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EEC-484/584 Computer Networks

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(Part of the s are based on Drs. Kurose & Ross's s for their Computer Networking book) ... When new packet arrives from application layer, it is given ... – PowerPoint PPT presentation

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Title: EEC-484/584 Computer Networks


1
EEC-484/584Computer Networks
  • Lecture 12
  • Wenbing Zhao
  • wenbing_at_ieee.org
  • (Part of the slides are based on Drs. Kurose
    Rosss slides for their Computer Networking book)

2
Outline
  • Reminder
  • Nov. 14 (Wed) CSU IST data center tour
  • Nov. 12 (Mon) no class, in honor of the Veterans
    Day
  • Quiz3 results
  • Introduction to transport layer
  • Multiplexing/demultiplexing
  • Reliable data transfer mechanisms
  • Sliding window protocols (part I)

3
EEC 484 Quiz3 Results
  • High 98, low 75, average 89.3
  • Q1 46.7/50, Q2 18.5/20, Q3 9.2/10, Q4 15/20

4
EEC 584 Quiz3 Results
  • High 100, low 75, average 84.4
  • Q1 40.7/50, Q2 19/20, Q3 8.5/10, Q4 16.2/20

5
Transport Layer
  • Our goals
  • Understand principles behind transport layer
    services
  • multiplexing/demultiplexing
  • reliable data transfer
  • flow control
  • congestion control
  • Learn about transport layer protocols in the
    Internet
  • UDP connectionless transport
  • TCP connection-oriented transport
  • TCP congestion control

6
Transport vs. Data Link Layer
  • Similarities deal with error control,
    sequencing, flow control
  • Difference operating environments

Environment of the transport layer
Environment of the data link layer
7
Transport vs. Network Layer
  • Network layer logical communication between
    hosts
  • Transport layer logical communication between
    processes
  • Relies on, enhances, network layer services

8
Internet Transport-Layer Protocols
  • Reliable, in-order delivery (TCP)
  • congestion control
  • flow control
  • connection setup
  • Unreliable, unordered delivery UDP
  • no-frills extension of best-effort IP
  • Services not available
  • delay guarantees
  • bandwidth guarantees

9
Multiplexing/Demultiplexing
delivering received segments to correct socket
gathering data from multiple sockets, enveloping
data with header (later used for demultiplexing)
process
socket
application
P4
application
application
P1
P2
P3
P1
transport
transport
transport
network
network
network
link
link
link
physical
physical
physical
host 3
host 2
host 1
10
How Demultiplexing Works
  • Host receives IP datagrams
  • Each datagram has source IP address, destination
    IP address
  • Each datagram carries 1 transport-layer segment
  • Each segment has source, destination port number
  • Host uses IP addresses port numbers to direct
    segment to appropriate socket

32 bits
source port
dest port
other header fields
application data (message)
TCP/UDP segment format
11
Reliable Data Transfer
  • characteristics of unreliable channel will
    determine complexity of reliable data transfer
    protocol (rdt)

12
Reliable Data Transfer
  • Basic reliable data transfer mechanisms
  • Acknowledgement
  • Retransmission
  • Sequence numbers

13
Sliding Window Protocols
  • Full-duplex Use same connection for data in both
    directions (A?B and B?A)
  • Interleave data and ack packets
  • B piggybacks its ack for As packet onto Bs next
    packet
  • Savings of header in separate ack packet
  • If B sends data infrequently, use timeout to
    determine when B should send ack in separate ack
    packet

14
Sliding Window Protocols
  • Each packet contains sequence number in ranges
    0..2n-1 (for n-bit sequence numbers)
  • Sending window list of consecutive sequence
    numbers of packets that sender is permitted to
    send

3
ack
15
Sliding Window Protocols
  • When new packet arrives from application layer,
    it is given next highest sequence number, and
    upper edge of window is incremented
  • When ack arrives from receiver, lower edge of
    window is incremented
  • Within sending window, packets sent but not acked
  • Sender must keep those packets for possible
    retransmission
  • If max window size w, need w buffers

16
Sliding Window Protocols
  • Receiving window list of consecutive sequence
    numbers of packets that receiver is permitted to
    accept
  • When packet with (seq num lower edge of window)
    arrives
  • Packet is passed to higher layer
  • Ack is generated
  • Window slid down by 1 (remains same size as was
    initially)

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