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©2000, Cisco Systems, Inc. www.cisco.com
OSIReference Model
Presented by Muktianto
©2000, Cisco Systems, Inc. www.cisco.com
OSI Layer Overview
1-3Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Why a Layered Network Model?
• Reduces complexity
• Standardizes interfaces
• Facilitates modular engineering
• Ensures interoperable technology
• Accelerates evolution
• Simplifies teaching and learning
Application
Presentation
Session
Transport
Network
Data Link
Physical1
2
3
4
5
6
7
1-4Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Layer Functions
Application
Presentation
Session
Transport
Network
Data Link
Physical1
2
3
4
5
6
7 Network processes to applications
Data representation
Inter host communication
End-to-end connections
Addresses and best path
Access to media
Binary transmission
1-5Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Peer-to-Peer Communication
Physical
Data Link
Network
Transport
Session
Presentation
Application
Physical
Data Link
Network
Transport
Session
Presentation
Application
segment
packet
frame
bit
1-6Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Data Encapsulation
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host A
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host B
Data
Network
HeaderData
Frame Frame
Header Trailer
Network
HeaderData
010010011010101
©2000, Cisco Systems, Inc. www.cisco.com
Upper Layer Overview
1-8Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Application Layer
Word ProcessingSpreadsheetDatabaseDesign/ManufacturingProject PlanningOthers Browser FilezilaMs. Outlook
Electronic MailFile TransferRemote AccessClient/Server ProcessNetwork ManagementOthers
Electronic Data InterchangeWorld Wide WebE-Mail GatewaysSpecial-Interest Bulletin BoardsFinancial Transaction ServicesInternet Navigation UtilitiesConferencing (Video, Voice, Data)Others
Internetwork application can extend beyond the enterprise
1-9Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Presentation Layer
• Text• Data
ASCIIEBCDICEncrypted
• Graphics• Visual Images
PICTTIFFJPEGGIF• Sound
• VideoMIDIMPEGQuick Time
Provides code formatting and conversion for applications
1-10Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Session Layer
Network File System (NFS)Structured Query Language (SQL)Remote-Procedure Call (RPC)X Window SystemAppleTalk Session Protocol (ASP)DNA Session Control Protocol (SCP)
Service Request
Service Reply
Coordinates applications as they interact on different hosts
©2000, Cisco Systems, Inc. www.cisco.com
Transport Layer Overview
1-12Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Transport Layer
• Segments upper-layer applications
• Establishes an end-to-end connection
• Sends segments from one end host to another
• Optionally, ensures data reliability
1-13Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Segment Upper-Layer Applications
Application
Presentation
Session
Transport segments share traffic stream
Transport Application port
DataApplication
portData
Application port
Data
Electronic Mail
File Transfer
Terminal Session
1-14Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Establishes Connection
SENDER RECEIVER
Synchronize
Negotiate Connection
Synchronize
Acknowledge
Connection EstablishedNegotiate Connection
(Send Segments)
1-15Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Sends Segments with Flow Control
Buffer Full
ProcessSegments
Buffer OK
Stop
SENDER RECEIVER
Transmit
Not Ready
Ready
Resume TransmissionGo
1-16Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Reliability with Windowing
Send 1 Window size = 1
SENDER RECEIVERSend 2
Send 3
Recv 1 Ack 2Recv 2 Ack 3
Send 1 Window size = 3
SENDER RECEIVER
Send 2Send 3
Recv 1Recv 2Recv 3Ack 4Send 4
©2000, Cisco Systems, Inc. www.cisco.com
Network Layer Overview
1-18Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Network Layer: Path Determination
Layer 3 functions to find the best path through the internetwork
Which Path?
1-19Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Network Layer: Communicate Path
Addresses represent the path of media connections
1
2
3
4
5
6
7
8
9
1011
1-20Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Addressing: Network and Host
• Network address - Path part used by the router• Host address - Specific port or device on the network
1.1
2.1
3.1
1.2
1.3
Network Host
1 123
2 1
3 1
1-21Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Routing Uses Network Addresses
• Network portion of address used to make path selections• Node portion of address refers to router port to the path
Destination Network
Direction and Router Port
1.0
2.0
3.0
1.1
2.1
3.1
1.0
3.13.0
2.1
2.0
1.1
1-22Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Network-Layer Protocol Operations
X Y
A
B
C
Application
Presentation
Session
Transport
Network
Data Link
Physical
X
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Y
A B C
Each router provides its services to support upper-layer functions
©2000, Cisco Systems, Inc. www.cisco.com
Physicaland
Data LinkOverview
1-24Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Physical and Data-Link Types
Data Link(frames)
Physical(bits,
signals,clocking)
Ethernet
802.2 LLC
802.3
802.5
FDDI
Dial on
DemandSDLC HDLC
X.25
Frame Relay
ISDN
PPP
V.24EIA/TIA-232 G.703
V.35EIA/TIA-449 EIA-530
HSSI
LAN WAN
Separate physical and data link layers for LAN and WAN
1-25Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
LAN Data Link Sublayers
Network
Data Link
Physical
LLC
MAC
Logical Link Control
Media Access Control
MAC Frame 802.2 LLC Packet or Datagram
• LLC refers upward to higher-layer software functions• MAC refers downward to lower-layer hardware functions
1-26Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Physical and Logical Addressing
0000.0c12.3456
1-27Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
MAC Address
Vendor Code Serial Number
0000.0c12.3456
ROM
RAM
MAC address is burned into ROM on a network interface card
24 bits 24 bits
1-28Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Finding the MAC Address
Broadcast Host Z MAC ? Host Z
ARP RequestHost Y Host Z
Host Y MAC
Host Z MAC
ARP ReplyExample 1 : TCP/IP destination local
Broadcast Host Z MAC ? Host Z
ARP Request
Host YHost Z
Host Y MAC
Router MAC
ARP ReplyExample 2 : TCP/IP destination not local
Router A
RoutingTable:Net forHost Z
• An example: TCP/IP Address Resolution Protocol (ARP)• ARP finds the MAC address for a data-link connection
1-29Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
WAN Technology Overview
SDLC
HDLCLAPBPPP
X.25Frame RelayISDN
1-30Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Physical Layer: WAN
DSU/CSU
EIA/TIA-232V.35X.21HSSIothers
(Modem)
DTEData Terminal Equipment
End of the user’s device on the WAN link
DCEData Circuit-Terminating
EquipmentEnd of the WAN provider’s
side of the communication facility
1-31Networking Fundamentals © 2000, Cisco Systems, Inc. www.cisco.com
Data Link Layer: WAN Protocols
DSU/CSU
(Modem)
DSU/CSU
(Modem)
• SDLC - Synchronous Data Link Control
• HDLC - High-Level Data Link Control• LAPB - Link Access Procedure Balanced• Frame Relay - Simplified version of HDLC framing
• PPP - Point-to-point Protocol
• X.25 - Packet level protocol (PLP)• ISDN - Integrated Services Digital Network (data-link signaling)
©2000, Cisco Systems, Inc. www.cisco.com
End Of Session