1-5 Device Overview

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© 2000, Cisco Systems, Inc. 2-1

Device Overview



© 2000, Cisco Systems, Inc. www.cisco.com ICND v1.0a—2-2

Objectives

On completion of this chapter, you will beable to perform the following tasks:

•

Describe how data traffic is exchangedbetween source and destination devices

•Identify the roles and functions of a hub,switch, and router, and where they best fit in

the network•Select the appropriate Cisco equipment for agiven set of network requirements




Application

Presentation

Session

Transport

Network

Data Link

Physical

OSI Model PDU Functional Responsibilities Examples

Written Exercise: OSI Model




TCP

UDPSPX

802.3 / 802.2HDLC

EIA/TIA-232

V.35

IPIPX

EXAMPLES

Role of Data Flow Layers

Transport

Data Link

Physical

•Reliable or unreliable delivery

•Error correction before retransmit

•Combines bits into bytes and

bytes into frames•Access to media using MAC address

•Error detection not correction

•Move bits between devices

•Specifies voltage, wire speed and

pin-out cables

NetworkProvide logical addressing whichrouters use for path determination




Physical Layer Functions

Defines

•Media type

•Connector type

•Signaling type

E t h

e r n e

t

8 0 2 . 3

V . 3

5

P

h y s i c a l

E I A

/ T I A

- 2 3 2




Physical Layer: Ethernet/802.3

Hub

Hosts

Host

10Base2—Thin Ethernet10Base5—Thick Ethernet

10BaseT—Twisted Pair


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Hubs Operate at Physical layer

A B C D

Physical

•All devices in the same collision domain

•All devices in the same broadcast domain

•Devices share the same bandwidth



Hubs: One Collision Domain

•More end stations means

more collisions•CSMA/CD is used



Data Link layer Functions

Defines

•Physical source anddestination addresses

•Higher layer protocol(Service Access Point)associated with frame

•Network topology

•Frame sequencing

•Flow control

•Connection-orientedor connectionless

D a t a L

i n k

P h y s

i c a l

EIA/TIA-232v.35

E t h

e r n e

t

F r a m

e R

e l a

y

H D L C

802.2

802.3



DataSource add FCSLengthDest add

Variable266 4

0000.0C xx.xxxx

Vendorassigned

IEEE assigned

MAC Layer - 802.3

Data Link Layer Functions (cont.)

Preamble

Ethernet IIuses “Type”here and

does not use802.2.

MAC Address

8# Bytes



DataDest

SAP

Source

SAP

DataSource add FCSLengthDest add

Variable11

802.2 (SAP)

MAC Layer - 802.3

Data Link Layer Functions (cont.)

Ctrl

1 or 2

3 2

Preamble

DataDest SAP

AASource SAP

AA

Variable11

802.2 (SNAP)

Ctrl

03

1 or 2

OR

OUIID

Type

# Bytes

# Bytes



•Each segment has its own collision domain

•All segments are in the same broadcast domain

Data Link

Switches and Bridges Operateat Data Link Layer

OR1 2 3 1 24



Switches

•Each segment has itsown collision domain

•Broadcasts areforwarded to allsegments

Memory

Switch



Network Layer Functions

•Defines logicalsource anddestination

addressesassociated with aspecific protocol

•

Defines pathsthrough network

•Interconnectsmultiple data links

N e t w o r k

IP, IPX

D a t a L i n k

P h y s i c a l

EIA/TIA-232v.35

E t h e

r n e

t

F r a m e

R e

l a y

H D L C

802.2

802.3



DataSource

address

Destination

addressIP

Network Layer Functions (cont.)

Header

172.15.1.1

NodeNetwork

LogicalAddress

Network Layer End Station Packet



Routers: Operate at theNetwork Layer

•Broadcast control

•Multicast control

•Optimal pathdetermination

•Traffic management

•

Logical addressing•Connects to WANservices



Network Device Domains

Hub Bridge Switch Router

Collision Domains:

1 4 4 4

Broadcast Domains:

1 1 1 4



Network Structure Defined byHierarchy

DistributionLayer

Core Layer

AccessLayer



Access Layer Characteristics

End station entry point to the network

Access Layer



Distribution LayerCharacteristics

•Access LayerAggregation Point

•

Routes traffic•Broadcast/MulticastDomains

•

Media Translation•Security

•Possible point for remote access

Distribution Layer


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Core Layer Characteristics

•

Fast transport to enterprise services

•No packet manipulation

Core Layer

1-5 Device Overview

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