Learning Outcomes

1
Learning Outcomes
159.334
At the end of this session, the students should
be able to
Explain what the Internet is all about
Ask yourself these questions at the end of the
session
Explain what is a protocol
Describe what comprises the network edge
Describe what comprises the network core
Explain connection-oriented service
Explain connectionless service
Compare circuit-switched network against
packet-switched network
Answer the short exercises given in the session
2
Introduction
Whats the Internet?
UNIX-based workstations
laptop
Digital cameras
Automobile
Email server
Web-page server
WebTV
PDAs with wireless Internet connections
toaster
Household appliances
HOSTS or END SYSTEMS
3
Whats the Internet?
Nuts and bolts of the Internet

• Hardware components
• Software

Networking Infrastructure

• provides services to distributed applications
• infrastructure where new applications are
  being constantly invented and deployed

4
Whats the Internet?
Nuts and Bolts View

• global network of networks

• Interconnects millions (soon billions) of
  computing devices

• provides

• Global communication

• Storage

• Computation infrastructure

End-to-End System
Core
End System
End System
edge
edge
5
SETI_at_HOMEMASSIVELY DISTRIBUTED COMPUTING FOR SETI
http//setiathome.ssl.berkeley.edu/
6
The Bigger Picture

• network edge applications and hosts
• network core
• routers
• network of networks
• access networks, physical media communication
  links

7
End-to-End System
Whats the Internet? Nuts and Bolts View
End SystemHOST
Core
End System
End System
Connect end systems to the network core
Transport data
Communication links
Characterized in terms of bandwidth
Made up of different types of physical media
Link transmission rate
Coaxial cable
Measured in bits/second
Copper wire
Fiber optics
Radio Spectrum
8
Where is the Network Core?
?
9
Whats in the Links?
NETWORK CORE
Router
End System
End System
X
End System
End System
path or route
End System
Router
Internet uses packet switching to allow for
multiple communicating end systems to share a
path, or parts of a path, at the same time
Takes a chunk of information arriving on one of
its incoming communication links and forwards
that chunk of information on one of its outgoing
communication links
10
Now lets see how are links formed in terms of
clusters
i
11
Whats a protocol?

• a human protocol and a computer network protocol

Got the time?
Get http//www.massey.ac.nz/
12
Whats a protocol?

• Human Protocols
• Something we execute all the time
• Offer a greeting
• Wait for a response
• Analyze the response
• Act accordingly

• Network Protocols
• Similar to human protocol, except that entities
  are machines rather than humans
• all communication activities in the Internet are
  governed by protocols

• In order for protocols to work, both entities
  must observe the same protocol.
• There is a set of conventional actions taken
  when messages are sent and received.

Networking understanding the what, why and how
of networking protocols
13
Whats a protocol?
A protocol defines format and order of
messages sent and received among network
entities and actions taken on the
transmission and/or receipt of a message, or
other event

• All activities in the Internet that involves 2
  or more communicating entities are governed by a
  protocol.
• There are protocols in
• Routers
• Protocols determine a packets path from source
  to destination
• NIC
• hardware-implemented protocols control the flow
  of the bits on the wire
• End Systems
• congestion-control protocols control the
  rate at which packets are transmitted between
  sender and receiver

Communicating Entities Hardware, Software
components
Different protocols are used to accomplish
different communication tasks
14
BASIC TERMINOLOGIES
Protocols
- control the sending and receiving of
information within the Internet - run
by End Systems, routers, etc.
TCP
Two of the most important protocols in the
Internet (principal protocols)
IP
TCP Transmission Control Protocol
IP Internet Protocol specifies the format of
the packets that are sent and received among
routers and end systems
Global network of networks (The Internet)
Made possible through standards developed by
(IETF) Internet Engineering Task Force
RFCs (Request for Comments)
define protocols such as TCP, IP, HTTP, SMTP
15
Whats the Internet? A Service View

• Provides a communication infrastructure that
  allows distributed applications running on its
  end systems to exchange data with each other.

