Transcript 4th Edition: Chapter 1 - Universidad de Sevilla

Computer Networking
2014/2015
Departamento de
Tecnología Electrónica
Contents
 Chapter 1: Introduction
 Chapter 2: The Application Layer
 Chapter 3: The Transport Layer
 Chapter 4: The Network Layer
 Chapter 5: The Link Layer and Local Area
Networks
Introduction
1-2
Departamento de
Tecnología Electrónica
Computer Networking
Chapter 1
Computer Networks
and the Internet
Some of these slides have
copyright from:
Computer Networking: A
Top Down Approach ,
5th edition.
Jim Kurose, Keith Ross
Addison-Wesley, April
2009.
Introduction 1-3
Chapter 1: Introduction
Our goal:



get used to terminology
more depth, detail later
in course
approach:
 use Internet as
example
Overview:







what’s the Internet?
what’s a protocol?
network edge; hosts, network
access, physical media
network core: packet/circuit
switching, Internet structure
performance: loss, delay,
throughput
protocol layers, service models
history
Introduction 1-4
Chapter 1. Computer networks and the
internet
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 History
Introduction 1-5
What’s the Internet? Overview
PC
 millions of connected
server
wireless
laptop
cellular
handheld
computing devices: hosts =
end systems
 running network apps
 communication
access
points
wired
links
router
links
 fiber, copper,
radio, satellite
 transmission
rate = bandwidth
 routers: forward
packets (chunks of
data)
Mobile network
Global ISP
Home network
Regional ISP
Institutional network
Introduction 1-6
“Fun” Internet appliances
Web-enabled toaster +
weather forecaster
IP picture frame
Slingbox: watch,
control cable TV remotely
Internet
refrigerator
Internet phones
Introduction 1-7
What’s the Internet? HW and SW components

protocols control sending,
receiving of msgs
Mobile network
Global ISP
 e.g., TCP, IP, HTTP, Ethernet

Internet: “network of
networks”
 hierarchical
 public Internet versus private
intranet

Internet standards
Home network
Regional ISP
Institutional network
 RFC: Request for comments
 IETF: Internet Engineering Task
Force
Introduction 1-8
What’s the Internet? A service view


communication infrastructure
enables distributed applications:
 Web, VoIP, email, online
games, e-commerce, file
sharing
communication services
provided to apps:
 reliable data delivery from
source to destination
 “best effort” (unreliable) data
delivery
Introduction 1-9
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
Introduction 1-10
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
Introduction 1-11
Chapter 1. Computer networks and the
internet
1.1 What is the Internet?
1.2 Network edge

end systems, access networks, links
1.3 Network core

circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 History
Introduction 1-12
A closer look at network structure

network edge:
applications and hosts

access networks,
physical media: wired
or wireless
communication links

network core:
 interconnected routers
 network of networks
Introduction 1-13
The network edge

end systems (hosts):
 run application programs
 e.g. Web, email
 at “edge of network”

peer-peer
client/server model
 client host requests, receives
service from always-on server
client/server
 e.g. Web browser/server; email
client/server

peer-peer model:
 minimal (or no) use of dedicated
servers
 e.g. BitTorrent
Introduction 1-14
Access networks and physical media
Q: How to connect end
systems to an edge router?
 residential access nets
 institutional access
networks (schools,
companies,…)
 mobile access networks
Keep in mind:
 bandwidth (bits per second)
of access network?
 shared or dedicated?
Introduction 1-15
Residential access networks
Dial-up Modem
central
office
home
PC



home
dial-up
modem
telephone
network
Internet
ISP
modem
(e.g., AOL)
uses existing telephony infrastructure
 home directly-connected to central office
up to 56Kbps direct access to router (often less)
can’t browse, phone at same time: not “always on”
Introduction 1-16
Residential access networks
Digital Subscriber Line (DSL)
Existing phone line:
0-4KHz phone; 4-50KHz
upstream data; 50KHz-1MHz
downstream data
home
phone
Internet
DSLAM
telephone
network
splitter
DSL
modem
home
PC
central
office
uses existing telephone infrastructure
 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

