ist 228\ch1\internetworking1 chapter 1: internetworking internetworking basics network segmentation...
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IST 228\Ch1\Internetworking 1
Chapter 1: Internetworking
• Internetworking Basics• Network segmentation• How bridges, switches, and routers
are used to physically segment a network
• How routers are used to create internetwork
• OSI model
IST 228\Ch1\Internetworking 2
Internetworking Models
• Most networks are designed as a stack of layers, each one built upon the one below it. Why?
Layer 3
Layer 2
Layer 1
Layer 3
Layer 2
Layer 1
Physical Medium
Layer 3 protocol
Layer 2 protocol
Layer 1 protocol
Layer 2/3 interface
Layer 1/2 interface
Host 1 Host 2
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• Each layer provides services to the higher levels.
• Each layer behaves as a black box.• Layer n on one machine talks to layer n
on another machines.• The corresponding layer in the layered
structure are called peers. • The communication between peers must
follow certain rules, known as protocol.• No data are directly transferred between
layers. Actual communication is through a physical medium below layer 1.
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An Analogy
Ik vind konijnen leuk
L: Ducth
Fax:#
Ik vind konijnen leuk
L: Dutch
I like rabbits
Message
Information for the remote translator
Information for the remote secretary Ik vind
konijnen leuk
L: Ducth
Fax:#
Ik vind konijnen leuk
L: Ducth
J’aime bien les lapins
Urdu & English Chinese & French
Professor B
Translator
Secretary
use fax
use Dutch
Secretary
Translator
Professor A
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Open Systems Interconnection (OSI) Reference Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
• Provides user interface• Initiates services
• Transfer data into standard format before transmission
• Keeps data different applications’ data separate
• Control the data exchange
• End-to-end data error free data transmission
• Logical addressing for data packets Routing and error handling
• Moves bits between devices• Specifies voltages, cables, and
cables
• NIC software function• How data in packaged• Error detection
Th
e low
er
levels
Th
e u
pp
er
levels
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Reasons for Layering
• Simplifies the network model• Enables programmers to specialize in
a particular level or layer of the networking model
• Provides design modularity• Encourages interoperability• Allows for standardized interfaces to
be produced by networking vendors
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The Application Layer (Layer 7)• The layer where users communicate to the
computer• Contains protocols and utilities that provides
services to network applications– (True/False) MsWord, Eudora Mail, Netscape are in the
application layer.– Eudora (application) uses SMTP (Simple Mail Transfer
Protocol) (protocol).
• E-mail:– Message formats such as RFC 822 – SMTP, POP3 (Post Office Protocol Version 3), IMAP
(Internet Message Access Protocol)
• WWW: – HTML (The HyperText Markup Language), XML (eXtensible
Markup Language), XSL (eXtensible Style Language) – HTTP (The HyperText Transfer Protocol)
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The Presentation Layer (Layer 6)• The presentation layer prepares the data
from the application layer for transmission over the network or from the network to the application layer.
• Include protocols specifying how to represent data (MPEG, JPEG, PIC, WAV)
• Responsible for data translation, formatting, encryption, compression.
• We need these services because different computers use different internal representation for data (integers and characters)
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The Session Layer (Layer 5)
• Enables two applications on the network to have an ongoing conversation
• Provide following services– Communication setup and teardown– Control for data exchange– Data synchronization definition– Failure recovery
• Examples: – Structured Query Language (SQL)– X Windows– AppleTalk Session Protocol (ASP)
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The Transport Layer (Layer 4)
• Provides – end-to-end error free data transport services– establish a logical connection– data segmentation into maximum transmission
unit size– messaging service for session layer
• Protocols in this layer can be– connection-oriented : require an
acknowledgment of the receipt of data packets. – connectionless : do not require an
acknowledgment of the receipt of data packets.
