Network Theory – OSI and TCP/IP Models

@ONE Spring Hands-On Institute

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Network Theory – OSI and Network Theory – OSI and TCP/IP ModelsTCP/IP Models


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Internetworking:Internetworking:An OverviewAn Overview


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What is Networking?What is Networking?

• Networking - the interconnection of workstations, peripherals, terminals and other devices*


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Yesterday’s NetworksYesterday’s Networks

• The advent of the desktop PC brought with it small, closed networks in the mid-1980s.

An old-school LAN (local-area network)


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Today’s Computer NetworksToday’s Computer Networks

• Today, networks are everywhere:– School, work, home

– Coffee shops, airports, state parks

– Emerging technologies such as EV-DO and WiMAX promise metro-wide networks in the air.


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What happened?What happened?

• Over the past 20 years, computer networks have evolved:

Small, proprietary, closed systems

One huge, global, collection of networks (an internetwork)

The Internet


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What happened?What happened?

• Vendors realized that standardizing their products would help them make money.

• Various groups got together and proposed networking standards.

• The Internet (b.1969) offered an attractive de facto set of standards.


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Network Protocols and Network Protocols and StandardizationStandardization


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Network ProtocolsNetwork Protocols

• Early networks:– proprietary technologies– single vendor only

• Today:– Standards-based technologies– Macs, PCs, cell phones, watches, toasters, and

earrings can all share data as long as they all speak to each other according to the same set of rules, or protocol.


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Network ProtocolsNetwork Protocols

• Protocol - a set of rules, or an agreement, that determines the format and transmission of data.

SNA (Systems Network Architecture) = IBM

IPX (Internet Packet eXchange) = Novell

IP (Internet Protocol) = US Department of Defense

XNS (Xerox Network System) = Xerox

NetBEUI (NetBIOS Extended User Interface) = IBM

AppleTalk = Apple

DECnet = Digital Equipment Corporation

VINES = Banyan


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TCP/IP: Internet ProtocolTCP/IP: Internet Protocol

• One protocol has become the de facto standard for all computer networks.

• IP v4 = The Internet Protocol (version 4)• All hosts on the Internet use the IP protocol• The Internet actually uses a family, or suite, of

protocols called TCP/IP which includes:– TCP, or Transmission Control Protocol: (adds reliability

and sequencing to Internet conversations)– HTTP: (web stuff)– FTP: (file transfer)– DNS: (naming system that brought us .com and www)– SMTP: (mail, SPAM, and other delights of the Info Age)


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TCP/IP: Internet ProtocolTCP/IP: Internet Protocol

All of these devices use the TCP/IP protocol “stack” to communicate. In this case, they are using HTTP to browse the web.

All of these devices need an IP Address to be on the Internet.

TCP/IP’s developers never envisioned that this protocol could support a global network of entertainment and commerce.


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Reality CheckReality Check

• In the mid-1980s, Cisco (like all other vendors) focused on “multi-protocol” platforms.

• Because TCP/IP has emerged as the dominant protocol, our focus is entirely on IP networks.

• So, this is an Introduction to Cisco IP Network Devices


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Types of NetworksTypes of Networks


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LANsLANs

• Local-Area Networks (LANs) emerged in the mid 1980s

• LANs– connects workstations, peripherals, and

other devices in a single building– LANs made it possible to efficiently share

such things as files and printers


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Early LANs IsolatedEarly LANs Isolated

Seattle

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San Francisco

New York


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Wide Area Networks (WANs)Wide Area Networks (WANs)

Seattle

San Francisco

New York

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LAN, CAN, MAN, and WANLAN, CAN, MAN, and WAN

• LAN - limited geographic area– office, home, small building (enterprise)

• CAN - Campus-Area Network– University, Company Tech Center (enterprise)

• MAN - Metropolitan-Area Network– citywide network, (typically involves a service provider)

• WAN - large geographic area– city-to-city, worldwide, Internet (typical involves a service

provider)

• PAN – personal area network– Cell phone, watch, PDA, bluetooth stuff (you!)


