CECS 474 Computer Network Interoperability
CHAPTER 20
Internetworking:
Concepts, Architecture, & Protocols
Tracy Bradley Maples, Ph.D.
Computer Engineering & Computer Science
California State University, Long Beach
Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)
Why Internetworking?
"One of the most utterly scintillating notions presented in the text is that there is no
such thing as an internet. Universal service exists by deftly combining software and
hardware into a virtual network system, where the communication system is an
abstraction."
Dr. Jennifer Seitzer
University of Dayton
LANs
• Low cost
• Limited distance
WANs
• High cost
• Unlimited distance
Thus, no single networking technology is best for all needs.
Universal Service
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A fundamental concept in networking
Pioneered by the telephone system
Allows an arbitrary pair of computers to communicate
Highly desirable
Difficult in a heterogeneous world
Heterogeneity
Incompatibilities among networks exist.
There are different:
• Electrical properties
• Signaling and data encoding
• Packet formats
• Physical Addresses
Ultimately:
Although universal service is highly desirable, incompatibilities among network
hardware and physical addressing prevent an organization from building a bridged
network that includes arbitrary technologies.
--Comer
Solution: Build an Internetwork
• Begin with heterogeneous network technologies
• Connect the physical networks
• Create software to make the resulting system appear homogeneous
The result is called an internetwork or internet.
Connecting Heterogeneous Networks
Special purpose computer systems are used to connect heterogeneous networks:
• Dedicated
• Work with LAN or WAN technologies
• Known as an
-- Internet router
-- Internet gateway
An Internet Router
• The cloud denotes an arbitrary network technology
• One interface per network is needed
Main Concept:
A router can interconnect networks that use different technologies, including different
media and media access techniques, physical addressing schemes, or frame formats.
--Comer
Internet Architecture
• Use multiple:
-- Networks
-- Routers interconnecting networks
• The Host computer connects to a network
• A single router has limited
-- CPU power and memory
-- I/O capability
Goal of Internetworking
Create a communication system that is:
• Seamless
• Uniform
• General-purpose
• Universal
• Hides heterogeneity from the user
The Internet Concept
Hiding Heterogeneity
To create a "virtual" network:
Invent
-- An addressing scheme
-- A naming scheme
• Implement with the scheme with protocol software
Note: The protocol software is needed on both hosts and routers.
The Internet Protocols
• Known as TCP/IP
• Many protocols comprise the suite
• Designed to work together
• Divided into five conceptual layers
TCP/IP Layering
Note: This TCP/IP layering is an actual implementation of protocols, unlike the
ISO model.
TCP/IP Layers
Layer 5: Application Layer
• Everything else (i.e., how one application uses the Internet)
• Similar to OSI Layer 6 and 7
Layer 4: Transport Layer
• Specifies how to provide reliable transfer from one application on one
computer to an application on another
• Similar to OSI Layer 4
Layer 3: Internet Layer
• Format of packets
• Mechanisms for forwarding packets
• Not in the OSI Model
Layer 2: Network Interface Layer
• MAC frame format
• MAC addressing
• Interface between computer and the network (i.e., the NIC)
• Similar to OSI Layer 2
Layer 1: Physical Layer
• Basic network hardware
• Similar to OSI Layer 1