Networking • Basic network components and layered architecture • Internet and WWW basics • IP, TCP, URL, HTTP Jean Walrand, Communication Networks, a first course, Mc. Graw-Hill 1998 (2 nd edition). CSCI 1106, Fall 2008 1
Types of computer networks: • Point-to-point connection (link) between two computers e. g. PPP, SLIP • Store-and-forward transmission: packets A B C e. g. token ring • Datagram packet switching: destination address in packet • also, LAN, WAN, ATM (virtual circuit switching), wireless CSCI 1106, Fall 2008 2
• multiple access networks (e. g. ALOHA, Ethernet) CSCI 1106, Fall 2008 3
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Review of components • Hosts – Considered a “node” or “end point” in the network (client/server/printer) – Processes all levels of the protocol stack • Hubs – acts as an “extender” - similar in effect to taking all incoming lines and twisting the wires together – Does not do any processing - acts only at the physical layer • Bridges – attaches two physically identical LANs together, physical layer processing – forwards only traffic which is destined for “the other side” • Switches – depending on level of switch complexity, anywhere from a hub to a router • Routers – Processing at the Network layer – Route packets between networks with potentially different lower level protocol stacks (i. e. , different physical and data link layers) • Gateways – Processes all levels of the protocol stack – Used to connect networks with different protocol stacks CSCI 1106, Fall 2008 8
Layered communication model Message received Message sent Layer n Layer 2 Layer 1 Sender Communication medium Recipient Coulouris, Dollimore, Kindberg, Distributed Systems, Addison Wesley 2001 (3 rd ed) CSCI 1106, Fall 2008 9
ISO-OSI layer model Open systems interconnection reference model A B communication services 7. Application 7. local syntax, secure, efficient connections 6. Presentation 6. communication services, e. g. file transfer, email, … e. g. compression, security, format conversion connections 5. Session 5. supervises connections between end systems delivery of messages 4. Transport 4. supervises end-to-end transmission 3. Network 3. guides the packet from source to destinations 2. Data Link 2. implements packet delivery service between two nodes on the same physical link 1. Physical 1. Implements digital communication link that delivers bits CSCI 1106, Fall 2008 10
Layer Application Presentation Session Transport Network Data link Physical Description Protocols that are designed to meet the communication requirements of specific applications, often defining the interface to a service. Protocols at this level transmit data in a network representation that is independent of the representations used in individual computers, which may differ. Encryption is also performed in this layer, if required. At this level reliability and adaptation are performed, such as detection of failures and automatic recovery. This is the lowest level at which messages (rather than packets) are handled. Messages are addressed to communication ports attached to processes, Protocols in this layer may be connection-oriented or connectionless. Transfers data packets between computers in a specific network. In a WAN or an internetwork this involves the generation of a route passing through routers. In a single LAN no routing is required. Responsible for transmission of packets between nodes that are directly connected by a physical link. In a WAN transmission is between pairs of routers or between routers and hosts. In a LAN it is between any pair of hosts. The circuits and hardware that drive the network. It transmits sequences of binary data by analogue signalling, using amplitude or frequency modulation of electrical signals (on cable circuits), light signals (on fibre optic circuits) or other electromagnetic signals (on radio and microwave circuits). CSCI 1106, Fall 2008 Examples HTTP, FTP , SMTP, CORBA IIOP Secure Sockets (SSL), CORBA Data Rep. TCP, UDP IP, ATM virtual circuits Ethernet MAC, ATM cell transfer, PPP Ethernet base- band signalling, ISDN 11
What is a protocol `A protocol is a set of rules governing message interchanges which occur between a number of computers in a distributed system; each of these messages implement functions of the system. A protocol is also used to establish a connection and allow entities to exchange data about themselves, for example the operating system they are using and the format of the data that they intend passing; this is known as a handshake. ‘ D. Ince CSCI 1106, Fall 2008 12
