COMT 429 The Internet Protocols COMT 429

History 1969First version of a 4 node store and forward network, the ARPAnet 1972Formal demonstration of ARPAnet with 20 packet switches and 50 hosts mid-70sUNIX distributed to academic and research sites. DEC PDP-11 systems gain wide acceptance. Initial research on TCP. 1980DEC VAXs appear and replace PDP-11. Berkley UNIX provided with TCP implementation. 1983ARPAnet goes to TCP full-time. Sun Computers incorporate TCP/IP.

COMT 429 Protocol Overview Ethernet, X.25, HDLC etc. IP ICMP ARP RARP (Auxiliary Services) TCP UDP HTTP (WWW) Remote Login File Transfer X.25 Packet Layer

COMT 429 Network Hierarchy “Backbone” “Gateway”

COMT 429 Types of Connections  Connection-Oriented Protocols – Requires Set-Up and Termination – Provides Sequencing, Flow Control, Error Handling  Connection-Less Protocols – Also referred to as “Datagram” or “Best Effort” Delivery – Typically does include Error Detection

COMT 429 Connection Types in TCP/IP Data Link Layer and Physical Network Network Layer Transport Layer TCP: Connection Oriented UDP: Connection-less Connection-less Depends on the network

COMT 429 The IP Protocol TCP/IP

COMT 429 IP Header Version TimeoutProtocolHeader Checksum Source Address Destination Address Header LenClass of Service Total Length Identification DMFragment Position

COMT 429 UDP Header Source PortDestination Port Length Checksum

COMT 429 TCP Header Source PortDestination Port Sequence Number Acknowledgement Number Window (flow cntrl)misc Flags ChecksumUrgent Options

COMT 429 Addressing IP Addresses are 32 bits long, originally using one of three formats: 0NNNNNNN HHHHHHHH HHHHHHHH HHHHHHHH or 10NNNNNN NNNNNNNN HHHHHHHH HHHHHHHH or 110NNNNN NNNNNNNN NNNNNNNN HHHHHHHH N = Network Address Bit H = Host Address Bit

COMT 429 Notation  Dotted Decimal: – = = C D –  The Network: –  Broadcast on that network: –

COMT 429 Routing in an Autonomous System  Assign a network class that grants enough host addresses.  The internet routes based on one network number  Do we find a host inside the autonomous system? OU Internet CS (Morton) RTVC

COMT 429 Subnetworks  Divide the Host Section  Network – Use half of the host id as a subnetwork –10NNNNNN NNNNNNNN SSSSSSSS HHHHHHHH  Network Mask  – Internet network – Internal Network – Host 17

COMT 429 An Example “Backbone” Web Server: Web Browser

COMT 429 The Request  User types into the browser:  “

COMT 429 Browser Interpretation  “  Protocol to use is HTTP (HyperText Transfer Protocol); the transport protocol is TCP  The requested server is named  The SAP address is 80  The requested file is “index.htm”

COMT 429 Name Resolution  is not an actual address  Make a call to the “resolver” (or, in most PCs, the “stub resolver”) to get a numeric address.  The answer may come from local storage, or may itself require a network transmission using the Domain Name System (DNS) protocols.  The name space and the address space are unrelated, except that they can be translated into each other.

COMT 429 HTTP Message  The browser assembles a text message:  First line: – GET index.htm  Optional additional lines: – Browser type – HTTP version number – Transmission option negotiation

COMT 429 Request to TCP  Browser makes a call to TCP, asking to open a connection to the numeric browser address

COMT 429 Request to IP  TCP creates a header with the origin and destination SAPs  TCP sets a “flag” (bit) to request a new connection (SYN)  TCP may set other parameters and options

COMT 429 Locate the Gateway  IP needs to find a way to get the TCP PDU (called a segment) to the destination address.  Since the destination is on a different network, it needs a gateway.

COMT 429 Locate the Physical Gateway Address  IP knows the global (IP) address of the gateway.  To make a request of the data link layer, it needs the physical (MAC - Media Access Control) address of the gateway.  The ARP protocol is used to broadcast a request for the “owner” of the IP gateway address.  The gateway responds to the broadcast; IP learns the MAC address from the response.

COMT 429 Dispatch the SYN Packet  IP creates one or more packets (usually one in this case).  The header has the origin and destination IP addresses and other options.  The packet goes to the Ethernet driver, which attaches the MAC (Ethernet origin and destination), and sends the packet to the gateway.

COMT 429 Routing  The gateway receives the packet, and determines that it is not: – addressed to the gateway itself (at the IP level) – addressed to any networks the gateway is attached to  The gateway examines its routing table, and selects a circuit to send the packet out on.

COMT 429 Receipt  receives the packet.  IP removes its headers after error-checking the header  TCP removes its headers, after error-checking the entire packet.  TCP consults the owner of SAP 80, and determines that the web browser is willing to create the connection.

COMT 429 Response  TCP creates an empty packet  The packet acknowledges the receipt of the SYN  TCP responds to any options that may have been requested in the SYN

COMT 429 Request Transmission  The browser is informed that the connection has been created.  The actual text message (the GET…) is now handed to TCP  TCP attaches its header and contacts IP  IP attaches its header and uses the Ethernet driver to send the packet to the gateway  etc.

COMT 429 Response  The packet is received and checked by IP and TCP; they each remove their headers.  TCP notifies the web server  The web server reads the GET request  The server creates a header with responses to the options requested by the browser  The server adds a line to the header indicating the format of the file (MIME)  The header is followed by a blank line and the actual file content.

COMT 429 Standards Setting Internet Operations and Management Routing SecurityTransport User ServicesGeneralApplications Areas Working Groups Area Directors IETF ISOC IABIESG IANA