Remote login
email
Web surfing
Instant messaging
Internet telephony
the Web distributed application that use the
communication services provided by the Internet

• Provides communication services to distributed
  applications

Connection-Oriented Reliable Service
Guarantees that data is delivered orderly and
completely (sender to receiver)
Connectionless Unreliable Service
Delivery is not guaranteed
16
Question
?
Why would we opt for a connectionless unreliable
service when there is a connection-oriented
reliable service that is available?
Hold on to that thought for a while
17
A closer look at the Network Edge
What happens in the network edge?
End Systems (Hosts) - run application
programs e.g., WWW, email at edge of
network
The sending End System doesnt know how messages
are actually sent.
It only needs to know what services are provided,
and so the nuts and bolts of the Internet
serves as a black box that transfers messages
between distributed communicating components.

• Client/Server Model
• client host
• Requests
• Receives service from server
• e.g. WWW client (browser)/server email
  client/server

Client/Server Model - Most prevalent structure
for Internet applications although not all
applications are purely client, or purely of
server type (e.g. P2P file sharing)
18
The Network Edge

• Connection between two End Systems (e.g. Web
  application or Internet phone application)
• Nothing more than allocated buffers and state
  variables

Connection
Internet provides two type of services to
End-System Applications

• Connection-oriented service (TCP)

Apps using TCP HTTP (WWW), FTP (file
transfer), Telnet (remote login), SMTP (email)

• Connectionless service (UDP)

Apps using UDP streaming media,
teleconferencing, Internet telephony
19
Network edge connection-oriented service
performs handshaking

• Goal data transfer between end system.
• handshaking setup (prepare for) data transfer
  ahead of time
• Hello, hello back human protocol
• set up state in two communicating hosts

• TCP service RFC 793
• Provides
• Reliable data transfer
• loss handled using acknowledgements and
  retransmissions
• Flow Control
• Ensures that the sender wont overwhelm receiver
• Congestion Control
• Instructs senders to slow down sending rate
  when network is congested
• Prevents gridlock

Q
TCP - Transmission Control Protocol -
Internets connection-oriented service
20
Network Edge TCP Service
Case No retransmission

• Handshaking Procedure

Control packet
CONNECTION ESTABLISHED
DATA
acknowledgement
SERVER
CLIENT
Reliable data transfer is achieved through
acknowledgements and retransmissions

Data is delivered without error and in proper
order
21
Network Edge TCP Service
Case Retransmission of Request

• Handshaking Procedure

Control packet
Client is waiting for Acknowledgement
Client assumes packet was lost, decides to
retransmit
DATA
acknowledgement
SERVER
CLIENT
Reliable data transfer is achieved through
acknowledgements and retransmissions

Data is delivered without error and in proper
order
22
Network Edge TCP Service
Problem occurs when one communicating End-System
transmits faster than the other End System
This End-System does not receive an
acknowledgement yet, and so it issues another
packet
Control packet
SERVER
CLIENT

• Flow control

forces the sending End System not to send too
many packets too fast for the receiver
TCP/IP provides the Flow control service
23
Network Edge TCP Service
Problem Gridlock sets-in when there is packet
loss due to router congestion
The sending systems message is lost due to
congestion, and is alerted when it stops
receiving acknowledgements of packets sent
CLIENT
SERVER

• Congestion control

forces the End Systems to decrease the rate at
which packets are sent during periods of
congestion
We will see more of this when we view the applet
from Kuroses site
24
Network edge connectionless service
No handshaking procedure End-Systems just simply
send the packet

• Goal data transfer between end systems
• same as before!
• UDP - User Datagram Protocol RFC 768
  Internets connectionless service
• unreliable data transfer
• no flow control
• no congestion control

25
Something to ponder on
?
Besides bandwidth and latency, what other
parameter is needed to give a good
characterization of the quality of service
offered by a network used for digitized voice
traffic?
Bandwidth how many bits per second a network
can transport
Latency how many seconds it takes for the first
bit to get from the client to
the server
26
Answer
A uniform delivery time is needed for voice, so
the amount of jitter in the network is important.
This could be expressed as the standard
deviation of the delivery time. Having short
delay but large variability is actually worse
than a somewhat longer delay and low variability.
27
The Network Core

