cisco – semester 1 – chapter 2 network fundamentals and the osi model
TRANSCRIPT
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
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