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Who is Who in the Internet ?
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Internet Engineering Task Force (IETF): The IETF is
the protocol engineering and development arm of the
Internet. Subdivided into many working groups, which
specify Request For Comments or RFCs. (www.ietf.org)
IRTF (Internet Research Task Force): The Internet
Research Task Force is a composed of a number of
focused, long-term and small Research Groups.
 E.g., Anti-spam group, delay tolerant networking group,
Network management group, Routing research group,
Peer-to-peer research group (www.irtf.org)
Internet Architecture Board (IAB)
The Internet Engineering Steering Group (IESG)
Internet Standardization Process
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All standards of the Internet are published as RFC
(Request for Comments).
A typical way of standardization is:
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Internet Drafts
RFC
Proposed Standard
Draft Standard (requires 2 working implementation)
Internet Standard (declared by IAB)
Consensus based standardization
At The Not So Very
Beginning
Necessity
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Proliferation of Computers in Public and Business
Utilities
Availability of Data Based Services (no pun
intended)
End User Growth
Communication Technology Evolved
Research and Commercial Motives
Sample Applications
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Remote Access to Resources
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Shared access to data/files
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Online audio/video lectures, web casting, demos
Remote Data Operations and Computation
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FTP, NFS, AFS
Remote Computer Aided Learning
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E.g., Telnet
E.g., Airline reservation systems, inventory control systems
Other applications like, e-mail, ftp, http, p2p, instant
messaging, news groups etc
Now: IP-* (Telephony, TV, Radio, Movies, Music etc)
Network Classification Parameters
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Latency
Bandwidth
Loss rate
Number of end systems
Service interface (how to invoke?)
Other details
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Reliability
Communication capability: unicast, multicast, broadcast
Applicability: E.g., Real-time (e.g., postal service?)
Switching technology: message vs. packet
Network Classification Parameters...
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Communication Medium: Electrons and photons
Links: Optical fiber, copper, satellite, etc
Switches: Electronic/optical, crossbar/Banyan
Protocols: TCP/IP, ATM, MPLS, SONET,
Ethernet, PPP, X.25, FrameRelay, AppleTalk,
IPX, SNA
Functionalities: Routing, error control, congestion
control, Quality of Service (QoS)
Applications: FTP, WEB, X windows, SSH
Types of Computer Networks
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Geographical distance
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Information type
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Local Area Networks (LAN): Ethernet, Token ring, FDDI
Metropolitan Area Networks (MAN): DQDB and later, SMDS
Wide Area Networks (WAN): X.25, ATM, frame relay
Data networks vs. telecommunication networks
Application type
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Special purpose networks: airline reservation network, banking
network, credit card network, telephony
General purpose network: Internet
Types of Computer Networks
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Right to use
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Ownership of protocols
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proprietary: SNA, DNA
open: IP
Technologies
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private: enterprise networks
public: telephony network, Internet
terrestrial vs. satellite
wired vs. wireless
Protocols
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IP, AppleTalk, SNA
Definition of Computer Network
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A computer network is an interconnected
collection of autonomous computers.
Two computer are interconnected if they are able to
exchange information
 Two computer are autonomous if they are capable of
operating independently, that is, neither is capable of
forcibly starting, stopping, or controlling the other
 Network users (not necessarily application users) are
aware of the network existence
Autonomous
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Just to be clear –What are not Computer
Networks
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Master/slave systems (ref. any centralized cluster)
Single-host networks (E.g., UNIX)
Multi-computers, such as the hypercube (ref. parallel computing)
In terms of (operating) systems, there is some distinction between
network systems and distributed systems
 Distributed system gives the view of a single computer to the user (user
not aware of networking behind scenes)
 Failure of any node in the system might stop other nodes from operating
correctly (non-autonomous)
 Focus is on software, distributed computation, that can do better
resource sharing, concurrent processing etc
Important problems: load balancing, fault-tolerance, mutual exclusion
Now That We are Clear
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How to build a computer network?