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• Connection-oriented protocols:
sender receiverSynchronize
Negotiate connection
Connection Establish
Synchronize
Acknowledge
Data Transfer
Virtual Circuit
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sender receiver
Buffer full
GO
• Flow Control• The segments delivered back to the sender upon
their reception• Any segment not acknowledged are retransmitted.• Segments are sequence back into their proper order
upon arrival at their destination• Manageable data flow is maintained in order to
avoid congestion
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• Windowing: The quantity of data segment (in bytes) is sent without receiving an acknowledgment (ack) is called a window.
sender receiver
receive 1
ack. 2
send 1
send 2 receive 2
ack. 3
send 3
sender receiver
send 1
send 2
ack. 4
send 3
send 4
Window size of 1
Window size of 3
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• Acknowledgments:sender receiver
send 1
send 2
ack. 4
send 3
send 4
send 5
send 6
ack. 5
send 5
Connection lost!
ack. 7
1 2 3 4 5 6 1 2 3 4 5 6
Positive Acknowledgment
with retransmission
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The Network Layer (Layer 3)
• Provides services– to manage devices addressing– to tracks the location of devices on the
network– to determine the best way to move data
on the network
• The network layer must transport traffic between devices that are not directly connected.
• Routers are specified at this layer.
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The Data Link (Layer 2)
• Services– Identification of the source and destination
nodes via their physical address (Media Access Control (MAC) address)
– Definition of how data is packaged for transport as frames
– Error detection– Flow control of information sent across the link
• Has two sublayers:– Media Access Control (MAC) 802.3– Logical Link Control (LLC) 802.2
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The Physical Layer (Layer 1)
• This layer communicates directly with the various types of actual communication media
• Services– definition of the physical characteristics
of the network hardware, including cable and connector
– Encoding– Transmission of signals on the wire
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Example:568B twisted pair wiring scheme
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Layer 1 Network Devices: Repeaters • The number of nodes on a network and the length
of cable used influence the quality of communication on the network
• Attenuation– Natural degradation of a transmitted signal over distance
• Repeaters work against attenuation by repeating signals that they receive on a network
• Why are repeaters Layer 1 devices?
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Layer 1 Network Devices: Hubs• Generic connection device used to tie several
networking cables together to create a link between different stations on a network
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• Hubs that are plugged into electric power are called active hubs
• A hub that merely connects different cables on a network and provides no signal regeneration is called a passive hub and is not a repeater
• “Hub” is a generic term applied to many different network-connection devices
• If a hub in some way segments or subdivides the traffic on a network, it is an intelligent, or switching, hub
• For the purpose of the CCNS exam, the term hub—by itself—is a device that does not segment the network
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Network Segmentation• Segmentation
– Process of breaking a network into smaller broadcast or collision domains
• Ethernet network, which are characterized by IEEE 802.3 standard, define the use of a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method– Backoff algorithm : Mathematical calculation
performed by computers after a collision occurs on a CSMA/CD network
– Backoff period : Random time interval used after a collision has been detected on an Ethernet network
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Network Segmentation via Bridges
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Layer 2 Devices: Bridges
• Operate at the Data Link layer of the OSI model
• Filters traffic between network segments by examining the destination MAC address– Based on this destination MAC address,
the bridge either forwards or discards the frame
– When a client sends a broadcast frame to the entire network, the bridge will always forward the frame
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• Transparent Bridges : Also called learning bridges because they build a table of MAC addresses as they receive frames– This means that they “learn” which
addresses are on which segments– Ethernet networks mainly use transparent
bridges• Source-routing bridges : Rely on the
source of the frame transmission to provide the routing information– Usually employed by Token Ring networks
• Translation bridges : Can connect networks with different architectures
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Layer 2 Devices: Switches• Increase network performance by reducing
the number of packets transmitted to the rest of the network
• Like bridges, operate at the Data Link layer of the OSI model
• In an Ethernet network, computers are usually connected directly to a switch
• Virtual circuit– Private connections between two points created
by a switch that allows the two points to use the entire available bandwidth between those two points without contention