ethernet
broadband: multiple channels on
cable HFC
Fiber optic cable: glass fiber carrying
light pulses, each pulse a bit
high-speed operation: high-speed point-to-point
transmission (e.g., 10’s-100’s Gps)
low error rate: repeaters spaced far apart ; immune to electromagnetic noise
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The Network Core
How data moves through the network
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The Network Core
mesh of interconnected routers
Packet switched or circuit switched? circuit switching:
dedicated circuit per call: telephone net
packet-switching: data sent thru net in discrete “chunks”
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Circuit Switching: FDM and TDM
FDM
frequency
time
TDM
frequency
time
4 users
Example:
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Introduction: copyright J.F Kurose and K.W. Ross 1-44
Circuit switched wasteful?
When not transmitting over circuit? TDM: Empty time slots FDM: Unused channels
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Network Core: Packet Switching
Packetize data Put in Queue If link available, go
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A
B
C100 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
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Network Core: Packet Switching
each packet uses full link bandwidth
resources used as needed
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A
B
C100 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
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Network Core: Packet Switching
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If one path through network crowded can follow another
But how?
A
B
C100 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
Routing
How do packets find their way through the network?
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Data Header
Source/Destination Address
Packet Packet
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Speed
Will a packet arrive instantly at the ultimate destination?
R R RL
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Packet-switching: store-and-forward
takes L/R seconds to transmit (push out) packet of L bits on to link at R bps
store and forward: entire packet must arrive at router before it can be transmitted on next link
delay = 3L/R (assuming zero propagation delay)
Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay =
15 sec
R R RL
more on delay shortly …
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Packet switching versus circuit switching
great for bursty data resource sharing simpler, 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 (chapter 7)
Is packet switching a “slam dunk winner?”
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Internet structure: network of networks
roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,
Cable and Wireless), national/international coverage treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
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Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
….
………
POP: point-of-presence
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Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider
Tier-2 ISPs also peer privately with each other.
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Internet structure: network of networks
“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet
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Internet structure: network of networks
a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
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Delay, loss, and throughput
Do all packets make it?At what delay?
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A
B
Introduction: copyright J.F Kurose and K.W. Ross 1-58
How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link
capacity packets queue, wait for turn
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A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
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Four sources of packet delay
1. nodal processing: check bit errors determine output link
A
B
propagation
transmission
nodalprocessing queueing
2. queueing time waiting at output
link for transmission depends on
congestion level of router
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Delay in packet-switched networks3. Transmission delay: R=link bandwidth
(bps) L=packet length (bits) time to send bits into
link = L/R
4. Propagation delay: d = length of physical
link s = propagation speed in
medium (~2x108 m/sec) propagation delay = d/s
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A
B
propagation
transmission
nodalprocessing queueing
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Nodal delay
dproc = processing delay typically a few microsecs or less
dqueue = queuing delay depends on congestion
dtrans = transmission delay = L/R, significant for low-speed links
dprop = propagation delay a few microsecs to hundreds of msecs
proptransqueueprocnodal ddddd
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“Real” Internet delays and routes
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
* means no response (probe lost, router not replying)
trans-oceaniclink
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Throughput
throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time
server, withfile of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec pipe that can carry
data at rate
Rs bits/sec)
pipe that can carrydata at rate
Rc bits/sec)
server sends bits
(fluid) into pipe
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Throughput: if push 1 frame1 frame per delayTrans: L/RS + prop Proc+Queue
L/RC + prop
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Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
link on end-end path that constrains end-end throughput
bottleneck link
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Throughput: Internet scenario
6 connections (fairly) share backbone bottleneck link R
bits/sec
Rs
Rs
Rs
Rc
Rc
Rc
R
per-connection end-end throughput: min(Rc,Rs,R/6)
in practice: Rc or Rs is often bottleneck
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Layered architecture Software stack
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API
ApplicationApplication
TranslationTranslation
DriverDriver
API
ApplicationApplication
TranslationTranslation
DriverDriver
Physical cables/switches/routersPhysical cables/switches/routers
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Internet protocol stack application: supporting network
applications FTP, SMTP, HTTP
transport: process-process 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
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ISO/OSI reference model presentation: allow applications
to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers! these services, if needed, must
be implemented in application needed?
application
presentation
session
transport
network
link
physical
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sourceapplicatio
ntransportnetwork
linkphysical
HtHn M
segment Ht
datagram
destination
application
transportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
Switch/bridge
Encapsulationmessage M
Ht M
Hn
frame
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Think of it as Network layers talking to other network layers, transport layers talking to other transport layers, application layers…
Think of it as Network layers talking to other network layers, transport layers talking to other transport layers, application layers…
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applic
ati
on
transp
ort
netw
ork
link
physi
cal
Ht Hn HlM
Encapsulation
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Remember book organization
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application
presentation
session
transport
network
link
physical
Chapter 2
Chapter 3Chapter 4
Chapter 5
Routing
Bridging/Switching
Routing
Bridging/Switching
TCPIP
Transmission Control Protocol / Internet Protocol.
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