Data Communication Data Communication Communication

Home , Data communication, Logical link control, Presentation layer, Session layer

CSC414 Data Data Communication Computer Communications Data From System - Messages to be shared between Greeting and the sender and receiver Body Fundamentals Packets OSI Model Closing - Envelopes used to address messages Signature Protocols Stamp - Establish accurate and appropriate Digital Forensics Center Recipient meaning to the messages Return Address Department of Computer Science and Statics THINK BIG WE DO - Understood by both senders and receivers Street U R I City - Standard interaction between entities Zip Code http://www.forensics.cs.uri.edu State Code

Communications channel Protocols for Communication - Logical Connection Transmission Control Protocol / Internet Protocol - Used to capably and reliably OSI Model TCP/IP Model Examples transport messages Application Layer HTTP;SMTP;SSH;FTP Application Layer Physical connection Presentation Layer MIME Encoding; SSL - Independent of the messaging Session Layer Sockets Transport Layer - Includes signaling that represents the Transport Layer TCP; UDP messages being transported Network Layer Network Layer IP; DHCP

Data Link Layer Data Link Layer MAC Address

Physical Layer Physical Layer 100BASE-TX

OSI Model OSI Model

Application Layer Presentation Layer - Layer where message is created - Presents data to application in a form it can use - Includes any application that provides software that can OSI Model - Makes application independent of data representation OSI Model communicate with the network layer Application Layer Application Layer - Translate ASCII characters to Unicode Characters - Protocols are specific to purpose of application - Encryption and decryption of messages Presentation Layer - Web Browsing - HTTP http://www.uri.edu:80/courses/cs/index.html - Example protocols - File Transfer - FTP protocol computer directory file - SSL - Secure Sockets Layer - Mail - SMTP address port - MIME - Multi-purpose Internet Mail Extensions - Requested data and files use URLs - Used to encode mail attachments - Universal Resource Locators - URL includes protocol information OSI Model OSI Model

Session Layer http://www.uri.edu:8080/courses/cs/index.html Transport Layer - Establishes a dialogue between two - Provides services that support reliable end-to-end Alternative cooperating applications or processes at the OSI Model communications OSI Model ends of the communication link Port Application Layer - Generates the final address of the destination Application Layer - Responsible for Presentation Layer - Responsible for all end-to-end communication facilities Presentation Layer - Establishing the session between the applications Session Layer - Packetization of a message, Session Layer - Controlling the dialogue Protocol Port Use - breaking up of the message into packets of reasonable size Transport Layer - Terminating the session FTP 20 file transfer SSH 22 secure login - Example protocols - Example SMTP 25 mail - TCP - Transmission Control Protocol - Sockets or ports finger 79 Info about system HTTP 80 web browsing - Socket to socket communications - Used as an end point or connection point on the POP3 110 mail computer MySQL 3030 database requests - UDP - User Datagram Protocol (streaming video)

OSI Model OSI Model

Network Layer Data Link Layer Medium Access Control (MAC) - Addressing and routing of packets to proper destination - Reliable transmission and delivery of packets between Address used at this layer - Unreliable, connectionless, packet switching service OSI Model two adjacent nodes OSI Model - Does not guarantee delivery nor check for errors Application Layer - Packets at this layer are called frames Application Layer

- Communications within a local network: Presentation Layer - Software logical link control sublayer Presentation Layer - No routing is required because nodes are directly addressable - Error correction, flow control, retransmission, packet Session Layer reconstruction and IP datagram/frame conversions Session Layer - Physical addresses for corresponding IP addresses are looked up in a table Transport Layer Transport Layer - IP appends a header with the physical address and passes the datagram to - Numbers frames and reorders received frames to recreate the original message the data link layer (layer 2) Network Layer Network Layer - Communications sent outside of the local network - Hardware medium-access control sublayer Data Link Layer - At each intermediate node, the network layer removes the current node Routers and gateways - Defines procedures for access the channel and detecting errors address and determines the next node address function at this layer - Responsible for services such as data encoding, collision - New address is added to the packet and passed to the data link layer (layer 2) handling, synchronization, and multiplexing

OSI Model Data Communication

Physical Layer Message Transmission Sender's My Message - Layer at which communication actually takes place Computer consisting of a bare stream of bits OSI Model OSI Model - Primarily implemented in hardware by a network interface Application Layer Application Layer My Message controller (NIC) Presentation Layer Presentation Layer My Message - Physical access protocol includes Session Layer Session Layer My Message - Definition of the medium Transport Layer Transport Layer My Message - Signaling method, signal parameters, carrier frequencies, lengths of pulses, synchronization and timing issues Network Layer Network Layer My Message

- Method used to physically connect the computer to the medium Data Link Layer Data Link Layer My Message

Physical Layer Physical Layer My Message Data Communication Data Communication

Message Transmission Message Transmission Sender's Sender's Receiver's Computer Computer Computer OSI Model OSI Model Application Layer Application Layer

Presentation Layer My Message Presentation Layer

Session Layer My Message Session Layer

Transport Layer My Message Transport Layer Network Layer Intermediate Node Network Layer Router Data Link Layer Data Link Layer

Physical Layer My Message Physical Layer My Message

Data Communication

Message Transmission Sender's Receiver's Computer Computer Data Communications OSI Model Application Layer and the Presentation Layer OSI Model Session Layer

Transport Layer Digital Forensics Center Network Layer Department of Computer Science and Statics THINK BIG WE DO Data Link Layer

Physical Layer "The Network" or "Internet" U R I http://www.forensics.cs.uri.edu