Lecture06 - Thursday, April 17 Quiz #1 Scores are posted...

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Thursday, April 17 Quiz #1 Scores are posted Pick up Questions? Lab #2 Due Friday before midnight Midterm #1 Tuesday, April 22, in class Program #1 Due Friday, May 2 accepted through Sunday, May 4, with 10% late penalty
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Today’s topics Transport-layer protocols UDP Error detection Socket programming Program #1
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Transport services and protocols provide logical communication between app processes running on different hosts transport protocols run in end systems sender : breaks app messages into segments , passes to network layer receiver : reassembles segments into messages, passes to application layer more than one transport protocol available to apps Internet: TCP and UDP application physical transport network data link logical end-end transport
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Transport vs. network layer network layer: logical communication between hosts transport layer: logical communication between processes Household case: 12 kids (East coast house) sending letters to 12 kids (West coast house) Ann is responsible for the house at East coast Bill is responsible for the house at West coast Postal service is responsible for between houses Household analogy: processes = kids messages = letters hosts = houses house addresses = IP address kids’ names = port numbers transport-layer protocol = Ann and Bill network-layer protocol = postal service link-layer protocol = routing physical-layer = planes, control towers, etc
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Internet transport-layer protocols unreliable, unordered delivery: UDP no-frills reliable, in-order delivery (TCP) connection setup congestion control flow control application transport network data link physical logical end-end transport
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Multiplexing/demultiplexing Multiplexing at sending hosts: gathering data from multiple sockets, encapsulating data with header (later used for demultiplexing) Demultiplexing at receiving host: delivering received segments to correct socket
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How demultiplexing works host receives IP datagrams (at the network layer) each datagram has source IP address, destination IP address each datagram carries 1 transport-layer segment each transport-layer segment has source, destination port number host uses IP addresses & port numbers to direct segment to appropriate socket source port # dest port # 32 bits application data (message) other header fields TCP/UDP segment format
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Connectionless demultiplexing UDP socket identified by two-tuple: ( dest IP address, dest port number) When host receives UDP segment: checks destination port number in segment directs UDP segment to
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Lecture06 - Thursday, April 17 Quiz #1 Scores are posted...

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