Transcript Closure - The University of Sydney

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NETS 3303
Networked Systems
Revision
Bjorn Landfeldt, The University of Sydney
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Overall
• Understand WHY protocols were designed
the way they were
• Understand what is good and bad with the
designs
• Read through relevant RFCs
• There are some fundamental mechanisms in
the protocol stack. Understand these
mechanisms.
Bjorn Landfeldt, The University of Sydney
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Layered Model
• Divide a task into pieces and then solve
each piece independently (or nearly so).
• Establishing a well defined interface
between layers makes porting easier.
• Major Advantages:
Code Reuse
Extensibility
Bjorn Landfeldt, The University of Sydney
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IP Model Basics
User data
Synchronisation
Application
Transport
Network
Data-link
Physical
Bjorn Landfeldt, The University of Sydney
End-to-end flow control
Multiplexing
Global Addressing
Packetisation
Framing
Local Addressing
Voltage
Modulation
Example functions
In different layers
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Data-link Layer
•
•
•
•
Provides access to local network
Supplies local address
Transports traffic over one hop only
Many different technologies with different
characteristics
• Wired and wireless
Bjorn Landfeldt, The University of Sydney
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IP
• IP operates in the network layer
– packet delivery service (end-to-end).
– translation between different data-link
protocols.
Bjorn Landfeldt, The University of Sydney
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IP
• IP provides connectionless, unreliable
delivery of IP datagrams.
• Connectionless: each datagram is
independent of all others.
• Unreliable: there is no guarantee that
datagrams are delivered correctly or at all.
Bjorn Landfeldt, The University of Sydney
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IP Addresses
• IP addresses are logical addresses (not
physical)
• 32 bits.
• Includes a network ID and a host ID.
• Every host must have a unique IP address.
• IP addresses are assigned by a central
authority (the NIC at SRI International).
Bjorn Landfeldt, The University of Sydney
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ICMP
• “Companion” to IP, used for queries and
error signalling.
• Common usage:
– Host or network unreachable
– Redirect
– Echo request/reply (ping)
Bjorn Landfeldt, The University of Sydney
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Transport Layer
• User Datagram Protocol, UDP adds:
– Multiplexing (ports)
– Error detection (CRC over entire packet)
• Transport Control Protocol, TCP also adds:
– Error correction
– Flow control
– Robustness in case of failure
Bjorn Landfeldt, The University of Sydney
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TCP Characteristics
• Connection oriented
– Three way handshake
• Reliable
– Error detection
– Error correction
• Buffer management and flow control
– Sliding window
– Slow Start and Congestion Avoidance
• Stream oriented
Bjorn Landfeldt, The University of Sydney
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UDP vs. TCP
• TCP introduces latencies
– Session set-up
– Data retransmission
• Flow control mechanism unsuitable for
CBR applications
• TCP – Stream oriented, UDP – Datagram
oriented
• TCP – reliable, UDP - unreliable
Bjorn Landfeldt, The University of Sydney
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Types of Traffic
• Different applications generate different
types of traffic e.g.
–
–
–
–
Web pages (delay sensitive)
FTP (BW sensitive)
Streamed Media (BW sensitive)
Conversational Multimedia (delay and BW)
Bjorn Landfeldt, The University of Sydney
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Cast?
• Unicast – flow from one host to another
host
• Broadcast – flow from one host to all local
hosts
• Directed Broadcast – flow from one host to
all hosts on a foreign network
• Multicast – flow between hosts in a group
Bjorn Landfeldt, The University of Sydney
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RTP
• TCP unsuitable for RT media
• UDP has two major drawbacks:
– Lack support for lost or reordered packets
– Lack support for jitter compensation
• RTP provides these functions
Bjorn Landfeldt, The University of Sydney
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That’s it
Bjorn Landfeldt, The University of Sydney