Week 1 – Introduction to Networking Continued
COMP90007 Internet Technologies
Lecturer: Semester 2, 2021
© University of Melbourne 2021
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Recap: Protocol Hierarchies
Exampleinformationflowsupportingthevirtualcommunicationinlayer5
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Relationship of Services and Protocols
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Relationship of Services and Protocols
Service = set of primitives that a layer provides to a
layer above it
Provided through the interfaces between layers (service provider vs. service users)
Defines what operations the layer is prepared to perform on behalf of its users
Abstract: nothing about how these operations are implemented
Protocol = a set of rules governing the format and meaning of packets that are exchanged by peers within a layer
Packets sent between peer entities
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Relationship of Services and Protocols
Object-Oriented Programming
public class Car
{
public int fuel;
public int speed;
public String plate_num;
public void accelerate(int num)
{…}public void decelerate (int num)
{…} }
Interface:
• Comments • Headings
of methods
services protocols
user
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Reference Models
• The OSI Reference Model
• The TCP/IP Reference Model
• A Comparison of OSI and TCP/IP
• A Critique of the OSI Model and Protocols
• A Critique of the TCP/IP Reference Model
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Reference Model
Concepts and their relationship
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Why Do We Need a Reference Model?
A reference model provides a common baseline for the development of many services and protocols by independent parties
It’s engineering best practice to have an “abstract” reference model, and corresponding implementations are always required for validation purposes
Since networks are very complex systems, a reference model can serve to simplify the design process
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OSI Reference Model
Open Systems Interconnection (OSI)
ISO, (revised 1995)
7 Layers
Layer divisions based on principled decisions
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OSI Layer Division Principles
1. Alayershouldbecreatedwhereadifferentabstraction is needed.
2. Eachlayershouldperformawell-definedfunction.
3. Thelayerboundariesshouldbechosentominimisethe
information flow across the interfaces.
4. Thenumberoflayersshouldbelargeenoughthat distinct functions need not to be thrown together in the same layer out of necessity; and small enough that the architecture does not become unwieldy.
5. Thefunctionofeachlayershouldbechosenwithaview toward defining internationally standardised protocols.
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OSI Reference Model
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TCP/IP Reference Model
Transmission Control Protocol/Internet Protocol
& (1974) 4 layers
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TCP/IP Reference Model (2)
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TCP/IP Reference Model (3)
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Comparing OSI and TCP/IP Models
Different numbers of layers
OSI distinguishes the following three concepts explicitly
Services Interfaces Protocols
TCP/IP has successful protocols
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A Critique of the OSI Model
Why OSI did not take over the world? Bad technology
Bad implementations
Bad timing
Bad politics
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A Critique of the OSI Model: Bad Timing
When is good timing for a standard?
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A Critique of the TCP/IP Model
Problems:
Not a general model
Service, interface, and protocol not distinguished
Did not split physical and data link layers
Minor protocols deeply entrenched, hard to replace
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Hybrid Model
The hybrid reference model to be used in this subject
A typical network scenario Browser Server
HTTP
TCP
IP
802.11
HTTP
TCP
IP
802.11
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Origins of Internet: The ARPANET
(a) Structure of the telephone system.
(b) Baran’s proposed distributed switching system.
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The ARPANET
Growth of the ARPANET (a) December 1969. (b) July 1970. (c) March 1971. (d) April 1972. (e) September 1972.
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Architecture of the Internet
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Network Standardisation
Body
Area
Examples
ITU (International Telecommunication Union)
Telecommunications
ADSL MPEG4
IEEE (Institute of Electrical and Electronics Engineers)
Communications
Ethernet WiFi
IETF (Internet Engineering Task Force)
Internet
HTTP/1.1 DNS
W3C (The World Wide Web Consortium)
Web
HTML5 standard
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