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.