What is a Network? Computer network TCP / IP a set of computers - PDF document

What is a Network? • Computer network TCP / IP – a set of computers using common protocols to communicate over connecting transmission media. • Protocol – a formal description of message formats and the rules two or more machines follow to exchange messages. CS3 - AWT/Swing 1 CS3 - AWT/Swing 2 Protocols The ISO OSI Model OSI Hi Top Layer APPLICATION TCP connection req. PRESENTATION Hi TCP connection SESSION Got the reply. TRANSPORT time? Get http://gaia.cs.umass.edu/index.htm 2:00 NETWORK <file> DATA LINK time Bottom Layer PHYSICAL CS3 - AWT/Swing 3 CS3 - AWT/Swing 4 The TCP/IP Protocol Suite The TCP/IP Protocol Suite • TCP/IP is a set of protocols that were Application Telnet, FTP, e-mail, etc. created specifically to allow development of network and internetwork communications Transport TCP, UDP on a global scale • TCP/IP is the most commonly used Network IP protocols within the internet. • TCP/IP is normally considered to be a four- Link device driver and interface card layer system. CS3 - AWT/Swing 5 CS3 - AWT/Swing 6

The TCP/IP Reference Model Standardization OSI INTERNET • Who controls the TCP/IP protoocol suite? APPLICATION APPLICATION Telnet, ftp, etc. – The Internet Society (ISOC) a professional society to PRESENTATION facilitate, support, and promote the evolution and SESSION growth of the Internet TRANSPORT TRANSPORT TCP, UDP – The Internet Architecture Board (IAB) the technical NETWORK INTERNET IP, ICMP, IGMP oversight and coordination body – The Internet Engineering Task Force (IETF) is the DATA LINK HOST TO Device driver and card NETWORK near-term, standards-oriented group. PHYSICAL – The Internet Research Task Force (IRTF) pursues long- term research projects. CS3 - AWT/Swing 7 CS3 - AWT/Swing 8 RFCs IP: Internet Protocol • All official standards in the internet • IP is the workhorse protocol of the TCP/IP community are published as a Request for protocol suite Comments , or RFC . • IP provides an unreliable, connectionless, • All RFCs are available at no charge through datagram delivery service electronic mail, FTP, or the Web. • RFC791 is the official specification of IP • A nice place to get RFCs is at • Sits in the Internet Layer of the TCP/IP – http://www.rfc-editor.org/ Model CS3 - AWT/Swing 9 CS3 - AWT/Swing 10 Addressing IP Addresses • A distinction is made between names, • Every host on the internet must have a addresses, and routes unique Internet Address (an IP address) – A name indicates what we seek • IP addresses are 32-bit numbers and are – An address indicates where it is divided into two components: the host – A route indicates how to get there address and the network address • IP deals primarily with addresses. It is the – The number of bits assigned to the host and task of higher level protocols to make the network varies depending on the class of the mapping from names to addresses. address CS3 - AWT/Swing 11 CS3 - AWT/Swing 12

Dotted Decimal Notation Dotted Decimal Notation • IP addresses are normally written as four • Two sections numbers (octets), one for each byte of the – Net address. • identifies the network to which a computer belongs • Will always contain the first octet – 129.21.38.169 – Host • Identifies an individual machine • Will always contain the last octet CS3 - AWT/Swing 13 CS3 - AWT/Swing 14 IP address classes IP address classes • Class A • Class C – For very large networks – For small businesses – 1 st octet identifies net (1-126) / Octet 2-4 identifies host – Octet 1-3 identifies net / Octet 4 identifies host – Can support 16million+ (2 24 -2) hosts • 1 st octet = 192 – 223 • Class B – Can support 254 hosts – For medium sized networks (like college campuses) • Class D / Class E – Octet 1-2 identifies net / Octet 3-4 identifies host – Multicast • Octet 1 = 128 – 191 – Can support 65K hosts (2 16 -2) CS3 - AWT/Swing 15 CS3 - AWT/Swing 16 IP Address Classes Special IP addresses • The easiest way to differentiate between the • 0.0.0.0 classes is to look at the first number – The default network for any machine • 127.0.0.1 Class Range A 0.0.0.0 to 127.255.255.255 – Loopback address – to send messages to B 128.0.0.0 to 191.255.255.255 C 192.0.0.0 to 223.255.255.255 yourself D 224.0.0.0 to 239.255.255.255 E 240.0.0.0 to 247.255.255.255 • 255.255.255.255 – Broadcast – send messages to all on a network. CS3 - AWT/Swing 17 CS3 - AWT/Swing 18

