Networking Support In Java Nelson Padua Perez Chau Wen Tseng Department of Computer Science University of Maryland College Park Advanced Programming Concepts Objected oriented support in Java for Exception handling Streams Threads Graphics user interfaces GUIs Networking Look at networking as example of OO design 1 Overview Networking Background Concepts Java s objected oriented view Java s networking API Application Program Interface Network applications This lecture Next lecture Networking Background Definition Set of computers using common protocols to communicate over connecting media History 1969 ARPANET 1986 NSFnet 1995 Internet 2 Networking Concepts Protocols Network model Internet addresses Ports Sockets URLs Reliability Connection vs packet oriented TCP vs UDP Protocols Definition Formal description of formats and rules Used for Message formats Sequence order of actions Needed by computers to exchange information Vital for networking 3 Protocols Email Delivery Network Model Open Systems Interconnection OSI model Multiple layers 7 One function each Each layer relies on previous layer Designed to reduce complexity using abstraction 4 Network Model Layers Physical layer Transmit data as 0 s and 1 s over connection Data link layer Between two physically connected computers Network layer Between any two computers connected to network Transport layer Deliver network data to application Application layer Between two applications using network Network Model VOIP Example Voice over IP VOIP Physical Data link Network Transport Application 5 Internet IP Address Unique address for machine on internet Get from ISP when connecting to internet Allows network to find your machine Format 32 bit unsigned integer Domain name 128 8 128 8 cs umd edu Name and address for local machine Localhost 127 0 0 1 Internet IP Address Domain Name System DNS DNS servers on internet Can look up IP address associated with name DNS server may need to query other DNS servers edu DNS server queries umd edu server to find cs umd edu Machine can have multiple IP addresses Virtual machines 6 Internet IP Address Problem Running out of 32 bit IP addresses Caused by initial address allocation Stanford MIT given more IP addresses than China Switching to 128 bit IP addresses in IPv6 1 million addresses per square meter on Earth Ports Abstraction to identify refine destination Provide multiple destinations at single IP address Format Unsigned 16 bit integer 0 to 65 535 Ports 0 to 4096 often reserved restricted Many ports pre assigned to important services 21 ftp 23 telnet 25 SMTP 80 http file transfer remote terminal email web 7 Sockets Application level abstraction Represents network connection Implemented in software Supports both UDP and TCP protocols History Introduced in Berkley UNIX in 1980s Networking API Sockets Socket is bound to port number Receives data packet Relays to specific port app app app app app port port port port port TCP or UDP port data Transport Layer Packet 8 Uniform Resource Locators URLs Represent web resources Web pages Arbitrary files Examples http www cs umd edu index html ftp www cs umd edu pub doc csd policies pdf https login yahoo com file dir my txt Uniform Resource Locators URLs Consists of Protocol http ftp https secure http file IP address or domain name Port optional http www cs umd edu 80 Reference to anchor optional 9 Reliability Reliable Data guaranteed to Arrive in order More overhead Slower Reliability Unreliable Data not guaranteed to Arrive lost data Arrive in order out of order data Less overhead Faster Transfers responsibility to higher layer Extra work for higher layer Compensate with timeouts Estimate packet lost if longer than average round trip 10 Reliability Reliable layers Data link Unreliable layers Physical Network Can be either Transport Reliable TCP Unreliable Application UDP Ways To Connect 1 Connection oriented 2 Packet oriented 11 Connection Oriented Approach Reserve single communication channel Send stream of data along channel Also called Circuit switching Stream oriented Example Telephone call current Connection Oriented Protocol 12 Connection Oriented Advantages Simpler scheme Easier to use Higher quality communication Less likely to lose data at network layer Packet Oriented Approach Break message up into packets Transmit packets separately Assemble packets at destination Also called Packet switching Connectionless Example US Mail VOIP Voice over IP 13 Packet Oriented Protocol Packet Oriented Advantages Can share communication channel Higher utilization of channels Can utilize multiple channels at once Can reroute around failed channels 14 Internet Network layer Internet Protocol IP Transport layer User Datagram Protocol UDP Transmission Control Protocol TCP Internet 15 Internet Protocol IP Packet oriented Packets routed between computers Unreliable User Datagram Protocol UDP Packet oriented Message split into datagrams Send datagrams as packets on network layer Unreliable but fast Application must deal with lost packets Examples Ping Streaming multimedia Online games 16 Transmission Control Protocol TCP Connection oriented Message split into datagrams Send datagrams as packets on network layer Provides illusion of reliable connection Extra messages between sender recipient Resend packets if necessary Ensure all packets eventually arrive Store packets and process in order Transmission Control Protocol TCP Reliable but slower Application can treat as reliable connection Despite unreliability of underlying IP network Examples ftp file transfer telnet remote terminal http web 17
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