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* build: Update copyright to 2021Dimitri Staessens2021-01-0340-40/+40
| | | | | | | Happy New Year, Ouroboros! Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix flow_accept without opensslDimitri Staessens2020-12-122-5/+7
| | | | | | | | DH key creation was returning -ECRYPT if opennssl is not installed, instead of success (0). Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix return value in function returning voidDimitri Staessens2020-12-121-1/+1
| | | | | | | This causes builds to fail on systems where OpenSSL is not available. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* ipcpd: Add congestion avoidance policiesDimitri Staessens2020-12-023-6/+24
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This adds congestion avoidance policies to the unicast IPCP. The default policy is a multi-bit explicit congestion avoidance algorithm based on data-center TCP congestion avoidance (DCTCP) to relay information about the maximum queue depth that packets experienced to the receiver. There's also a "nop" policy to disable congestion avoidance for testing and benchmarking purposes. The (initial) API for congestion avoidance policies is: void * (* ctx_create)(void); void (* ctx_destroy)(void * ctx); These calls create / and or destroy a context for congestion control for a specific flow. Thread-safety of the context is the responsability of the flow allocator (operations on the ctx should be performed under a lock). ca_wnd_t (* ctx_update_snd)(void * ctx, size_t len); This is the sender call to update the context, and should be called for every packet that is sent on the flow. The len parameter in this API is the packet length, which allows calculating the bandwidth. It returns an opaque union type that is used for the call to check/wait if the congestion window is open or closed (and allowing to release locks before waiting). bool (* ctx_update_rcv)(void * ctx, size_t len, uint8_t ecn, uint16_t * ece); This is the call to update the flow congestion context on the receiver side. It should be called for every received packet. It gets the ecn value from the packet and its length, and returns the ECE (explicit congestion experienced) value to be sent to the sender in case of congestion. The boolean returned signals whether or not a congestion update needs to be sent. void (* ctx_update_ece)(void * ctx, uint16_t ece); This is the call for the sending side top update the context when it receives an ECE update from the receiver. void (* wnd_wait)(ca_wnd_t wnd); This is a (blocking) call that waits for the congestion window to clear. It should be stateless (to avoid waiting under locks). This may change later on if passing the context is needed for different algorithms. uint8_t (* calc_ecn)(int fd, size_t len); This is the call that intermediate IPCPs(routers) should use to update the ECN field on passing packets. The multi-bit ECN policy bases the value for the ECN field on the depth of the rbuff queue packets will be sent on. I created another call to grab the queue depth as fccntl is write-locking the application. We can further optimize this to avoid most locking on the rbuff. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Reduce timerwheel CPU consumptionDimitri Staessens2020-11-252-1/+10
| | | | | | | | | | | The timerwheel is checked during IPC calls (fevent, flow_read), causing huge load on CPU consumption in IPCPs, since they have a lot of fevent() threads for QoS. The timerwheel will need further optimization), but for now I reduced the default tick time to 5 ms and added a boolean to check that the wheel is actually used. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Don't default to lockless rbuffDimitri Staessens2020-11-221-1/+1
| | | | | | | | I mistakenly set the default to the (buggy) lockless rbuff implementation instead of the pthread one in commit 3aec660e. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* Revert "lib: Unmount stale RIB directories"Sander Vrijders2020-11-111-10/+1
| | | | | | | | This reverts commit 978266fe4beba21292daad2d341fe5ff22e08aba. We were incorrectly unmounting the directory under normal conditions. Signed-off-by: Sander Vrijders <sander@ouroboros.rocks> Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
* lib: Add Rendez-Vous mechanism for flow controlDimitri Staessens2020-10-113-31/+130
| | | | | | | | | | | | | This adds the rendez-vous mechanism to handle the case where the sending window is closed and window updates get lost. If the sending window is closed, the sender side will send an RDVS every DELT_RDV time (100ms), and give up after MAX_RDV time (1 second). Upon reception of a RDVS packet, a window update is sent immediately. We can make this much more configurable later on (build options for defaults, fccntl for runtime tuning). Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Block on closed flow control windowDimitri Staessens2020-10-112-18/+129
| | | | | | | | | | | If the sending window for flow control is closed, the sending application will now block until the window opens. Beware that until the rendez-vous mechanism is implemented, shutting down a server while the client is sending (with non-timed-out blocking write) will cause the client to hang indefinitely because its window will close. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Refactor flow_writeDimitri Staessens2020-10-111-20/+11
| | | | | | | Refactor flow_write cleanup. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Send and receive window updatesDimitri Staessens2020-10-113-9/+38