Assigning IP Addresses IP Addresses • Since every interface must have a unique IP • Note that each piece of network hardware address, there must be a central authority also has a unique “Ethernet (MAC) for assigning numbers Address” • That authority is the Internet Network – For IP over ethernet, conversion from IP to MAC address must be made. Information Center , called the InterNIC. – Conversion table usually kept in cache • The InterNIC assigns only network ids, the – Address Resolution Protocol (ARP) used to assignment of host ids is up to the system query hardware for addresses administrator • NOT a TCP/IP Protocol! CS3 - AWT/Swing 19 CS3 - AWT/Swing 20 IP Other Internet Protocols • ICMP • Routing and delivery of “packets” – Internet Control Message Protocol – Supports packets containing error, control, and – Only responsible for sending “packets” from informational methods. one point to another – Defined on top of IP – E.g. used by ping. – Doesn’t care what’s in the packet or if packets • IGMP are part of a larger message. – Internet Group Management Protocol – Standard for IP multicasting over the Internet – Defined on top of IP CS3 - AWT/Swing 21 CS3 - AWT/Swing 22 Transport Layer Types of Transfer • Networks typically provide two types of transfer • The transport layer is responsible for – Connection-oriented – Disassembling and assembling streams of data • often reliable – Addressing packets (and send to IP) • stream based • Point to point – like phone call – Error checking – Connectionless • often unreliable • datagram based • Sends independent packets of data – like Postal Mail – Order of delivery is not important – Delivery not guaranteed, CS3 - AWT/Swing 23 CS3 - AWT/Swing 24

Connection-oriented Transfer Connectionless Transfer Server Server Create Socket Create Socket Client Client Create Socket C Create Socket o n n e c Accept t i o n E s t a b l i s h m e n t Connect Communication Read/Write Read/Write Communication Read/Write Read/Write CS3 - AWT/Swing 25 CS3 - AWT/Swing 26 Transport Layer The TCP/IP Protocol Suite User User User User application • TCP Process Process Process Process – Transmission Control Protocol – Connection based protocol that provides a TCP UDP transport reliable flow of data • UDP ICMP IP IGMP network – User Datagram Protocol – Sends independent packets of data with no Hardware link ARP RARP Interface guarantee of arrival CS3 - AWT/Swing 27 CS3 - AWT/Swing 28 Transmission Control Protocol TCP Streams • A stream of 8-bit bytes is exchanged across • TCP provides a connection-oriented, a TCP connection. reliable, byte stream service (RFC793) • The treatment of the byte stream by TCP is • TCP is an independent, general purpose similar to the treatment of a file by the protocol that can be adapted for use with UNIX operating system. delivery systems other than IP. • Connections provided by TCP allow concurrent transfer in both directions. Such connections are called full duplex . CS3 - AWT/Swing 29 CS3 - AWT/Swing 30

TCP Ports User Datagram Protocol • TCP uses protocol port numbers to identify • UDP is a simple, unreliable, datagram- the ultimate destination within a machine. oriented, transport layer protocol (RFC768). • How does one determine the port to 0 15 16 31 communicate with? 16-bit source port 16-bit destination port 8 bytes – Well-known Ports 16-bit length 16-bit checksum – Randomly Assigned Ports data (if any) • Questions CS3 - AWT/Swing 31 CS3 - AWT/Swing 32 User Datagram Protocol UNIX Networking • In the early 80s UNIX was being developed • Designed for applications where streams of by several organizations data need not be disassembled or assembled • One of the most influential development – Messages that fit in a single packet groups was UCB • Will not keep track of what is send nor – 4BSD provided support for the DARPA resend if not received Internet networking protocols, TCP/IP • Some consider 4BSD responsible for the popularity of the TCP/IP protocols CS3 - AWT/Swing 33 CS3 - AWT/Swing 34 Application Layer: Sockets Socket • Berkeley sockets are one of the most widely • A socket represents a connection (line of used communication APIs communication) between 2 processes: • A socket is an object from which messages – Usually on different machines, but can be on the same machine are sent and received – Communication is usually bi-directional • Based on some protocol • Different Sockets will implement different protocols The “Network” – Analogous to ChatSession object in project. CS3 - AWT/Swing 35 CS3 - AWT/Swing 36