Transcript 2-foundation

Introduction to Computer
Networks
Foundation
Ilam University
Mozafar Bag-Mohammadi
1
Outline
 Introduction
 Statistical
Multiplexing
 Inter-Process Communication
 Network Architecture
 Performance Metrics
2
Introduction
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Building a network to support diverse
ranges of applications
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Distributed computing.
Multimedia.
Telecommunication.
E-commerce, etc.
What kind of technology do we need?
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Hardware.
Software.
3
First Step
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What is computer Network?
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Different views.
Differences from other networks, Its generality.
What is requirements? Different
perspective:
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Network provider
Network designer
Application programmer
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Design goals
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Connectivity
Scalability
Simplicity
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Efficiency
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For designers.
Most importantly for users.
cost
performance
Support for common user services.
5
Building Blocks
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Nodes: PC, special-purpose hardware…
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hosts
switches, routers and gateways
Links: coaxial cable, optical fiber…
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point-to-point
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multiple access
…
6
Switched Networks
A network can be defined recursively as...
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two or more nodes
connected by a link, or

two or more networks
connected by two or
more nodes
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Strategies
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Circuit switching: carry bit streams
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Packet switching: store-and-forward
messages
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Connection oriented.
Original telephone network
Dedicated resource.
Connectionless (IP) or connection oriented (ATM)
Shared resource.
Packet switching is the focus of computer
Networks.
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Addressing and Routing
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Address: byte-string that identifies a node
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usually unique
Routing: process of forwarding messages to
the destination node based on its destination
address
Types of addresses
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unicast: node-specific
broadcast: all nodes on the network
multicast: some subset of nodes on the network
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Multiplexing (resource sharing)
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Time-Division Multiplexing (TDM)
Frequency-Division Multiplexing (FDM)
L1
R1
L2
R2
L3
Switch 1
Switch 2
R3
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Statistical Multiplexing
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On-demand time-division
Schedule link on a per-packet basis
Packets from different sources interleaved on link
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scheduling
fairness, quality of service
Buffer packets that are contending for the link
Buffer (queue) overflow is called congestion
…
11
Packet Switching
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A node in a packet switching network
incoming links
Node
outgoing links
Memory
12
Inter-Process Communication
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Turn host-to-host connectivity into process-to-process
communication regardless where the process are.
Give a unified view and fill gaps between what
applications expect and what the underlying technology
provides.
Host
Host
Host
Application
Channel
Application
Host
Host
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IPC Abstractions
Request/Reply (Client-server)
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Guarantee delivering data, and might protect privacy and integrity.
distributed file systems (NFS)
digital libraries (web)
File Transfer (FTP)
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Stream-Based- sequence or stream of bits.
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Video on demand:
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Video Conferencing-
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sequence of frames. Delay constrained, but can be fetched before
hand.
For example, a 1/4 NTSC with 352x240 pixels and 24 bit color.
(352 x 240 x 24)/8=247.5KB
Assuming 30 frame per second => 7500KBps = 60Mbps
tightly delay bounded. VIC From Berkeley.
Both application can tolerate packet loss.
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Reliability in the network?
What Goes Wrong in the Network?
 Bit-level errors (electrical interference), a bit
is corrupted or a burst error.
 Packet-level errors (congestion)
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Messages are delayed
Messages are deliver out-of-order
Packet loss
Third parties eavesdrop
Link and node failures
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Performance Metrics
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Bandwidth (throughput)
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data transmitted per time unit
link versus end-to-end
notation
 KB = 210 bytes
 Mbps = 106 bits per second
Latency (delay)
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time to send message from point A to point B
one-way versus round-trip time (RTT)
components
Latency = Propagation + Transmit + Queue
Propagation = Distance / c (light speed)
Transmit = Size / Bandwidth
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Bandwidth versus Latency
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Relative importance
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Latency bounded- sending 1-byte by client, 1ms vs
100ms dominates sending a message on a 1Mbps or
100Mbps link
Bandwidth Bounded- sending 25MB image: 1Mbps vs
100Mbps dominates 1ms vs 100ms delayed channel.
Infinite bandwidth
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RTT dominates
Throughput = TransferSize / TransferTime
TransferTime = RTT + 1/Bandwidth x TransferSize
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1-MB file to 1-Gbps link the same as 1-KB packet to 1Mbps link.
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Delay x Bandwidth Product
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Amount of data “in flight” or “in the pipe”
Example: 100ms x 45Mbps = 560KB
Delay
Bandw idth
We are usually more interested in 2 times of this value
Since it take RTT to hear from receiver.
18
Layering
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Use abstractions to hide complexity and
decompose to manageable components.