Introduction 1-17
Residential access networks
Cable modems



uses cable TV infrastructure, rather than telephone
infrastructure
HFC: hybrid fiber coax
 asymmetric: up to 30Mbps downstream, 2 Mbps
upstream
network of cable, fiber attaches homes to the ISP
router
 homes share access to the router
 unlike DSL, which has dedicated access
Introduction 1-18
Residential access networks
Cable modems
Typically 500 to 5,000 homes
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Introduction 1-19
Residential access networks
Fiber to the Home
optical
fibers
Internet
OLT
ONT
optical
fiber
central office
optical
splitter
ONT: Optical Network Terminator
OLT: Optical Line Terminator
ONT
ONT


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 (Gpbs: down 10-20 Mpbs, up 2-10 Mbps)
Introduction 1-20
Institutional access networks
Ethernet Internet access
100 Mbps
Ethernet
switch
institutional
router
to institution’s
ISP
100 Mbps
1 Gbps
100 Mbps

typically used in companies, universities, etc



server
Also used in residential networks
10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet
today, end systems typically connect to Ethernet switch
Introduction 1-21
Mobile access networks
Wireless access networks

shared wireless access network
connects end system to router
 via base station a.k.a “access point”

wireless LANs:


802.11b/g (WiFi): 11 or 54 Mbps
wider-area wireless access
 provided by telecom operator
 ~1Mbps over cellular system (EVDO,
HSDPA)
 next up (?): WiMAX (10’s Mbps) over
wide area
router
base
station
mobile
hosts
EVDO: Evolution-Data Optimized
HSDPA: High Speed Downlink Packet Access
Introduction 1-22
Home networks
Typical home network components:
 DSL or cable modem
 router/firewall/NAT
 Ethernet
 wireless access point
to/from
cable
headend
cable
modem
router/
Firewall
/ NAT
Ethernet
Home Station Fibra Óptica Teldat i-1104W
(MoviStar)
http://www.movistar.es/particulares/ayuda/internet/adsl/equipami
ento-adsl/routers/Teldat-i-1104w
wireless
laptops
wireless
access
point
Introduction 1-23
Physical Media


bit: propagates between
transmitter/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
Introduction 1-24
Guided Physical Media
Twisted Pair (TP)

two insulated copper wires


Category 3: traditional phone wires, 10 Mbps Ethernet
Category 5: 100Mbps Ethernet
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 Gpbs)
low error rate: repeaters spaced far apart; immune to electromagnetic noise
Introduction 1-25
Unguided Physical Media: radio




signal carried on
electromagnetic spectrum
no physical “wire”
bidirectional
propagation environment
effects:
 reflection
 obstruction by objects
 interference
Radio link types:

terrestrial microwave
 e.g. up to 45 Mbps channels

LAN (e.g., WiFi)
 11Mbps, 54 Mbps

wide-area (e.g., cellular)
 3G cellular: ~ 1 Mbps

satellite
 Kbps to 45Mbps channel (or
multiple smaller channels)
 270 msec end-end delay
 geosynchronous versus low
altitude
Introduction 1-26
Chapter 1. Computer networks and the
internet
1.1 What is the Internet?
1.2 Network edge

end systems, access networks, links
1.3 Network core

circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 History
Introduction 1-27
The Network Core


mesh of interconnected
routers
the fundamental question:
how is data transferred
through network?
 circuit switching:
dedicated circuit per call:
telephone network
 packet-switching: data
sent through network in
discrete “chunks”
Introduction 1-28
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
Introduction 1-29
Network Core: Circuit Switching
network 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
Introduction 1-30
Baseband and broadband
1 path
3 channels
DEMULTIPLEXOR
Broadband
MULTIPLEXOR
Baseband
- No modulation
- Original signal
Introduction
1-31
Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
Introduction 1-32
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
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
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
 node receives complete
packet before forwarding
Introduction 1-33
Packet Switching: Statistical Multiplexing
100 Mb/s
Ethernet
A
C
statistical multiplexing
1.5 Mb/s
B
queue of packets
waiting for output
link
D

