Wide Area Networks; The Internet

Information Technology I Computer Networks III � Wide Area Networks and Packet Switching � Network Protocols and the OSI Layers � The Internet � Internet Infrastructure Wide Area Networks (recap) Information Technology I Basic WAN structure Host Router Communication lines Router Router Host Host Router Router Subnet Host Switching � Circuit switching � � � Set up dedicated end-to-end channel for duration of connection Used for phone network Message switching � For sending data messages (e.g., email) � No wasted channels as with circuit switching � Each intermediate node stores and forwards the message Packet switching � � Divide data messages into small packets Each packet is "message switched" - Packets can take different routes If one is lost, don’t resend whole message Information Technology I Why break messages into packets? � If part of message is lost or garbled, resend only the affected packet(s) � Speed � Store-and-forward delay is minimized (pipelining) � Each intermediate node has to receive and store a message, then forward it A can send packet 1 to B while receiving packet 2 from S. Not possible if whole message sent at once Packets can take different routes (parallelism) - packet 1 goes S -> A -> B -> R packet 2 goes S -> C -> D -> R A B S R C D Network Protocols and the OSI Layers Information Technology I LAN (point-to-point) network protocols � “Data Link” protocols - provide point-to-point error-free transmission break data into frames attach error-detecting info into data wait for acknowledgments and retransmit, if necessary handle collisions (in broadcast networks) Communications Communications Communications Channel Processor Processor Workstation Workstation Protocols for Packet Switching � Assume data link protocols provide error-free point-to-point transmission � Sender must break messages into packets - attach sequence number - attach destination address, other admin info to packets � Receiver must reassemble message from packets - use sequence numbers in case packets arrive out of order - request retransmission of lost, garbled packets � Intermediary nodes must route packet - find best next node in path for each packet - route packets to next node A B C D S R Information Technology I Network protocol layers so far � Network Layer - � Data Link Layer - � routes data from one host to another routes packets to next node attaches destination address, other admin info into data Assumes error-free point-to-point transmission provides point-to-point error-free transmission breaks packets into frames attaches error-detecting info into data Assumes existence of physical transmission medium Physical Layer - converts bits to signals and back - carries signals over wires OSI Abstraction Layers � 7: Application layer � � 6: Presentation layer � � Establishes and terminates connections between applications 4: Transport layer � � Handles encryption, compression, other translation of messages 5: Session layer � � E.g., terminal emulation, file transfer Divides messages into packets;assembles packets into messages 3: Network layer � Finds routes for packets; transmits them to next node � 2: Link layer � 1: Physical layer � � Breaks packets into frames; sends frames between nodes Sends bits over wires Information Technology I Information Exchange Process through OSI Layers Example: Voice communication over a packet-switched company network � Communication between managers in Germany and Wichita, Kansas � Company network does not have a direct link between Germany and Kansas � New York is an intermediate link Information Technology I Some Example Protocols � Physical layer � � Data Link layer � � Ethernet, Token ring, ISDN Network layer � � standards for data lines, radio transmission, etc. Novell IPX, Appletalk, IP Application layer � telnet, ftp, Netscape (HTTP), Eudora (email) Important Idea � Layered protocols allow protocols on one layer to interoperate with several different protocols on lower layers � � � Ethernet can be used with coaxial cable, infrared, microwave, etc. Novell or Appletalk can be used with Ethernet, Token Rings, ISDN,etc. Eudora, telnet can be used with any network Information Technology I The Internet The Internet � Grew out of ARPANET, NSFNET � � as more and more independent networks adopted the Arpanet protocol suite and connected themselves to it through gateways Internet statistics � � � � � � � � 265 million hosts in 2001 60 million hosts in 1999 36 million in 1998 16,1 million in 1997 9.5 million in 1996 4.9 million in 1995 2.2 million in 1994 1.3 million in 1993 Information