Layering in Networked Computing: OSI Model TCP/IP Model Protocols at Each Layer
Layering in Networked Computing: OSI Model TCP/IP Model Protocols at Each Layer
Layering in Networked Computing: OSI Model TCP/IP Model Protocols at Each Layer
OSI Model
TCP/IP Model
Protocols at each layer
Learning outcomes
Hardware Hardware
& &
Software Software
1
DEVICE A DEVICE B
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Evolution of the 7-Layers (1)
Application Application
Technical Technical
Standards Standards
Two Layer Model
– Problem: Applications were being developed to run over ever-increasing
number of media/signaling systems.
– Solution: Separate application aspects from technical (signaling and routing)
aspects
– Application Layer: Concerned with user interface, file access and file transfer
1
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Evolution of the 7-Layers (3)
Application Application
Network Network
Data-Link Data-Link
Physical Physical
• Physical Layer
–Describes physical aspects of network: cards, wires, etc
–Specifies interconnect topologies and devices
• Network Layer
–Defines a standard method for operating between nodes
–Address scheme is defined (IP)
–Accounts for varying topologies
• Data-Link
–Works with Network Layer to translate logical addresses (IP) into hardware
addresses (MAC) for transmission
–Defines a single link protocol for transfer between two nodes
Evolution of the 7-Layers (4)
Application Application
Transport Transport
Network Network
Data-Link Data-Link
Physical Physical
• Five Layer Model – Increase Quality of Service (QOS)
•Variable levels of data integrity in network 1
•Additional data exchanges to ensure connectivity over worst conditions
•Became the Transport Layer
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Evolution of the 7-Layers (5)
Application Application
Session Session
Transport Transport
Network Network
Data-Link Data-Link
Physical Physical
• Six Layer Model - Dialogue Control and Dialogue Separation
– Means of synchronizing transfer of data packets
– Allows for checkpointing to see if data arrives (at nodes and end
stations) 1
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Evolution of the 7-Layers (6)
Application Application
Presentation Presentation
Session Session
Transport Transport
Network Network
Data-Link Data-Link
Physical Physical
2
Gives end-user applications access
to network resources
Where is it on my computer?
– Workstation or Server Service in
MS Windows
3
Presentation Layer
3
Session Layer
Allows applications to
maintain an ongoing session
Where is it on my
computer?
– Workstation and Server
Service (MS)
– Windows Client for
NetWare (NetWare)
3
Transport Layer
Responsibilities:
– Network addressing
– Routing
Example:
– IP from TCP/IP 3
Network layer
Network-wide addresses
Used to transfer data across subnets
Used by routers for packet forwarding
Example:
– IP Address
Where is it on my computer?
– TCP/IP Software
Data Link Layer
3
Data link layer
7 - Application All
6 - Presentation People
5 - Session Seem
4 - Transport To
3 - Network Need
2 - Data Link Data
1 - Physical Processing
TCP/IP model development
Layer 4: Application
Layer 3: Transport
Layer 2: Internet
Layer 1: Network access
The application layer
Layer Protocols
Internet IP ICMP
Network Access
ETHERNET PACKET RADIO
(Host-to-network)
Protocols at the application layer
HTTP:
– browser and web server communicatin
FTP :
– file transfer protocol
TELNET:
– remote login protocol
POP3: Retrieve email
– POP3 is designed to delete mail on the server as soon as the user has
downloaded it
Reliable
IP
– Path selection ,
– routing and addressing
ICMP (Internet Control Message Protocol )
– sends error messages relying on IP
a requested service is not available
a host or router could not be reached
Protocols at the link layer
Ethernet
– Uses CSMA/CD
Token Ring
Data Formats
Application data message
application
layer
network IP TCP
packet
layer header header data
64 to 1500 Bytes
Comparing TCP/IP with OSI
OSI Model TCP/IP Hierarchy Protocols
7th
Application Layer
6th
Presentation Layer Application Layer
5th
Session Layer
4th
Transport Layer
Transport Layer
3rd
Network Layer
Network Layer
2nd
Link Layer
Link Layer
1st
Physical Layer
OSI
OSI Model Equipment Words to TCP/IP
Model Pneumonic Equipment Data Protocols
Name Purpose Remember Model
Layer
Redirector,
Layer 7 Application All FTP, Telnet, Browsers Application
Regular Computer SMTP,
or A Special SNMP, Common Data
Layer 6 Presentation People Computer Data Application
Gateway. Used to Netware Format
combine networks Core
using different NFS, SQL, Dialogues and
Layer 5 Session Seem communication Application
RPC, X-Win Conversations
protocols Quality of
Layer 4 Transport To Computer Segment TCP and UDP Service, and Transport
Reliability
Segment Network Routable
Path Selection,
into Smaller Protocols.
Layer 3 Network Need Router Packet Routing, and Internet
Broadcast (IP, IPX,
Addressing
AppleTalk)
Domains
Bridge (2
Data Link Segment Network NDIS, ODI, Frames and
Ports) or Network
Layer 2 -MAC Data into Smaller Frame MAC Address, Media Access
Switch and Ether Talk Control (MAC) Access
-LLC Collision Domains
NIC
Repeater,
One Collision AND
Hub (Multi- Signals and Network
Layer 1 Physical Processing One Broadcast Bit Physical
Media
port), Access
Domain
Cabling
Internet applications
Example of servers
– File servers
– Web servers
Example of client applications
– Browsers
– Email clients
What is a socket?
Port 1
3 http://www.hawkclan.com/zxonly/iso/slide2.html
4 http://www.pku.edu.cn/academic/research/computer-
center/tc/html/TC0102.html, William L. Whipple &
Sharla Riead, 1997.