A special acknowledge goes to J.F Kurose and K.W. Ross Some of the slides used in this lecture are adapted from their original slides that accompany the book “Computer Networking, A Top-Down Approach” All material copyright J.F Kurose and K.W. Ross, All Rights Reserved CS 283Computer Networks Spring 2013 Instructor: Yuan Xue

Roadmap 1.1 Local Area Network  Network edge  direct-link network  multiple access network  end systems, physical media, links, framing, access network 1.2 Internetworking  Network core  network structure, packet switching 1.3 Protocol layers, service models 1.4 Performance  delay, loss and throughput Self-Reading:  Networks under attack: security  History

From host-to-host data delivery to app-to-app communication service Web Serv er brow ser server client MSN client MSN server Two views of Internet : “Infrastructure” and “Service” view

What’s the Internet: “Infrastructure” view  Internet: “network of networks”  loosely hierarchical  public Internet versus private intranet Home network Institutional network Mobile network Global ISP Regional ISP

What’s the Internet: a service view  communication infrastructure supports distributed applications:  Web, VoIP, , games, e-commerce, file sharing  communication services provided to apps:  reliable data delivery from source to destination  “best effort” (unreliable) data delivery

End-to-End Protocols  Problem  Turn host-to-host packet delivery service into a logical communication channel between application processes.  End-to-end protocols of Internet  Multiplexing on a host  port  Different services: UDP –Best effort connectionless TCP –Reliable Connection-oriented »Connection establishment »Reliable transmission »Congestion control

What’s a protocol? human protocols:  “what’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection response Get time TCP connection request

Internet protocol stack: Network layer application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network link physical  network: routing of datagrams from source to destination  link: data transfer between neighboring network elements  physical: bits “on the wire”

Internet protocol stack: Transport layer application transport network data link physical application transport network data link physical logical end-end transport transport network link physical  transport: process- process data transfer  network: routing of datagrams from source to destination  link: data transfer between neighboring network elements  physical: bits “on the wire”

Finally…

Internet protocol stack  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  Ethernet, (WiFi), PPP  physical: bits “on the wire” application transport network link physical

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 Encapsulation message M HtHt M HnHn frame

Stack Deployment Link Network (IP) Network (IP) Transport (TCP) Application (HTTP) Link Network (IP) Transport (TCP) Application (HTTP) Link Network (IP) Link … Internet network End host Physical

Implementation Multi/Demultiplex port CW port Congestion window port Congestion window port HTTP Application Transport Network Link Fragment/Reassemble Forward Routing IP Address Routing table Forwarding table IEEE SMTPFTP UDPTCP CW port Stream Frame Packet payload Transport header (e.g.TCP) payload IPTCP payloadIPTCPMAC Skype User space OS Kernel Hardware

ISO/OSI reference model  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine- specific conventions  session: synchronization, checkpointing, recovery of data exchange  Internet stack “missing” these layers!  these services, if needed, may be implemented in application/transport layer application presentation session transport network link physical

Why layering? Dealing with complex systems:  explicit structure allows identification, relationship of complex system’s pieces  modularization eases maintenance, updating of system  change of implementation of layer’s service transparent to rest of system  Allow the growth of a healthy eco-system  Google, MS, cisco, Sprint, etc..  layering considered harmful?

Roadmap 1.1 Local Area Network  Network edge  direct-link network  multiple access network  end systems, physical media, links, framing, access network 1.2 Internetworking  Network core  network structure, packet switching 1.3 Protocol layers, service models 1.4 Performance  delay, loss and throughput Self-Reading:  Networks under attack: security  History

Understand and Measure Internet Performance

How do loss and delay occur? packets queue in router buffers  packet arrival rate to link exceeds output link capacity  packets wait in a buffer (queue) A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers

Four sources of packet delay A B propagation transmission nodal processing queueing d nodal = d proc + d queue + d trans + d prop d proc : nodal processing  check bit errors  determine output link  typically < msec d queue : queueing delay  time waiting at output link for transmission  depends on congestion level of router d trans : transmission  Recall its calculation

Four sources of packet delay A B propagation transmission nodal processing queueing d nodal = d proc + d queue + d trans + d prop d trans : transmission delay:  L: packet length (bits)  R: link bandwidth (bps)  d trans = L/R d prop : propagation delay:  d: length of physical link  s: propagation speed in medium (~2x10 8 m/sec)  d prop = d/s d trans and d prop very different

 R: link bandwidth (bps)  L: packet length (bits)  a: average packet arrival rate traffic intensity = La/R  La/R ~ 0: avg. queueing delay small  La/R -> 1: avg. queueing delay large  La/R > 1: more “work” arriving than can be serviced, average delay infinite! average queueing delay La/R ~ 0 Queueing delay (revisited) La/R -> 1

Packet loss  queue (aka buffer) preceding link in buffer has finite capacity  packet arriving to full queue dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not at all A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)

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

Throughput (more)  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

Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec RsRs RsRs RsRs RcRc RcRc RcRc R  per-connection end-end throughput: min(R c,R s,R/10)  in practice: R c or R s is often bottleneck

Throughput (more)  If the sender sends the data at R s bits/sec, but the receiver receives the data at R r bits/sec (< R s bits/sec), where is the rest of data?  Can a sender ask for a reliable data transfer service at rate R s bits/sec on Internet?  How can I measure the maximum possible throughput for my application(flow/traffic)?

How to perform measurement  Delay/Route  Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:  sends three packets that will reach router i on path towards destination  router i will return packets to sender  sender times interval between transmission and reply. 3 probes

Demo traceroute: traceroute: Points of interest: Three delay measurements trans-oceanic link no response (probe lost, router not replying) Etc…

How to perform measurement  TCP/UDP Bandwidth, UDP loss  iperf tool: provides measurement of maximum TCP and UDP bandwidth performance and reports bandwidth, delay jitter, datagram loss.  Iperf demo