E
sequence of A & B packets has no fixed timing pattern
 bandwidth shared on demand: statistical multiplexing.
Introduction 1-34
Packet-switching: store-and-forward
L
R



R
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)
R
Example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 transmission delay = 15
sec
more on delay shortly …
Introduction 1-35
Packet switching versus circuit switching
Packet switching allows more users to use network!
Example:
 1 Mb/s link
 each user:
• 100 kb/s when “active”
• active 10% of time
N
users
1 Mbps link
 circuit-switching:
 10 users
 packet switching:

with 35 users, probability >
10 active at same time is less
than .0004
Q: what happens if > 35 users ?
Introduction 1-36
Packet switching versus circuit switching
Is packet switching the best option by far?



great for bursts of data
 resource sharing
 more simple, 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
Q: human analogies of reserved resources (circuit switching) versus
on-demand allocation (packet-switching)?
Introduction 1-37
Internet structure: network of networks
NAP or IXP
Internet Service Provider (ISP)
(Suministrador de Servicio de Internet)
Regional Service Provider (RSP)
(Suministrador de Servicio Regional)
Network Service Provider (NSP)
(Suministrador de Servicio de Red)
Network Access Point (NAP) o
Internet eXchange Point (IXP)
(Punto de acceso a la red)
NSP
RSP
ISP
Customers
Tier 1
RSP
ISP
Customers
NSP
Tier 2
RSP
ISP Tier 3 ISP
Customers
Customers
ISP
Customers
Introduction 1-38
Internet structure: network of networks
Introduction 1-39
Chapter 1. Computer networks and the
internet
1.1 What is the Internet?
1.2 Network edge

end systems, access networks, links
1.3 Network core

circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 History
Introduction 1-40
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
packet being transmitted (delay)
A
B
packets queuing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Introduction 1-41
Four sources of packet delay
transmission
A
propagation
B
nodal
processing
queuing
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing
dqueue: queueing delay
 check bit errors
 determine output link
 typically < msec
 time waiting at output link for
transmission
 depends on congestion level of
router
Introduction 1-42
Four sources of packet delay
transmission
A
propagation
B
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay:
dprop: propagation delay:
 L: packet length (bits)
 R: link bandwidth (bps)
 dtrans = L/R
 d: length of physical link
 s: propagation speed in medium
(~2x108 m/sec to 2x108 m/sec)
 dprop = d/s
dtrans and dprop
very different
Introduction 1-43



R: link bandwidth (bps)
L: packet length (bits)
a: average packet arrival
rate
average queuing
delay
Queuing delay (revisited)
traffic intensity
= La/R
L·a/R ~ 0: avg. queuing delay small
 L·a/R -> 1: avg. queuing delay large
 L·a/R > 1: more “work” arriving
than can be serviced, average delay infinite!
La/R ~ 0

La/R -> 1
Introduction 1-44
Packet loss
queue (a.k.a buffer) preceding link in buffer has finite
capacity
 packet arriving to full queue dropped (a.k.a lost)
 lost packet may be retransmitted by previous node,
by source end system, or not at all

buffer
(waiting area)
A
B
packet being transmitted
packet arriving to
full buffer is lost
Introduction 1-45
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,
with
server
sends
bits
file ofinto
F bits
(fluid)
pipe
to send to client
pipe
can carry
link that
capacity
at rate
Rfluid
s bits/sec
Rs (bits/sec)
link capacity
pipe
that can carry
Rcfluid
bits/sec
at rate
Rc (bits/sec)
Introduction 1-46
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
bottleneck link
link on end-end path that constrains end-end throughput
Introduction 1-47
Throughput: Internet scenario
per-connection endend throughput:
min(Rc,Rs,R/10)
 in practice: Rc or Rs is
often bottleneck

