11. Interconnecting DS Flashcards
Role of the interconnect and the idea of a protocol stack
Interaction Goals?
Interaction is for coordination and cooperation.
coordination: timeline of events matters
Cooperation: could degrade into uncontrolled competition for resources
Interaction modes?
By sharing address space.
By synchronous communication mechanisms
By Message passing (Protocols)
What is an interconnect?
Physical or logical connection between two electronic devices or networks
Pros and cons of a short interconnect?
Relatively cost neutral.
Need to be aware of process concurrency, synchronisation of interactions, indeterminacy of failures.
What do we need to be aware of for a significantly long interconnect?
Not cost-neutral.
Size matters.
Message exchange is needed, network effects are felt
What different computer (instruction/memory) architectures are there?
SISD- single instruction single data
SIMD- single instruction, multiple data
MISD- multiple instructions, single data
MIMD- multiple instructions, multiple data
Describe SISD
centralised, sequential.
At each cycle we obtain one data item and fetch one instruction to operate on it.
Without an interconnect, a single algorithm has cost neutral access to a single data space
Describe SIMD
Data-level parallelism.
At each cycle, we obtain many data items and fetch one single instruction to operate on them in parallel. Modern GPUs are of this kind.
If we introduce an interconnect, we can apply an algorithm to distinct partitions of data space we have distributed for that purpose. Access to data through interconnect- not cost neutral
Describe MISD
Many programs applied to a single dataset (or item).
At each cycle, we obtain one data item and fetch multiple instructions to operate on it in parallel. Used in fault tolerance.
Use the interconnect to apply several algorithms to the same data. Access to the data is not cost neutral- through interconnect.
Describe MIMD
Many instructions operate on their own dataset. inherently-distributed systems. Interconnect binds self-sufficient, autonomous components.
At each cycle we obtain many data items and fetch multiple instructions to operate on them. Modern PCs are of this kind.
Interconnect is not cost neutral but the grain of functionality is much larger.
What is the advantage of MIMD?
Scalability by the addition/removal of complete, fully functional components.
Scaling out: if the problem grows, you grow the system by adding more of the same components.
Scaling up: if the problem grows, you change the system for a new, larger one
What is MIMD also known as? What is the interconnect?
Shared nothing architecture. The interconnect is a full blown network.
This exists independently as a complex, physical fabric. Its use is mediated by complex, sophisticated software.
Message exchange over the interconnect requires?
Naming and addressing.
Transportation and routing
The internet is software driven. Its software architecture is best known as a protocol stack. Describe each layer
Top:
Application Semantics (send/retrieve emails)
Transport- making sure a logical channel exists for messages to flow through
Internet- making sure bits reach their destination.
Link- making sure there is a real channel
Physical- about the physics of it all
Give example protocols for each layer. Why is it an hourglass model?
Application- HTTP Transport - TCP Internet- IP Link- MAC Physical- Wifi
Hourglass: very varied applications at top, very varied devices at bottom, as simple as possible between
