Design of a Diversified Router: Common Router Framework

1. Design of aDiversified Router:Common Router Framework Summary by Mike Wilson Originals by Jon Turner, John DeHart, Fred Kuhns

2. MR-1 . . . MR-n QM Common Router Framework (CRF) Functional Blocks Parse HeaderFormat • Blocks run on IXP 28XX microengines • Have fast neighbor transfer registers for pipeline • Some blocks use queues in fast memory • Packet data is stored in slow memory (DRAM) • Parse • Third-party code for each virtual router • Extracts key values from packet, used to look up results for Header Format • Header Format • Third-party code for each virtual router • Re-writes packet based on lookup results Lookup Tx Rx DeMux MR-1 . . . MR-n

3. MR-1 . . . MR-n QM Common Router Framework (CRF) Functional Blocks Parse HeaderFormat • Requirements • Parse, Header Format must not impact other virtual routers • Memory isolation • Resource allocation • Processor sharing Lookup Tx Rx DeMux MR-1 . . . MR-n

4. MR-1 . . . MR-n QM Common Router Framework (CRF) Functional Blocks Parse HeaderFormat • Memory Isolation • Each third-party block receives a block of SRAM and block of DRAM • Packet memory is allocated as packets arrive • Inter-router isolation is done by static analysis at admission • Routers may access their own SRAM, their own DRAM, and any packet they are currently processing • Routers may allocate new packets or save partially processed packets • Because of speed requirements, run-time checks are not an option • Currently done manually – this is an upcoming topic of interest • Should not be an exceptionally difficult problem for routers that do not save pointers between invocations Lookup Tx Rx DeMux MR-1 . . . MR-n

5. MR-1 . . . MR-n QM Common Router Framework (CRF) Functional Blocks Parse HeaderFormat • Resource Allocation • Done at admission time on a general-purpose controller • New routers request resources when they request fast path instantiation • Resource manager determines whether the request can be granted and admit or reject the fast path • Resources do not change dynamically Lookup Tx Rx DeMux MR-1 . . . MR-n

6. MR-1 . . . MR-n QM Common Router Framework (CRF) Functional Blocks Parse HeaderFormat • Processor sharing • Must be via static analysis at admission time – we have no pre-emption mechanism • Can analyze program for WCET (Worst-Case Execution Time) • We have a method for static analysis of code • Analyze blocks to find paths that run over budget, warn developer • Crop those paths which cannot be proven to stay under budget • Partial Program Admission • Scheduling is done by packet arrival • This is a significant limitation. To run at line rate, all virtual routers must be able to maintain line rate. • 10Gbps with min-sized packets, 85 cycles per packet • In our newest design, we have re-organized to fix this. Lookup Tx Rx DeMux MR-1 . . . MR-n

7. NPE Version 2 Block Diagram NPUA Sram2NN (1 ME) SRAM SRAM GPE Decap, Parse, LookupA, AddShim (8-10 MEs) RxA (2 ME) TxA (2 ME) StatsA (1 ME) SRAM TCAM SPI Switch SPI Switch Switch Blade flow control? FreeList MgrB (1 ME) StatsB (1 ME) SRAM SRAM TxB (2 ME) HdrFmt/ SubEncap (4 MEs) QueueManager (4 MEs) LookupB&Copy (2 ME) RxB (2 ME) SRAM Scr2NN (1 ME) SRAM NPUB

8. New Requirements • Header Format is now after Queue Managers • We can use the QMs to allow for “slow” virtual routers. • QM only allows packets into Header Format at a limited rate • Rate is chosen to match the processing needs • Parse input rate is controlled via queuing in the line cards(not shown in diagram) • Router instantiation: • Developer provides code block, desired WCET, desired bandwidth • We transform the program to remove all “over budget” paths • Using the new WCET and bandwidth, resource manager determines queue release rates, proper sharing of excess resources • Resource manager admits or rejects new router