Rs
Rs
Rs
R
Rc
Rc
Rc
10 connections (fairly) share backbone
bottleneck link R bits/sec
Introduction 1-48
Chapter 1. Computer networks and the
internet
1.1 What is the Internet?
1.2 Network edge

end systems, access networks, links
1.3 Network core

circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 History
Introduction 1-49
Protocol Layers
Networks are complex,
with many “pieces”:
 hosts
 routers
 links of various
media
 applications
 protocols
 hardware, software
Question:
Is there any hope of
organizing the structure of
the network?
Or at least our discussion of
networks?
Introduction 1-50
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

a set of steps
Introduction 1-51
Layering of airline functionality
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
Layers: each layer implements a service
 via its own internal-layer actions
 relying on services provided by layer below
Introduction 1-52
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
Introduction 1-53
Layer architecture scheme (I)
 Entity
 It’s an active element in the system
 It uses protocols to supply services
 Peer entity (one for every level)
 Functions
 Set of tasks for every level
 Not all the functions are held in both ends
 E.g., the baggage layer implements check-in and check out functions.
 Services
 Set of provisions provided by a layer (supplier) to its inmediate upper
layer (user).
 They are formally specified by a set of primitives or operations.
 E.g.: service to check in baggage
Introduction 1-54
Layer architecture scheme (II)
 Protocol: Set of rules that determines format and meaning of data
exchange between two peer entities that are “talking”.
 This way, the protocol defines:
 The message format to exchange.
 The rules for exchanging the messages.
 Entities use a protocol to provide services (to the upper layer).
Transmitter
Receiver
Layer N + 1
Layer N + 1
...
N_SAP
N layer entity
Layer N
Layer N - 1
...
...
N layer protocol
N_PDU
Layer N
Layer N - 1
...
Introduction 1-55
Services of a layer
 Primitives:
 Set of structures of information that implements the services of a layer
 Types:
 Request  issued by user of service in source
 Indication  issued by supplier of service (by own initiative or not)
 Response  issued by user of service in destination
 Confirm  issued by supplier of service
Destination end
Source end Request
Layer N+1
Layer N
1
Service
Layer N+1
Layer N
4
Confirm
To the bottom in
transmission
2
Response
Service
3
Indication
To the bottom in
transmission
To the top in reception
To the top in
reception
Introduction 1-56
Functions, Services and Primitives
Layer N+1
 Confirmed:
 They require a response
 They implement the four
primitives
 Not confirmed:
 They don’t require response
 They implement request and
indication
 Partially confirmed:
 Provider responds
 They implement request,
indication and confirmation
 Initiated by provider:
 When triggering a condition
 They implement indication in
both directions
N-Service User
Layer N
N-Service
Provider
Service.Request
Layer N+1
N-Service User
Service.Indication
Service.Confirmation
Service.Request
Service.Request
Confirmed
Service.Response
Not
Confirmed
Service.Indication
Service.Indication
Partially
confirmed
Service.Confirmation
Service.Indication
Initiated by
provider
time
Transmission
Service.Indication
time
Transmission
Introduction 1-57
Layers, entities and SAPs
 Vertical
communication:
 Physical
 Inside the own
system
 Horizontal
communication:
 Logical
 Peer protocol;
layer N protocol
 Among different
systems
End A
End B
N-service primitive
N-service primitive
N layer protocol
N-PDU
N-1-service
primitive
Layer peer entity
N-1-service
primitive
N-1 layer protocol
N-1 -PDU
N-2-service
primitive
Layer N-1 peer entity
N-2 layer protocol
N-2-service
primitive
N-2 -PDU
Layer N-2 peer entity
Introduction 1-58
Encapsulation
Transmitter
(N+1)-PDU
Layer N+1
(N)-ICI
IDU: Interface Data Unit
ICI: Interface Control Information
PCI: Protocol Control Information
UD: User Data
SAP: Service Access Point
SAP
(N)-IDU
Encapsulation
Layer N
(N)-ICI
(N)-SDU
(N)-PCI
(N)-UD
(N)-PDU
Introduction 1-59
De-encapsulation
Receiver
(N+1)-PDU
Layer N+1
(N)-ICI
IDU: Interface Data Unit
ICI: Interface Control Information
PCI: Protocol Control Information
UD: User Data
SAP
(N)-IDU
De-encapsulation
Layer N
(N)-ICI
(N)-SDU
(N)-PCI
(N)-UD
(N)-PDU
Introduction 1-60
Segmentation
Transmitter
(N+1)-PDU
Layer N+1
(N)-ICI
IDU: Interface Data Unit
ICI: Interface Control Information
PCI: Protocol Control Information
UD: User Data
SAP
(N)-IDU
(N)-ICI
(N)-SDU
(N)-PCI
(N)-PCI
(N)-PDU
Encapsulation
Layer N
(N)-PDU
Introduction 1-61
Desegmentation
Receiver
(N+1)-PDU
Nivel N+1
(N)-ICI
IDU: Interface Data Unit
ICI: Interface Control Information
PCI: Protocol Control Information
UD: User Data
SAP
Nivel N
(N)-ICI
(N)-SDU
(N)-PCI
(N)-PCI
(N)-PDU
De-encapsulation
(N)-IDU
(N)-PDU
Introduction 1-62
How many layers?


