Transcript Chapter 1 -- Protocols - California State University, Long Beach

CECS 474 Computer Network Interoperability
CHAPTER 1
Network Protocols
Tracy Bradley Maples, Ph.D.
Computer Engineering & Computer Science
Cal ifornia State University, Long Beach
Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)
Protocol Suites and Layering Models
Defn: Protocols are agreements about how communication should take place.
They specify:
 Format of messages
 Meaning of messages
 Rules for exchanging messages
 Procedures for handling problems
Network hardware functions at a very low level.
Hardware related problems can occur that need to be addressed by protocols:
 Bits can be corrupted or destroyed
 Entire packets can be lost
 Packets can be duplicated
 Packets can be delivered out of order
2
Protocols can also be used to distinguish among:
 Multiple computers on a network
 Multiple applications on a computer
 Multiple copies of a single application on a computer
Sets of Protocols
 Sets of protocols are designed to work together.
 Each protocol solves a small part of the communications problem
 Sets of protocols are known as:
-- Protocol Suites
-- Protocol families
 They are designed in layers.
3
Protocol Design
 Protocols are divided into layers
 Each layer is devoted to one sub-problem
Example: The ISO (International Standards
Organization) OSI (Open System Interconnection) 7layer Reference Model
The OSI 7-Layer Model
The 7-Layer Model:
 Was defined fairly early in the development of networks
 Is now somewhat dated
 Does not include the internet layer
4
The OSI 7-Layers
Layer 1: Physical
 The underlying hardware
Layer 2: Data Link (media access)
 Hardware frame definitions
Layer 3: Network
 Packet forwarding
Layer 5: Session
 Login and passwords
Layer 6: Presentation
 Data representation
Layer 7: Application
 Individual application programs
Layer 4: Transport
 Reliability
5
The Layering Model
Protocol software follows the
layering model, with:
 One software module per layer
 Modules that work together
 Incoming or outgoing data
passing from one module to
another
The entire set of protocol
layers (or modules) is known
as a stack.
6
Layers and Packet Headers
Each layer:
 Prepends a header to the outgoing packet
 Removes a header from the incoming packet
This process is known as data encapsulation.
7
Layering Principle
Software implementing layer N at the destination receives exactly the message sent
by software implementing layer N at the source. --Comer
8
TCP/IP Layering
Notwithstanding the push by researchers to adopt the OSI model, it became clear
that TCP/IP was technically more flexible and superior. TCP/IP is the primary protocol
stack used today.
Note: This TCP/IP layering is an actual implementation of protocols, unlike the ISO model.
9
TCP/IP Layers
Layer 1: Physical
 Basic network hardware
 Similar to OSI Layer 1
Layer 2: Network Interface
 MAC frame format
 MAC addressing
 Interface between computer
and the network (i.e., the NIC)
 Similar to OSI Layer 2
Layer 3: Internet
Layer 4: Transport
 Specifies how to provide reliable
transfer from one application on
one computer to an application
on another
 Similar to OSI Layer 4
Layer 5: Application
 Everything else (i.e., how one
application uses the Internet)
 Similar to OSI Layer 6 and 7
 Format of packets
 Mechanisms for forwarding
packets
 Not in the OSI Model
10