IT 210:Web-based IT

Fall 2012Lecture: Network Basics, OSI, &

Internet Architecture

Outline for Today Network OSI Model Internet Architecture

Networks & OSI Model

Networks

Networks : Building Blocks Nodes: PC, smartphone, special-purpose

hardware… hosts switches

Links: coax cable, optical fiber, wireless connection… point-to-point

multiple access…

OSI Model

Models

Abstraction

Layers

Internet Architecture

Internet Protocols and the OSI Model

Ref: From Foruzan Text

Internet Protocol Suite

Key Internet Protocols: IP/TCP

Protocols for transferring data across multiple networks (e.g., the Internet)

Properties Vendor-independent (nobody owns them) Work with different network types,

hardware addressing schemes, and routes “end-to-end” principle (sort of…) Use layered approach (abstraction) to

create virtual network Resilient to broken nodes in network

Layers in TCP/IP Model

Application LayerApplication LayerWeb, E-Mail, File TransferWeb, E-Mail, File Transfer

Transport Layer (TCP)Transport Layer (TCP)Reliable ConnectionsReliable Connections

Internetwork Layer (IP)Internetwork Layer (IP)Simple, Fast, UnreliableSimple, Fast, Unreliable

Link Layer (Ethernet, WiFi)Link Layer (Ethernet, WiFi)Physical ConnectionsPhysical Connections …

FTP HTTP NV TFTP

TCP UDP

IP

NET1 NET2 NETn

Internet Protocol (IP) Provides connectionless packet delivery Defines:

Internet addressing scheme Format of packets Packet forwarding

IP datagram = IP Internet packet with header (source, destination, type) and data

Packets may arrive out of order or not at all

IP Addresses Assigned to destination points such as computers

or servers (*defines a connection, not a device) Composed of 2 parts: network ID (prefix assigned

by ISPs) and host ID (suffix assigned by local sysadmin)

Classful addressing (first bits specify size of prefix and suffix) allows for mixture of large and small networks

216.24.63.132

Transmission Control Protocol (TCP)

Purpose is to assure reliability given IP’s unreliable nature

Keeps a copy of sent data packets until receives an acknowledgement of their receipt

If it takes too too long then sends again Orders packets Provides individual connections

between applications

UDP vs. TCP

Summary1. Information broken into packets that are

labeled with an IP address. IP addresses indicate a destination network (via its prefix) and destination host connection (via its suffix)

2. Packets sent across network to IP router, which forwards to the “next” router, until final router delivers to destination network. Packets may be received out of order or even be lost.

3. TCP assures reliability by verifying receipt and order of packets.

A Look Under the Hood!

Social, political, and economic implications of Internet Architecture Stop Online Piracy Act (see

http://mashable.com/2011/11/16/sopa-infographic/)

Censorship in China versus Wikileaks Lack of “priority” messages for those who

can pay Shutting down the Internet in Egypt Pornography, viruses, etc.