the osi model chapter 2. topics the osi model identify organizations that set standards for...
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The OSI Model
Chapter 2
Topics
The OSI Model• Identify Organizations that set
standards for networking• Identify the seven layers of the
OSI• Explain specific functions
belonging to each OSI model layer
• Understand how nodes communicate through the layers
• Discuss the structure and purpose of data packets and frames
• Describe the two types of addressing
Networking Standards Organizations
• ANSI• EIA/TIA• IEEE• ISO• ITU• ISOC• IANA and ICANN
OSI Model
Application
SDP110
Professional Workstation 5000
Session
LAN 1 LAN 2Network
Physical
Presentation
Transport
Data Link
The OSI Process
Application
Presentation
Session
Transport
Network
Data-link
Physical
Application
Presentation
Session
Transport
Network
Data-link
Physical
Packet flow
OSI Layer Interaction
Presentation
Session
Transport
Network
Data link
Physical
Application
D N T S DATA
Presentation
Session
Transport
Network
Data link
Physical
Application
PP
NN
SS
PP
AA
SDP110
Professional Workstation 5000
SDP110
Professional Workstation 5000
SDP110
Professional Workstation 5000
SDP110
Professional Workstation 5000
A
DataData
Physical Physical
P
TT
DD
• Provides the user interface.• Connects the user to the network.• Provides file transfer service, mail
service, terminal emulation, and other services.
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
SDP110
Professional Workstation 5000
The Application Layer
Application
Presentation
Session
Transport
Network
Data Link
Physical
Presentation
• Encodes and decodes data.• Determines the format and structure
of data.• Compresses and decompresses data.• Encrypts and decrypts.
decoder ring
X A
BCD
The Presentation Layer
Application
Presentation
Session
Transport
Network
Data Link
Physical
Session
• Establishes and maintains connection.
• Manages upper layer errors.• Handles remote procedure calls.• Synchronizes communicating nodes.
The Session Layer
Application
Presentation
Session
Transport
Network
Data Link
Physical
Transport
• Takes action to correct faulty transmission.
• Controls the flow of data.• Acknowledges successful receipt of data.• Fragments and reassembles data.
Return receipt for
sender
The Transport Layer
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
• Moves information to the correct address.
• Assembles and disassembles packets.• Addresses and routes data packets.• Determines best path for moving data
through the network.
LAN 1 LAN 2
The Network Layer
Application
Presentation
Session
Transport
Network
Data Link
Physical
Data Link
10010011 0000011 1010011 001011110010011 0000011 1010011 0010111
01
01
01
01
00
11
00
10
10
10
10
10
01
10
01
• Controls access to the communication channel.
• Controls the flow of data.• Organizes data into logical frames.• Identifies specific computer on the network.• Detects errors.
Data from upper layers
The Data Link Layer
Application
Presentation
Session
Transport
Network
Data Link
PhysicalPhysical
• Provides electrical and mechanical interfaces for a network.
• Specifies type of media used to connect network devices.
• Specifies how signals are transmitted on the network.
The Physical Layer
OSI Reference Model Layer Layer Name Header Protocols & Services Details
7Application
(All)Protocol Data Unit
Telnet, FTP, SMTP, HTTP, File and Print, E mail, (WWW), EDI, SMB, NCP
User requests network services here. Database and application services but not the applications
6Presentation
(People)Protocol Data Unit
ASCII, EBCDIC, TIFF, JPEG, GIF, PICT, MIDI, MPEG, QuickTime
Data representation and translation. Formats data for “presentation” to the layers above and below. Encryption, compression and translation.
5Session (Seem)
Protocol Data UnitRPC, ZIP, SCP, SQL, X Window, NetBIOS, NFS, ASP, DNA SCP
Establishes, maintains and manages communication sessions between computers. Think dialog control.
4Transport
(To)Segments
TCP, NBP, UDP, NCP, SPX, ADP, Windowing, flow control, synchronization
Reliable transmission of data segments. Sets the stage for disassembly and assembly of data before and after transmission. Remember: end-to-end connectivity.
3Network (Need)
Datagrams or Packets
IP, IPX, RARP, ARP, BootP, DHCP, ICMP, BGP, OSPF, RIP.
