程序代做CS代考 dns Week 1 – Introduction to Networking Continued – cscodehelp代写

Week 1 – Introduction to Networking Continued
COMP90007 Internet Technologies
Lecturer: Semester 2, 2021
© University of Melbourne 2021
1

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
5

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
6

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
8

OSI Reference Model
 Open Systems Interconnection (OSI)
 ISO, (revised 1995)
 7 Layers
 Layer divisions based on principled decisions
9

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
16

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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