1Chapter TCPIP

• TCP/IP


  Transmission Control Protocol/Internet Protocol - suite of communications protocols used to connect hosts on the Internet
• TCP/IP suite


  • Not a single protocol, but a four-layer communication architecture that provides network features like end-to-end communications, unreliable communications line fault handling, packet sequencing, internetwork routing

  
• DARPA model


  Four-layer conceptual model that the TCP/IP protocol suite maps to, named after the U.S. government agency that initially developed TCP/IP

  
• Layers of DARPA model

  • Application
  • Transport
  • Network or Internet
  • Data link or network interface

  
• Each layer in the TCP/IP suite corresponds to one or more layers of the seven-layer OSI model

  
• Network Interface/Data Link Layer

  • Responsible for the networking scope of the local network connection, performs data link functions like adding packet headers and transmitting frames over a physical medium, translates network addressing to data link addressing
• Internet/Network Layer


  • Responsible for addressing, packaging, and routing functions, core protocols include ARP, IP, ICMP, IGMP

  
• Transport Layer


  • Provides session and datagram communication services to the Application layer, core protocols are TCP and UDP

  
• TCP


  Reliable, connection-oriented delivery service that establishes connections, sequences and acknowledges packets, and recovers lost packets
• UDP


  Connectionless, unreliable datagram service that does not guarantee arrival or sequencing of packets, used for low-latency, loss-tolerant applications
• TCP header fields


  • Source/dest ports
  • Sequence/ack number
  • Data Offset
  • Flag bits
  • Window
  • Checksum
  • Urgent pointer
  • Option
  • Padding
• UDP header fields


  • Source Port
  • Destination Port
  • Length
  • Checksum
• IP


  • Connectionless, unreliable datagram protocol responsible for addressing and routing packets, does not guarantee delivery or sequencing
• IP header fields


  • Version
  • IHL
  • Type of Service
  • Length
  • ID/Flags/Offset
  • Time to Live
  • Protocol
  • Header Checksum
  • Source Address
  • Destination Address
  • Options
  • Padding
• IP packet


  Total length of the IP packet. Although there is a theoretical maximum of 64Kbytes, most networks operate with much smaller packets, though all must accept at least 576bytes
• Source Port


  Part of the IP packet header
• Destination Port


  Part of the IP packet header
• Length


  Part of the IP packet header
• Checksum


  Part of the IP packet header, covers the header only
• ID/Flags/Offset


  Fields that enable a gateway to split up the datagram into smaller segments. The ID field ensures the receiver can piece together the fragments, the offset tells how far down the datagram this fragment is, and the flags can be used to mark the datagram as non fragmentable
• Time to live


  A count which limits the lifetime of a datagram on the catenet. Each time it passes through a gateway, the count is decremented by one. If it reaches zero, the gateway does not forward it. This prevents permanently circulating datagrams
• Protocol


  Indicates which higher level protocol is being carried, e.g. TCP or UDP

  
• Source/dest Address


  To assist the gateways to route datagrams by the most efficient path, each IP address is structured into a Network Number and a local address. There are three classes of network providing different numbers of locally administered addresses
• Options


  The final part of the header, used to enforce security or network management
• Padding


  Used to align the header to the next 32-bit boundary
• TCP/IP Applications


  • Hypertext Transfer Protocol (HTTP)
  • Simple Mail Transfer Protocol (SMTP)
  • Dynamic Host Configuration Protocol (DHCP)
  • Domain Name System (DNS)
  • File Transfer Protocol (FTP)
  • Telnet
  • MIME
  • POP
• HTTP


  The protocol that enables the connection between a web server and a client. It is an application layer protocol for distributing information in the World Wide Web (WWW). It is based on the client–server architecture. The server uses port 80 and the client is a web browser
• SMTP


  An Internet standard for electronic mail (email) transmission. It uses TCP port 25. User-level client mail applications typically use SMTP only for sending messages to a mail server for relaying, and use POP3 or IMAP for retrieving messages
• DHCP


  Used to dynamically (automatically) assign TCP/IP configuration parameters to network devices (IP address, Subnet Mask, Default Gateway). A DHCP client communicates with a DHCP server to obtain this information

  
• FTP


  A file-moving utility that allows record oriented, block, or image transfer of files. It can provide conversion facilities between different file formats and architectures. It also has a recovery facility to resume transfers after network failures
• Telnet

  A virtual terminal facility that allows a user to connect to a remote system as if the user's terminal were hard-wired to that remote system
• MIME


  An Internet standard that extends the format of email to support text in character sets other than ASCII, non-text attachments, message bodies with multiple parts, and header information in non-ASCII character sets
• POP


  Also called POP3, a protocol used by a mail server in conjunction with SMTP to receive and hold mail for hosts. The POP3 mail server receives e-mails and filters them into the appropriate user folders. When a user connects to retrieve their mail, the messages are downloaded from the mail server to the user's hard disk
• The aim of this chapter was to give an overview of TCP/IP Suite and the various protocols. Data communication is a wide and complex field, and covering all the protocols and concepts is beyond the scope of this material. Additional reading may be required to gain expertise in this field