A. Zahid, EE450 1
Network Layered ArchitectureOSI Reference Model & TCP/IP Protocol Suite
Professor A. ZahidEE450: Computer Networks
A. Zahid, EE450 2
ProtocolsHuman Protocols:• what’s the time?• I have a question• Introductions
… specific msgs sent… specific actions
taken when msgs received, or other events
Network Protocols:• Machines rather than
humans• All communication
activity in Internet governed by protocols
Protocols define format, order of msgs sent and received
among network entities, and actions taken on msg transmission, receipt
A. Zahid, EE450 3
Get http://www.cnn.com/politics.html
Human v.s. Network Protocols
Hi
Hi
Got thetime?
2:00
TCP connectionrequest
TCP connectionreply
<file>time
A. Zahid, EE450 4
Key Elements of a Protocol
• Syntax– Data formats, compression, encryption, etc..– Signal levels
• Semantics– Control information such as flow & congestion– Error detection and control mechanisms
• Timing– Speed matching– Sequencing
A. Zahid, EE450 5
Standards• Required to allow for interoperability
between equipment• Advantages
– Ensures a large market for equipment and software
– Allows products from different vendors to communicate
• Disadvantages– Freeze technology
A. Zahid, EE450 6
OSI Reference Model
A. Zahid, EE450 7
Data Transmission in OSI Model
A. Zahid, EE450 8
Summary of Layer Functions
A. Zahid, EE450 9
The Internet is based on TCP/IP
A. Zahid, EE450 10
TCP/IP Protocol Suite• Developed by the US Defence Advanced Research
Project Agency (DARPA) for its packet switched network (ARPANET)
Application Layer
Transport (TCP) Layer
Network (IP) Layer
Network Access (Data Link) Layer
Physical Layer
A. Zahid, EE450 11
TCP/IP Protocol Suite & OSI
A. Zahid, EE450 12
Layer Communications
• Peer layers communicate via protocols• Adjacent layers communicate via service
interfaces• Protocol control information (PCI) is added
to Service data unit (SDU) at each layer to form a Protocol data unit (PDU)– (SDU)N = (PDU)N+1
– (PDU)N = (SDU)N +(PCI)N
A. Zahid, EE450 13
Protocol Data Unit (PDU)User/Application Data
Transport layer header
Transport layer PDU
Network layer headerNetwork layer PDU
A. Zahid, EE450 14
Layering: Logical CommunicationsEach layer:• distributed• “entities”
implement layer functions at each node
• entities perform actions, exchange messages with peers
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical application
transportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
data
transport
transport
ack
A. Zahid, EE450 15
Layering: Physical Communicationsapplicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
A. Zahid, EE450 16
Layered Architecture & Networks
• Each host needs a unique global address referred to as the IP address
• Each application on a multitaskingcomputer needs a unique address, referred to as the Port number, within the computer