EECS 325425, Fall 2005 August 29

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EECS 325/425, Fall 2005August 29

• Shudong Jin
• jins_at_case.edu
• sxj63_at_case.edu

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Course Information

• Handouts
• Course objectives and topics
• Policy and schedule etc
• http//vorlon.cwru.edu/sxj63/EECS325-F05/
• Case Blackboard

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What is A Computer Network?

• What happen when I click on this link?
• http//mlb.mlb.com/NASApp/mlb/index.jsp?c_idcle
• In less than 1 second, dozens of computers in the
  country are involved hundreds of kilo bytes
  travel thousands of miles (access networks to
  backbone to access networks).
• We will not learn to know how much profit ISPs
  (e.g. ATT) make from this.
• But we will learn more than a dozen protocols who
  work together HTTP, FTP, DNS, TCP, UDP, IP, BGP,
  OSPF, ARP, Ethernet CSMA, wireless
• So what is a protocol?

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The Internet packet-switched network

• packet-switching network A switched network that
  transmits data in the form of packets
• Large files are divided into segments by the
  sender
• The receiver reassembles them
• Both sender and receiver are end-hosts
  well-known servers, and billions of users, etc.
• E.g. IBM EC web sites
• ISPs build networks (with up to thousands of
  routers) to provide services to the customers
• E.g. ATT
• Routers transparent to users, but collectively
  doing the networking to help the end-hosts.
• E.g. CISCO

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Some basic concepts

• Bandwidth
• Delays
• Processing delay
• Propagation delay (how large is the
  coast-to-coast delay?)
• Transmission delay
• Queuing delay (why do we need queues? Small queue
  or large queue?)
• Round-trip time (RTT)
• An application in host A sends a 1KB data packet
  to host B via a single duplex link with BW
  100KBps. Then host B sends back a 100-byte
  acknowledgement packet. Assume propagation delay
  is 5ms and each host requires 0.5ms processing
  delay per packet.
• Q what is the RTT observed by the application?
• Packet losses (how to handle them?)
• Due to data corruption, e.g., collision
• Due to drops
• Due to excessive delay
• Throughput
• What do you see when you are downloading a large
  file using FTP?