IST 228\Ch1\Internetworking1 Chapter 1: Internetworking Internetworking Basics Network segmentation...

$: IST 228\Ch1\Internetworking1 Chapter 1: Internetworking Internetworking Basics Network segmentation How bridges, switches, and routers are used to physically.$
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


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


• 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.


An Analogy

Ik vind konijnen leuk

L: Ducth

Fax:#


L: Dutch

I like rabbits

Message

Information for the remote translator

Information for the remote secretary Ik vind

konijnen leuk

L: Ducth

Fax:#


L: Ducth

J’aime bien les lapins

Urdu & English Chinese & French

Professor B

Translator

Secretary

use fax

use Dutch

Secretary

Translator

Professor A


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


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


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)


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)


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)


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.


• Connection-oriented protocols:

sender receiverSynchronize

Negotiate connection

Connection Establish

Synchronize

Acknowledge

Data Transfer

Virtual Circuit


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


• 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


• 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


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.


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


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


Example:568B twisted pair wiring scheme


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?


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


• 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


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


Network Segmentation via Bridges


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


• 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


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

IST 228\Ch1\Internetworking1 Chapter 1: Internetworking Internetworking Basics Network segmentation...

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