• mesh of interconnected routers

28
The Network Core

• the fundamental question how is data transferred
  through net?
• circuit switching dedicated circuit per call
  telephone net
• packet-switching data sent through net in
  discrete chunks

Approaches to building a Network Core
29
The Network CORE
Circuit Switching vs. Packet Switching
A Restaurant Analogy
What resources must be reserved?
Circuit-switched Networks
Resources are reserved for the duration of the
communication session
Restaurant which requires reservation

• With a reservation, you can order right away
  when you get there
• guaranteed seats

Packet-switched Networks
Messages use the resources on demand thus, may
have to wait (queue) for access to a
communication link
Restaurant which does not require any reservation

• you may have to wait on a queue to be served
• no sure seats

30
Network Core Circuit Switching

• End-end resources reserved for call
• link bandwidth, switch capacity
• Switches on the path between sender and receiver
  maintain connection state for the duration of the
  session
• Resources are dedicated thus, no sharing
• Advantage circuit-like (guaranteed) performance
• call set-up required
• (unless infinite resources are available)

Circuit
31
Network Core Circuit Switching

• How is it implemented?

• By dividing the link bandwidth into pieces
• frequency division
• time division

Inefficiency Resource piece is idle if not used
by owning call (no sharing)
32
Circuit Switching FDM and TDM
4KHz
Network dedicates a frequency band to each
connection for the session
Frame
Slot
Network dedicates one time slot in every frame of
the connection
33
Question
?
How long does it take to send a file of 640,000
bits from Host A to Host B over a
circuit-switched network? Assume that all links
in the network use TDM with 24 slots and have a
bit rate of 1.536 Mbps. Also suppose that it
takes 500 msec. to establish an end-to-end
circuit before Host A can begin to transmit the
file. Further assume that propagation delay is
negligible.
34
Question
Answer
How long does it take to send a file of 640,000
bits from Host A to Host B over a
circuit-switched network? Assume that all links
in the network use TDM with 24 slots and have a
bit rate of 1.536 Mbps. Also suppose that it
takes 500 msec. to establish an end-to-end
circuit before Host A can begin to transmit the
file.
GIVEN Size of file to send 640,000 bits
SOLUTION Each circuit has a transmission rate
of (1.536 Mbps)/24 64kbps (or 64,000 bps). So,
it takes (640,000 bits)/(64,000 bps) 10 sec. to
transmit the file. Considering the circuit
establishment time, we add 0.5 sec therefore, It
takes 10.5 sec. to transmit the file. The
transmission time would be 10 sec. if the
end-to-end circuit passed through 1 link or 100
links. (but the actual end-to-end delay also
includes a propagation delay)
Establishment time transmission time
35
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

Q
36
We stopped here last time ?
37
Network Core Packet Switching
Q
Sender Nodes A and B
Receiver Node E
38
Network Core Packet Switching
Consider a message that is 7.5 x 106 bits long.
Suppose that between source and destination,
there are 2 packet switches and 3 links, and that
each link has a transmission rate of 1.5 Mbps.
Assuming that there is no congestion in the
network, how much time is required to move the
message from source to destination with packet
switching?
(7.5 Mbps/1.5 Mbps) 3 15 sec.
39
Packet Switching Store and Forward Behaviour
Example

• store and forward behaviour

Pattern that can be deduced from the packet flow
depicted in the Figure Time of arrival
packet_num 2
Lets see the applet of message segmenting to see
how this works
40
Packet Switching vs. Circuit Switching
Suppose that users share a 1 Mbps link, where
each user alternates between generating data at a
constant rate of 100 Mbps, and periods of
inactivity. Also assume that each user is active
only 10 of the time. Compare the performance of
Circuit Switching against Packet Switching.
41
Packet Switching vs. Circuit Switching

• Packet switching allows more users to use network!