If it’s routing, it takes place here. Decides how data will be routed across the network, in addition to the structure and use of logical (IP) addressing. Routers operate here.
2
Data Link Sublayers are MAC and LLC
(Data)
Frames
MAC, LLC, Frame Relay, LAPB, PPP, calculating CRC or FCS, controls access to the physical medium
Deals with the links and mechanisms to move data. Topology (Ethernet or Token Ring) is defined here. Switches and Bridges operate here. Remember: Framing.
1Physical
(Processing) Bits (1s and 0s)
Ethernet, Token Ring, HSSI, 802.3, bit synchronization, physical connector specifications.
The electrical and physical specifications for the network media that carry data bits across a network. Hubs and repeaters operate here.
OSI Layers and Components
Device OSI Model Layer
Hub Layer 1 (physical)
Switches Layer 2 (Data Link)
Bridges Layer 2 (Data Link)
Routers and some switches
Layer 3 (Network)
NICs Layer 1 (physical)
WAPs Layer 1 (physical) andLayer 2 (Data Link)
Physical Layer Topologies
• Bus• Star• Ring• Mesh
A Physical Bus Topology
Terminator TerminatorT-connector T-connectorT-connector
A Physical Star Topology
Hub
Node
A Physical Ring Topology
A Physical Mesh Topology
Physical Layer Devices
• NIC• Transceivers• Repeaters• Hubs• MAUs
The Network Interface Card
• Basic component of a network infrastructure
A Transceiver on a Cable Modem Card
Transceiver chipTransceiver chip
The Repeater
• Repeaters are used to extend the maximum length of a network segment.
• There is a limit to the number of 10Mbps repeaters that can be used in serial on a network without separating them by at least a layer 2 device.
• The 5-4-3 Rule dictates how many repeaters can be used on a network and where they can be placed.
The Hubs
• Passive Hubs– A passive hub is typically unpowered and
makes only physical, electrical connections.
• Active Hubs– An active hub is usually powered and it
actually regenerates and cleans up the signal.
NetTech Solutions
The Multistation Access Unit MAU
• A MAU is a Physical layer device that is unique to Token Ring networks.
The Data Link Layer
• The Data Link layer is actually made up of two sublayers:– The Media Access Control
(MAC) sublayer– The Logical Link Control (LLC)
sublayer
Physical
Data Link MAC
LLC
Data Link Layer Concepts
• Frames– A frame is a unit of data
transmission.
Physical
Data Link
Network
Transport
Bits
Frames
Packets
SegmentsApplication
Messages, Datagrams, or user data
The Hardware MAC Address
• A 48-bit value, commonly represented as a 12-digit hexadecimal number.– Each two-digit set is separated by colons,
like so:– 07:57:AC:1F:B2:76
• The first three sets of digits (07-57-AC) are known as the Organizationally Unique Identifier (OUI)
• The last three sets (1F-B2-76) is referred to as the device ID.
A MAC Address
Operating SystemOperating System MethodMethod
Win9x winipcfg
WinNT/2000/2003/XP ipconfig /all
Linux ifconfig –a
Novell config
Cisco IOS sh int interface_name
Six bytes longSix bytes long
OUI or Company identifier
OUI or Company identifier
Universal LAN MAC address
Universal LAN MAC address
Physical Address. . . . . . . . . : 07-57-AC-1F-B2-76
Finding the MAC address
Logical Topology
• The logical topology dictates the way the information flows.
• The Data Link layer can describe the method of media access.
• Three terms:– Contention– Polling– Token Passing
Media Access Methods
• Common Media Access Methods include:– Media Access
• Contention-based or competitive• Controlled or deterministic
– Multiplexed Media Access– Polling– Token-Based Media Access– CSMA/CD– CSMA/CA– Contention Domains
CSMA/CD
3. Transmit3. Transmit
4. Collision4. Collision
5. Wait5. Wait
1. Data to transmit1. Data to transmit
2. Check network2. Check network
CSMA/CA
5. Transmit5. Transmit6. Monitor for jam signal6. Monitor for jam signal
1. Data to transmit1. Data to transmit
2. Check network2. Check network 3. Jam signal3. Jam signal
4. Wait4. Wait
Contention Domains
Contention Domain A Contention Domain B
Project 802
• One of the major components of the Data Link layer is the result of the Institute of Electrical and Electronics Engineers’s (IEEE’s) 802 subcommittees and their work on standards for local area and metropolitan area networks (LANs/MANs).
