Transcript What`s Flash?

Networks
Slides taken from: Computer Networking by Kurose and
Ross
What’s the Internet
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millions of connected
computing devices:
hosts, end-systems
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pc's workstations, servers
PDA's phones, toasters
running network apps
communication links
fiber, copper, radio,
satellite
routers: forward packets
(chunks) of data thru
network
What’s the Internet
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protocols: control sending, receiving
of msgs
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Internet: "network of networks"
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e.g., TCP, IP, HTTP, FTP, PPP
loosely hierarchical
Internet standards
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RFC: Request for comments
IETF: Internet Engineering Task Force
What’s Protocol
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human protocols:
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"what's the time?"
"I have a question"
introductions
... specific msgs sent
... specific actions taken when msgs
received, or other events
network protocols:
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machines rather than humans
all communication activity in Internet governed
by protocols
protocols define format, order of msgs sent
and received among network entities, and
actions taken on msg transmission, receipt
Protocols
Network edge
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end systems (hosts):
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run application programs
e.g., WWW, email
at "edge of network"
client/server model
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client host requests, receives service
from server
e.g., WWW client (browser)/ server;
email client/server
Connection-orientated Service
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Goal: data transfer between end sys.
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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]
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reliable, in-order byte-stream data transfer
loss: acknowledgements and retransmissions
flow control:
 won't sender overwhelm receiver
congestion control:
 senders "slow down sending rate" when
network congested
Network Core
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mesh of interconnected routers
the fundamental question: how is
data transferred through net?
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circuit switching: dedicated circuit per
call: telephone net
packet-switching: data sent thru net in
discrete "chunks"
Packet Switching
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To improve the efficiency of transferring
information over a shared communication line,
messages are divided into fixed-sized, numbered
packets
Network devices called routers are used to direct
packets between networks
Messages
sent by
packet
switching
Protocol Layers
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Networks are made of many "pieces":
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hosts
routers
links of various media
applications
protocols
hardware, software
Question:
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Is there any hope of organizing structure of
network?
Organization of air travel
Organization of air travel: a
different view
Protocol Stack
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application: supporting network
applications
 ftp, smtp, http, telnet
transport: host-host 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"
Protocol Layering and Data
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Each layer takes data from above
adds header information to create
new data unit
passes new data unit to layer below
Data Message
In Class Assignment
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Use telnet to connect to your CSCI account
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Open a DOS command prompt window and type:
telnet candler.cs.unca.edu
Login to your CS account:
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Your login name is
<first-6-characters-of-last-name><First-initial><Secondinitial>
Your password is
<the four letters "csci"><last four digits of student id>
Use the yppasswd command to change your password.
Use FTP to transfer a file to your CSCI account
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Use your favorite editor (e.g., wordpad, notepad, word) to
create a file---the contents of the file don’t matter.
Store the file in the directory c:\files; create that directory if
necessary.
Follow these directions to transfer that file via FTP to your
CSCI directory.