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Agree upon the communication technique (circuit
switching or store-and-forward switching)
Develop communication languages for hosts to interact
(protocols)
Implement appropriate functionality without affecting
the computer’s performance (designing the protocol
stack)
Develop network-centric algorithms (routing,
reliability, congestion control)
Types of Communication Networks
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Exchange mechanism
Communication
Network
Switched
Communication
Network
Circuit-Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Communication
Network
Datagram
Network
Virtual Circuit Network
Broadcast vs. Switched
Communication Networks
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Broadcast communication networks
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information transmitted by any node is received by every
other node in the network in range
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E.g.,: usually in LANs (Ethernet, Wireless) , Radio
Problem: coordinate the access of all nodes to the shared
communication medium (Multiple Access Problem)
Switched communication networks
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information is transmitted to a sub-set of designated nodes
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Examples: WANs (Telephony Network, Internet), ATM
Problem: how to forward information to intended node(s)
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This is done by special nodes (E.g., bridges, routers,
switches) running routing protocols
A Taxonomy of Communication
Networks
Communication
Network
Switched
Communication
Network
Circuit-Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Communication
Network
Datagram
Network
Virtual Circuit Network
Circuit Switching
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Three phases
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2.
3.
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circuit establishment
data transfer
circuit termination
If circuit not available: “Busy signal”
Examples
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Telephone networks
ISDN (Integrated Services Digital Networks)
Timing in Circuit Switching
Host 1
Node 1
Node 2
Host 2
processing delay at Node 1
propagation delay
between Host 1
and Node 1
Circuit
Establishment
propagation delay
between Host 2
and Node 1
Data
Transmission
DATA
Circuit
Termination
Circuit Switching
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A node (switch) in a circuit switching network
incoming links
Node
outgoing links
Circuit Switching:
Multiplexing/Demultiplexing
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Time divided in frames and frames divided in slots
Relative slot position inside a frame determines which
conversation the data belongs to
Needs synchronization between sender and receiver
In case of non-permanent conversations
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Needs to dynamic bind a slot to a conservation
How to do this?
A Taxonomy of Communication
Networks
Communication
Network
Switched
Communication
Network
Circuit-Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Communication
Network
Datagram
Network
Virtual Circuit Network
Packet Switching
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Data are sent as formatted bit-sequences, so-called packets.
Packets have the following structure:
Header
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Data
Trailer
Header and Trailer carry control information (e.g., destination
address, check sum)
Each packet is passed through the network from node to node along
some path (Routing)
At each node the entire packet is received, stored briefly, and then
forwarded to the next node (Store-and-Forward Networks)
Typically no capacity is allocated for packets
Packet Switching
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A node in a packet switching network
incoming links
Node
Memory
outgoing links
Packet Switching:
Multiplexing/Demultiplexing
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Data from any conversation can be transmitted at
any given time
How to tell them apart?
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use meta-data (header) to describe data
A Taxonomy of Communication
Networks
Communication
Network
Switched
Communication
Network
Circuit-Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Communication
Network
Datagram
Network
Virtual Circuit Network
Datagram Packet Switching
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Each packet is independently switched
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Each packet header contains destination address
No resources are pre-allocated (reserved) in
advance
Example: IP networks
Timing of Datagram Packet Switching
Host 1
transmission
time of Packet 1
at Host 1
Node 1
Packet 1
Host 2
Node 2
propagation
delay between
Host 1 and
Node 2
Packet 2
Packet 1
Packet 3
processing
delay of
Packet 1 at
Node 2
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Datagram Packet Switching
Host C
Host D
Host A
Node 1
Node 2
Node 3
Node 5
Host B
Node 6
Node 4
Node 7
Host E
A Taxonomy of Communication
Networks
Communication
Network
Switched
Communication
Network
Circuit-Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Communication
Network
Datagram
Network
Virtual Circuit Network
Virtual-Circuit Packet Switching
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Hybrid of circuit switching and packet switching
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data is transmitted as packets
all packets from one packet stream are sent along a preestablished path (=virtual circuit)
Guarantees in-sequence delivery of packets
However: Packets from different virtual circuits
may be interleaved
Example: ATM networks
Virtual-Circuit Packet Switching
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Communication with virtual circuits takes place
in three phases
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2.
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VC establishment
data transfer
VC disconnect
On demand circuit setup, several packets may
share same virtual link
Packet-Switching vs. CircuitSwitching
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Most important advantage of packet-switching over
circuit switching: Ability to exploit statistical
multiplexing:
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However, packet-switching needs to deal with congestion:
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efficient bandwidth usage; ratio between peek and average rate is
3:1 for audio, and 15:1 for data traffic
more complex routers
harder to provide good network services (e.g., delay and
bandwidth guarantees)
In practice they are combined:
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IP over SONET, IP over Frame Relay