AN OVERVIEW Rocky K. C. Chang13 Sept. 2010

The web 2

3

4  Web browser in a host  Finding resources (web, search facilities)  DNS: resolving names to IP addresses  HTTP  TCP/IP in the host  Ethernet  Switches  Routers  TCP/IP in the server  HTTP  …

Two layers 5

The web services ( architecture.php) architecture.php 6

Cloud computing 7

The network 8

The network 9

The networking problem 10

The main problem 11  Given some form of “addresses”, how can we send packets of information to another user?

The main problem 12  “Addresses”  “We” and “users”  One or more users?  “Packets of information”  Sent and received?

Other important problems 13  Reliability  Effective sharing of resources  Fair sharing of resources  Providing different types of services  Security  Ease in configuration  Free  …

Layering 14  A layer is an abstraction.  Layering simplifies the task.  Layering based on functionalities or implementations?  Layering requires specified interactions between layers.  Layering does not imply good performance.  Layers are not independent in terms of performance.

A layering example 15

Another layering example 16

A simpler one 17

Protocols 18

Services and protocols 19  Service: an act of helpful activity  Protocol:  the customs and regulations dealing with diplomatic formality, precedence, and etiquette.  an original draft, minute, or record from which a document, esp. a treaty, is prepared.  A formal description of message formats and the rules two computers must follow to exchange those messages.

Protocols 20  Each protocol defines two interfaces:  Service interface: the operations that local objects can perform on the protocol.  Peer interface: the form and meaning of messages exchanged between protocol peers to implement the communication service.

Protocols 21 Protocol entity Message format and interpretation Services Protocol entity Message format and interpretation Services

An example: A 4-layer protocol stack 22

An example: AppleTalk 23

An example: A LTE protocol stack 24

Protocol messages 25  A header and a payload  The header contains sufficient information for implementing the intended services.  The header is an overhead to the payload.  The payload generally contains a header from another protocol.  Protocol encapsulation

The TCP/IP messages 26

The OSI messages 27

Conclusions 28  Web is a driving force for turning the Internet into a “playground” for many.  Two major layers: applications and networks  Other courses devoted to web technologies and development  This course is about the network layer.  Important concepts: layering, protocols, services, protocol messages, and their inter-relationship.

Acknowledgements 29  Thanks to all the sources where the diagrams were extracted from.