montek singh comp790-084 nov 10, 2011. design questions at various leves ◦ network adapter design...
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Design questions at various leves◦ Network Adapter design◦ Network level: topology and routing◦ Link level: synchronization and timing
Discussion◦ benefits and challenges◦ key research problems
Today: More on Network-on-Chip
Sockets abstraction◦ orthogonalize computation and communication
hide networking details the core-side interface provides send/receive
commands Standardization
◦ Open Core Protocols (OCP)◦ Virtual Component Interface (VCI)◦ Advanced eXtensible Interface (AXI)◦ Device Transaction Level (DTL)
Adapter level
Adapter responsibilities◦ encapsulation of traffic
for the underlying communication◦ management of services
that the network provides
Implementations: several◦ Muttersbach et al.◦ Bjerregaard et al.◦ Radulescu et al.◦ HERMES◦ Bhojwani/Mahapatra◦ …
Adapter level
Network responsibility◦ deliver messages from source to destination◦ hardware support for basic communication
commands (send/receive)◦ well-built network should appear as a logical wire
[Dally/Towles 2001]
Two main considerations◦ topology
layout and connectivity◦ protocol
how nodes and links are used, routing etc.
Network level
Network responsibility◦ deliver messages from source to destination◦ hardware support for basic communication
commands (send/receive)◦ well-built network should appear as a logical wire
[Dally/Towles 2001]
Two main considerations◦ topology
layout and connectivity◦ protocol
how nodes and links are used, routing etc.
Network level
Circuit vs. packet switching◦ circuit: the entire path is set up and reserved for
the entire duration of data transport◦ packet: each packet is forwarded on a per-hop
basis Connection-oriented vs. connectionless
◦ connection: dedicated logical path established prior to data transport may or may not be circuit-switched (logically)
Protocol questions
Deterministic vs. adaptive routing◦ deterministic: path is determined by source and
destination pair, alone◦ adaptive: dynamically determined, incl.
arbitration, congestion, load balancing, etc. Minimal vs. nonminimal routing
◦ always shortest path or not? Delay vs. loss model
◦ delay model: data packets never dropped, but may be delayed
◦ loss model: data packets may be dropped due to congestion, requiring retransmission
Protocol questions
Central vs. distributed control◦ central: global routing decisions (e.g., bus
control)◦ distributed: decisions made locally
Protocol questions
Flow control: control the flow of data with some objective (delay, loss, etc.)
Virtual channels: 2 to 16 VCs per physical channel!◦ avoid deadlocks since they are mutually
independent◦ optimize wire utilization by letting several VCs
share a wire◦ improve performance because of fewer stalls◦ provide differentiated services for QoS
Protocol: Flow Control
Synchronization◦ different clock domains◦ maybe network is asynchronous
Challenges:◦ metastability◦ arbitration◦ synchronization
Link level questions
Globally Asynchronous Locally Synchronous◦ network is elastic, asynchronous◦ cores may be clocked
Link level: GALS
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