CS 447 Networks and Data Communication Packet Encapsulation Concept and Application Department of Computer Science Southern Illinois University Edwardsville Fall, 2015 Dr. Hiroshi Fujinoki E-mail: hfujino@siue.edu

CS 447 Networks and Data Communication Concept of packets Without Packets User Data Computer Network Internet Request Response Request (1) Response with tag (2) Request (3) Response (4) Computer Network User Data Internet Request Response Request (1) Response with tag (2) Request (3) Response (4) With Packets Packet (e.g. destination address) Packet Header (e.g. packet sequence #) Packet_Encapsulation/001

CS 447 Networks and Data Communication Concept of packet encapsulation: Layered Protocol Architecture OSI 7-Layer Model TCP/IP Model Host Computer Host Computer User Data User Data 4 layers Network Cable 7 layers Network Cable Packet_Encapsulation/002

CS 447 Networks and Data Communication Packet Encapsulation Visualized (1): Protocol Data Unit (PDU) Header User Data (User Data Packet) TCP Layer TCP Packet IP Layer IP Packet Network Layer Frame Datalink Layer Physical Layer Frame Physical Layer Header = Information specific to each protocol layer A packet = Header + PDU Packet_Encapsulation/003

CS 447 Networks and Data Communication Packet Encapsulation Visualized (2): Protocol Data Unit (PDU) Header User Data (User Data Packet) TCP Layer TCP Packet IP Layer IP Packet Network Layer Frame Datalink Layer Packet Encapsulation Physical Layer Frame Physical Layer Packet_Encapsulation/004

CS 447 Networks and Data Communication Packet Encapsulation Visualized (3): TCP Layer TCP Packet User Data A packet in TCP layer IP Layer IP Packet PDU in IP layer A packet (header + PDU) in an upper protocol layer = PDU in the next protocol layer Packet_Encapsulation/005

CS 447 Networks and Data Communication Packet Encapsulation Visualized (3): A packet in TCP layer TCP Layer TCP Packet IP Layer IP Packet PDU in IP layer At IP protocol layer, information in TCP header will be handled as if it were a part of user data Packet Encapsulation Any change in TCP will not affect internal design of IP Packet_Encapsulation/006

information in the packet header CS 447 Networks and Data Communication What is possible if we have packet encapsulation? User Data Communicate using the information in the packet header User Data 4 3 2 1 4 3 2 1 Internet Request Response Request (1) Response with tag (2) Request (3) Response (4) NW Corresponding protocol layer can communicate Packet_Encapsulation/007

CS 447 Networks and Data Communication Definition of Packet Encapsulation: The entire packet in a lower protocol layer becomes the PDU for the next upper protocol layer A protocol layer can handle packets from the lower layer without knowing anything about the layer This property guarantees the independence of each protocol layer in a protocol stack Without packet encapsulation, each protocol layer has to know the rules in any lower layers Without packet encapsulation, most of the advantages in the layered structure will not be utilized Packet_Encapsulation/008

CS 447 Networks and Data Communication External and Internal Operations External Operation The top four layers in OSI 7-layer model Sender Receiver Transport Layer Application Layer Presentation Layer Session Layer Transport Layer Application Layer Presentation Layer Session Layer Network Layer DataLink Layer Physical Layer Network Layer DataLink Layer Physical Layer Internal Operation The bottom three layers in OSI 7-layer model Protocol layers Underlying Network Ext_Int/001

D A B C CS 447 Networks and Data Communication External Operation Virtual Circuit Datagram A D Virtual Circuit Internal Operation B Datagram C Ext_Int/002

CS 447 Networks and Data Communication Packets will be re-ordered Example: External Virtual Circuit and Internal Datagram Sender Receiver 3 2 1 3 2 1 External Operation (Virtual Circuit) Internal Operation (Datagram) External Operation (Virtual Circuit) Internal Operation (Datagram) TCP IP 3 2 1 3 2 1 Datagram Network Protocol layers 1 2 3 Ext_Int/003

CS 447 Networks and Data Communication Example: External Datagram and Internal Datagram Packets will not be re-ordered Sender Receiver 3 2 1 3 2 1 External Operation (Datagram) External Operation (Datagram) UDP IP Internal Operation (Datagram) 3 2 1 Internal Operation (Datagram) 3 2 1 Datagram Network Protocol layers 1 2 3 Ext_Int/004

CS 447 Networks and Data Communication Example: External Virtual Circuit and Internal Virtual Circuit Sender ISDN Telephone Network Receiver 3 2 1 2 1 3 External Operation (Virtual Circuit) Internal Operation 2 1 3 3 2 1 Virtual Circuit Network Protocol layers 2 1 3 Ext_Int/005

CS 447 Networks and Data Communication Example: External Datagram and Internal Virtual Circuit Sender Receiver External Operation (Datagram) External Operation (Datagram) Internal Operation (Virtual Circuit) Internal Operation (Virtual Circuit) Virtual Circuit Network Protocol layers 2 1 3 Ext_Int/006

CS 447 Networks and Data Communication External Operation Virtual Circuit Datagram Analog Public Telephone Virtual Circuit ISDN Telephone (Digital Telephone Network) Internal Operation Datagram TCP/IP (Internet) UDP/IP (Internet) Ext_Int/007