Data Encapsulation and TCP Protocol Data Units

Data Encapsulation

• Encapsulation adds a new string of information to an existing unit to create new information.
• A datagram is formed by adding headers and trailers to a data payload.
• Decapsulation is the reverse of encapsulation, removing headers and tails to obtain the data payload.
• Data payload is the information to be transmitted.
• A data unit (packet), in hierarchical communication, is data sent from an upper layer to a lower layer, also called the data payload of the lower layer.
• A packet is a data unit exchanged and transmitted on a network.
• Packet structure consists of a header + data payload + tail.
• The packet's format and contents can change during transmission.
• A header is an information segment added before the data payload during packet assembly.
• A tail is an information segment added after the payload.

TCP Protocol Data Units

• Protocol Data Unit (PDU) is a specific block of information transferred over a network and describes data types transferred from each layer.
• The Application Layer's data is received by a software application.
• The Presentation Layer's data is formatted for presentation.
• The Session Layer's data is passed to network communication.
• The Transport Layer's segment includes a TCP header and data.
• The Network Layer's packet contains the source and destination address.
• The Data Link Layer's frame is 10 bits.
• The Physical Layer's raw bits are 1s or 0s transmitted physically.

TCP/IP Internet Layer Common Protocols

• Internet Protocols (IP) define a packet and an addressing scheme, transfers data between the internet and network access layers, and routes packets to remote hosts.
• Internet Control Message Protocol refers to a TCP/IP Protocol that handles errors and controls the process of sending data between computers.
• TCP/IP uses ICMP to send reports of problems about packets that return to the original source that sent the packet.
• Internet Group Management Protocol (IGMP) refers to TCP/IP that handles multicasting, where hosts use IGMP to keep local routers aware of their multicast group membership.
• Address Resolution Protocol (ARP) is a TCP/IP protocol that obtains the physical address of a node from a specific IP number by binding a high-level IP address to a low-level physical hardware address.
• Reverse Address Resolution Protocol (RARP) allows a host without local permanent data storage to find its internet address given its physical address.

Common Net Access Layer Protocols

• Ethernet refers to a family of LANs covered by IEEE 802.3 standards and provides a best-effort delivery system using a CSMA/CD access method.
• Point-to-Point Protocol (PPP) refers to a protocol used for data transfer across a serial line.
• Fiber Distributed Data Interface (FDDI) is a set of ANSI protocols for sending digital data over fiber optic cable.
• Asynchronous Transfer Mode (ATM) refers to a wide area protocol that features high data rates and equal-sized packets/cells suitable for test, audio, and video data transfer.
• Frame Relay is a WAN protocol for LAN internetworking that provides a fast and efficient method of transmitting information from one user device to another across multiple switches and routers.
• Proxy ARP is used when a network terminal needs to pass data from one to another without changing its current IP address information.