• Example 1 Mbit link shared by all users
• each user
• Generates 100Kbps when active
• (at constant rate)
• active 10 of time
• circuit-switching
• 10 users can only be supported
• 1,000,000 bits/sec divided by 100,000 bits/sec.
• packet switching
• with 35 users, probability gt 10 are active is
  less than .0004
• probability lt 10 users are active is 0.9996

Implies that 10 users can be using the circuit
without competing, just like circuit-switching
(bandwidth is equally distributed)
Packet switching allows for more than 3 times the
number of users as compared to circuit-switching
42
Question
?
A factor in the delay of a store-and-forward
packet-switching system is how long it takes to
store and forward a packet through a switch. If
switching time is 10 µsec, is this likely to be a
major factor in the response of a client-server
system where the client is in Palmerston North
and the server is in Auckland? Assume the
propagation speed in copper and fiber to be 2/3
the speed of light in vacuum.
Speed of light 3 x 108 meters/sec.
43
Question
Answer
A factor in the delay of a store-and-forward
packet-switching system is how long it takes to
store and forward a packet through a switch. If
switching time is 10 µsec, is this likely to be a
major factor in the response of a client-server
system where the client is in Palmerston North
and the server is in Auckland? Assume the
propagation speed in copper and fiber to be 2/3
the speed of light in vacuum.
No. The speed of propagation is 200,000 km/sec or
200 meters/µsec. In 10 µsec the signal travels 2
km. Thus, each switch adds the equivalent of 2 km
of extra cable. If the client and server are
separated by 5000 km, traversing even 50 switches
adds only 100 km to the total path, which is only
2. Thus, switching delay is not a major factor
under these circumstances.
44
Network Core Packet Switching

• Advantages Great for bursty data
• resource sharing
• no call set-up
• Drawbacks
• Excessive congestion, packet delay and loss
• protocols needed for reliable data transfer,
  congestion control
• Issue How to provide circuit-like behaviour?
• bandwidth guarantees needed for audio/video apps
• this is still an unsolved problem

45
Packet-switched networks

• Goal move packets among routers from source to
  destination
• 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 set-up time,
  remains fixed through call
• routers maintain per-call state

46
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?

47
ACCESS NETWORKS
ISPs
National and International Upper-Tier ISPs
High-speed routers interconnected with high-speed
fiber-optic links
e.g. UUNet and Sprint
Lower-Tier ISPs
Web Site content providers
Users
Managed independently
Runs the IP protocol, conforms to certain naming
and address conventions
48
Delay and Routes in the Internet
TraceRoute(diagnostic program) -defined in RFC
1393
DESTINATION HOST
SOURCE HOST
Program
Program

• SOURCE
• records time elapsed (time received- time packet
  sent)
• determines the round-trip delays to all
  intervening routers
• Round-trip delays include
• Transmission delay
• Propagation delay
• Router processing delay
• Queuing delay (varies with time)
• records name address of router (or destination
  HOST) that returns the message
• reconstructs the route taken by the packets
  (source-to-destination)

• If there are (N-1) routers, then SOURCE sends N
  special packets
• Each packet is addressed to the ultimate
  destination
• marked 1 to N

• When DESTINATION host receives the Nth packet
• DESTINATION destroys the packet, then
• returns the message back to the source

• When the ith router receives the ith packet
  marked i
• router destroys the packet
• Sends a message containing name and address of
  router back to the source

