3_Computer_Networks

3_Computer_Networks - Distributed Database Systems Computer...

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Distributed Database Systems Computer Networks (Chap. 3 - Ozsu) 605.741 David Silberberg
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D. Silberberg Distributed Database Systems Computer Networks 2 Why the Network is Important Distribution is an important aspect of distributed database systems Network Bandwidth limits the amount of data that can be shipped between processors – Limits the speed of executing joins – Can determine the join strategies Network Latency limits the start time of distributed operations – If there is a choice of network paths to use, the latency can affect which one is selected – May determine the query execution order – May affect the design of the distributed database
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D. Silberberg Distributed Database Systems Computer Networks 3 Why the Network Topology is Important • We are used to treating the network as a black box • However, the underlying network topology may influence query execution plans • We will define different topology options today … • … and demonstrate how they influence query processing in future lectures
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D. Silberberg Distributed Database Systems Computer Networks 4 Why Protocols are Important • Protocols influence the type of service one can get from the network • The examples throughout the course assume standard TCP/IP protocols • However, different protocol options will be presented today as food for thought – Quality of Service (QoS) is important in many domains – A QoS-based DDBMS may require a modified query processing approach to maintain QoS • Different protocols have different costs – Important information for query planning and execution
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D. Silberberg Distributed Database Systems Computer Networks 5 Computer Networks • Interconnected set of autonomous computers that exchange information • Computers are called by different names nodes hosts sites • Sites usually imply software, as well as hardware
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D. Silberberg Distributed Database Systems Computer Networks 6 Data Communication - Definitions Signals are electronic or electromagnetic encoding of data Transmission is the propagation of the signals • Equipment is connected by links - physical • Links have one or more channels - logical • Signals are – Digital (e.g., telephone - new) – Analog (e.g., telephone - old)
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D. Silberberg Distributed Database Systems Computer Networks 7 Channels have Capacities Rate of data that can be transmitted Capacity is commonly referred to as bandwidth Analog - (highest - lowest) frequency/second Digital - bits/second Analog telephone channels – 33 Kbps Digital telephone channels – 56 or 64 Kbps T1 Broadband channels – 1.5 Mbps DSL – up to 3 Mbps Ethernet – 10+ Mbps Fast-E(thernet) – 100 Mbps Gig-E(thernet) – 1,000 Mbps •…
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D. Silberberg Distributed Database Systems Computer Networks 8 Communication Operation Modes • Digital data over analog medium is modulated ( bits turned to amplitude, frequency, and phase ) • Higher bandwidths allow multiplexing – Frequency (FDM) –T im e (TDM ) • Operating mode – Simplex – Half-duplex – Full-duplex
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D. Silberberg
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This note was uploaded on 12/23/2009 for the course DBST 663 taught by Professor Tba during the Spring '09 term at MD University College.

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3_Computer_Networks - Distributed Database Systems Computer...

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