Download SCORE: A Scalable Architecture for Implementing Resource

CSCE 201
Computer Networks
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Reading Assignment
Required:
– Security Awareness: Chapter 3
Recommended:
– Internet Society (ISOC) homepage, http://www.isoc.org
– Computer Network,
http://en.wikipedia.org/wiki/Computer_network
– Easttom: Chapter 2
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Before Internet

Isolated, local packet-switching networks
– only nodes on the same network could
communicate

Each network is autonomous:
– different services
– different interfaces
– different protocols
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Before Internet (cont)
ARPANET: sponsored by Defense Advanced Research Projects
Agency (DARPA):
• 1969: interconnected 4 hosts
• 1970: host-to-host protocol: Network Control Protocol (NCP)
• 1972: first application: e-mail
Stanford Research Institute (SRI)
Univ. of California at
Santa Barbara (UCSB)
Univ. of California at LA (UCLA)
Univ. of Utah
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Internet
Connect Existing Networks:


ARPANET, Packet Radio, and Packet Satellite
NCP not sufficient Develop new protocol

1970s: Transmission Control Protocol (Kahn and Vinton)
– Based on packet switching technology
– Good for file transfer and remote terminal access

Divide TCP into 2 protocols
– Internet Protocol (IP): addressing and forwarding of packets
– Transmission Control Protocol (TCP): sophisticated services, e.g. flow
control, recovery




1980: TCP/IP adopted as a DoD standard
1983: ARPANET protocol officially changed from NCP to TCP/IP
1985: Existing Internet technology
1995: U.S. Federal Networking Council (FNC) define the term
Internet
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Goals (Clark’88)
Connect existing networks
1. Survivability
2. Support multiple types of services
3. Must accommodate a variety of networks
4. Allow distributed management
5. Allow host attachment with a low level of
effort
6. Be cost effective
7. Allow resource accountability
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Internet Challenge

Interconnected networks differ (protocols,
interfaces, services, etc.)
 Solutions:
1.
2.
Reengineer and develop one global packet switching
network standard: not economically feasible
Have every host implement the protocols of any network it
wants to communicate with: too complex, very high
engineering cost
3. Add an extra layer: internetworking layer



Hosts: one higher-level protocol
Network connecting use the same protocol
Interface between the new protocol and network
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Layering

Organize a network system into logically
distinct entities
– the service provided by one layer is based only
on the service provided by the lower level
entity
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Without Layering
Application
Transmission
Media

SMTP
FTP
Coaxial
cable
HTTP
Fiber
optic
Each application has to be implemented for
every network technology!
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With Layering

Intermediate layer provides a unique abstraction
for various network technologies
Application
SMTP
FTP
HTTP
Intermediate
layer
Transmission
Media
Coaxial
cable
Fiber
optic
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Layering

Advantages
– 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
– Information hiding – inefficient implementations
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TCP/IP Networking Model
 TCP/IP has
a different layered model
Application Layer
Transport Layer (TCP)
Error Correction
Reliable Connection
Internetwork Layer (IP)
WAN Connectivity
Unreliable Datagram Service
Network Access Layer
Physical Connection
LAN Connection
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Network Access Layer




Responsible for physical connection
– Shape
– Size
– Voltages
Responsible for rules of how to put bits on the “wire”
These are the building blocks for the network
The goal of the physical layer is to move information
across one “hop”
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Internet Layer

Transports data from one end-user system to another
end-user systems by hopping across as many physical
connections as necessary
 Provides a mechanism to connect many LANs
together effectively
 Connectionless and unreliable datagram protocol
 Protocols:
– Internet Protocol
– Routing Protocol
– Supporting Protocol
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IP Header
0
4
Version HLen
8
16
TOS
Identification
TTL
19
31
Length
Flags
Fragment offset
20 bytes
Protocol
Header checksum
Source address
Destination address
Options (variable)

Comments
– HLen – header length only in 32-bit words (5 <= HLen <= 15)
– TOS (Type of Service): now split in
Differentiated Service Field (6 bits)
 remaining two bits used by ECN (Early Congestion Notification)
Length – the length of the entire datagram/segment; header + data
Flags: Don’t Fragment (DF) and More Fragments (MF)
Fragment offset – all fragments excepting last one contain multiples of 8 bytes
Header checksum - uses 1’s complement

–
–
–
–
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IP Addresses






IP provides logical address space and a corresponding
addressing schema
IP address is a globally unique or private number
associated with a host network interface
Every system which will send packets directly out
across the Internet must have a unique IP address
IP addresses are based on where station is connected
IP addresses are controlled by a single organization address ranges are assigned
They are running out of space!
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Routing Protocols
• Enable routing decisions to be made
• Manage and periodically update routing tables, stored at each router
• Autonomous collection of routers:
•Under single administration
•Use same routing protocol: Interior Gateway Protocol (IGP)
•Use Exterior Gateway Protocol (EGP) to communicate other
systems
• Router : “which way” to send the packet closer. (Keep routing table
small and allow to handle unlimited number of systems.)
• Protocol types:
•Reachability
•Distance vector
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Supporting Protocols

Handle specific tasks
– Address Resolution Protocol (ARP)
– Reverse Address Resolution Protocol (RARP)
– Internet Control Message Protocol (ICMP)
– Internet Group Management Protocol (IGMP)
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The Domain Name System

Each system connected to the Internet also has one or
more logical addresses.
 Unlike IP addresses, the domain address have no
routing information - they are organized based on
administrative units
 There are no limitations on the mapping from domain
addresses to IP addresses
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Domain Name Resolution




Domain Name Resolution: looking up a logical name
and finding a physical IP address
There is a hierarchy of domain name servers
Each client system uses one domain name server
which in turn queries up and down the hierarchy to
find the address
If your server does not know the address, it goes up
the hierarchy possibly to the top and works its way
back down
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Transport Layer (TCP)




Present a reliable end-to-end pipe to the application
Data either arrives in the proper order or the
connection is closed
Keeps buffers in the sending and destination system to
keep data which has arrived out of order or to
retransmit if necessary
Provides individual connections between applications
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TCP Connection Establishment

Three-way handshake
– Goal: agree on a set of parameters: the start sequence
number for each side
Server
Client (initiator)
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Application Layer

Uses the reliable TCP connections to accomplish
useful work over the network
– client-server applications
– standard applications




telnet (port 23)
mail (port 25)
finger (port 79)
ftp (port 21)
Each application uses a “port” and a protocol
 Each port can have many connections

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