| | | | | | | | | This adds sending and receiving window updates for flow control. I used the 8 pad bits as part of the window update field, so it's 24 bits, allowing for ~16 million packets in flight. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Add compiler configuration for FRCPDimitri Staessens2020-10-115-93/+153
| | | | | | | | | | | | | This allows configuring some parameters for FRCP at compile time, such as default values for Delta-t and configuration of the timerwheel. The timerwheel will now reschedule when it fails to create a packet, instead of setting the flow down immediately. Some new things added are options to store packets for retransmission on the heap, and using non-blocking calls for retransmission. The defaults do not change the current behaviour. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix locking for FRCTDimitri Staessens2020-09-261-2/+4
| | | | | | | | Flows should be locked when moving the timerwheel. For frcti_snd, a rdlock is enough. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Complete retransmission logicDimitri Staessens2020-09-255-383/+667
| | | | | | | | | | | | | | | | | | | | | | | | | | | This completes the retransmission (automated repeat-request, ARQ) logic, sending (delayed) ACK messages when needed. On deallocation, flows will ACK try to retransmit any remaining unacknowledged messages (unless the FRCTFLINGER flag is turned off; this is on by default). Applications can safely shut down as soon as everything is ACK'd (i.e. the current Delta-t run is done). The activity timeout is now passed to the IPCP for it to sleep before completing deallocation (and releasing the flow_id). That should be moved to the IRMd in due time. The timerwheel is revised to be multi-level to reduce memory consumption. The resolution bumps by a factor of 1 << RXMQ_BUMP (16) and each level has RXMQ_SLOTS (1 << 8) slots. The lowest level has a resolution of (1 << RXMQ_RES) (20) ns, which is roughly a millisecond. Currently, 3 levels are defined, so the largest delay we can schedule at each level is: Level 0: 256ms Level 1: 4s Level 2: about a minute. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Allow pure acknowledgment packets in FRCTDimitri Staessens2020-06-063-150/+297
| | | | | | | | | | | | | | | | | | | | This adds the logic to send a pure acknowledgment packet without any data to send. This needed the event filter for the fqueue, as these non-data packets should not trigger application PKT events. The default timeout is now 10ms, until we have FRCP tuning as part of fccntl. Karn's algorithm seems to be very unstable with low (sub-ms) RTT estimates. Doubling RTO (every RTO) seems still too slow to prevent rtx storms when the measured rtt suddenly spikes several orders of magnitude. Just assuming the ACK'd packet is the last one transmitted seems to be a lot more stable. It can lead to temporary underestimation, but this is not a throughput-killer in FRCP. Changes most time units to nanoseconds for faster computation. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Check rdrbuff sanitize for robust mutexesDimitri Staessens2020-05-291-0/+2
| | | | | | | | The sanitize function in the rdrbuff should only be compiled if robust mutexes are present on the system. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Refactor FRCTDimitri Staessens2020-05-042-72/+59
| | | | | | | | | | This is a small refactor of FRCT because I found some things a bit hard to read. I tried to refactor frcti_rcv to always queue the packet, but that causes unnecessarily retaking the lock when calling queued_pdu and thus returning idx is a tiny bit faster. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix retransmission DRF updateDimitri Staessens2020-05-021-4/+0
| | | | | | | | | | The retransmission was always disabling the DRF flag. This caused problems with the loss of the first packet, which of course needs a DRF flag set. The retransmitted packet will now contain a the original DRF flag and an updated ack number. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Create an rxmwheel per flowDimitri Staessens2020-05-024-128/+149
| | | | | | | | | The single retransmission wheel caused locking headaches as the calls for different flows could block on the same rxmwheel. This stabilizes the stack, but if the rdrbuff gets full there can now be big delays. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix updating retransmission wheelDimitri Staessens2020-05-014-23/+28
| | | | | | | | | | Fixes infinite rescheduling with RTO getting lower than the timerwheel resolution. For very low RTO values we'd need a big packet buffer with the current memory allocator implementation (rdrbuff). Setting a (configurable) minimum RTO (250 us) reduces this need. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Unmount stale RIB directoriesSander Vrijders2020-04-301-1/+10
| | | | | | | | If Ouroboros crashed, the RIB directory might still be mounted. This checks if this is the case, then unmounts it. Signed-off-by: Sander Vrijders <sander@ouroboros.rocks> Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
* lib: Stabilize FRCP under packet loss conditions0.17.3Dimitri Staessens2020-04-302-59/+68
