Transcript Document
TCP/IP TCP/IP • The Transmission Control Protocol/Internetworking Protocol (TCP/IP) is a set of protocols, or protocol suite, that defines how all the transmissions are exchanged across the Internet. • An internet under TCP/IP operates like a single network connecting many computers of any size and type. Internally, an internet (or, more generally, the Internet) is an interconnection of independent physical networks linked together by internetworking devices. An internet According to TCP/IP TCP/IP • A host in TCP/IP is a computer. • Transmission Control Protocol (TCP) was developed before the OSI model. Therefore, the layers in the TCP/IP protocol do not match exactly with those in the OSI model. • The TCP/IP protocol is made of five levels: physical, data link, network, transport and application. TCP/IP and the OSI Model TCP/IP • At the transport layer TCP/IP defines two protocols: TCP and User Datagram Protocol (UDP). • At the network layer the main protocol defined by TCP/IP is the Internetworking Protocol (IP). • At the physical and data link layers, TCP/IP does not define any specific protocol. It supports all the standard and proprietary protocols. Encapsulation • The data unit created at the application layer is called a message. TCP/IP • TCP or UDP creates a data unit that is called either a segment or a user datagram. • • The IP layer creates a data unit called a datagram. The movement of the datagram across the Internet is the responsibility of the TCP/IP protocol. Network Layer • At the network layer TCP/IP supports the IP protocol. IP, in turn, contains four supporting protocols: ARP, RARP, ICMP, and IGMP. TCP/IP Internetwork Protocol (IP) • IP is the transmission mechanism used by the TCP/IP protocols. It is an unreliable and connectionless datagram protocol- a best-effort delivery service. • The term best-effort mean that IP provides no error checking or tracking. • If reliability is important, IP must be paired with a reliable protocol such TCP. • IP transports data in packets called datagrams, each of which is transported separately. TCP/IP • Datagrams can travel along different routes and may arrive out of sequence or duplicated. IP does not keep track of the routes and has no facility for reordering datagrams once they arrive. Because it is a connectionless service, IP does not create virtual circuits for delivery. Datagram • A datagram is a variable-length packet (up to 65,536 bytes) consisting of two parts: header and data. Datagram approach IP Datagram • Version The first field defines the version number of the IP. The current version is 4 (IPv4). • Header length (HLEN) The HLEN field defines the length of the header in multiples of four bytes. The four bits can represent a number between 0 and 15, which, when multiplied by 4, gives a maximum of 60 bytes. • Service type The service type field defines how the datagram should be handled. It includes bits that define the priority of the datagram. • Total Length • Identification The identification field is used in fragmentation. A datagram, when passing through different networks, may be divided into fragments to match the network frame size. When it happens, each fragment is identified with a sequence number in this field. • Flags The bits in the flags deal with the fragmentation • Fragmentation offset The fragmentation offset is a pointer that shows the offset in the original datagram (if fragmented) • Time to live The time to live defines the number of hops a datagram can travel before it is discarded. The source host, when it creates the datagram, sets this field to an initial value. Then, as datagram travels through the Internet, router by router, each router decrements this value by 1. If this value becomes 0 before the datagram reaches its final destination, the datagram is discarded. This prevent the datagram from going back and forth forever between routers. • Protocol The protocol field defines which upper-layer protocol data are encapsulated in the datagram (TCP, UDP, etc) • Header checksum This is a 16-bit field used to check the integrity of the header, not the rest of the packet. • Source address The source address field is a four-byte (32-bit) Internet address. • Destination address The destination address is a four-byte (32-bit) Internet address. • Options This field can carry information about routing, timing, management, and alignment. ADDRESSING •Each Internet address consists of four bytes (32 bits), defining three fields: class type, netid, and hostid. •These parts are of varying length, depending on the class of the address. Internet Classes •Currently class A and class B are full. Addresses are available in class C only. •Class D is reserved for multicast addresses. Multicasting allows copies of a datagram to be passed to a select group of hosts rather than an individual host. IP Addresses in Decimal Notation To make the 32-bit form shorter and easier to read, Internet addresses are usually written in decimal form with decimal points separating the bytes- dotted-decimal notation. Class Ranges of Internet Addresses Network and Host Addresses A Network with Two Levels of Hierarchy A Network with Three Levels of Hierarchy Addresses with and without Subnetting Masking • Masking is a process that extracts the address of the physical network from an IP address (if there are subnetworks), otherwise the subnetwork address. Masking 123 0 1 1 1 1 0 1 1 192 1 1 0 0 0 0 0 0 ----------------------------------------------64 0 1 0 0 0 0 0 0 ARP Other Protocols in the Network Layer • TCP/IP supports four other protocols in the network layer: ARP, RARP, ICMP, and IGMP. • Address Resolution protocol (ARP) associates an IP address with the physical address. ARP is used to find the physical address of the node when its Internet address is known. • Reverse Address Resolution Protocol (RARP) allows a host to discover its Internet address when it knows only its physical address. • Internet Control Message Protocol (ICMP) is a mechanism used by hosts and routers to send notifications of datagram problems back to the sender. If a router is unable to route or deliver the datagram because of unusual conditions or because of network congestion, ICMP allows it to inform the original source. • The Internet Message Protocol (IGMP) has been designed to help a multicast router identify the hosts in a LAN that are members of a multicast group.