Depending on the desired set of functions for the
network architecture
Two main network architectures:
 TCP/IP: used on the Internet.
 Five layers.
 Describe functions, services and protocols
 Modelo de referencia OSI (Open System
Interconnection).
 Seven layers.
 ISO standard (International Organization for
Standardization).
 Describe functions and services.
Internet protocol stack

application: supporting network
applications
 FTP, SMTP, HTTP

transport: process-process data transfer
application
transport
 TCP, UDP

network: routing of datagrams from
source to destination
 IP, routing protocols

link: data transfer between neighboring
network elements
network
link
physical
 Ethernet, 802.111 (WiFi), PPP

physical: bits “on the wire”
Introduction 1-64
ISO/OSI reference model



presentation: allow applications to
interpret meaning of data, e.g.,
encryption, compression, machinespecific 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
Introduction 1-65
How are layers implemented?
Note
aplication
transport
network
data link
physical
Programs
Operating
System
Not all layers are present in the
devices used on the Internet.
Software
Note
hardware
Hardware that implements data link and
physical layers is know as network interface,
or NIC (Network Interface Card).
source
message
segment
M
Ht
M
datagram
M
frame
Hn Ht
Hl Hn Ht
M
Encapsulation
application
transport
network
link
physical
link
physical
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
M
router
Introduction 1-67
Chapter 1. Computer networks and the
internet
1.1 What is the Internet?
1.2 Network edge

end systems, access networks, links
1.3 Network core

circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6. History
Introduction 1-68
Internet History
1961-1972: Early packet-switching principles




1961: Kleinrock - queueing
theory shows effectiveness of
packet-switching
1964: Baran - packetswitching in military nets
1967: ARPAnet conceived by
Advanced Research Projects
Agency
1969: first ARPAnet node
operational

1972:
 ARPAnet public demonstration
 NCP (Network Control Protocol) first
host-host protocol
 first e-mail program
 ARPAnet has 15 nodes
Introduction 1-69
Internet History
1972-1980: Internetworking, new and proprietary nets






1970: ALOHAnet satellite network
in Hawaii
1974: Cerf and Kahn - architecture
for interconnecting networks
1976: Ethernet at Xerox PARC
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
Introduction 1-70
Internet History
1980-1990: new protocols, a proliferation of networks





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
Introduction 1-71
Internet History
1990, 2000’s: commercialization, the Web, new apps
 early
1990’s: ARPAnet
decommissioned
 1991: NSF lifts restrictions on
commercial use of NSFnet
(decommissioned, 1995)
 early 1990s: Web
 hypertext [Bush 1945, Nelson
1960’s]
 HTML, HTTP: Berners-Lee
 1994: Mosaic, later Netscape
 late 1990’s: commercialization of
late 1990’s – 2000’s:




