3/1/2015 1 Computer Networks EEE 448 Lecture #2 Dept of Electrical and Electronics Engineering Çukurova University Organizing Network Functionality 2 • Networks are built from many components – Networking technologies • Ethernet, Wifi, Bluetooth, Fiber Optic, Cable Modem, DSL – Network styles • Circuit switch, packet switch • Wired, Wireless, Optical, Satellite – Applications • Email, Web, FTP, Bittorrent, Skype • How do we make all this stuff work together?! Problem Scenario 3 Web Email Bittorrent Ethernet 802.11 Bluetooth VoIP Cellular • This is a nightmare scenario • Huge amounts of work to add new apps or media • Limits growth and adoption More Problems 4 Bittorrent Ethernet 802.11 Bittorrent Application endpoints may not be on the same media 5 How does the Internet Look Like? Key Questions 6 • How do we divide functionality into layers? – Routing – Congestion control – Error checking • How do we distribute functionality across devices? – Example: who is responsible for security? Switch Switch Router Security Fairness And many more…
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Fundamentals of Computer Networks ECE 478/578 · EEE 448 Lecture #2 Dept of Electrical and Electronics Engineering Çukurova University Organizing Network Functionality 2 • Networks
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Increased overhead for apps that don’t need functionality
• But, in-network performance may be better
Moderate Interpretation
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• Think twice before implementing functionality in the network
• If hosts can implement functionality correctly, implement it a lower layer only as a performance enhancement
• But do so only if it does not impose burden on applications that do not require that functionality
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The Internet Engineering Task Force
• Standardization is key to network interoperability – The hardware/software of communicating parties are often not built
by the same vendor yet they can communicate because they use the same protocol
• Internet Engineering Task Force – Based on working groups that focus on specific issues
• Request for Comments – Document that provides information or defines standard – Requests feedback from the community
– Can be “promoted” to standard under certain conditions • consensus in the committee • interoperating implementations
The Internet Architecture
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The Internet Architecture
Ethernet FDDI
FTP HTTP TFTP
TCP
DNS
UDP
IP
Net 1 Net 1
FTP: File Transfer Protocol
HTTP: Hypertext Transport Protocol
TFTP: Trivial File Transfer Protocol
TCP: Transmission Control Protocol
UDP: User Datagram Protocol
IP: Internet Protocol
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TCP/IP Model
Application Layer Application programs using the network
Transport Layer (TCP/UDP)
Management of end-to-end message transmission,
error detection and error correction
Network Layer (IP)
Handling of datagrams : routing and congestion
Data Link Layer Management of cost effective and reliable data delivery,
access to physical networks
Physical Layer
Physical Media
Comparison of the two architectures
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hardware interface
TCP
IP
UDP
user processor
user processor
OSI Layer 5-7
OSI Layer 4
OSI Layer 3
OSI Layer 1-2
ARP ICMP RARP
UDP: User Datagram Protocol: ICMP: Internet Control Message Protocol IP: Internet Protocol ARP: Address Resolution Protocol RARP: Reverse ARP
Network Structure
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Port Number
user proc.A
user proc.B
user proc.C
user proc.D
user proc.E
user proc.F
user proc.G
IDP IP
SPP PEX TCP UDP
Ethernet interface
Ethernet interface
Ethernet interface
Ethernet interface
TCP/IP protocol suite
XNS protocol suite
Ethernet cable 2
Ethernet cable 1
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Hierarchical Addressing Scheme
• Connection defines the communication link between two processes
data
data UDP header
data UDP header
IP header
UDP header
data IP header
Ethernet trailer
Ethernet header
16-bit UDP source port # 16-bit UDP dest. port #
protocol = UDP internet 32-bit source addr internet 32-bit dest. addr
frame type = IP Ethernet 48-bit source addr Ethernet 48-bit dest. addr
Ethernet frame
UDP = User
Datagram Protocol
The Physical Layer
• defines the mechanical, electrical, and timing interfaces to the network.
– theoretical analysis of data transmission
– three kinds of transmission media :
• guided : copper wire and fiber optics
• Wireless: terrestrial radio
• satellite
Physical layer
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To be transmitted, data must be transformed to electromagnetic signals.
Physical layer: The Theoretical Basis
• Information can be transmitted on wires by varying some physical property such as voltage or current.
• we can model the behavior of the signal and analyze it mathematically (f(t))
• Fourier Analysis : – periodic function, g(t) with period T can be constructed as the sum of a
(possibly infinite) number of sines and cosines:
Physical layer: The Theoretical Basis
• A data signal that has a finite duration (which all of them do) can be handled by just imagining that it repeats the entire pattern over and over forever.
• Computation of series coefficients :
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Physical layer: The Theoretical Basis
• Bandwidth-Limited Signals
– example: the transmission of the ASCII character ''b''
encoded in an 8-bit byte.
• bit pattern : 01100010
• Root-mean-square:
Physical layer: The Theoretical Basis
– all transmission facilities diminish different Fourier components by different amounts, thus introducing distortion.
– Usually, the amplitudes are transmitted undiminished from 0 up to some frequency fc [measured in cycles/sec or Hertz (Hz)] with all frequencies above this cutoff frequency attenuated.
– The range of frequencies transmitted without being strongly attenuated is called the bandwidth (0 - fc )
– The bandwidth is a physical property of the transmission medium and usually depends on the construction, thickness, and length of the medium
Physical layer: The Theoretical Basis
– The number of the highest harmonic passed through is roughly 3000/(b/8) or 24,000/b
– Relation between data rate and harmonics :
Guided Transmission Media
• Magnetic Media – Bandwidth characteristics is excellent
– Delay characteristics is poor
• Twisted Pair – A twisted pair consists of two insulated copper wires, typically about
1 mm thick.
– Twisting is done because two parallel wires constitute a fine antenna.