Reseau Cyclades

1
SECTION 5

• Reseau Cyclades
• The Cyclades Computer Network

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Cyclades

• Context background for the Internets Ancestor
  the Cyclades Network. Design Problem.
• Gross architecture
• Cigale plus hosts.
• Datagram or connectionless structure of Cigale.
• Connections virtual calls and the Transport
  Station.
• Background for Transport protocols.

3
Textbook reading

• none

4
Cylades Setting the stage

• 1970s telephone network PSTN
• 1-10 seconds to build a circuit call setup time
• Tolls for local calls except in N. America
• BER 10-2
• 300 b/s modem 1 000
• 56 KB/s modem 20 000

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Cylades Setting the stage

• French computing
• Incompatible mainframe computers
• IBM, GE, CII
• With incompatible proprietary O/Ss
• OS/360, GECOS, . . .
• A few minicomputers _at_ 20 000
• No PCs
• No microprocessor yet
• Dumb terminals

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Design Problem

• Combine
• 56 Kb/s noisy expensive links
• Minicomputers _at_ 20 000
• Hosts, and
• Dumb terminals
• To build telnet and ftp services

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Elements of solution

• Decompose the problem
• Separate the communications subnetwork Cigale
• From the overall network Cyclades

host
host
Cigale
host
host
Cyclades
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Cyclades architecture

• Functionality of subnet
• Move packets, period. I.E.
• Present it a packet
• represented at Level 3 as a datagram and
• Offered to Cigale by the Level 3 network access
  protocol and
• It tries to deliver the packet-- may fail why?

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Cigale is best-effort datagram service . . .

• Cigale has NO knowledge of circuits, calls, which
  gt
• No call setup fast access
• Easy interworking - just pass packets to the
  other network
• Late or lazy binding of resources
• e.g. Switch buffers, time on links
• to packets

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Lazy binding

• Implies
• Good utilization of resources
• Dont seize a resource until you REALLY need it ,
  BUT
• Unpredictable latency bandwidth for streams
  of packets
• Bad for traffic needing latency or bandwidth
  guarantees - Quality of Service
• i.e. multimedia

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Cigale abstract machine

• Every packet carries an opcode field
• Opcodes include
• Send
• Drop
• Echo
• Timestamp
• The machine has ONE datatype packet

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Cyclades

• WHAT ABOUT CALLS??

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Calls?

• Interactive terminal access telnet
• File transfer ftp
• Batch access Remote Job Entry
• web page viewing etc etc
• All require
• Sequencing
• EDAC by ARQ Automatic Repeat reQuest
• Dupe filtering
• Flow control
• - the definition of a virtual circuit or virtual
  call
• Which killer app does NOT??

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Virtual Circuits?

• VC construct is essential but
• Exists
• entirely in the hosts physically
• At OSI L4 logically
• At Internet Level 4 logically
• Implemented as the Station de Transport
  Transport Station or TS cf Internet tcp
• Soo

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Transport Station
host
host
L3
cigale
L2
TS
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Implications

• TS is not bound to one host - TS and user can
  move from host to host
• Multiple TSs per host are possible
• User groups can change their TS design without
  affecting subnet
• Subnet can change without affecting TS
• But . . .

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Implications

• Subnet operator cannot
• Do eager resource binding -no fixed path for a
  stream of packets
• Control congestion by per-stream methods
• Do billing per-stream
• therefore cannot Guarantee absolute QoS

18
Cyclades design

• Its Datagram-only subnet design carried into
  Internet without acknowledgement