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1
Next Few Classes
Networking basics Protection & Security
2
Distributed Systems distributed system: set of physically separate
processors connected by one or more communication links
no shared clock or memory
Many systems today distributed in some way e-mail, p2p system, network printers, remote
backup, web...
P2
P1
P3P4
3
Parallel vs. Distributed Systems
Tightly-coupled systems: “parallel processing” Processors share clock, memory, run one OS Frequent communication
Loosely-coupled systems: “distributed computing” Each processor has own memory, runs
independent OS Infrequent communication
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Advantages of Distributed Systems
Resource sharing Computational speedup Reliability Communication
5
Networks Goal: provide efficient, correct, robust
message passing between two separate nodes
Local area network (LAN) – connects nodes in single building, fast & reliable (Ethernet, WLAN) Media: twisted-pair, coax, fiber, radio Bandwidth: 10Mbps – 1Gbps
Wide area network (WAN) – connects nodes across large geographic area (Internet) Media: fiber, microwave links, satellite channels,
radio Bandwidth: 1.544MB/s (T1), 45 MB/s (T3),…,
1Gbps
6
LAN Topologies
Two basic topologies: Point-to-point Bus
Connection of nodes impacts: Speed: maximum & average
communication time Reliability: fault tolerance Expense
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Point-to-Point Topology: Fully-connected
Each message takes one “hop” Node failure – no effect on
communication with others Expensive – impractical for WANs
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Point-to-Point Topology: Partially connected
Links between some, but not all nodes Less expensive, less tolerant to failures
Single node failure can partition network Sending message takes several hops
Needs routing algorithms
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Point-to-Point Topology: Tree
Tree structure: network hierarchy Messages past between direct descendants
Max message cost? Not failure tolerant
Any interior node fails – network partitioned
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Point-to-Point Topology: Star
Star network: all nodes connect to central node Each message takes how many hops? Not failure tolerant Inexpensive – sometimes used for LANs
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Point-to-Point Topology: One-directional Ring
Given n nodes, max hops? Inexpensive Fault-tolerant?
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Bus Network Topologies
Bus nodes connect to common network
Linear bus – single shared link Nodes connect directly to each other via
bus Inexpensive (linear in # of nodes) Tolerant of node failures Traditional Ethernet LAN
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Bus Network Topologies
Ring bus – single shared circular link Same technology & tradeoffs as
linear bus
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WAN Topology: Internet Graph
15
Principles ofNetwork Communication
Data broken into packets Basic unit of transfer
Packets sent through network Routers at switching points control packet
flow
Road analogy: Packets = cars Network = roads router = traffic lights (intersection) Too many packets on shared link/node =
traffic jam
16
What’s a protocol?a human protocol and a computer network protocol:
Q: Other human protocols?
Hi
Hi
Got thetime?
2:00
TCP connection req
TCP connectionresponse
Get http://www.engr.uconn.edu/~bing
<file>
time
17
What’s a protocol?
human protocols: “what’s the time?” “I have a question” introductions
… specific msgs sent… specific actions
taken when msgs received, or other events
network protocols: machines rather
than humans all communication
activity in Internet governed by protocols
protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission,
receipt, other events
18
Internet Protocol Stack application: supporting network
applications FTP, SMTP, HTTP
transport: host-host data transfer TCP, UDP
network: routing of datagrams from source to destination
IP, routing protocols link: data transfer between
neighboring network elements PPP, Ethernet
physical: bits “on the wire”
application
transport
network
link
physical
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Layering: Physical Communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
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Protocol Layering and Data
Each layer takes data from above adds header information to create new data unit passes new data unit to layer below
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
21
Summary
Virtually all computer systems contain distributed components
Networks connect them Key tradeoffs:
Speed Reliability Expense