1 Network Concepts Rong Wang CGS3285 School of Computer Science University of Central Florida Spring2004

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., RECOMMENDED READING From textbooks: Chapter 7 of Data Communications: From Basics to Broadband, 3rd Edition by William J. Beyda (ISBN: ) Page 8~13 and Chapter 2 of Data Communications and Networking, 3rd Edition, Behrouz A. Forouzan (ISBN: )

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., NETWORKS Network A set of devices (often referred to as nodes) connected by communication links. Node A device that is capable of sending and/or receiving data generated by other nodes o the network (e.g., a computer, printer…) Distributed processing A task is divided among multiple computers Network criteria Performance Reliability Security

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., TYPE OF CONNECTION Point to point A dedicated link is provided between two devices Multipoint More than two specific devices share a single link Point – to – point connection Multipoint connection

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., TYPE OF CONNECTING TOPOLOGY

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., MESH TOPOLOGY Every device has a dedicated point- to-point link to every other devices Dedicated Link carries traffic only between the two devices it connects A fully connected mesh network has n(n-1)/2 physical channels to link n devices Every device on the network must have n-1 input/output (I/O) ports Advantage Less traffic, robust, secure, easy to maintain Disadvantage Need more resource (cable and ports), expensive

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., STAR TOPOLOGY Each device has a dedicated point-to-point link only to a central controller, usually called a hub. No direct traffic and link between devices Advantage Less expensive Easy to install and reconfigure Robustness Disadvantage Single point of failure

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., BUS TOPOLOGY A multipoint topology All devices are linked through a backbone cable Nodes are connected to the bus cable by drop lines and taps. Drop line A connection running between the device and the main cable Tap A connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core Advantage: Ease of installation Disadvantages Difficult reconnection and fault isolation Broken or fault of the bus cable stops all transmission

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., RING TOPOLOGY Each device is dedicated point-to-point connection only with the two devices on either side of it A signal is passed along the ring in the direction, from device to device, until it reaches its destination Each device in the ring incorporates a repeater Advantage Relatively easy to install and reconfigure Fault isolation is simplified Disadvantage Unidirectional traffic

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., NETWORK MODEL A network model is a layered architecture Task broken into subtasks Implemented separately in layers in stack Functions need in both systems Peer layers communicate Protocol: A set of rules that governs data communication It represents an agreement between the communicating devices

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., INTERNET LAYERS

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., PEER – TO – PEER PROCESS Communication must move down through the layers on the sending device, over to receiving device Are the receiving device, communication must move up through the layers Each layer in the sending device adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it At the receiving device, the message is unwrapped layer by layer, with each process receiving and removing the data meant for it

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., PEER-TO-PEER PROCESS The passing of the data and network information down through the layers of the sending device and backup through the layers of the receiving device is made possible by interface between each pair of adjacent layers Interface defines what information and services a layer must provide for the layer above it.

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., AN EXCHANGE USING INTERNET MODEL

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., PHYSICAL LAYER Responsible for transmitting individual bits from one node to the next Function Physical characteristics of interfaces and media Representation of bits Data rate Synchronization of bits e.g., RC-232-c interface

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., DATA LINK LAYER Responsible for transmitting frames from one node to the next Function Framing: Physical addressing Flow control Error control Access control

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., NODE-TO-NODE DELIVERY

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., Example 1 In following Figure a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., NETWORK LAYER Source-to-destination delivery, Responsible from the delivery of packets from the original source to the final destination Functions Logical addressing routing

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., SOURCE – TO – DESTINATION DELIVERY

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., Example 2 In the Figure we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., TRANSPORT LAYER Process-to- process delivery Responsible for delivery of a message from one process to another Functions Port addressing Segmentation and reassembly Connection control Flow control Error control

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., RELIABLE PROCESS-TO-PROCESS DELIVERY OF A MESSAGE

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., Example 3 Following Figure shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet.

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., APPLICATION LAYER Responsible for providing services to the user Functions Mail services File transfer and access Remote log-in Accessing the World Wide Web

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., SUMMARY OF DUTIES

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., A UNIVERSAL ARCHITECTURE? Each manufacturer has its own architecture Need for a single architecture to connect equipment from different manufacturers International Standards Organization (ISO) developed a general architecture model known as the “ Open Systems Interconnection ” or OSI Model Seven layers TCP/IP is the de facto standard Provides a common method for describing communication architectures, tasks and functions. Meant to help connect equipment from multiple manufacturers Supported in principle but not in fact Often referred to as a “ Reference Model ”

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., OSI - THE MODEL A layered model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., OSI LAYERS

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., OSI MODEL First four layers Almost the same as first four layers of Internet model Session layer The network dialog controller, It establishes, maintains and synchronize the interaction between communicating system Function Dialog control Synchronization Presentation layer Concerned with the syntax and semantics of the information exchanged between two system Functions Translation Encryption Compression Application layer Enables the user to access the network Functions Network virtual terminal File transfer, access and management Mail services Directory services

Based on Data Communications and Networking, 3rd Edition. by Behrouz A. Forouzan, © McGraw-Hill Companies, Inc., FITTING THE PIECES TOGETHER Physical Layer Analog and Digital signals Data rates Transmission impairments Line coding Transmission mode Parallel vs. serial Synchronous vs. asynchronous Direction of transmission Modulation and demodulation Multiplexing Guided and Unguided transmission media Data link layer Error detection, correction and error control