49
TraceRoute
Trace3x
Route trace From MIT to Massey University

• Trace Route from MIT
• IMPORTANT This tool works by sending a series of
  UDP packets with different port numbers and TTL
  (Time To Live). If you are running firewall
  software, your software may interpret the
  incoming packets as a hostile "port scan"
  originating from this server (jis.mit.edu). Rest
  assured, your system is not being attacked.
• 1 W92-RTR-1-W92SRV21.MIT.EDU (18.7.21.1) 0.425
  ms 0.287 ms 0.259 ms
• 2 EXTERNAL-RTR-1-BACKBONE.MIT.EDU (18.168.0.18)
  21.179 ms 244.069 ms 223.625 ms
• 3 leg-208-30-223-5-CHE.sprinthome.com
  (208.30.223.5) 0.589 ms 0.459 ms 0.542 ms
• 4 144.232.21.50 (144.232.21.50) 2.951 ms
  3.146 ms 2.966 ms
• 5 sl-bb21-chi-6-2.sprintlink.net
  (144.232.19.205) 21.073 ms 48.427 ms 20.784 ms
• 6 sl-bb24-chi-9-0.sprintlink.net
  (144.232.26.77) 141.917 ms 229.305 ms 219.150
  ms
• 7 sl-bb21-sj-8-0.sprintlink.net
  (144.232.20.161) 68.260 ms 68.102 ms 68.044 ms
• 8 sl-bb22-sj-15-0.sprintlink.net
  (144.232.3.162) 68.016 ms 68.036 ms 68.608 ms
• 9 144.232.20.47 (144.232.20.47) 73.346 ms
  73.617 ms 73.508 ms
• 10 sl-newzeal-1-0.sprintlink.net
  (144.223.243.18) 70.804 ms 71.082 ms 70.787 ms
• 11 p5-2.sjbr1.global-gateway.net.nz
  (203.96.120.213) 71.132 ms 70.990 ms 70.903 ms
• 12 203.96.120.118 (203.96.120.118) 195.054 ms
  195.579 ms 196.648 ms
• 13 203.96.120.201 (203.96.120.201) 198.228 ms
  211.397 ms 197.358 ms
• 14 massey-uni-ak-int.tkbr4.global-gateway.net.nz
  (202.49.163.230) 202.604 ms 218.925 ms 199.836
  ms
• 15
• 16

Trans-atlantic link
6 columns n, name of router, address of router,
trip delay1,trip delay2,trip delay3
- indicates packet loss
50
Tracert (from xtra to mit)
C\gttracert web.mit.edu Tracing route to
web.mit.edu 18.7.22.69 over a maximum of 30
hops 1 1 ms 1 ms 1 ms
192.168.1.1 2 2 ms 2 ms 2 ms
192.168.8.1 3 56 ms 59 ms 55 ms
219-89-32-1.dialup.xtra.co.nz 219.89.32.1 4
53 ms 54 ms 222.152.127.169 5
66 ms 202.50.236.105 6
Request timed out. 7 482
ms so-0-2-0.labr3.global-gatewa
y.net.nz 202.50.232.26 8
Request timed out. 9 341 ms
290 ms g11-2-107.core01.lax05.atlas.cogentco.com
154.54.11.145 10 243 ms 213 ms
t3-4.mpd01.lax01.atlas.cogentco.com
154.54.6.189 11 217 ms 280 ms
g9-0-0.core01.lax01.atlas.cogentco.com
154.54.2.117 12 344 ms 325 ms
p2-0.core01.dfw01.atlas.cogentco.com
154.54.5.93 13 282 ms
p15-0.core02.dfw01.atlas.cogentco.com
66.28.4.26 14 250 ms
p15-0.core01.mci01.atlas.cogentco.com
66.28.4.38 15
Request timed out. 16 367 ms
p15-0.core01.ord01.atlas.cogentco.com
66.28.4.61 17 386 ms 434 ms
