01-Intro - BI M 310: C pute Ne om r tworks e dne Tim : We...

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1 BIM 310: Computer Networks Time: Wednesday 9:30-12:00, Thursdays 11:00-13:00 Location: BLab4 Instructor: Emre Kaçmaz – Alper Bilge Grading: Midterm I – 20% Midterm II – 25% 1 Final – 40% Homeworks - 15%
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2 High-level picture of the problem Transmission System Sender Node Destination Node Problem: Transmit a message M from a source node to one or more destination node(s) through a transmission system=computer network Nodes: Things that send/receive messages . Examples are PCs, labtops, PDAs, Internet telephones etc.
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3 Transmission System Sender Node Destination Node mesh of interconnected routers (switches) inter-connected in an arbitrary topology the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks”
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4 Circuit-Switching: Idea End-end resources reserved for “call” call setup required After the call, the resources (the circuit bandwidth) is dedicated and is not shared with other calls circuit-like (guaranteed) performance This course is not about circuit-switching, but we will touch on it so that you get an idea on how it works
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5 Circuit-Switching: Data Flow After the call is setup, the data flows through the circuit bit by bit No store or forward delay at the routers (switches) As soon as a bit from the connection arrives at a router, it is immediately forwarded over the outgoing link without any delay So the transmission time is independent of the # of links from the source to the destination
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6 CS: Sharing Link Capacity How do several calls using the same link share the link? In the example above, we have 2 calls sharing 2 links in the middle of the network 2 Approaches Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM)
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7 Circuit-Switching: FDM FDM: Divide the link capacity into several frequency bands (space-wise division) and allocate each band to a different call Each circuit gets the fraction of the bandwidth continuously (all the time) Also used by radio/TV transmission through the air
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8 Circuit-Switching: TDM TDM: Divide the link capacity in time into several slots and allocate each slot to a different call Each circuit gets ALL of the link bandwidth periodically Used by wireless telephones (GSM)
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9 Circuit Switching Example 1890-current: Phone network Fixed bit rate Mostly voice Not fault-tolerant Components extremely reliable Global application-level knowledge throughout network
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10 Circuit Switching: Summary Establish a dedicated circuit before sending data Dedicated resources Data flows through the circuit No store and forward at the switches (routers) Good for constant-bit-rate traffic such as voice BUT Dedicated resources means if no data is flowing the circuit, the allocated resources are idle Leads to waste of network resources
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01-Intro - BI M 310: C pute Ne om r tworks e dne Tim : We...

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