| | | | | | | | | | | There were a bunch of bugs in FRCP that urgently needed fixing. Now data QoS is usable even with heavy packet loss (within some parameters). The current RTT estimator is the IETF one. It should be updated to the improved one used in the Linux kernel once the A-timer (ACKs without data) and graceful shutdown are implemented. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* irmd: Fix cleanup of shm_flow_set0.17.1Dimitri Staessens2020-03-201-1/+1
| | | | | | | | | The shm_flowset destroy was using the irmd pid, resulting in wrong unlinks. The irmd was not cleaning up the process table, resulting in shm leaks if there were still running processes on exit. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix thread management in thread pool managerDimitri Staessens2020-03-201-1/+1
| | | | | | | | | The thread pool manager wasn't counting working threads when deciding to create new ones, resulting in constant starting of new threads when threads were busy. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Return number of written bytes on flow_write0.17.0Dimitri Staessens2020-03-151-3/+2
| | | | | | | | | This is more in line with the write() system call and prepares for partial writes. Partial writes are disabled by default (and not yet implemented). Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Change return type of fevent to ssize_tDimitri Staessens2020-03-151-3/+3
| | | | | | | | The return type was still an int, but since it returns the number of events, it should be an ssize_t. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* irm: Revise naming APIDimitri Staessens2020-03-152-21/+146
| | | | | | | | | | | | | | | | | | | | | | | This revises the naming API to treat names (or reg_name in the source) as first-class citizens of the architecture. This is more in line with the way they are described in the article. Operations have been added to create/destroy names independently of registering. This was previously done only as part of register, and there was no way to delete a name from the IRMd. The create call now allows specifying a policy for load-balancing incoming flows for a name. The default is the new round-robin load-balancer, the previous behaviour is still available as a spillover load-balancer. The register calls will still create a name if it doesn't exist, with the default round-robin load-balancer. The tools now have a "name" section, so the format is now irm name <operation> <name> ... Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix deadlock in threadpool managerDimitri Staessens2020-03-141-9/+23
| | | | | | | | There was a rare deadlock upon destruction of the threadpool manager because the threads were cancelled/joined under lock. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib, ipcpd: piggyback ECDHE on flow allocationDimitri Staessens2020-02-255-234/+233
| | | | | | | | | | | The initial implementation for the ECDHE key exchange was doing the key exchange after a flow was established. The public keys are now sent allowg on the flow allocation messages, so that an encrypted tunnel can be created within 1 RTT. The flow allocation steps had to be extended to pass the opaque data ('piggybacking'). Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix shm_rbuff testDimitri Staessens2020-02-161-0/+8
| | | | | | | | | The rbuff_destroy function asserts that we do not try to destroy an rbuff that still contains packets. The test now empties the rbuff before destroying it. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* ipcpd: Configure PFF from routing policyDimitri Staessens2020-02-162-9/+6
| | | | | | | | | | | | The Packet Forwarding Function (PFF) was user-configurable using the irm tool. However, this isn't really wanted since the PFF is dictated by the routing algorithm. This moves the responsability for selecting the correct PFF from the network admin to the unicast IPCP implementation. Each routing policy now has to specify which PFF it will use. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Move hashtable from lib to unicastDimitri Staessens2020-02-164-352/+0
| | | | | | | | | | The hashtable is only used for forwarding tables in the unicast IPCP. This moves the generic hashtable out of the library into the unicast IPCP to prepare a more tailored implementation specific to routing tables containing address lists. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* build: Update copyright to 20200.16.0Dimitri Staessens2020-01-0242-42/+42
| | | | | Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Clean up fail path in constructorsDimitri Staessens2019-10-281-15/+17
| | | | | | | The node construction path is revised using gotos to avoid repetition. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Add check that flow_id is validSander Vrijders2019-10-061-0/+5
| | | | | | | | In fset_add, the flow_id was passed to the shm_flow_set without checking if it was actually valid. Signed-off-by: Sander Vrijders <sander@ouroboros.rocks> Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
* build: Allow older OpenSSL versions for randomDimitri Staessens2019-10-053-4/+6
| | | | | | | | | Ubuntu 16 comes with older versions of OpenSSL, glibc and libgcrypt. Ouroboros will now fall back to OpenSSL even if the version is <= 1.1.0. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* build: Check OpenSSL version >= 1.1.0Dimitri Staessens2019-09-291-10/+15
| | | | | | | | | The cryptographic functions require at least OpenSSL 1.1.0. The build will now check for this version and disable OpenSSL support when this requirement is not met. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix swapped ECDH crypt callsDimitri Staessens2019-08-091-2/+2