p14-0.core01.alb02.atlas.cogentco.com
154.54.1.57 18 345 ms 448 ms
p6-0.core01.bos01.atlas.cogentco.com
154.54.7.42 19 282 ms 285 ms
g8.ba21.b002250-1.bos01.atlas.cogentco.com
66.250.14.210 20 408 ms
MIT.demarc.cogentco.com 38.112.2.214 21 342
ms W92-RTR-1-BACKBONE.MIT.EDU
18.168.0.25 22 344 ms
WEB.MIT.EDU 18.7.22.69 23 342 ms
380 ms WEB.MIT.EDU 18.7.22.69 Trace
complete. C\gt
Tracert (also known as traceroute) is a Windows
based tool that allows you to help test your
network infrastructure.
51
Tracert (from Massey to MIT)
D\Massey Papers\159334\Codes\Game Protocol
v3.6gttracert web.mit.edu Tracing route to
web.mit.edu 18.7.22.69 over a maximum of 30
hops 1 lt1 ms lt1 ms lt1 ms
it023453-vlan205.massey.ac.nz 130.123.246.129
2 lt1 ms lt1 ms lt1 ms it028100-vlan801.ma
ssey.ac.nz 10.100.254.3 3 1 ms lt1 ms
lt1 ms 210.7.32.1 4 1 ms lt1 ms lt1 ms
210.7.36.67 5 142 ms 142 ms 142 ms
210.7.47.22 6 142 ms 142 ms 142 ms
abilene-1-lo-jmb-706.sttlwa.pacificwave.net
207.231.240.8 7 179 ms 187 ms 180 ms
dnvrng-sttlng.abilene.ucaid.edu 198.32.8.50 8
189 ms 189 ms 202 ms kscyng-dnvrng.abilene.
ucaid.edu 198.32.8.14 9 201 ms 214 ms
201 ms iplsng-kscyng.abilene.ucaid.edu
198.32.8.80 10 202 ms 215 ms 202 ms
chinng-iplsng.abilene.ucaid.edu 198.32.8.76 11
202 ms 206 ms 207 ms ge-0-0-0.10.rtr.chic.n
et.internet2.edu 64.57.28.1 12 219 ms 230
ms 220 ms so-3-0-0.0.rtr.wash.net.internet2.edu
64.57.28.13 13 225 ms 224 ms 224 ms
ge-1-0-0.418.rtr.chic.net.internet2.edu
64.57.28.10 14 229 ms 229 ms 229 ms
nox300gw1-Vl-110-NoX-ABILENE.nox.org
192.5.89.221 15 229 ms 229 ms 229 ms
nox230gw1-Vl-802-NoX.nox.org 192.5.89.254 16
481 ms 230 ms 230 ms nox230gw1-PEER-NoX-MIT-1
92-5-89-90.nox.org 192.5.89.90 17 230 ms
230 ms 230 ms W92-RTR-1-BACKBONE.MIT.EDU
18.168.0.25 18 230 ms 230 ms 230 ms
WEB.MIT.EDU 18.7.22.69 Trace
complete. D\Massey Papers\159334\Codes\Game
Protocol v3.6gt
52
ACCESS NETWORKS
ISP Internet Service Provider
End Systems access the Internet through ISPs
ISPs - Network of routers and communication links
Residential ISPs (e.g. AOL, MSN)
University ISPs (e.g. Stanford University)
Corporate ISPs (e.g. Ford Motor Company)
Different types of Network Access provided by ISPs
Residential broadband access (DSL, cable modem)
56 kbps dial-up modem access
High-speed LAN access
Wireless access
53
Standard Telephone Modem
Translates digital data into analog data
Max. speed 56kbps
Least expensive, but slow
Residential Access Point-to-Point Access
Ties up your phone line to the Internet, making
unavailable for making voice calls
54
Wireless access networks