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Application message TCP header port IP header TCP Ethernet header IP Ethernet frame CSCI 1106, Fall 2008 15
IP Header CSCI 1106, Fall 2008 16
• Around 4 billion IP addresses CSCI 1106, Fall 2008 17
Transport layer protocols • TCP (Transmission Control Protocol): – connection-oriented – Reliable packet delivery in sequence • UDP (User Datagram Protocol): – – – connectionless (datagram) Unreliable packet delivery Packets may arrive out of sequence or duplicated Less overhead Simply adds port addressing to IP Checksum is optional • Internet Control Message Protocol – Used by the nodes in the internet to implement IP CSCI 1106, Fall 2008 18
TCP and UDP Header CSCI 1106, Fall 2008 19
Name Port/Protocol ftp-data 20/tcp ftp 21/tcp telnet 23/tcp smtp 25/tcp bootps 67/udp bootpc 68/udp # BOOTP/DHCP client hostnames 101/tcp hostname sunrpc 111/udp rpcbind sunrpc 111/tcp rpcbind finger 79/tcp pop 3 110/tcp # Post Office nntp 119/tcp usenet imap 143/tcp # Internet Message Access ssh 22/tcp # Secure SHell who 513/udp whod kerberos 750/udp kdc xaudio 1103/tcp Xaserver stel 10005/tcp # Secure Telnet CSCI 1106, Fall 2008 Comment mail # BOOTP/DHCP server # usually to sri-nic # Network News Transfer # Kerberos key server # X Audio Server 20
The Internet around 1990 Jean Walrand, Communication Networks, a first course, Mc. Graw-Hill 1998 (2 nd edition). The first three chapters give you a nice overview of the working of networks and the Internet. CSCI 1106, Fall 2008 21
MCI backbone Retrieved from: http: //global. mci. com/about/network/maps/? flash=1&theme=/, Sept 5/2003 See this site also for interesting network statistics (e. g. latencies) CSCI 1106, Fall 2008 22
Internet network architecture ISP ISP NAP ISP Backbone Network Service Provider ISP ISP Internet Service Provider Private Networks / hosts Adapted from Electronic Commerce: A Managerial Perspective. Turban, Lee, King and Chung, 2000. Pg. 385 CSCI 1106, Fall 2008 23
a. cs. dal. ca CSCI 1106, Fall 2008 b. atr. go. jp 24
URL: A Global Address http: //www. cs. dal. ca/cs 1200/week 1/x. html CSCI 1106, Fall 2008 • • Scheme Server name Path File 25
a. cs. dal. ca 123. 777. 19. 6 CSCI 1106, Fall 2008 b. atr. go. jp 168. 12. 13. 3 26
Routing and congestion control Send information of nodes and links to each node of the network. This might include some physical properties such as maximal size of packets, typical time delays, … Build map of network Use routing algorithm to build routing tables for example: OSPF (Open Shortest Path First) if every router uses the same algorithm and maps they build consistent tables Hierarchical Routing: `use local map to get to the highway, use highway map to get to your destination town, use local map to get to your friends house’. More sophisticated routing on `highway’ (BGP, Border Gateway Protocol) How is congestion controlled? CSCI 1106, Fall 2008 27
How is congestion controlled? Flow control TCP Destination publishes maximal acceptable window size in reply message Source destination discovers congestion from unusually long delay times of response additive increase, multiplicative decrease CSCI 1106, Fall 2008 28
Application layer: Programming example in Java The JAVA Socket class Socket old. Sock = new Socket("penny. open. ac. uk", 1048); remote computer penny in the domain open. ac. uk with communication occurring via port 1048. Input. Stream CSCI 1106, Fall 2008 29
Network (internet) applications WWW & Semantic Web CSCI 1106, Fall 2008 30
Tim Berners-Lee CSCI 1106, Fall 2008 31
World Wide Web server Borg Internet Public_html Index. html Parts of the puzzle • URL • HTTP • HTML Web browser Your Machine CSCI 1106, Fall 2008 32
HTTP: Hyper Text Transfer Protocol • Lightweight protocol that browsers and servers use to communicate with one another • On top of (in the application layer of) the TCP/IP model • HTTP session begins when a client’s browser requests a Web page. Once the server responds by sending the page requested, the HTTP session ends CSCI 1106, Fall 2008 33