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LAN vs WANLAN vs WAN

• Early LANs and WANs typically used very different:– Protocols– Devices– Signaling– Media (physical connections, wire, RF)

Typical Early LANs Typical Early WANs

High bandwidth Low bandwidth

Cheap Costly

Intermittent, on-demand connectivityAlways “on”

Small geographical area Large geographical area


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Early LAN vs WANEarly LAN vs WAN

• Different network types, different devices:

Hub, Repeater

Bridge

LAN Switch

Router

Modem, CSU/DSU

Switch

Access Server

Router

Common LAN Devices Common WAN Devices


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Early LAN vs WANEarly LAN vs WAN

• Emerging technologies and dominance of TCP/IP spurred widespread adoption of new device types:

Switch

Multilayer Switch

Firewall

Router

Today’s LAN Devices

DSLAM

Optical Transport

Router

Today’s WAN Devices

VPN Gateway

IP Telephony (LAN/WAN)

IP Phone IP PBX

Wireless (LAN/WAN)

Bridge Access Point


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Today’s LAN/WANToday’s LAN/WAN

• Several factors have blurred the distinctions between WANs and LANs and the devices that operate in each.

• However, for the purposes of our discussions, we will talk about devices as either “LAN” or “WAN”


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The OSI Reference ModelThe OSI Reference Model


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Enter ISOEnter ISO

• ISO – International Organization for Standardization (Geneva)– Voluntary, non-treaty organization charted by the UN

• From the earliest days of networking, it was clear to ISO that standards were needed.

• Standardization aids: development, interoperability, education…


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ISO’s OSI ModelISO’s OSI Model

• ISO looked at existing network protocols (TCP/IP, XNS, SNA) and came up with OSI RM.

• OSI RM - Open Systems Interconnection Reference Model


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OSI Reference ModelOSI Reference Model


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7 - Application Layer7 - Application Layer

• Network processes to applications– Provides network services

to user applications


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6 – Presentation Layer6 – Presentation Layer

• Data Representation– Code Formatting– Negotiation of data

transfer– Ensures information sent

by the application can be transmitted on the network

– Data encryption


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5 – Session Layer5 – Session Layer

• Interhost communication– Establishes, maintains,

and manages sessions between applications


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4 – Transport Layer4 – Transport Layer

• End-to-end connections– Segmentation – Reassembly into data

stream– Offers potential of reliable

transport


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3 – Network Layer3 – Network Layer

• Addresses and best path– Logical addressing is used

at this layer• IP, AppleTalk, IPX, etc.

– Routers reside at this layer


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2 - Data-Link Layer2 - Data-Link Layer

• Access to media– Physical transmission

across the medium– Error notification, network

topology and flow control– Uses MAC (physical)

addresses– Switches and bridges

reside at this layer


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1 – Physical Layer1 – Physical Layer

• Binary Transmission– Provides the electrical,

mechanical, procedural and functional means for activating and maintaining the physical link between systems.

– The media resides at this layer


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Data Encapsulation ExampleData Encapsulation Example

End System

Intermediate Systems


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Data EncapsulationData Encapsulation


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TCP/IP vs OSI ModelTCP/IP vs OSI Model


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Cisco NetworkingCisco Networking


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Brief(est) History of LANsBrief(est) History of LANs


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Early LANsEarly LANs

• In the 1980s, several LAN technologies competed to offer Layer 1/Layer 2 services:– Token Ring (IBM)– Ethernet (Xerox, et al)– ARCnet (Datapoint)

• Later on:– FDDI, Fiber Distributed Data Interface– ATM, Asynchronous Transfer Mode


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The IEEE Working GroupsThe IEEE Working Groups

802.1

802.2

802.3

802.4

802.5

802.6

802.7

802.8

802.11

Networking Overview and Architecture

Logical Link Control

Ethernet

Token Bus

Token Ring

MANs

Broadband

Fiber Optic

Wireless Ethernet

...and more!


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TodayToday

• Ethernet is the de facto standard.

• It has crushed its competitors in the LAN space, and has been adopted for Wireless networks and Metro WANs.


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Ethernet and TCP/IPEthernet and TCP/IP

• Ethernet and TCP/IP are the most pervasive protocols

Data Link Layer

Physical Layer

Network Layer

Session Layer

Transport Layer

Presentation Layer

Application Layer

TCP/IP

Ethernet


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Device Functions at Layers Device Functions at Layers

Documents

Network Theory – OSI and TCP/IP Models