• shared wireless access network connects end
  system to router
• wireless LANs
• radio spectrum replaces wire
• e.g., Lucent Wavelan 11 Mbps
• Serves within a radius of tens of meters

55
Each wireless network technology available today
offers some advantage over the others. For those
looking to build a new WLAN, 802.11g is the most
promising option to consider.
Wireless LAN Access
Also known as wireless Ethernet and Wi-Fi
Based on IEEE 802.11 technology (1997, 1999,
2002, 2003)
Provides a shared transmission rate of 11Mbps, 54
Mbps
Wireless Access
http//compnetworking.about.com/cs/wireless80211/a
/aa80211standard.htm
56
Wide-Area Wireless Access Networks

• CDPD (Cellular Digital Packet Data)
• - wireless access to ISP router via cellular
  network
• Base station is managed by telecommunications
  provider
• serves users within a radius of tens of
  kilometers
• works under the analog cellular system
• CDPD usage is on the decline.

57
Wide-Area Wireless Access Networks

• 3G
• - used in the context of mobile phone standards.
• services associated with 3G provide the ability
  to transfer simultaneously both voice data (a
  telephone call) and non-voice data (such as
  downloading information, exchanging email, and
  instant messaging)
• high-speed internet access and video telephony
• uses 5 MHz channel carrier width
• allows the transmission of 384kbps for mobile
  systems and 2Mbps for stationary systems

58
(ISDN) Integrated Services Digital Network
Digital phone line
Simultaneous use of a telephone to make voice
calls while connected to the Internet
Private connection not competing for part of a
shared network with other users
Residential Access Point-to-Point Access
integrated services digital network digital
telephony data-transport services offered by
regional telephone carriers.
128Kbps all-digital connect to router
ISDN Digital Subscriber Line (IDSL)
digital transmission bypasses the telephone
company's central office equipment that handles
analog signals
IDSL provides always-on connections and transmits
data (144 kbit/s ) via a data network rather than
the carrier's voice network.
59
Comparison Chart taken from one ISP
http//www.azstarnet.com/service/dslfaq/idsl/2.htm
l
60
DSL, ADSL (Asymmetric Digital Subscriber Line)
Devices
Dont tie up your phone line
Always-on connection with the Internet
Private connection not competing for part of a
shared network with other users
Broadband Residential Access
Downside high price, service must be available
for the physical location of your home (within
5.5 km) of a telephone company central switching
office (CO) or local telephone exchange
Uses FDM
Since DSL network provides a dedicated Internet
connection via private telephone wires, you can
bypass dial-up intruders or shared network hackers
up to 1 Mbps home-to-router (upstream) up to 8
Mbps router-to-home (downstream)
61
Residential access cable modems
62
Cable Modem
Send data over your cable-television companys
line
Always connected some stand-alone devices that
can be connected to your network, others are
internal or USB devices
Speed up to 1 million bits/sec. (Mbps)
Broadband Residential Access Cable Modem
Automatically hooked to ISP
Connects to a network of other cable-modem users
( everyone is trying to use a portion of the same
network bandwidth)
Tied-up to local cable company (cable modem
service ISP service)
Doesnt interfere with television broadcasting
63
Residential access cable modems

• HFC Hybrid Fiber-optic Coaxial network
• 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

64
Institutional access local area networks

• company/univ local area network (LAN) connects
  end system to edge router
• Ethernet
• shared or dedicated/switched cable connects end
  system and router
• 10 Mbs, 100Mbps, Gigabit Ethernet
• deployment institutions, home LANs happening now
• LANs chapter 5

Ethernet Switch This 10/100 switch from Omnitron
has 16 ports and automatically senses the
transmission rate of the line and adjusts
accordingly.
65
Home networks

• Typical home network components
• ADSL or cable modem
• router/firewall
• Ethernet
• wireless access
• point

66
Question
?
An image of 1024x768 pixels with 3 bytes/pixel.
Assume the image is uncompressed. How long
does it take to transmit over a 56-kbps modem
channel? Over a 1-Mbps cable modem? Over a
10-Mbps Ethernet? Over 100-Mbps Ethernet?
Clue Mega 1 x 106 Kilo 1 x 103
1024
768
67
Question
Answer
How long does it take to transmit over a 56-kbps
modem channel? Over a 1-Mbps cable modem?
Over a 10-Mbps Ethernet? Over 100-Mbps Ethernet?
1024
768
SOLUTION The image is 1024 x 768 x 3 bytes or
2,359,296 bytes. This is 18,874,368 bits. At
56,000 bits/sec., it takes about 337.042 sec.
At 1,000,000 bits/sec, it takes about 18.874
sec. At 10,000,000 bits/sec., it takes about
1.887 sec. At 100,000,000 bits/sec., it takes
about 0.189 sec.
68
Physical Media

• Physical link transmitted data bit propagates
  across link
• guided media
• signals propagate in solid media copper, optic
  fibre
• 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
• Category 6 Gigabit Ethernet

69
Physical Media coax, optic fibre

• Coaxial cable
• wire (signal carrier) within a wire (shield)
• baseband single channel on cable
• broadband multiple channel on cable
• bidirectional
• common use in 10Mbps Ethernet

70
Physical Media Radio

• signal carried in electromagnetic spectrum
• no physical wire
• bidirectional
• propagation environment effects
• reflection
• obstruction by objects
• interference

