Instructor: Christopher Cole Some slides taken from Kurose & Ross book IT 347: Chapter 1

Top-down? Networking layers Application layer = “high growth area” The Web, P2P, media streaming, etc. application presentation session transport network link physical

Internet protocol stack Introduction 1-3 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. application transport network link physical

Encapsulation Introduction 1-4 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch message M HtHt M HnHn frame

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.

What’s a protocol? Introduction 1-7 a human protocol and a computer network protocol: Q: Other human protocols? Hi Got the time? 2:00 TCP connection request TCP connection response Get time

The network edge: Introduction 1-8 end systems (hosts): run application programs e.g. Web, at “edge of network”  client/server model  client host requests, receives service from always-on server  e.g. Web browser/server; client/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Skype, BitTorrent Home network Institutional network Mobile network Global ISP Regional ISP

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 (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

Internet structure: network of networks Introduction 1-13 a packet passes through many networks! Tier 1 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP

Okay, any Questions?

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. d nodal = d proc + d queue + d trans + d prop 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.

Throughput Introduction 1-16 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 server, with file of F bits to send to client link capacity R s bits/sec link capacity R c bits/sec pipe that can carry fluid at rate R s bits/sec) pipe that can carry fluid at rate R c bits/sec) server sends bits (fluid) into pipe

Throughput (more) Introduction 1-17 R s < R c What is average end-end throughput? R s bits/sec R c bits/sec  R s > R c What is average end-end throughput? R s bits/sec R c bits/sec link on end-end path that constrains end-end throughput bottleneck link

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