| | | | | | | | | | The client and server side were swapped. This wasn't a big issue, but now we are sure that the flow allocation response for the server has arrived at the client (packet reordering could cause the server key to arrive before the flow is allocated at the client). Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix free in key derivationDimitri Staessens2019-08-091-1/+1
| | | | | | | The wrong pointer was being free'd in case of a derivation error. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Add per-message encryption with OpenSSLDimitri Staessens2019-08-035-17/+605
| | | | | | | | | | | | | | | | | | | This adds a per-message symmetric encryption using the OpenSSL library. At flow allocation, an Elliptic Curve Diffie-Hellman exchange is performed to derive a shared secret, which is then hashed using SHA3-256 to be used as a key for symmetric AES-256 encryption. Each message on an encrypted flow adds a small crypto header that includes a random 128-bit Initialization Vector (IV). If the server does not have OpenSSL enabled, the flow allocation will fail with an -ECRYPT error. Future optimizations are to piggyback the public keys on the flow allocation message, and to enable per-flow encryption that maintains the context of the encryption over multiple packets and doesn't require sending IVs. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* irmd, lib: Improve libgcrypt initDimitri Staessens2019-07-291-2/+7
| | | | | | | | | | The proper initialization of libgrypt requires a call to gcry_check_version. The library initialization should first run a check if the application (or some other library) hasn't already initialized libgcrypt before attempting to initialize libgcrypt. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* build: Refactor normal to unicastDimitri Staessens2019-07-292-2/+2
| | | | | | | | This completes the renaming of the normal IPCP to the unicast IPCP in the sources, to get everything consistent with the documentation. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* ipcpd: Fix use after free and uninitalized valueSander Vrijders2019-06-211-2/+2
| | | | | | | | | | This fixes a use after free in an error condition, and makes sure that pid is set in the flow_set early on, so flow_set_destroy won't create a prefix with an uninitialized pid in case of an error in shm_flow_set_create. Signed-off-by: Sander Vrijders <sander@ouroboros.rocks> Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
* lib: Add tests for the shm_rbuffDimitri Staessens2019-06-212-0/+106
| | | | | | | | | This adds some tests for the shm_rbuff after some reports that the queue length would be erroneously reported as 0 when the rbuff was full. The test passes for the reported case. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Fix blocking writes to smaller rbuffDimitri Staessens2019-04-171-5/+4
| | | | | | | | | This fixes writing at high speeds when the rbuff is smaller than the rdrbuff. The pthread_cond_wait calls were blocking on the wrong condition variable. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Set independent size for rbuffDimitri Staessens2019-04-066-15/+137
| | | | | | | | | | This allows setting the size of the rbuffs in a system independently of the main packet buffer using SHM_RBUFF_SIZE. The benefit of setting a smaller rbuff size is that a single process can't fully occupy the main packet buffer. Signed-off-by: Dimitri Staessens <dimitri.staessens@ugent.be> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* build: Set specific compiler flags for SWIG target0.15.2Dimitri Staessens2019-03-212-3/+0
| | | | | | | | | | The compiler flags for the SWIG target were added to the global CMAKE_C_FLAGS used for the entire project. This sets the flags uniquely for the SWIG target. The eth has a similar case for the c99 flag. There was a lingering include in dev.c that was removed. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* ipcpd: Revise UDP IPCPDimitri Staessens2019-03-182-2/+8
| | | | | | | | | | | The UDP IPCP now uses a fixed server UDP port (default 3435) for all communications. This allows passing firewalls more easily since only a single port needs to be opened. The client port can be fixed as well if needed (default random). It uses an internal eid, so the MTU of the UDP layer is reduced by 4 bytes, similar to the Ethernet IPCPs. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* ipcpd: Refactor create_r and flow_req_arrDimitri Staessens2019-03-041-6/+4
| | | | | | | | | | | The API calls for the IPCP to inform the IRMd of IPCP creation and incoming flow request had the pid_t in the call. This pid_t is removed and the getpid() call is now placed inside the function. Also refactors the cleanup for the main() functions of some of the lower IPCPs. Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks> Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
* lib: Add initial rtt estimator to FRCTDimitri Staessens2019-02-082-18/+89
| | | | | | | | | | | | This adds a simple round-trip time estimator to FRCT. The estimate is a weighted average with deviation. The retransmission is scheduled after rtt + 2 times the deviation. A retransmit doubles the rtt estimate to avoid the no-update case when rtt suddenly increases. The rtt is estimated in microseconds and the granularity for retransmits is 256 microseconds. Signed-off-by: Dimitri Staessens <dimitri.staessens@ugent.be> Signed-off-by: Sander Vrijders <sander.vrijders@ugent.be>
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