Technology I ARPANET (1970s) Stanford Router MIT Communication lines Router Router Router UCLA Router CMU Stanford campus network NSFNET (1980s) MIT campus network NSFNET UCLA campus network Information Technology I Stanford campus network Growth of NSFNET Commercial regional network MIT campus network NSFNET Link to international networks UCLA campus network The Internet: a Network of Networks Independently operated regional networks U.S. Internet Backbone Link to European backbone Information Technology I Internet Properties � All hosts on the Internet communicate using common network protocols � � Different parts of the Internet are operated by different entities � � TCP/IP, first developed for ARPANET governments, telephone companies, universities etc. No single organization controls or owns the Internet A bird’s eye view of the Internet Information Technology I What does it mean to be on the Internet? � Run TCP/IP protocol � Have an IP address � Have ability to send IP packets to other machines on the Internet TCP/IP Protocol Stack � Same layering ideas as OSI, (slightly) different layer definitions � � � IP corresponds to network layer TCP corresponds to transport layer Protocol only defines network and transport layer. � can be used on top of many different physical network organizations Information Technology I Internet Addresses (IP addresses) Host Host 18.171.0.30 155.22.11.250 Host 12.34.23.40 Host 192.37.40.51 TCP/IP Explained � IP is lowest layer (equiv. to OSI network layer) � � � Moves a packet from one host to another Connectionless protocol (no guarantee of reliable delivery) Each packet contains a 32-bit address of the destination host - Each host has its own unique address - Internet is running out of addresses - - � 18.171.0.30 is my machine’s Partly because addresses allocated inefficiently MIT has all of 18 (4M addresses) but not that many computers Eventually move to more than 32-bit addresses TCP (equiv. to OSI transport layer) � � Establishes a reliable connection between processes on two hosts TCP makes up for unreliability of IP by resending lost blocks Information Technology I Understanding Internet Addresses � 18.154.0.27 � � � � uniquely assigned to a specific Internet connection point (NOT machine!) by NIC 32-bit address each number between dots is the decimal rep of 8 bits in the address In this case: - 18 specifies MIT (MIT owns all addresses 18.xxx.yyy.zzz) 54 specifies the subnet corresponding to building E56 0.27 is host number within the subnet � Every internet address can optionally have a descriptive host name (e.g.LASAGNA.MIT.EDU) � Other variations are possible Internet Infrastructure Information Technology I Internet Overview The Internet Backbone Providers 11 Network Access Points (NAPs) � � � � � � � � San Francisco: Pacific Bell & MAE-West Chicago: Ameritech & MAE-Chicago New York: SprintLink Washington DC: MAE-East & MAE-East+ FIX-East: Univ Maryland FIX-West: NASA Ames Los Angeles: MAE-LA Dallas: MAE-Dallas Peering: interconnection between backbone providers Private peering between operators to avoid NAP bottlenecks Information Technology I Internet ‘Tiering’ Levels � Tier 1 (nearly 50) � � � � MCI Worldcom (UUNET, MCI (divested)) Sprint GTE Cable & Wireless � Tier 2: National Backbone Level � Tier 3: Regional Networks � Tier 4: ISPs � Tier 5: Consumer and Business Markets Information Technology I IPv6: Next Generation IP (IPng) � designed to solve shortage of addresses in IPv4; � adds additional features to IPv4, such as security, autoconfiguration, and multicasting; � provides QoS features making the Internet more suitable for real-time applications; � need for a smooth transition from IPv4 to IPv6. Additional features of IPv6 � Security � � Autoconfiguration � � packet-level encryption (especially for Internet-based VPNs) enable an IPv6 host to configure its IPv6 address without (or with very limited) human intervention Multicasting � can send packets simultaneously to several IP addresses; useful for videoconferencing, Web-casts Information Technology I QoS features in IPv6 � IPv4 provides only best-effort service � Goal: make IPv6 more suitable for real-time applications (e.g., audio and video) � How: packets will be assigned different priorities (prioritization-based QoS) and will be treated differently based on these priorities Need for a Smooth Transition from IPv4 to IPv6 � new IPv6 routers should not affect existing IPv4 routers � IPv4 routers can be upgraded to IPv6 routers easily and at any time � IPv6 packets should travel over IPv4 pieces of the Internet; mechanism: tunneling.