client request: Server response: GET /index. html HTTP/1. 1 User-Agent: Lynx/2. 4 Connection: Keep-Alive Host: www. openaccess. com Accept: text/html HTTP/1. 1 200 OK Date: Thu, 22 July 1998 18: 40: 55 GMT Server: Apache 1. 3. 5 (Unix) PHP/3. 0. 6 Last-Modified: Mon, 19 July 1997 16: 03: 22 GMT Content-Type: text/html Content-Length: 12987. . . MIME type (Multipurpose Internet Mail Extension) CSCI 1106, Fall 2008 34
HTTP is stateless!!! • stateless because every request that a browser makes opens a new connection that is immediately closed after the document is returned • even a web page with many objects (graphics, sound, video, etc) requires separate HTTP requests for each object • each operation is unaware of any other connection • the server cannot maintain state information about successive requests easily CSCI 1106, Fall 2008 35
Web client/server communication • Like any other client/server application, web browsers and servers need a way to: 1. Locate each other so they can send requests and responses back and forth • Uniform Resource Locator (URL) 2. Communicate with one another • Hypertext Transport Protocols (HTTP) (See networking section) CSCI 1106, Fall 2008 36
Interactivity • HTML is a presentation language – not a programming language • controls the appearance of the information on the client’s screen but does not support processing or manipulating information • early web browsers were limited to displaying static pages • But … many business applications require interactivity Client-side & server-side processing CSCI 1106, Fall 2008 37
TML (XML) <thomas> <lecture type=‘early’> <opening> Guten Morgen </opening> <message> bla </message> <lecture> <research> <paper> </research> </thomas> CSCI 1106, Fall 2008 38
DTD <!ELEMENT ele_name (list of child elements +*? )> Leaf element: <!ELEMENT name (#PCDATA)> <!ATTLIST ele_name att_type att_value> <!ENTITY ent_name “ent_value”> CSCI 1106, Fall 2008 39
DTD XML Document XML Parser & Syntax Validator valid / not valid DTD Document For example MSXML CSCI 1106, Fall 2008 40
XSLT XML Document XSLT Processor XML Document XSLT Document CSCI 1106, Fall 2008 41
XSLT Include in XML document <? xml-stylesheet type=“text/xsl” href=“URL” ? > XSLT document: <xsl: stylesheet version = “ 1. 0” xmlns: xsl = “url of xslt” xmlns = “url of xhtml”> <xsl: templates match = “root”> <html> <head> </head> <body> <h 1> …. . <xsl: for-each select = “tag”> <span style =“ whatever”> message </span> <xsl: value-of select = “subtag” /> <other html tags> …. </xsl: for-each> </html> </xsl: template> </xsl: stylesheet> CSCI 1106, Fall 2008 42
Tim Berners-Lee CSCI 1106, Fall 2008 43
• Web Hub – Content Management Console Google News Admin XML Content Modify Repository Control Panel Modify Database CSCI 1106, Fall 2008 Retrieve General Public P u b Front End Site l i c Member’s Section Alum ni 44
Web service architecture http: //www. w 3. org/2002/ws/ CSCI 1106, Fall 2008 Adopted from Clabby, 2002 45
SOAP • Simple Object Access Protocol • XML-based protocol • Exchange of information between applications over HTTP • Seems to become the widely accepted solution to electronic data interchange (EDI) and remote procedure call (RPC, CORBA, etc) http: //www. w 3. org/TR/soap 12 -part 0/ CSCI 1106, Fall 2008 46
Semantic Web stack CSCI 1106, Fall 2008 47
From http: //www. w 3. org/2001/sw/ Semantic Web The Semantic Web provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries. It is a collaborative effort led by W 3 C with participation from a large number of researchers and industrial partners. It is based on the Resource Description Framework (RDF), which integrates a variety of applications using XML for syntax and URIs for naming. "The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation. " -- Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May 2001 CSCI 1106, Fall 2008 48
Create meaning for automated processing: intelligent agents RDF: (Web) Resource Description Framework http: //www. w 3. org/TR/rdf-primer/ Web Ontology: OWL http: //www. w 3. org/TR/owl-features/ Standardized Query Language: SPARQL Simple example: [Really Simple Syndication (RSS 2. 0)] RDF Site Summary (RSS 1. 0 and RSS 0. 90) Rich Site Summary (RSS 0. 91) CSCI 1106, Fall 2008 49
Intro videos Semantic Web: http: //www. youtube. com/watch? v=OGg 8 A 2 zf. WKg RDF: http: //www. youtube. com/watch? v=ldl 0 m-5 z. Lz 4 CSCI 1106, Fall 2008 50
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