Relation to the OSI Model
802 Network standards
• 802.1 LAN/MAN Management (and Media Access Control Bridges)• 802.2 Logical Link Control• 802.3 CSMA/CD• 802.4 Token Bus• 802.5 Token Ring• 802.6 Distributed Queue Dual Bus (DQDB) Metropolitan Area Network (MAN)• 802.7 Broadband Local Area Networks• 802.8 Fiber-Optic LANs and MANs• 802.9 Isochronous LANs• 802.10 LAN/MAN Security• 802.11 Wireless LAN• 802.12 Demand Priority Access Method• 802.15 Wireless Personal Area Network• 802.16 Wireless Metropolitain Area Network• 802.17 Resilient Packet Ring• 802.18 LAN/MAN Standards Committee
Data Link Layer Devices
• Three main devices manipulate data at the Data Link layer:– Bridges– Switches– Wireless access points (WAPs)
Various Network Technologies
Technology Speed(s) Access Method Topologies Media
IEEE 802.3 10, 100, CSMA/CD Logical bus Coax or1000, UTP10,000Mbps
IEEE 802.5 4, 16, Token passing Physical star STP or 100Mbps, logical ring UTP
IEEE 802.11 1, 11, CSMA/CA Cellular RF 54Mbps through air
FDDI 100Mbps Token passing Physical star, Fiber optic logical ring (UTP
implemented as TP-PMD)
Layer Two Devices
• Bridge• Switch
A Bridge Routing Table
3B-07-81-15-AC-10
3B-07-81-72-12-A1
3B-07-81-29-81-83
3B-07-81-82-46-AC
3B-07-81-A3-29-37
3B-07-81-91-76-80
Bridge
Local table for Int 13B-07-81-15-AC-103B-07-81-72-12-A13B-07-81-29-81-83
Local table for Int 13B-07-81-15-AC-103B-07-81-72-12-A13B-07-81-29-81-83
Local table for Int 23B-07-81-82-46-AC3B-07-81-A3-29-373B-07-81-91-76-80
Local table for Int 23B-07-81-82-46-AC3B-07-81-A3-29-373B-07-81-91-76-80
Bridge Broadcasting
Broadcast
Unicast
Types of Bridges
• Transparent: – Connects networks of the same type
(Ethernet and Ethernet)
• Source-route: – Connects Token Ring networks
• Translational: – Connects dissimilar network types
(Ethernet and Token Ring)
• Remote: – Connects different networks across
a remote connection
Routed Network vs. Switched Network
ROUTED vs. SWITCHED
Reads protocol address Reads only MAC address
Sends unknown data to a single gateway Sends unknown data to all interfaces
Blocks broadcasts Forwards broadcasts to all interfaces
Removes MAC addresses and attaches new Does not change address at all
MAC
Leaves the protocol address unchanged
Connections Within a SwitchEight-port switch
Client 1 Server 1 Client 2Server 2
MAC Address Table
Port Address
2 A3:24:A3:3A:DF:23
4 A3:4F:A3:3A:DF:24
5 A3:24:AA:B3:CE:00
7 23:6A:65:AF:AF:01
The Wireless Access Point
• The WAP contains at least one radio antenna that it uses to communicate with its clients via radio frequency (RF) signals.
The OSI Model’s Middle Layers
• The Network Layer• The Transport Layer
Physical
Data Link
Network
Transport
Session
Presentation
Application
Network Layer Concepts
• There are two key concepts in this layer– Logical network addressing– Routing
Logical Network Addressing
• Each device needs two addresses to communicate over a network– Physical address– Logical address
Protocols
• The language of communication for computers.
• IPX/SPX– A 32-bit value represented as an
eight-digit hexadecimal number for the network portion.
Network Address Node Address
00004567:006A7C11FB56
TCP/IP
• A 32-bit value represented as a dotted decimal.– Four Octets separated by a dot.
