Lecture 4 B (Networks) PDF

Systems and Architecture Module Code : G51SYS Objectives  To discuss about the use Repeaters, Bridges, Hubs and Switches in a network.  To differentiate between the two types of bridges CCN.2 Repeaters An electrical signal becomes weaker as it trave...

Systems and Architecture Module Code : G51SYS Objectives  To discuss about the use Repeaters, Bridges, Hubs and Switches in a network.  To differentiate between the two types of bridges CCN.2 Repeaters An electrical signal becomes weaker as it travels. To overcome such limitations, some LAN technologies allow two LANs to be joined together with a “repeater”. It continuously monitors electrical signals on each LAN. CCN.3 Repeaters Drawbacks Repeaters do not understand between a valid frame and other electrical signals. When a collision/interference occurs on one segment a repeater recreates the signals on the other segment including an overlapping signal that correspond to a collision CCN.4 Bridges  Bridge is an electronic device used to interconnect LAN segments together.  To improve the performance of an existing LAN by dividing the LAN into two segments and adding a bridge between them  Bridge listens to traffic on each segment in promiscuous mode and forward all frames  Bridges are more popular than repeaters because they do not forward the erroneous frames (e.g. collisions and noise).  Two LAN segments connected by a bridge behave like a single LAN CCN.5 Transparent bridges  Transparent bridges require no initial programming.  Also known as adaptive or learning bridge because they learn the locations of computers automatically  After installation on a network, they “learn” the location of network devices by associating the source address in incoming packets with the line they were received on.  Bridges can then forward packets appropriately by analyzing a data packet’s destination address. If the destination address is on the segment from which the packet came, the bridge discards it.  If not, the packet is sent out on the appropriate line. CCN.6 Source-routing bridge  In a source-routing network, the entire route to the destination station is contained in the packet sent by the source.  The source-routing bridge’s job is, therefore, quite easy. It merely passes that packet to the device that is next in line, as specified by the route in the packet.  This might be another bridge, or it might be the destination device. CCN.7 Learning Bridge CCN.8 Loop problem in Bridges – example 1 At time t0, station A transmits a frame addressed to station B. The frame is captured by both bridges. Each bridge updates its database to indicate that station A is in the direction of LAN X, and retransmits the frame on LAN Y. Say that bridge  retransmits at time t1 and bridge  a short time later t2. Thus B will receive two copies of the frame. Furthermore, each bridge will receive the other's transmission on LAN Y. Note that each transmission is a frame with a source address of A and a destination address of B. Thus each bridge will update its database to indicate that station A is in the direction of LAN Y. Neither bridge is now capable of forwarding a frame addressed to station A. CCN.9 Bridges and LANs with Alternative Routes CCN.10 Bridge and a repeater  Bridges, unlike repeaters, can connect networks in different geographical locations that require a telecommunication link for connectivity.  Wireless bridges are also available for limited-distance remote connections. CCN.11 Hub twisted pair  Hub is a device that interconnects incoming data onto all outgoing connections. hub  Works at the physical layer  It accepts a frame and immediately forwards it.  It does not examine or modify the contents of the frame.  When any workstation transmits data to the hub, the hub sends a copy of the data to all other workstations (or devices) connected to the hub. CCN.12 Managed hub and unmanaged hub Managed hub Unmanaged hub  Possesses enough  Contains little or no intelligence at processing power. all.  It can be managed from a  Cannot be controlled from a remote remote location. location.  Participate in network  Cannot participate in any kind of management operations. network management operations.  Less expensive than managed hubs.  Interconnection of two or more workstations in a local area network. CCN.13 Switches  A combination of a hub and bridge  Interconnect multiple workstations like a hub, but can also filter out frames providing a segmentation of the network.  Provide significant decrease in interconnection traffic  Increase the throughput of the interconnected networks without any additional cabling or rearranging of the network devices. CCN.14 Switch vs Bridge Bridge Switch  Frame is handled by software  Handled by hardware  Analyzes and forwards one  Can handle multiple frames at a frame at a time time  Use store-and-forward  Can have cut-through operation operation Two functions which a bridge cannot perform Bridge cannot determine most efficient path. Traffic management function. CCN.15 Store-and-forward switch and cut-through switch.  A store-and-forward switch stores each incoming frame in its entirety, then examines it and forwards it.  A cut-through switch starts to forward incoming frames before they had arrived completely.  As soon as the destination address is in, the forwarding can begin. CCN.16 Repeaters, Hubs, Bridges, Switches Devices are named according to the layer they process A bridge or LAN switch operates in the Link layer CCN.17 Bridging Between Buildings A Cycle of bridges CCN.18 Bridging across Longer Distances A Linksys Wireless Bridge CCN.19 Review Questions  Briefly explain the difference between the following terms. Transparent bridge and source routing bridge. Managed hub and unmanaged hub.  Briefly describe the importance of the “Fiber Distributed Data Interface (FDDI)” ring standard in a network.  State Shannon’s theorem that predicts the maximum data rate that can be achieved over a noisy communication channel of a given bandwidth. CCN.20 Additional Slides for your extra knowledge Networking Hardware  Hub/Repeater Hub CCN.22 Networking Hardware  More Hubs Hub Hub Hub Hub Hub CCN.23 Networking Hardware  Bridge 1 3 HUB BRIDGE HUB 2 4 Collision domain Collision domain CCN.24 Networking Hardware  Switch CCN.25 Networking Hardware  VLAN 1 5 Switch Switch 2 6 4 8 3 7 CCN.26 Networking Hardware  NIC MAC address Message Header Payload CCN.27 References  Chapters 15,16,17 and 18. Computer Networks and Internets, Douglas E. Comer, Prentice Hall. 5th Edition.  Chapter 10. Data and Computer Communications 8th Edition by William Stallings CCN.28