[Claim 1]
A method implemented in a packet-switched network for scheduling
transmission of Ethernet frames, the method comprising:
10 a) determining a priority level of each Ethernet frame to transmit, based on
identification of data given in said Ethernet frame and related to a stream to which
said Ethernet frame belongs, said data distinguishing thereby:
* frames belonging to streams to be transmitted by successive cyclic bursts,
and having a first priory level,
15 * frames belonging to rate controlled streams, and having a second priory level,
and
* frames belonging to non-time critical traffic streams, having a third priority
level, lower than said first and second priority levels,
b) determining, among the frames having the highest priority level, a frame,
20 candidate for transmission, having a closest next time at which said candidate frame
is to be transmitted, and
c) estimating an end-of-transmission time of said candidate, and checking
whether a frame having a higher priority than the candidate does not have a next
transmission time occurring before the end-of-transmission time of the candidate,
25 and eventually transmitting the candidate.
[Claim 2]
The method of claim 1, wherein, after b), if said closest next transmission time
(MinNextTxTimep) is higher (S4) than a current time (T) given by a common clock of the
30 packet-switched network, b) is repeated with a priority level resulting from a decrement of
said highest priority level (p=p-1) and as long as the closest next transmission time
determined in b) is higher than said current time (T).
[Claim 3]
35 The method of claim 2, wherein said frames belonging to non-time-critical traffic
streams, and having thus said third priority level, are identified as belonging to a preemptable
27
5 traffic and transmittable whenever no frames of first and second priority levels are to be
transmitted,
And wherein, before testing whether said closest next transmission time
(MinNextTxTimep) is higher (S4) than said current time (T), it is determined whether said
candidate is a frame having said third priority level (OK-S3), and eventually said candidate
10 is defined as to be transmitted at least in part.
[Claim 4]
The method according to any one of the preceding claims, wherein the Ethernet frames
are, before their transmissions, stacked in FIFO queues depending respectively on their
15 priority levels, each queue corresponding to one priority level, and a head-of-queue frame
having a priority level p and the closest next transmission time (minNextTxTimep) among
the frames having the same priority level p is the next candidate-for-transmission frame
among all the frames of priority level p.
20 [Claim 5]
The method according to any one of the preceding claims, wherein, for implementing
b) with CB frames belonging to streams to be transmitted by successive Cyclic Bursts, each
stream having a predetermined period of burst transmission (CBPeriod(i)), next transmission
times of said CB frames are computed (S21) on the basis of the predetermined period of
25 burst transmission (CBPeriod(i)) of the respective streams to which said CB frames pertain,
so as to determine (S22) said closest next transmission time (minNextTxTimep).
[Claim 6]
The method according to claim 5, wherein a basis period of cycles of the network
30 (CyclePer) is determined as a greatest common divisor among the burst transmission periods
of the streams to which said CB frames pertain, and wherein next transmission times of CB
frames belonging to respective streams having respective different burst transmission
periods are determined relatively to a time of start of one network cycle or of successive
network cycles.
35
[Claim 7]
28
5 The method according to any one of claims 5 and 6, wherein at least one CB frame is
selected as a candidate for a next CB frame transmission if (S24) a current time (T) has not
reached yet an estimated end of transmission of a burst to which said at least one CB frame
belongs.
10 [Claim 8]
The method according to claim 7, wherein, for a CB frame candidate, a time of end of
transmission of said next CB frame is computed on the basis of a given length of said next
CB frame and is compared (S25) to the estimated end of burst transmission for the burst to
which said CB frame candidate belongs, and said CB frame candidate is transmitted only if
15 its time of end of transmission occurs before said estimated end of burst transmission.
[Claim 9]
The method according to any one of the preceding claims, wherein the second priority
level is lower than the first priority level.
20
[Claim 10]
The method according to claim 9, wherein, for RC frames belonging to express Rate
Controlled streams and having said second priority level, before transmitting a RC frame, an
end-of-transmission time of said RC frame is computed on the basis of a given length of said
25 RC frame, and said RC frame is determined as to be transmitted only if (S31) said
transmission end time occurs before a minimum among closest next times determined for
any frame having a higher priority level than the RC frame.