Transcript document

Chapter Four
Welcome to OSI
Objectives
• Get an introduction to the Open Standards
Interconnect (OSI) model of networking.
• Examine the seven layers of OSI.
• Get a general feel for the purpose of each of
the layers.
Why Use Layers?
• New standards can be developed at one layer
without having to rework all the others.
• Knowledge of what goes on at each layer helps
the troubleshooting process.
• It simplifies learning the process.
The Seven Layers
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Application = Layer 7
Presentation = Layer 6
Session = Layer 5
Transport = Layer 4
Network = Layer 3
Data Link = Layer 2
Physical = Layer 1
Remembering the Layers
• Layer 7 to Layer 1
– Apple Pie Seems To Need Dill Pickles
• Layer 1 to Layer 7
– People Don’t Need To See Private Auctions
Moving Data Between Layers
• Each layer at one device only communicates
with its counterpart on the other device.
– These are peer entities.
• No layer does the work or fixes the problems of
another layer.
• Data moves from layer to layer by way of
service access points.
Protocol Data Units
• Data takes a specific form at different layers.
Layer #
Layer Name
PDU
7
Application
Message
6
Presentation
Message
5
Session
Message
4
Transport
Segment
3
Network
Packet
2
Data Link
Frame
1
Physical
Bits
The Application Layer
• Acts as an interface between user apps and the
network
• PDU of the layer is a message
• The first line of command for a process called
flow control
– Making sure data moves at a rate acceptable to
both parties involved in the transfer
Application Layer Protocols
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Network Terminal Protocol (Telnet)
File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Post Office Protocol (POP)
Domain Names Services (DNS)
Hyper Text Transfer Protocol (HTTP)
Routing Information Protocol (RIP)
AppleShare
Presentation Layer
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Makes sure data is in the correct format
Manages uniform character sets
Handles data encryption
Manages data compression
The Session Layer
• Sets up and breaks down virtual connections
between communicating devices
• Maintains connection while it is active
• Juggles multiple open connections at the same
time
Session Layer Protocols
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Network File System (NFS)
Structured Query Language (SQL)
Remote Procedure Call (RPC)
X Window
Network Basic Input/Output Services (NetBIOS)
User Datagram Protocol (UDP)
NetWare Core Protocol (NCP)
AppleTalk Session Protocol (ASP)
AppleTalk Data Stream Protocol (ADSP)
The Transport Layer
• Breaks data stream down into manageable
chunks called segments
• Performs packet-level error detection/
correction
• Monitors time to live (TTL) to determine if
packets have been lost
• Handles end-to-end flow control
Transport Layer Protocols
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Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
NWLink
Sequenced Packet Exchange (SPX)
Name Binding Protocol (NBP)
AppleTalk Transaction Protocol (ATP)
Zone Information Protocol (ZIP)
Sequenced Packet Protocol (SPP)
Packet Exchange Protocol (PEP)
The Network Layer
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Manages traffic between different networks
Controls network addressing functions
Responsible for routing
PDU of the Network layer
– The packet
Network Layer Protocols
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Internetwork Packet Exchange (IPX)
Routing Information Protocol (RIP)
Datagram Delivery Protocol (DDP)
Routing Table Maintenance Protocol (RTMP)
Internet Protocol (IP)
Address Resolution Protocol (ARP)
Reverse Resolution Protocol (RARP)
Internet Control Message Protocol (ICMP)
Open Shortest Path First (OSPF)
The Data Link Layer
• Subdivided into to sub-layers
– Media Access Control (MAC)
– Logical Link Control (LLC)
• Determines methods by which data moves
across the medium
• Defines network access methods
Data Link Protocols
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802.3 Ethernet
802.3u Fast Ethernet
802.3.z Gigabit Ethernet
802.5 Token Ring
802.11 Wireless Signaling
802.12 Demand Priority
Integrated Services Digital Network (ISDN)
Fiber Distributed Data Interface (FDDI)
X.25
The Physical Layer
• Defines the network media
• Defines the physiology of connectors and plugs
• Places the data onto the wire as bits
The 802 Standards
• The Institute of Electrical and Electronic
Engineers (IEEE, or I-triple-E, as they’re
lovingly known) defined the committees in
February 1980.
• 802 Committees oversee the development of
new technologies and standards within their
defined area.