Cisco – Semester 1 – Chapter 2

Network Fundamentals

And

The OSI Model

Types of Networks

• LANs• WANs• MANs

SANs• Internet• Intranet• Extranet• VPNs

History

• <50 Semiconductor made smaller, more reliable computers possible

• 50s IC combined many transistors on one piece of semiconductor

• 60s Mainframes and terminals were norm• 70s Smaller computers; introduction of

PC• 80s IBM PC and shared data files

Network Protocols

• Protocols – rules for communication

• Organizations that set Protocols– IEEE – ANSI– TIA– EA– ITU formerly CCITT

LANS

• Cover limited geographic areas called campuses

• Provide many users access to high-bandwidth media

• Provide full-time connectivity• Connect adjacent devices• Types

– Ethernet, Token Ring, FDDI

WANS

• Operate in wide geographic areas• Allow end users to communicate real time• Provide full-time remote services connected to

local services• Provide e-mail, WWW, FTP, and e-Commerce

services• Technologies

– Modem, ISDN, DSL, Frame Relay, T1, E1, Sonet

MANS

• Not too important

• Area covered is larger than a campus

• Interconnect several LANs

SANs

• High-performance network that moves data between servers and storage resources

• Features– Performance– Availability– Scalability

VPN

• Builds a secure tunnel to enable two branch offices to communicate across Internet

• Types– Access VPNs – SOHO– Internet – link regional and remote office to

headquarters– Extranet – link business partners to

headquarters

VPN Advantages

• Provide privacy for TCP/IP applications

• Provides encryption services between clients and servers

• Provides mobility to employees with secure network access

International Standards Organization

InteroperabilityThe ISO recognized that there was a need to create a network model that would help network builders implement networks that could communicate and work together

Released model in 1984OSI reference model is networking scheme that supports networking standards

The 7 Layers

• 7 Application

• 6 Presentation

• 5 Session

• 4 Transport

• 3 Network

• 2 Data Layer

• 1 Physical

Why Layers?

• Reduces complexity

• Standardizes interface

• Facilitates modular engineering

• Ensures interoperability

• Accelerates evolution

• Easier to teach and learn (or so they say)

Physical Layer – Layer 1

• Defines the electrical and functional specifications for the link between end systems

• Defines voltage levels, physical data rates, maximum transmission distance, physical connections

• THINK MEDIA AND SIGNALS

Layer 2 – Data Link

• Provides reliable transit of data across a physical link

• Concerned with physical addressing (MAC) address), network topology, and media access, error notification, delivery of frames, and flow control

• THINK FRAMES AND MEDIA ACCESS CONTROL

Layer 3 – Network Layer

• Provides connectivity and path selection between two host systems

• THINK PATH SELECTION, ROUTING, AND ADDRESSING (logical or IP)

Layer 4 - Transport

• Provides a data transport service that shields the upper layers from transport implementation details

• Concerned with reliable transport between two hosts

• Establishes, maintains, and properly terminates virtual circuits

• Uses error detection-and-recovery and information flow control

• THINK QUALITY OF SERVICE AND RELIABILITY

Layer 5 - Session

• Establishes, manages, and terminates sessions between two communicating hosts.

• Provides its services to the presentation layer• Synchronizes dialogue between the two hosts'

presentation layers and manages their data exchange

• Provides data expedition, class of service, and exception reporting

• THINK DIALOG AND CONVERSATIONS

Layer 6 - Presentation

• Ensures the information sent is readable by receiving host

• Concerned with data structures & syntax

• Translates between multiple formats by using a common format

• Encodes, encrypts, and compresses

• THINK COMMON DATA FORMAT

Layer 7 - Application

• Provides network services to user applications

• DOES NOT provide services to any other OSI layer

• Provides services to applications outside the OSI model

• THINK BROWSERS

Layer Information

• In general each layer communicates with three other layers– The layer above– The layer below– The same layer in the peer host

• Know specifics of each layer– E.g. NetBuei– operates at layer 5

Encapsulation

• Wraps data with the necessary protocol information before sending to next layer and for network transit.

• Data receives headers (control information), trailers, and other information

• Data – Segments – Packets – Frames – Bits– THIS IS IMPORTANT (defines datagram at

each layer)

Headers

• Control information placed before the data

• Adds address information, et. al.

• Exact format depends on layer

Layers and Encapsulation

• Presentation – Data

• Transport – Segments

• Network – Packets

• Data Link – Frames

• Physical - Bits

Protocols

• Set of rules that determines format and transmission of data; aka standards

• Different protocols for different layers

• PDU – Protocol Data Unit – exchange between peer layers

TCP/IP

• Transmission Control Protocol/Internet Protocol

• Makes data communication possible between any two computers, anywhere in the world

• Speed approaches speed of light• WWW and Internet protocol – defacto

standard

TCP/IP Layers

• Application Layer– Combines Application, Presentation, & Session

• Transport Layer– Same as OSI Transport Layer

• Internet Layer– Same as OSI Network Layer

• Network Access Layer– Includes Physical & Data Link; Includes LAN and

WAN details

TCP/IP Protocols

• Application Layer– FTP, TFTP, HTTP, SMPT, DNS, TFTP, Telnet,

Redirector

• Transport Layer– UDP and TCP

• Internet Layer– IP

• Network Access Layer– LAN and WAN technology used

Model Similarities

• Network professionals need to know both

• Both use layers

• Both are packet switched (not circuit switched)

• Both have similar transport and network layers

Model Differences

• TCP/IP application layer includes OSI presentation and session layers

• TCP/IP network access layer includes OSI data link and physical layers

• TCP/IP protocols are standards used to build Internet

• No networks are built around OSI protocols• TCP/IP APPEARS simpler

Cisco Uses OSI Because

• Generic and protocol independent

• More details which makes it useful for teaching and learning

• More details which makes it useful for troubleshooting

• USE OSI MODEL but use TCP/IP PROTOCOLS