CSI 450 Review

Introduction What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts = end systems running network apps  communication links  fiber, copper, radio, satellite  transmission rate: bandwidth  Packet switches: forward packets (chunks of data)  routers and switches wired links wireless links router mobile network global ISP regional ISP home network institutional network smartphone PC server wireless laptop 1-2

Introduction Internet: “network of networks” Interconnected ISPs protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Internet standards RFC: Request for comments IETF: Internet Engineering Task Force What’s the Internet: “nuts and bolts” view mobile network global ISP regional ISP home network institutional network 1-3

What’s the Internet: a service view Infrastructure that provides services to applications: Web, VoIP, , games, e- commerce, social nets, … provides programming interface to apps hooks that allow sending and receiving app programs to “connect” to Internet provides service options, analogous to postal service mobile network global ISP regional ISP home network institutional network Introduction 1-4

Introduction 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 1-5

Network Layer4-6 Two key network-core functions forwarding : move packets from router’s input to appropriate router output routing: determines source- destination route taken by packets  routing algorithms routing algorithm local forwarding table header value output link dest address in arriving packet’s header

Introduction 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 1-7

ISO/OSI reference model

Introduction 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 1-9

Internet protocol stack

Encapsulation Of Application Data As It Moves Through The Layers Described In RFC 1122

Client-Server Architecture

Processes

Application Processes Sockets Process Socket TCP with buffers, variables Process Socket TCP with buffers, variables Internet

COMMON PORTS KNOW THESE

Introduction Internet history 1961: Kleinrock - queueing theory shows effectiveness of packet- switching 1964: Baran - packet- switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet public demo NCP (Network Control Protocol) first host-host protocol first program ARPAnet has 15 nodes : Early packet-switching principles 1-16

Introduction 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 Internet history 1-17

Introduction 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 Internet history 1-18

Introduction 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 Internet history 1-19

Introduction 2005-present ~750 million hosts Smartphones and tablets Aggressive deployment of broadband access Increasing ubiquity of high-speed wireless access Emergence of online social networks: Facebook: soon one billion users Service providers (Google, Microsoft) create their own networks Bypass Internet, providing “instantaneous” access to search, emai, etc. E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2) Internet history 1-20

Securing TCP TCP & UDP no encryption cleartext passwds sent into socket traverse Internet in cleartext SSL provides encrypted TCP connection data integrity end-point authentication SSL is at app layer Apps use SSL libraries, which “talk” to TCP SSL socket API  cleartext passwds sent into socket traverse Internet encrypted  See Chapter 7 Application Layer 2-21

Application Layer2-22 Web caches (proxy server) user sets browser: Web accesses via cache browser sends all HTTP requests to cache object in cache: cache returns object else cache requests object from origin server, then returns object to client goal: satisfy client request without involving origin server client proxy server client HTTP request HTTP response HTTP request origin server origin server HTTP response

Application Layer2-23 More about Web caching cache acts as both client and server server for original requesting client client to origin server typically cache is installed by ISP (university, company, residential ISP) why Web caching? reduce response time for client request reduce traffic on an institution’s access link Internet dense with caches: enables “poor” content providers to effectively deliver content (so too does P2P file sharing)

Transport Layer 3-24 Internet transport-layer protocols reliable, in-order delivery (TCP) congestion control flow control connection setup unreliable, unordered delivery: UDP no-frills extension of “best-effort” IP services not available: delay guarantees bandwidth guarantees 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 logical end-end transport

Transport Layer 3-25 TCP: Overview RFCs: 793,1122,1323, 2018, 2581  full duplex data:  bi-directional data flow in same connection  MSS: maximum segment size  connection-oriented:  handshaking (exchange of control msgs) inits sender, receiver state before data exchange  flow controlled:  sender will not overwhelm receiver point-to-point: one sender, one receiver reliable, in-order byte steam: no “message boundaries” pipelined: TCP congestion and flow control set window size

Transport Layer 3-26 UDP: User Datagram Protocol [RFC 768] “no frills,” “bare bones” Internet transport protocol “best effort” service, UDP segments may be: lost delivered out-of-order to app connectionless: no handshaking between UDP sender, receiver each UDP segment handled independently of others  UDP use:  streaming multimedia apps (loss tolerant, rate sensitive)  DNS  SNMP  reliable transfer over UDP:  add reliability at application layer  application-specific error recovery!

Network Layer4-27 Network layer  transport segment from sending to receiving host  on sending side encapsulates segments into datagrams  on receiving side, delivers segments to transport layer  network layer protocols in every host, router  router examines header fields in all IP datagrams passing through it 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 Layer4-28 NAT: network address translation local network (e.g., home network) /24 rest of Internet datagrams with source or destination in this network have /24 address for source, destination (as usual) all datagrams leaving local network have same single source NAT IP address: ,different source port numbers

Link Layer5-29 Link layer: introduction terminology:  hosts and routers: nodes  communication channels that connect adjacent nodes along communication path: links  wired links  wireless links  LANs  layer-2 packet: frame, encapsulates datagram data-link layer has responsibility of transferring datagram from one node to physically adjacent node over a link global ISP

Link Layer5-30 MAC addresses and ARP 32-bit IP address: network-layer address for interface used for layer 3 (network layer) forwarding MAC (or LAN or physical or Ethernet) address: function: used ‘locally” to get frame from one interface to another physically-connected interface (same network, in IP-addressing sense) 48 bit MAC address (for most LANs) burned in NIC ROM, also sometimes software settable e.g.: 1A-2F-BB AD hexadecimal (base 16) notation (each “number” represents 4 bits)

Multimedia networking: 3 application types Multmedia Networking 7-31  streaming, stored audio, video  streaming: can begin playout before downloading entire file  stored (at server): can transmit faster than audio/video will be rendered (implies storing/buffering at client)  e.g., YouTube, Netflix, Hulu  conversational voice/video over IP  interactive nature of human-to-human conversation limits delay tolerance  e.g., Skype  streaming live audio, video  e.g., live sporting event (futbol)

Network Security What is network security? confidentiality: only sender, intended receiver should “understand” message contents sender encrypts message receiver decrypts message authentication: sender, receiver want to confirm identity of each other message integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection access and availability : services must be accessible and available to users

Network Management 9-33 Network management: summary network management extremely important: 80% of network “cost” SNMP protocol as a tool for conveying information network management: more art than science what to measure/monitor how to respond to failures? alarm correlation/filtering?