192.168.0.100
255.255.255.0
IP Address
Subnet Mask
Packets
• The Network Layer divides the information into logical chunks called packets.
Routing
• Routing is the process of moving data throughout an internetwork, passing through several network segments using devices called routers, which select the path the data takes.
• Two ways data can get the information as to where to go.– Static routing table– Dynamic routing table
Static Routing Tables
• Manually configured• Useful on small networks• Lower cost routers• No route discovery traffic on
network
Dynamic Routing Tables
• Uses a routing protocol like:– RIP– OSPF– NLSP– IGRP– EIGRP
The Routing Process
Source100.1.10.19
Destination200.6.42.7
MAC address changes on
each hop
MAC address changes on
each hop
Subnet 1 Subnet 3
Destination IP address does not change
Destination IP address does not change
Subnet 2
Routing Table Information
Routing table on router A
Destination Next Hop Type Cost Interface
140.240.0.0 140.240.20.254 Direct 1 1
192.233.66.0 192.233.66.253 Direct 1 2
135.54.0.0 192.233.66.254 Remote 2 2
126.0.0.0 192.233.66.254 Remote 3 2
140.240.20.254 192.233.66.253 192.233.66.254 135.54.20.254 135.54.15.254 126.0.0.254
140.240.0.0 192.233.66.0 135.54.0.0 126.0.0.0
11 22 11 22 11 22
A B C
Routable and Non-routable
Protocol Routing Protocol Routable
IPX RIP YesIPX NLSP YesNetBEUI None NoTCP RIP YesTCP OSPF YesXNS RIP Yes
Routing Entry Components
Local port address
Local port address
Route cost (in hops)
Route cost (in hops)
Network ID of destinationNetwork ID
of destinationMask for this entryMask for this entry
Address of first hop
Address of first hop
To See the Routing Table
• To view a tcp/ip routing table, at the command prompt, type:c:\route print
• In Cisco IOS type:show ip route
Typical Default Routing Table Entries
Local broadcastLocal broadcast
Internetwork broadcast
Internetwork broadcast
MulticastMulticast
Default gatewayDefault gateway
Local loopbackLocal loopback
Local subnetLocal subnet
Network cardNetwork card
Network Layer Devices
• Routers,• Bridges, and • Switches
Physical
Data Link
Network
Transport
Session
Presentation
Application
The Difference
• Routers block broadcast• Switches allow broadcast• Router work on the Network
layer• Switches work on the Data
Link layer.
Layer 3 Switches
• Performs the multiport, virtual LAN, data-pipelining functions of a standard Layer 2 Switch, but it can also perform basic routing functions between virtual LANs.
Transport Layer
• Transport Layer Concepts– The Connection Type
• Connection-oriented• Connectionless
Physical
Data Link
Network
Transport
Session
Presentation
Application
Transport Layer Implementations
• The IPX/SPX Protocol
Synchronize
Negotiate connection
Synchronize
Acknowledge
Connection established
Actual data transfer(segements)
IPX/SPX Protocol Model
Ethernet IEEE802.3
Token Ring/ IEEE
802.5FDDI ARCnet PPP
IPX
NetBIOSemulator
Physical
Data Link
Network
Transport
Session
Presentation
Application
NetWare shell
(client)
Application NetWare core
protocol (NCP) RPC
RPC based
applicationLU 6.2 support
SPX
The OSI Model’s Upper Layers
• Closest to the User• Controls the way data is
packaged• Responsible for starting,
maintaining, and closing
Physical
Data Link
Network
Transport
Session
Presentation
Application
Network Protocols
• TCP/IP• IPX/SPX• NetBEUI• AppleTalk/AppleTalk over IP
Routing
• The IP address of the sender• The IP address of the destination• The IP address of the next router
to which the packet should be sent
AppleTalk/AppleTalk over IP
• Take note of the table on page 86
AppleTalk Addressing
• Uses an address that is 24 bits long.
• Sixteen of those bits are given to the network, and each network can support 254 nodes.
• First releases were not routable.
• Version 2 is with RTMP
Summary
• Summary and Exam Essentials Page 46
• Written Lab Page 47• Review Questions page
48