Abstraction naturally lead to layering
Alternative abstractions at each layer
Application programs
Request/reply Message stream
channel
channel
Host-to-host connectivity
Hardware
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Layering
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Advantages
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Modularity – protocols easier to manage and
maintain
Abstract functionality –lower layers can be
changed without affecting the upper layers
Reuse – upper layers can reuse the functionality
provided by lower layers
Disadvantages
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Information hiding – inefficient implementations
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Protocols
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Building blocks of a network architecture, or
layer abstraction.
Each protocol object has two different
interfaces
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service interface: operations on this protocol
peer-to-peer interface: messages exchanged with
peer
Term “protocol” is overloaded
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specification of peer-to-peer interface
module that implements this interface
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Interfaces
Host 2
Host 1
High-level
object
Protocol
Service
interface
Peer-to-peer
interface
High-level
object
Protocol
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Protocol Machinery
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Protocol Graph
 Nodes are protocols and edge are depends on.
 most peer-to-peer communication is indirect
 peer-to-peer is direct only at hardware level
Host 2
Host 1
File
application
Digital
Video
library
application
application
MSP
RRP
HHP
File
application
Digital
Video
library
application
application
MSP
RRP
HHP
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Protocol Machinery (cont)
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Multiplexing and Demultiplexing (demux key)
Encapsulation (header/body)
Host 2
Host 1
Application
program
Application
program
Data
Data
RRP
RRP
RRP Data
RRP Data
HHP
HHP
HHP RRP Data
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ISO OSI Reference Model
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ISO – International Standard Organization
OSI – Open System Interconnection
Started to 1978; first standard 1979
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ARPANET started in 1969; TCP/IP protocols
ready by 1974
Goal: a general open standard
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allow vendors to enter the market by using their
own implementation and protocols
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ISO Architecture
End host
Telnet, FTP, TFTP
MSB, integer
Manage TCP streams
Message, P2P(process)
Packet, routing
Frame, CRC
Raw bit pipe
End host
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
One or more nodes
within the network
•The last 3 protocols are implemented in all elements in the
Network.
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Encapsulation
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A layer can use only the service provided by the layer
immediate below it
Each layer may change and add a header to data
packet
data
data
data
data
data
data
data
data
data
data
data
data
data
data
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OSI Model Concepts
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Service – says what a layer does
Interface – says how to access the service
Protocol – says how is the service
implemented
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a set of rules and formats that govern the
communication between two peers
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Physical Layer (1)
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Service: move the information between two
systems connected by a physical link
Interface: specifies how to send a bit
Protocols: coding scheme used to represent
a bit, voltage levels, duration of a bit
Examples: coaxial cable, optical fiber links;
transmitters, receivers
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Datalink Layer (2)
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Service:
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framing, i.e., attach frame separators
send data frames between peers
others:
 arbitrate the access to common physical media
 ensure reliable transmission
 provide flow control
Interface: send a data unit (packet) to a machine
connected to the same physical media
Protocols: physical layer addresses, implement
Medium Access Control (MAC) (e.g., CSMA/CD)…
30
Network Layer (3)
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Service:
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deliver a packet to specified destination
perform segmentation/reassemble
others:
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packet scheduling
buffer management
Interface: send a packet to a specified
destination
Protocols: define global unique addresses;
construct routing tables
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Transport Layer (4)
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Services:
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provide an error-free and flow-controlled end-to-end
connection
multiplex multiple transport connections to one network
connection
split one transport connection in multiple network
connections
Interface: send a packet to specified destination
Protocols: implement reliability and flow control
Examples: TCP and UDP
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Session Layer (5)
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Service:
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full-duplex
access management, e.g., token control
synchronization, e.g., provide check points for long
transfers
Interface: depends on service
Protocols: token management; insert checkpoints,
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Presentation Layer (6)
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Service: convert data between various
representations
Interface: depends on service
Protocol: define data formats, and rules to
convert from one format to another
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Application Layer (7)
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Service: any service provided to the end user
Interface: depends on the application
Protocol: depends on the application
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Examples: FTP, Telnet, WWW browser
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Internet Architecture
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Defined by Internet Engineering Task Force
(IETF). Developed in mid 60s in the
ARPANET project.
No assumption about the network tech.
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET 1
NET 2
…
NET n
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Internet Architecture
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Hourglass Design, IP is the focal point. Delivery is
separated from end-to-end process channel.
No restrict layering
Application vs Application Protocol (FTP, HTTP)
Application
TCP
UDP
IP
Network
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OSI vs. TCP/IP
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OSI: conceptually define services, interfaces, protocols
Internet: provide a successful implementation
Application
Presentation
Session
Transport
Network
Datalink
Physical
OSI
Application
Transport
Internet
Host-tonetwork
Telnet
FTP DNS
TCP
UDP
IP
LAN
Packet
radio
TCP
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