71
Workgroup Bridge Connected to a LAN
http//www.cisco.com/en/US/products/hw/wireless/ps
458/products_configuration_guide_chapter09186a0080
07f7bf.html18981
72
Radio Ranges
A Bridge is a small, stand-alone unit that
provides a wireless infrastructure connection for
Ethernet-enabled devices.
The bridge operates in the 2.4-GHz license-free
Industrial Scientific and Medical (ISM) band.
Cellthe area of radio range or coverage in which
the bridge can communicate with the access point.
The size of a single cell depends upon the speed
of the transmission, the type of antenna used,
and the physical environment as well as other
factors.
Radio Ranges Because the bridge is a radio
device, it is susceptible to common causes of
interference that can reduce throughput and
range. Follow these guidelines to ensure the best
possible performance Install the bridge in an
area where large steel structures such as
shelving units, bookcases, and filing cabinets
will not obstruct radio signals to and from the
bridge. Install the bridge away from microwave
ovens. Microwave ovens operate on the same
frequency as the bridge and can cause signal
interference. Clear or open areas provide better
radio range than closed or filled areas. Also,
the less cluttered the work environment, the
greater the range.
73
Physical Media Radio
74
Delay and Loss in Packet-Switched Networks
- Length of Queue is finite

• Packets are lost when queue is full

Queue

• Incoming packet is dropped

Queue

• packet in queue is dropped

Lost packet
- Retransmitted by application or transport layer
protocol
75
Delay in packet-switched networks

• nodal processing
• check bit errors
• determine output link
• queueing
• time waiting at output link for transmission
• depends on congestion level of router

• packets experience delay on end-to-end path
• four sources of delay at each hop

76
Delay and Loss in Packet-Switched Networks
END-TO-END DELAY
Assuming that
- there are N-1 routers, and
- Queuing delays are negligible
DelayEND-to-END N(dproc dtrans dprop)
Later, well see a real measurement of END-to-END
delay
77
Queueing delay (revisited)

• Rlink bandwidth (bits/sec)
• Lpacket length (bits)
• aaverage packet arrival rate (packets/sec)

This estimates the extent of queuing
delay. Design your system so that traffic
intensity is no greater than 1.
78
Exercises
Chapter 1 True or False Questions
79
Exercises
We are sending a 30 Mbit MP3 file from a source
host to a destination host. All links in the path
between source and destination have a
transmission rate of 10 Mbps. Assume that the
propagation speed is 2 108 meters/sec, and the
distance between source and destination is 10,000
km.

• 1 . Initially suppose there is only one
  link between source and destination. Also suppose
  that message switching is used, with the message
  consisting of the entire MP3 file. The
  transmission delay
• 3 seconds
• 3.05 seconds
• 50 milliseconds
• none of the above.

80
Exercises
We are sending a 30 Mbit MP3 file from a source
host to a destination host. All links in the path
between source and destination have a
transmission rate of 10 Mbps. Assume that the
propagation speed is 2 108 meters/sec, and the
distance between source and destination is 10,000
km.

• 2 . Referring to the above question, the
  end-to-end delay (transmission delay plus
  propagation delay) is
• 3.05 seconds
• 3 seconds
• 6 seconds
• none of the above

81
Exercises
We are sending a 30 Mbit MP3 file from a source
host to a destination host. All links in the path
between source and destination have a
transmission rate of 10 Mbps. Assume that the
propagation speed is 2 108 meters/sec, and the
distance between source and destination is 10,000
km.

• 3 . Referring to the above question, how
  many bits will the source have transmitted when
  the first bit arrives at the destination.
• 1 bit
• 30,000,000 bits
• 500,000 bits
• none of the above

82
Exercises
We are sending a 30 Mbit MP3 file from a source
host to a destination host. All links in the path
between source and destination have a
transmission rate of 10 Mbps. Assume that the
propagation speed is 2 108 meters/sec, and the
distance between source and destination is 10,000
km.

• 4 . Now suppose there are two links
  between source and destination, with one router
  connecting the two links. Each link is 5,000 km
  long. Again suppose the MP3 file is sent as one
  message. Suppose there is no congestion, so that
  the message is transmitted onto the second link
  as soon as the router receives the entire
  message. The end-to-end delay is
• 3.05 seconds
• 6.1 seconds
• 6.05 seconds
• none of the above

83
End of Session ?