WIP LEDBAT

algo/ledbat.scm

@@ -3,13 +3,86 @@
 
 (define-record-type ledbat-params
   (fields 
+    ; The term "MSS", or the sender's Maximum Segment Size, used in this
+    ; document refers to the size of the largest segment that the sender
+    ; can transmit.  The value of MSS can be based on the path MTU
+    ; discovery [RFC4821] algorithm and/or on other factors.
+    mss
+    ; INIT_CWND and MIN_CWND SHOULD both be 2.  An INIT_CWND of 2 should
+    ; help seed FILTER() at the sender when there are no samples at the
+    ; beginning of a flow, and a MIN_CWND of 2 allows FILTER() to use more
+    ; than a single instantaneous delay estimate while not being too
+    ; aggressive.  Slight deviations may be warranted, for example, when
+    ; these values of INIT_CWND and MIN_CWND interact poorly with the
+    ; framing protocol.  However, INIT_CWND and MIN_CWND MUST be no larger
+    ; than the corresponding values specified for TCP [RFC5681].
+    init_cwnd 
+    min_cwnd 
+    ; ALLOWED_INCREASE SHOULD be 1, and it MUST be greater than 0.  An
+    ; ALLOWED_INCREASE of 0 results in no cwnd growth at all, and an
+    ; ALLOWED_INCREASE of 1 allows and limits the cwnd increase based on
+    ; flightsize in the previous RTT.  An ALLOWED_INCREASE greater than 1
+    ; MAY be used when interactions between LEDBAT and the framing protocol
+    ; provide a clear reason for doing so.
+    allowed_increase 
+    ;  The size of the base_delays list, BASE_HISTORY, SHOULD be 10.  If the
+    ; actual base delay decreases, due to a route change, for instance, a
+    ; LEDBAT sender adapts immediately, irrespective of the value of
+    ; BASE_HISTORY.  If the actual base delay increases, however, a LEDBAT
+    ; sender will take BASE_HISTORY minutes to adapt and may wrongly infer
+    ; a little more extra delay than intended (TARGET) in the meanwhile.  A
+    ; value for BASE_HISTORY is thus a trade-off: a higher value may yield
+    ; a more accurate measurement when the base delay is unchanging, and a
+    ; lower value results in a quicker response to actual increase in base
+    ; delay.
+    base_history
+    ; GAIN MUST be set to 1 or less.  A GAIN of 1 limits the maximum cwnd
+    ; ramp-up to the same rate as TCP Reno in Congestion Avoidance.  While
+    ; this document specifies the use of the same GAIN for both cwnd
+    ; increase (when off_target is greater than zero) and decrease (when
+    ; off_target is less than zero), implementations MAY use a higher GAIN
+    ; for cwnd decrease than for the increase; our justification follows.
+    gain 
+    ; TARGET MUST be 100 milliseconds or less, and this choice of value is
+    ; explained further in Section 3.3.  Note that using the same TARGET
+    ; value across LEDBAT flows enables equitable sharing of the bottleneck
+    ; bandwidth.  A flow with a higher TARGET value than other competing
+    ; LEDBAT flows may get a larger share of the bottleneck bandwidth.  It
+    ; is possible to consider the use of different TARGET values for
+    ; implementing a relative priority between two competing LEDBAT flows
+    ; by setting a higher TARGET value for the higher-priority flow.
+    target
+    ; The size of this list, CURRENT_FILTER,
+    ; may be variable, and it depends on the FILTER() function as well as
+    ; the number of successful measurements made within an RTT amount of
+    ; time in the past.  The sender should seek to gather enough delay
+    ; samples in each RTT so as to have statistical confidence in the
+    ; measurements.  While the number of delay samples required for such
+    ; confidence will vary depending on network conditions, the sender
+    ; SHOULD use at least 4 delay samples in each RTT, unless the number of
+    ; samples is lower due to a small congestion window.  The value of
+    ; CURRENT_FILTER will depend on the filter being employed, but
+    ; CURRENT_FILTER MUST be limited such that samples in the list are not
+    ; older than an RTT in the past.
+    current_filter))
 
 (define-record-type ledbat-state
   (fields current_delays base_delays last_rollover flightsize cwnd cto))
 
-(define (on-init params) 
-  (make-ledbat-state
+(define (ledbat-params-default)
+  (make-ledbat-params 
+    1498 ; mss
+    2 2 ; init_cwnd min_cwnd
+    1 ; allowed_increase
+    10 ; base_history
+    1 ; gain
+    100 ; target
+    5 ; current_filter
+))
 
-(define (on-data) )
+;(define (on-init params) 
+;  (make-ledbat-state
 
-(define (on-ack) )
+;(define (on-data) )
+
+;(define (on-ack) )