Download foundationsChap1

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Readings: Peterson & Davie, Chapter 1
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“We reject kings, presidents, and voting. We
believe in rough consensus and running code.”
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Website coming Friday!
Assignment 1 assigned on Friday.
◦ To be discussed today
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TODOs:
◦ Log into lab machines
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Sample Schedule
◦ http://courses.washington.edu/css432/syllabi/s08.html
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Sample FAQ
◦ http://courses.washington.edu/css432/prog/prog1_faq.
html
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What is a network?
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What is a physical Network?
We’ll investigate these empirically, starting
with the first assignment
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What is a virtual network?
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“Think of a network as providing the means for a
set of application processes that are distributed
over [multiple] computers to communicate”
We could make every application responsible for
their information exchange, but
◦ Lots of redundancy and errors with this approach
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Instead, lets distill common communication
patterns
◦ And offer those as services/protocols in a network stack
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App Developer
◦ What do I want?
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Network Architect
◦ Cost-effective design, reliable, QoS enabled
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Provider
◦ Account for usage, offer QoS gradients
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Links, Nodes, Clouds form network maps
Point-to-Point
◦ Quickly becomes unmanageable
Multiple-Access
◦ Multiplex a single bus/wire/channel across multiple hosts
◦ Limitations :geographical distance limitations and number
of nodes connected.
All styles of Networks must cope with Scalability
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The most common types of switched networks
include:
◦ Circuit-switched
 POTS
◦ Packet-switched
 Store-and-forward
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Fig 1.3, p8
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Switches, nodes (hosts), and links
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Packets refer to physical data on the wire,
with a well-defined size imposed by each
network
◦ Or subnetwork your packet moves through
 This could introduce packet fragmentation and
rebuilding (more on that later)
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Messages: a data payload usually exchanged
at the application level
◦ These messages may not fit into one packet
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Internetwork: a connection of independent
networks
◦ Visualize these as clouds
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Gateway: A Node that connects two or more
networks (a.k.a router)
◦ Quite similar in spirit to a switch, and thus these
terms are frequently blurred
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A network may be built by combining existing
networks
This implies a recursive structure
◦ Where the basis is some physical medium
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We can recursively build larger and larger
networks by connecting existing network
clouds
◦ Analog: Fib numbers
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A unique* way to identify all nodes on a
network
Much like a cell-phone number
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We need to “share” links effectively
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STDM
◦ Divide time into quanta and assign the link in a RR
fashion
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FDM
◦ Divide frequencies into channels, like TV
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Limitations: Dynamic resizing of the quantum
or adding new quanta/frequencies is required
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Or, On Demand time division multiplexing
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Effectively uses the link
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Could introduce starvation, so an upper
bound on block-size is determined
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Formally, a protocol graph with protocol
specifications (a standardization)
Multiple models have been proposed
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Architects leverage abstraction
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Key: Start with services offered by the layer
beneath you and build on top
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◦ OSI architecture
◦ Internet (IETF) architecture
◦ This naturally introduces layers in our Network
◦ Lowest layer relies on the underlying hardware
◦ High level services are implemented by lower level
services
Application Programs
Process-To-Process Channels
Host-To-Host Connectivity
Hardware
Application Programs
Process-To-Process Channels
Application Programs
RRC
MSC
Host-To-Host Connectivity
Host-To-Host Connectivity
Hardware
Hardware
A “Protocol Stack”
Peer Level
Host 1
Host 2
Application Programs
Application Programs
RRC
RRC
MSC
MSC
Host-To-Host Connectivity
Host-To-Host Connectivity
Hardware
Hardware
…1001…
Service Level Interfaces define the
semantics (form & meaning) o f
messages exchanged at a given level
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Each protocol communicates “with its peer”
indirectly by handing messages down the
protocol stack
The only layer to have a non-virtualized p2p
relationship is the hardware level
End host
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
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Physical Layer transmits bits
Data link layer collects bits into frames
◦ NIC and drivers typically implement this
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Network layer handles routing
◦ Packet-level data
◦ Note that these layers are implemented on switches
in the cloud, too
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Transport and up usually are found on the
host
◦ “There is less agreement about the definition of the
top three layers”
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Defined by Internet Engineering Task Force (IETF)
Hourglass Design
Application vs Application Protocol (FTP, HTTP)
Netscape, IE, Mosaic, etc.
FTP
HTTP
Reliable byte-stream channel TCP
TFTP
UDP
Focal point for the architecture IP
NET1
NV
NET2
Unreliable datagram deliver
Internet Protocol
…
NETn
Ethernet, FDDI, etc.
25
CSS 432
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The “meeting point” in our 4 layers
Also, the bottleneck or meeting point of
various networking technologies
FTP over FDDI, HTTP over Ethernet
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Transport Protocols
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◦ Sometimes called end to end
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TCP – reliable, in order, slow
UDP – unreliable, out
TCP
UDP
IP
Network
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We can apply the OSI model (loosely) to the
IETF model
Note that OSI was assembled after ARPANET
Payload
Protocol 1 Header
Pr ayload
Protocol 2 Header Protocol 1 Header
Payload
Subnet 1 Header Protocol 2 Header Protocol 1 Header
Payload
Application Programs
RRC
MSC
Host-To-Host Connectivity
Payload
Hardware
HHP Header
RRP Header
Payload
RRP Header
Payload
…
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RTT
Message Copying V.S. Passing
Process-per-protocol v.s. per-message
◦ Context Switching v.s. Function Calls
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Bandwidth & Latency
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We’ll be using this for the class.
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Coming up!