IT 210: Web-based IT Fall 2012 Lecture: 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 Layer Web, , File Transfer Transport Layer (TCP) Reliable Connections Internetwork Layer (IP) Simple, Fast, Unreliable Link Layer (Ethernet, WiFi) Physical Connections … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n

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

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

Summary 1. 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 infographic/) infographic/  Censorship in China versus Wikileaks  Lack of “priority” messages for those who can pay  Shutting down the Internet in Egypt  Pornography, viruses, etc.