@Yuan Xue 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 2011 Instructor: Yuan Xue

@Yuan Xue Synthesis: a day in the life of a web request journey down protocol stack complete! application, transport, network, link putting-it-all-together: synthesis! goal: identify, review, understand protocols (at all layers) involved in seemingly simple scenario: requesting www page scenario: student attaches laptop to campus network, requests/receives

@Yuan Xue A day in the life: scenario Comcast network /13 Google’s network / web server DNS server school network /24 browser web page

@Yuan Xue A day in the life… connecting to the Internet connecting laptop needs to get its own IP address, addr of first-hop router, addr of DNS server: use DHCP router (runs DHCP) DHCP UDP IP Eth Phy DHCP UDP IP Eth Phy DHCP  DHCP request encapsulated in UDP, encapsulated in IP, encapsulated in Ethernet frame  Ethernet frame broadcast (dest: FFFFFFFFFFFF ) on LAN, received at router running DHCP server  Ethernet demuxed to IP demuxed, UDP demuxed to DHCP

@Yuan Xue A day in the life… connecting to the Internet DHCP server formulates DHCP ACK containing client’s IP address, IP address of first-hop router for client, name & IP address of DNS server router (runs DHCP) DHCP UDP IP Eth Phy DHCP UDP IP Eth Phy DHCP  encapsulation at DHCP server, frame forwarded (via switch) through LAN, demultiplexing at client Client now has IP address, knows name & addr of DNS server, IP address of its first-hop router  DHCP client receives DHCP ACK reply

@Yuan Xue A day in the life… ARP (before DNS, before HTTP) before sending HTTP request, need IP address of DNS DNS UDP IP Eth Phy DNS  DNS query created, encapsulated in UDP, encapsulated in IP, encapsulated in Eth. In order to send frame to router, need MAC address of router interface: ARP  ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router interface  client now knows MAC address of first hop router, so can now send frame containing DNS query ARP query Eth Phy ARP ARP reply

@Yuan Xue A day in the life… using DNS DNS UDP IP Eth Phy DNS  IP datagram containing DNS query forwarded via LAN switch from client to 1 st hop router  IP datagram forwarded from campus network into comcast network, routed (tables created by RIP, OSPF, IS-IS and/or BGP routing protocols) to DNS server  demuxed to DNS server  DNS server replies to client with IP address of Comcast network /13 DNS server DNS UDP IP Eth Phy DNS

@Yuan Xue A day in the life… TCP connection carrying HTTP HTTP TCP IP Eth Phy HTTP  to send HTTP request, client first opens TCP socket to web server  TCP SYN segment (step 1 in 3-way handshake) inter- domain routed to web server  TCP connection established! web server SYN TCP IP Eth Phy SYN SYNACK  web server responds with TCP SYNACK (step 2 in 3- way handshake)

@Yuan Xue A day in the life… HTTP request/reply HTTP TCP IP Eth Phy HTTP  HTTP request sent into TCP socket  IP datagram containing HTTP request routed to  IP datagram containing HTTP reply routed back to client web server HTTP TCP IP Eth Phy  web server responds with HTTP reply (containing web page) HTTP  web page finally (!!!) displayed

@Yuan Xue Summary – what we’ve learnt How to use the Internet How Internet is designed -- journey down the protocol stack Why Internet is designed so (is it good?) -- design principle Build network application using socket programming Use existing tools/softwares (nslookup, ifconfig, tracert, Wireshark, etc) Application Transport Network Data Link Phy Congestion contr. Routing Algorithm Media access contr. Reliable data delivery

@Yuan Xue Internet History – Looking back  1961: Kleinrock - queueing theory shows effectiveness of packet-switching  1964: Baran - packet- switching in military nets  1969: first ARPAnet node operational  1972:  ARPAnet public demonstration  ARPAnet has 15 nodes : Early packet-switching principles

@Yuan Xue Internet History  1970: ALOHAnet satellite network in Hawaii  1974: Cerf and Kahn - architecture for interconnecting networks  1976: Ethernet at Xerox PARC  late70’s: proprietary architectures: DECnet, SNA, XNA  late 70’s: switching fixed length packets (ATM precursor)  1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best effort service model  stateless routers  decentralized control define today’s Internet architecture : Internetworking, new and proprietary nets

@Yuan Xue Internet History  1983: deployment of TCP/IP  1982: smtp protocol defined  1983: DNS defined for name-to-IP-address translation  1985: ftp protocol defined  1988: TCP congestion control  new national networks: Csnet, BITnet, NSFnet, Minitel  100,000 hosts connected to confederation of networks : new protocols, a proliferation of networks

@Yuan Xue Internet History  early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web  hypertext [Bush 1945, Nelson 1960’s]  HTML, HTTP: Berners-Lee  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps

@Yuan Xue Internet – Today and Moving forward 2010:  ~750 million hosts (IPv4 address running out)  Web becomes the new network application platform: YouTube, facebook, twitter  Web 2.0, social network  Wireless and mobile network, smart phone  Cloud computing  Cyber-physical systems  Sensors  Internet of things

@Yuan Xue Remember Akamai?

@Yuan Xue Internet Design What succeeds? HTTP, TCP/IP, Ethernet What fails? “Rich Seifert Top Ten List of Stupid Networking Ideas'‘ 1. ATM 2. IPv6 6. Jumbo frames 7. ISO Protocol Suite IP multicast FDDI IntServ

@Yuan Xue 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

@Yuan Xue 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, must be implemented in application  needed? application presentation session transport network link physical

@Yuan Xue Some Thoughts on Internet Design Packet switching (sharing/multiplexing) The end-to-end principle “whenever possible, protocol operations should be defined to occur at the end-points of a communications system, or as close as possible to the resource being controlled.” one of the central design principles of the Internet E.g., IP multicast  application-layer multicast; reliability at TCP and wireless network. Network design (core) needs to be simple; push the complexity to the end host (edge). Simple IP, complex application layer

@Yuan Xue Some Thoughts on Internet Design One idea to scalability  hierarchical design No state and soft state is better than hard state HTTP Randomness can simplify management CSMA Being adaptive to handle dynamics TCP Ethernet/WiFi What drives the Internet development? Killer application Economical/management consideration Sometimes, principle and theory

@Yuan Xue Move forward – from what we’ve learnt How to use the Internet How Internet is designed -- journey down the protocol stack Why Internet is designed so -- design principle Jobs everywhere.. Manage network -Troubleshooting Develop network app Develop web app Develop smartphone app ISP Cisco,huawei etc Networking research

@Yuan Xue Move forward Network Security  next semester Network Management Wireless and Mobile Network Sensor network Emerging Application and System Peer-to-peer systems Content-distribution network Cloud Quality of Service