1CN multiplexing for computer networks syllabus

multiplexing for computer networks syllabus multiplexing for computer networks syllabus

1. Introduction to network
Each day computer users use their computer for sending and
retrieving email, scheduling meetings, sharing files, preparing
reports, exchanging images, and maybe checking the current
price of an auction item on the Internet.
 All of this requires computers to access multiple networks and
share their resources.
The multiple networks required to accomplish this are the
local area network (LAN),
the campus area network(CAN),
the metropolitan area network (MAN)
wide area network (WAN).

2. Advantages of Networking
•Connectivity and Communication
•Data Sharing
•Hardware Sharing
•Internet Access
•Internet Access Sharing
•Data Security and Management
•Performance Enhancement and Balancing
•Entertainment

3. Figure 2-1
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

4. Figure 2-2
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Point-to-Point Line Configuration

5. Figure 2-2-continued
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Point-to-Point Line Configuration

6. Figure 2-2-continued
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Point-to-Point Line Configuration

7. Figure 2-3
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Multipoint Line Configuration

8. Figure 2-4
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Local area networks are defined in terms of the protocol and
the topology used for accessing the network.
The networking protocol is the set of rules established for
users to exchange information.
NETWORK TOPOLOGIES

9. Figure 2-5
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Mesh Topology
This provides for full redundancy in the network data paths but
at a cost. The additional data paths increase the cabling costs
and an increase in the networking hardware cost

10. Figure 2-6
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Star Topology
The most common networking topology in today’s LANs where all
networking devices connect to a central switch or hub

11. Hub
Broadcasts the data it receives to all devices connected to its ports
Multiport Repeater
Another name for a hub
Broadcast
Transmission of data by a hub to all devices connected to its ports
Switch
Forwards a frame it receives directly out the port associated with its
destination address
Ports
The physical input/output interfaces to the networking hardware

12. Figure 2-7
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Tree Topology

13. Figure 2-8
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Bus Topology
Bus Topology
The computers share the media (coaxial cable) for data transmission
ThinNet
A type of coaxial cable used to connect LANs configured
with a bus topology

14. Figure 2-9
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Ring Topology

15. Token-ring Topology
A network topology configured in a logical ring that complements the
token passing protocol
Token Passing
A technique where an electrical token circulates around a network—
control of the token enables the user to gain access to the network
IEEE
Institute of Electrical and Electronics Engineers, one of
the major standards-setting bodies for technological development
Deterministic
Access to the network is provided at fixed time intervals
Token-ring Hub
A hub that manages the passing of the token in a token-ring network

16. Figure 2-10
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Hybrid Topology

17. Advantages and Disadvantages
Topology Advantages Disadvantages
Bus Cheap. Easy to install
Difficult to reconfigure. Break in
bus disables entire network.
Star
Cheap. Easy to install.
Easy to reconfigure.
Fault tolerant.
More expensive than bus.
Ring Efficient. Easy to install.
Reconfiguration difficult. Very
expensive.
Mesh
Simplest. Most fault
tolerant.
Reconfiguration extremely
difficult.
Extremely expensive. Very
complex.

18. Figure 2-12
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Simplex

19. Figure 2-13
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Half-Duplex

20. Figure 2-14
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Full-Duplex

21. Figure 2-15
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

22. Figure 2-16
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Local Area Network

23. Figure 2-16-continued
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Local Area Network

24. Figure 2-17
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Metropolitan Area Network

25. Figure 2-18
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Wide Area Network

26. Figure 2-19
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998
Internetwork
(Internet)

27. The following are advantages of a wired network:
• Faster network data transfer speeds (within the LAN).
• Relatively inexpensive to setup.
• The network is not susceptible to outside interference.
The following are disadvantages of the wired network:
• The cable connections typically require the use of specialized tools.
• The cable installation can be labor-intensive and expensive.

28. A wireless home network is probably the most common home network
configuration in use today. The advantages of a wireless network are
many including the following:
• User mobility
• Simple installations
• No cables
Disadvantages of a wireless network can include
• Security issues.
• The data transfer speed within the LAN can be slower than wired
networks.

29. Wi-Fi
Wi-Fi Alliance—an organization that tests and certifies wireless
equipment for compliance with the 802.11x standards
Wireless Router
Device used to interconnect wireless networking devices
and to give access to wired devices and establish the broadband
Internet connection to the ISP

30. Hub—
This is used to interconnect networking devices. A drawback to
the hub is that it broadcasts the data it receives to all devices
connected to its ports. The hub has been replaced by the network
switch in most modern networks
Switch—
This is the best choice for interconnecting networking devices. It
can establish a direct connection from the sender to the
destination without passing the data traffic to other networking
devices

31. Network Adapter—
Wired and wireless network adapters are available. The type of
network adapter used in desktop computers is called the
Network Interface Card (NIC).
Wireless router—This device uses RF to connect to the
networking devices. A wireless router typically contains a router,
switch, and a wireless access point and is probably the most common
way to interconnect wireless LANs to the ISP’s access device. Note
that these devices also have wired network connections available on
the system

32. An example of a (a) wired and (b) wireless WiFi home network.

33. A home network using a wireless router connected to the ISP.

35. ANALYZING COMPUTER NETWORKS
Address Resolution Protocol (ARP)
Used to map an IP address to its MAC address
ARP Reply
A network protocol where the MAC address is returned
Echo Request
Part of the ICMP protocol that requests a reply from a computer

