Internetworking Fundamentals (Lecture #4) Andres Rengifo Copyright 2008.
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Internetworking Fundamentals (Lecture #4) Andres Rengifo Copyright 2008
Introduction to Internetworking (Cont.) Different type of LAN systems –High Speed Office LANs High speed user connectivity via 100Mbps links. Usually sharing the environment with a few network printers, scanners, etc removing the necessity to have one printing or scanning device per user. Server access is through the network via high speed backbone connections to centralized server farms that live somewhere in the network not in the same LAN where the users are located.
Introduction to Internetworking (Cont.) –Backend Networks These networks should be introduced in order to isolate the server to server traffic at very high rates of data transfer. It is a secure network where most of the application servers reside and are accessible by other servers. When a user’s request comes through a front end graphical interface such as a web browser, the link that is clicked takes the data over the production network to the backend server where it is processed. i.e. a trade or quote request.
Storage Area Networks –SANs provide a historical and chronological way of saving data to servers that can store information for a long time. –Typically storage was done via RAID tapes directly attached to each server or group of servers consuming a lot of real estate in a data center. –SAN networks introduce the idea of passing the same type of commands that a SCSI (Small Computing System Interface) cable provided for the read/write/copy, etc executed by the servers over a Fiber channel at very high speeds. This information is stored in very large disk arrays that are shared by other applications.
Backbone LANs –A backbone LAN was originally deployed along the “backbone” of a building usually from top floor to bottom floor through a riser closet which was in the same location on every floor. –Each end of the cable, known as Ethernet or ThickNet, was terminated with a 50 Ohms resistor to dissipate the signal at each end. –The distance could not surpassed 500 meters otherwise, there would be a need for a repeater since the signal would be distorted and with noise. –The thickness was 0.4 I nches and each tap to the backbone had to be separated by 2.5 meters or multiple of these in order for the signals not to reflect or add phase which would cause disruption and noise.
Topologies –Most of the topologies use MAC protocols or Data Link Layer protocols such as the IEEE 802.x suite of protocols to access media such as bus topologies, ring topologies, wireless networks, fiber optic channels, bridging and switching, etc. Bus –It is a shared environment where all stations are attached to a common wire via taps or repeaters that allow each station to transmit on the bus at full duplex modes. This type of topology requires two terminators, one at each end to dissipate the signal once it has been sent on the wire.
Introduction to Internetworking (Cont.) Tree –A tree topology is a generalization of a bus topology. There are multiple “branches” that stem of the bus. There is no closed loops in the topology and every branch has to have terminators as well in order to dissipate the signals. Each station on the bus or tree has a unique identifier which allows for two devices to send data to each other. –An advantage of a tree/bus topology is that any device that has a problem can be removed from the topology without affecting the others. –A disadvantage of a tree/bus topology is that there exists contention for bandwidth when two stations decide to send at the same time. This information sometimes collides creating packet loss and errors.
Ring –It consists of a set of repeaters joined by point to point links in a closed loop. The links are unidirectional and traffic is send in one direction only. –Data is transmitted in the form of frames and through all the repeaters attached to the ring. –One station trying to communicate with another will put the frame on the ring, the frame will pass through multiple stations until it finds the destination. –The destination copies the frame in its buffer, returns the original frame back to the ring. When the frame gets back to the original sender, it is discarded and removed from the ring.
Star –Centralized topology where there is a notion of a central switch controlling access between each station. –Delivery of data can be in two forms: »Broadcast – every port is flooded with the information »Frame switched – only the interested port will receive the data. –Advantage of this topology is that the centralize point can control delivery of traffic to every device. –Disadvantage of this topology is that the centralize switch is a single point of failure.
Medium Access Control Mechanisms –A mechanism that allows each node to access the medium in an orderly and efficient way to use the medium’s capacity. Round Robin Reservation Contention
Introduction to Internetworking (Cont.) The ALOHA network –Developed at the University of Hawaii and it is the predecessor of what we now know as Ethernet. –Multiple connected sources to a medium were able to send and receive data. When frames reached their destinations, acknowledgements would be issued to the sender but if there was no acknowledgement, a retransmission would take effect. –Multiple stations could be sending at the same time causing frames to collide. This led to data loss and congestion.
Introduction to Internetworking (Cont.) CSMA/CD –Carrier Sense Multiple Access with Collision Detect. This is the modern Ethernet. 1. If the medium is idle, transmit, otherwise, go to 2. 2. If the medium is busy, continue to listen until the channel is idle and then send immediately. 3. If a collision is detected during transmission, transmit a brief jamming signal to assure that all stations know that there has been a collision and then cease transmission. 4. After transmitting the jamming signal, wait a random period of time, then attempt to transmit again and repeat step 1.