IT 347: Chapter 1 Instructor: Christopher Cole Some slides taken from Kurose & Ross book
application presentation session transport network link physical Top-down? • Networking layers • Application layer = “high growth area” • The Web, P2P, media streaming, etc.
application transport network link physical Internet protocol stack • application: supporting network applications – send messages • FTP, SMTP, HTTP • transport: process-process data transfer – send segments • TCP, UDP • network: routing of datagrams from source to destination • IP, routing protocols • link: data transfer between neighboring network elements – send frames • PPP, Ethernet • physical: bits “on the wire” • Ethernet over twisted pair, coax, fiber, etc. Introduction
network link physical link physical M M M Ht M Hn Hn Hn Hn Ht Ht Ht Ht M M M M Ht Hn Ht Hl Hl Hl Hn Hn Hn Ht Ht Ht M M M source Encapsulation message application transport network link physical segment datagram frame switch destination application transport network link physical router Introduction
Hosts or End Systems • Computer, laptop, phone, gaming consoles, web cams, TVs (security systems, toasters, etc.) • Connected together with • Communication links (twisted pair, coax, fiber) • Packet switches (routers or link-layer switches) • Information is sent (and split up into) packets (header added to each package) • Transmission rate (each link is different)
ISPs connect you to the internet • Protocols control what happens • TCP and IP are important to internet • Internet standards by Internet Engineering Task Force (IETF) • They put out Requests for Comments (RFCs) • Define HTTP, SMTP, etc. • Project 1 has the protocol of creating a client-server program.
TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi Q: Other human protocols? Introduction
Mobile network Global ISP Home network Regional ISP Institutional network The network edge: • end systems (hosts): • run application programs • e.g. Web, email • at “edge of network” • client/server model • client host requests, receives service from always-on server • e.g. Web browser/server; email client/server • peer-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent Introduction
How do you connect? • Dial-up • Cable • shared • DSL • Downstream 50 kHz to 1 Mhz • Upstream 4 kHz to 50 kHz • Phone 0 to 4 kHz • Fiber to Home • FIOS (also shared?) • Other • WiMAX, 3G access • http://www.wigle.net (wireless networks)
Physical Media • Often, the cost is not the physical link, but the labor of installation • Twisted Pair Copper • 1 Gbps (faster now?) • Coaxial Cable • Fiber Optics • Incredibly long distances (overseas) • Internet Backbone • Satellite (hundreds of Mbps) • Radio
Packet Switching • Packets (long messages split up) • Source & Destination address • Go through each switch • Output queue • Packet loss • Circuit switching/packet switching • How does a packet get through? Forwarding table
ISPs and Internet Backbones • Relatively small number of Tier 1 ISPs all linked together (Sprint, Verizon, MCI, AT&T, Level3, Qwest) • How do you know if you are Tier 1? • These are Internet Backbone networks • Tier 2 are customers of Tier 1 and providers to rest • Sometimes peer with each other
Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks • a packet passes through many networks! Tier 1 ISP Tier 1 ISP Tier 1 ISP Introduction
Delays • Processing Delay: time it takes for router to read header of packet (microseconds) • Queuing Delay: time to wait in line to get pushed to the wire (0 time if there is nobody in the queue) • Transmission Delay: Time to push the packet out onto the wire. Depends on the speed of the link and length of packet. Packet Length = L bits, link speed = R Mbps. Transmission delay = L/R • Propagation Delay: depends on the distance between the two routers. d is distance between routers, and s is propagation speed of link (typically 2x10^8 meters/sec to 3). Measure d/s. • dnodal = dproc + dqueue + dtrans + dprop • traffic intensity: L/R is in important number again. If a is the average queuing delay, La/R should never be > 1 (otherwise packets will just stack up) • Other delays: modulation/encoding delay for modems, etc.
pipe that can carry fluid at rate Rsbits/sec) pipe that can carry fluid at rate Rcbits/sec) Throughput • throughput: rate (bits/time unit) at which bits transferred between sender/receiver • instantaneous: rate at given point in time • average: rate over longer period of time link capacity Rcbits/sec link capacity Rsbits/sec server, with file of F bits to send to client server sends bits (fluid) into pipe Introduction
Rs > RcWhat is average end-end throughput? Rsbits/sec Rcbits/sec Rcbits/sec bottleneck link link on end-end path that constrains end-end throughput Throughput (more) • Rs < RcWhat is average end-end throughput? Rsbits/sec Introduction
Network Security • The internet was not made with security in mind • SMTP protocol • Denial of Service attacks • Anybody can sniff packets • IP spoofing • Man in the middle attacks