CS 447 Networks and Data Communication Network Protocols and OSI 7-layer Reference Model Department of Computer Science Southern Illinois University Edwardsville Fall, 2015 Dr. Hiroshi Fujinoki E-mail: hfujino@siue.edu

CS 447 Networks and Data Communication Organization of a Computer Connected to a Computer Network Computer A Computer B Application Program Network Protocol Wire (Computer Network) Network Protocol/001

CS 447 Networks and Data Communication Protocol and Interface Computer A Computer B Application Program Protocol Protocol Wire (Computer Network) Network Protocol/003

CS 447 Networks and Data Communication Definitions A network protocol is:  a set of rules  that governs communication between two hosts  implemented as software Example - TCP - NetBIOS (Windows) - IP - etc. - IPX/SPX (Novel Netware) Network Protocol/002

CS 447 Networks and Data Communication Protocol and Interface Interface: a set of rules that governs communication between two directly facing protocol layers Computer A Computer B Application Program Protocol TCP IP MAC TCP IP MAC Layered structure Interface Wire (Computer Network) Protocol Stack Network Protocol/003

CS 447 Networks and Data Communication Summary A network protocol is a set of rules that govern communication between two host computers (in the same level) An interface is a set of rules that govern communication between two directly facing protocol layers (within a host computer) Network Protocol/004

CS 447 Networks and Data Communication “End-to-end” and “point-to-point” Host A Host B Point-to-point NIC Intermediate Routers End-to-end OSI_SevenLayer/001

CS 447 Networks and Data Communication OSI Seven Layer Model Application Program Purposes Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Layer Interface to user programs Presentation Layer Data filters (compression, encryption) Session Layer Manage end-to-end connection Transport Layer Provide reliable end-to-end connection Network Layer Manage point-to-point connection Datalink Layer Provide reliable point-to-point connection Physical Layer Dealing with electric signals signals NIC Wire (Network Cable) OSI_SevenLayer/002

CS 447 Networks and Data Communication TCP/IP Protocol Suite: Application Layer NFS (Network File Server) XDR (External Data Rep.) RPC (Remote Proc. Call) Network Hardware TCP UDP IP ARP RARP Telnet, FTP, SMTP, rlogin, DNS, HTTP, rcp, finger, etc.  Presentation Layer Session Layer Transport Layer  Network Layer  Datalink Layer  Physical Layer OSI_SevenLayer/003

CS 447 Networks and Data Communication Layer 1: Physical Layer Major Function: Dealing with electric signals Example: Manchester Signal Encoding NRZI Signal Encoding Bipolar-AMI Signal Encoding Define how the signals are represented Interpret electric signals, represent them as 1’s or 0’s OSI_SevenLayer/004

CS 447 Networks and Data Communication Layer 2: Data Link Layer Major Functions: Try to detect and correct signal errors, if any Forward the received signals to the network layer If uncorrectable errors, gives an error warning to the network layer Provide Media Access Control (MAC) - For “shared” network, control who can use the network first Examples of Shared Network:  Star (=hub)  Ring  Bus OSI_SevenLayer/005

CS 447 Networks and Data Communication Layer 3: Network Layer Major Function: Maintain an point-to-point connection - Keep track of the sequence number - Establish a connection - Continue to check the status of a connection - Delete a connection when it is done OSI_SevenLayer/006

CS 447 Networks and Data Communication Layer 4: Transport Layer Major Functions: Try to detect and correct packet errors (error control) for E2E Perform flow control - If the receiver wants to slow down, reduce transmission rate - If the network is congested, reduce the transmission rate Layer 5: Session Layer Major Functions: Establish/Manage/Delete (E2E) connections Full-Duplex/Half-Duplex Control QoS (specify maximum tolerable delay) OSI_SevenLayer/007

CS 447 Networks and Data Communication Layer 6: Presentation Layer Major Functions: Encryption, compression, etc Raw Data Encryption Presentation Layer Compressed Data Raw Data Compression Presentation Layer Encrypted Data Layer 7: Application Layer Major Function: Interface to your application programs Example: Network API (Application Program Interface) OSI_SevenLayer/008

CS 447 Networks and Data Communication Full-Duplex and Half-Duplex Full-duplex: a connection two host can talk simultaneously Half-duplex: a connection one of the two hosts can talk at a time Full-Duplex Circuit Transmitting Circuit Receiving NIC at host A NIC at host B Multiplexer OSI_SevenLayer/009

CS 447 Networks and Data Communication Half-Duplex Circuit NIC at host B Transmitting Circuit Transmitting Circuit Receiving Receiving Circuit Switch NIC at host A Half-duplex: One-way communication at a time OSI_SevenLayer/009