36. Physical Layer
Describes the media that interconnects networking devices
The main focus will be on the use of unshielded twisted-pair (UTP)
cable in computer networks, although an overview of shielded
twisted-pair (STP) is presented. Fiber optic cables are playing a very
important role in modern computer networks

37. 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
Twisted Pair (TP)
two insulated copper
wires
◦Category 3: traditional
phone wires, 10 Mbps
Ethernet
◦Category 5:
100Mbps Ethernet
Introduction 1-37

38. Coaxial cable:
two concentric copper
conductors
bidirectional
baseband:
◦single channel on cable
◦legacy Ethernet
broadband:
◦ multiple channels on
cable
◦ HFC
Introduction 1-38
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

39. TERMINATING CAT6/5E/5 UTP CABLES
This section introduces the techniques for terminating high-
performance UTP cables.

41. Introduction
1-
41
millions of connected
computing devices: hosts
= end systems
 running network apps
communication links
◦fiber, copper, radio, satellite
◦transmission rate =
bandwidth
routers: forward packets
(chunks of data)
local ISP
company
network
regional ISP
router
workstation
server
mobile

42. Introduction
1-
42
protocols control sending,
receiving of msgs
◦e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of
networks”
◦loosely hierarchical
◦public Internet versus private
intranet
Internet standards
◦RFC: Request for comments
◦IETF: Internet Engineering
Task Force
local ISP
company
network
regional ISP
router
workstation
server
mobile

43. Introduction
1-
43
communication
infrastructure enables
distributed applications:
◦Web, email, games, e-
commerce, file sharing
communication services
provided to apps:
◦Connectionless unreliable
◦connection-oriented reliable

44. Introduction
1-
44
a human protocol and a computer network protocol:
Q: Other human protocols?
Hi
Hi
Got the
time?
2:00
TCP connection
request
TCP connection
response
Get http://www.awl.com/kurose-ross
<file>
time

45. Introduction
1-
45
network edge:
applications and hosts
network core:
◦routers
◦network of networks
access networks, physical
media: communication
links

46. Introduction
1-
46
end systems (hosts):
◦run application programs
◦e.g. Web, email
◦at “edge of network”
client/server model
◦client host requests, receives
service from always-on server
◦e.g. Web browser/server; email
client/server
peer-peer model:
◦ minimal (or no) use of dedicated
servers
◦e.g. Skype, BitTorrent, KaZaA

47. Introduction
1-
47
Goal: data transfer
between end systems
handshaking: setup
(prepare for) data
transfer ahead of time
◦Hello, hello back human
protocol
◦set up “state” in two
communicating hosts
TCP - Transmission
Control Protocol
◦Internet’s connection-
oriented service
TCP service [RFC 793]
reliable, in-order byte-
stream data transfer
◦loss: acknowledgements
and retransmissions
flow control:
◦sender won’t overwhelm
receiver
congestion control:
◦senders “slow down
sending rate” when network
congested

48. Introduction
1-
48
End-end resources
reserved for “call”
link bandwidth, switch
capacity
dedicated resources: no
sharing
circuit-like (guaranteed)
performance
call setup required

49. Introduction
1-
49
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

50. Introduction
1-
50
FDM
frequency
time
TDM
frequency
time
4 users
Example:

51. Introduction
1-
51
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
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
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation

52. Introduction
1-
52
Sequence of A & B packets does not have fixed pattern,
shared on demand  statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.
A
B
C
100 Mb/s
Ethernet
1.5 Mb/s
D E
statistical multiplexing
queue of packets
waiting for output
link

53. Introduction
1-
53
Takes L/R seconds to
transmit (push out)
packet of L bits on to
link or R bps
Entire packet must
arrive at router before it
can be transmitted on
next link: store and
forward
delay = 3L/R (assuming
zero propagation delay)
Example:
L = 7.5 Mbits
R = 1.5 Mbps
delay = 15 sec
R R R
L
more on delay shortly …

54. Introduction
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54
1 Mb/s link
each user:
◦100 kb/s when “active”
◦active 10% of time
circuit-switching:
◦10 users
packet switching:
◦with 35 users,
probability > 10 active
less than .0004
Packet switching allows more users to use network!
N users
1 Mbps link
Q: how did we get value 0.0004?

55. Introduction
1-
55
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?”
Q: human analogies of reserved resources (circuit
switching) versus on-demand allocation (packet-switching)?

56. Introduction
1-
56
company/univ local area
network (LAN) connects
end system to edge router
Ethernet:
◦shared or dedicated link
connects end system
and router
◦10 Mbs, 100Mbps,
Gigabit Ethernet
LANs: chapter 5

57. Introduction
1-
57
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
◦3G ~ 384 kbps
Will it happen??
◦GPRS in Europe/US
base
station
mobile
hosts
router

58. Introduction
1-
58
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
Twisted Pair (TP)
two insulated copper
wires
◦Category 3: traditional
phone wires, 10 Mbps
Ethernet
◦Category 5:
100Mbps Ethernet

59. Introduction
1-
59
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

60. Introduction
1-
60
signal carried in
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)
e.g. 3G: hundreds of kbps
satellite
Kbps to 45Mbps channel (or
multiple smaller channels)
270 msec end-end delay
geosynchronous versus low
altitude

61. Introduction
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61
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?

62. Introduction
1-
62
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?

63. Introduction
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63
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

64. Introduction
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