more killer apps: instant
messaging, P2P file sharing
network security to forefront
est. 50 million host, 100 million+
users
backbone links running at Gbps
the Web
Introduction 1-72
Internet History
2010:
 ~750 million hosts
 voice, video over IP
 P2P applications: BitTorrent (file
sharing) Skype (VoIP), PPLive
(video)
 more applications: YouTube,
gaming, Twitter
 wireless, mobility
Introduction 1-73
Introduction: Summary
Covered a “ton” of material!
 Internet overview
 what’s a protocol?
 network edge, core, access
network
 packet-switching versus
circuit-switching
 Internet structure
 performance: loss, delay,
throughput
 layering, service models
 history
You now have:
 context, overview, “feel”
of networking
 more depth, detail to
follow!
Introduction 1-74
Departamento de
Tecnología Electrónica
Computer Networking – Unit 1: Computer Networks
and Internet
PROBLEMS AND EXERCISES
Introduction
1-75
Pr1: TDM
How long does it take to send a file of 640,000 bits from host A to
host B over a circuit-switched network?
 all link speeds: 1.536 Mbps
 each link uses TDM with 24 slots/sec
 500 msec to establish end-to-end circuit
Introduction 1-76
Pr2: End-to-end delay
Consider that packet of length L transmitted by end system A is going through
three links to a destination end system. These three links are connected
through two packet switches. Let di, si and Ri denote the length, propagation
speed, and the transmission rate of link i, for i=1,2,3. The packet switch
delays each packet by dproc. Assuming no queuing delays, what is the total
end-to-end delay for the packet in terms of di, si, Ri (i=1,2,3), and L?
Suppose now the packet is 1500 bytes, the propagation speed on both links
is 2.5x108 m/s, the transmission rate of the three links is 2 Mbps, the packet
switch processing delay is 3 msec, the length of the first link is 5000 km, the
length of the second link is 4000 km and the length of the last link is 1000
km. For these values, what is the end-to-end delay?
Introduction 1-77
Pr3: Queuing delay
A router is receiving a packet and has to determine the output
interface to which the packet should be forwarded. When the
packet arrives, another packet is being transmitted (half packet
has already been transmitted) and three other packets are
waiting to be transmitted. Packets are transmitted in order of
arrival.
Suppose all packets are 1500 bytes and the link rate is 2Mbps.
What is the queuing delay for the packet?
More generally, what is the queuing delay when all packets
have length L, the transmission rate is R, x bits of the currentlybeing-transmitted packet have been transmitted, and n packets
are already in the queue?
Introduction 1-78
Pr4: Encapsulation and segmentation
Suppose that, in the OSI model, a data link protocol has the
maximum size of D_SDU limited to 1000 bytes, and the network
protocol doesn’t have any maximum limitation for N_SDU to
the higher level. If T_PDUs are always 2000 bytes and N_PCI are
100 bytes, how many N_PDUs will network layer send? What is
the content of each N_PDU?
Introduction 1-79
Pr5: Segmentation
In modern packet-switched networks, the source host segments long, application-layer messages (for
example, an image or a music file) into smaller packets and sends the packets into the network.
The receiver then reassembles the packet back into the original message. We refer to this
process a message segmentation. Figure illustrates the end-to-end transport of a message with
or without message segmentation:
Packet without
segmentation
Source host
Packet
switch
Packet
switch
Destination host
Packet with segmentation
Source host
Packet
switch
Packet
switch
Destination host
Introduction 1-80
Pr6: Segmentation
Consider a message that is 8·106 bits long that is to be sent from source to destination. Use the
figure scheme. Suppose each link in the figure is 2 Mbps. Ignore propagation, queuing and
processing delays.
a)
Consider sending the message from source to destination without message segmentation.
How long does it take to move the message from the source host to the first packet switch?
Keeping in mind that each switch uses store and forward packet switching, what is the total
time to move the message from source host to destination host?
b)
Now suppose that the message is segmented into 4000 packets, with each packet being 2000
bits long. How long does it take the first packet to get from the source host to the first switch?
When the packet is sent from the source host to the first switch, the second packet is sent
from the source host to the first switch. When is the second packet fully received at the first
switch?
c)
How long does it take the file to get from source host to destination host when message
segmentation is used? Compare this result with your answer in part a) and discuss about it.
d)
Discuss the drawbacks of message segmentation.
Introduction 1-81