Download 3_The Internet - Systems and Computer Engineering

The Internet
Making a Connection: Packet Switching,
Addressing and Routing
Host
Computer or
Terminal
An Internet
Router
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The Internet
• The Internet, or more correctly,
• a digital packet-switched network
using the TCP/IP set of protocols,
• is
• A collection of hosts (computers and
other information devices)
• connected by a variety of digital
communications networks, consisting of
• digital communication links and
• switches, which are called routers.
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Protocols
• Information is transmitted on the
Internet as binary information, 1’s and
0’s, under the control of standardized
procedures called protocols.
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The TCP/IP Suite of Protocols
• Originated with ARPANET and DDN to
meet US DoD requirements
• Survivability
• no central point of failure security
• Network interoperability
• accommodate heterogeneous networks and
equipment
• Ability to handle surge traffic
• Allow priority
• Be always available
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Sending Information on the Internet
• Every entity (computer or router) on
the Internet has an address.
• The address is a 32-bit binary number
• 10000110010101011111111011100011
• The IP address is usually expressed
in dotted decimal form
• 134.117.254.227
• Part of the address is the NetID and
the remainder the HostID
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Packets
• The message to be sent is packaged
into packets
• A packet is a like an envelope that
holds a block of data
• Each packet includes
• The address of the sender
• The address of the destination
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• If the message is short
• it is sent in one packet
• If not
• it is fragmented and
• sent in a secession of packets.
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Routing (Switching)
• Packets are sent independently from
router to router
• Each router determines the next router
to be used by consulting a local
directory called a routing table
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Routing at Host
• If the NetID is the same as that of the
originating host, the packet is handled
locally
• IP address is converted to the physical
address of the host and the packet delivered
• If not the same, a memory-resident
routing table is consulted to determine
next recipient of the packet
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Routing at Router
• The NetID is analyzed to determine if this
is last hop.
• If not, the IP of the local router (using
memory-resident tables) selects the best
path to the destination
• Packet is encapsulated again and sent
one hop closer to final destination
• And so on
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Routing Information
• Hosts maintain sufficient information to
forward packets to other hosts or
interior routers within the same network
• Interior routers maintain sufficient
information to forward packets to hosts
within the same system
• Exterior routers maintain sufficient
information to forward packets to other
interior or exterior routers
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Routing Tables
• Each router keeps its memory-resident
tables with an optimum path to every
destination in the system
• Routing-table update involves
exchange of routing table information
between routers using a built-in data
communications system called ICMP.
• Every router in the Internet does this
call the time!!!!
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Internet Control Message Protocol: ICMP
• Provides feedback about problems in the
communications environment
• Error reporting
• Reachability testing
• Congestion Control
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Datagram Delivery
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Evolution of the Web
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Error Control
• The network makes no effort to detect
or correct errors in the transmitted
data.
• It is up to the recipient to detect errors
and ask for retransmission.
• This end-to-end task is handled by
TCP, or the Transmission Control
Protocol
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Transmission Control Protocol (TCP)
• TCP provides traditional connection
oriented data communications service
to programs - the reliable stream
transport service
• TCP provides a virtual circuit, called a
connection
• provides flow control, error checking
and interrupt capability
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TCP Services
• Multiplexing
• Connection Management
• establish
• maintain
• terminate
• Data Transport
•
•
•
•
•
•
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Full-duplex
Timely
Ordered
Labeled
Flow controlled
Error checked
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The Domain Name Service - DNS
• DNS is a hierarchical collection of
directories (databases) that play a vital
role in the Internet.
• DNS is the directory of IP addresses,
that contains the names associated
with IP addresses.
• Names, like sce.carleton.ca allow
people to use the Internet.
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Finding an IP Address
• When ask my browser to open a web page
at www.sce.carleton.ca, a query is sent
by my computer to the nearest DNS server
(at my ISP)
• If it knows the IP address it sends it back to
my computer, otherwise it sends a query to
the next level DNS server, maybe .ca
• This continues until an answer is found or
not.
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• When a match is found, say
134.117.4.60 or whatever, the IP
address is sent to my computer, which
sends a connect message to the web
site using this IP address.
• Every interaction with the Internet
goes through the same process.
• How can the Internet sustain – and
increase - its capacity????
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THE INTERNET
TCP/IP
PROTOCOLS
Domain
Name
Service
DNS
PACKET-SWITCHED
NETWORKS
email: Simple Mail Transport Protocol
(SMTP)
File Transfer Protocol (FTP)
telnet: remote terminal access
Internet Control Message (ICMP) Protocol
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Moving on
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Paths to Evolution
• Fundamental Technologies
•
•
•
•
Electronics
Communications
Software
Systems Engineering
• Provide better ways
•
•
•
•
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to organize and use
faster processors with
more memory
at lower cost
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