DE10059646B4 - Transmission of messages over a bus structure - Google Patents

Abstract

method for transmission from news about a bus structure, with one station s and several stations x ∈ X: = {a, b, c, ...}, where the messages from the station s to a station x and vice versa can be and wherein a station (x, s) prior to transmission of a message to a desired Send time (txs_w (k), tsx_w (k), k ∈ {0, 1, 2, ...}) checks whether the Bus already from another station (x, s) for messaging is used and the station (x, s) transmits the message only if the bus is not used, and in the other case the transmission time the message around a random one Period shifted to a transmission time (txs_r (k), tsx_r (k)) is, and where the desired Transmission times (txs_w (k + n), tsx_w (k + n), n∈ {1, 2, 3, ...}) following Broadcasts are shifted so that the difference between the desired Send time (txs_w (k + n), tsx_w (k + n)) and the actual Send time (txs_r (k + n), tsx_r (k + n)) each below one Threshold is ...

Description

The Invention relates to the transmission from news about a bus structure, such as e.g. a CSMA / CD (Carrier Sense Multiple Access with Collision Detection) based bus, and in particular the avoidance or compensation of jitter effects caused by not precisely defined transmission times caused by a bus structure become.

1 shows as an example of such a bus structure on CSMA / CD (Carrier Sense Multiple Access with Collision Detection) based bus, for example, according to the standard IEEE 802.3 Ethernet, are coupled by the N + 1 stations. There are exactly one station s and N stations {a, b, c, ...} on the bus, where an arbitrary station x of the bus is defined by x ∈ X: = {a, b, c, ...} is.

The Station s periodically sends to each station x ∈ X, in unicast and not in multicast mode. In the opposite direction each station sends x exclusively periodically to the station s.

2 shows the transmission timing between s and an arbitrarily selected station x for the desired ideal case. The time segment shown must be continued periodically.

t:

Zeit

tsx:

Startzeitpunkte einer Sendung von s nach x

txs:

Startzeitpunkte einer Sendung von x nach s

Δtxs:

Dauer einer Sendung von x nach s

Δtsx:

Dauer einer Sendung von s nach x

Δtx:

Zeit zwischen Empfangsbeginn einer Sendung und Beginn der nächsten Sendung auf x

psx:

Periode der Sendungen von s nach x

pxs:

Periode der Sendungen von x nach s

The following terms are defined:

t:

Time

tsx:

Start times of a program from s to x

txs:

Starting times of a program from x to s

Δtxs:

Duration of a transmission from x to s

Δtsx:

Duration of a transmission from s to x

Δtx:

Time between reception start of a program and beginning of the next program on x

psx:

Period of transmissions from s to x

pxs:

Period of transmissions from x to s

In the 2 used horizontal arrows should clarify the direction of the shipment.

The Durations of the transmissions Δtxs and Δtsx are essentially by the bus bandwidth and to be transmitted Data set given and can unaffected become. While These times are occupied by the bus.

The transmission period psx is constant and can not be influenced by s. The same applies to the transmission period pxs, which is also constant and can not be influenced by x. In general: psx = pxs = p for all x,

With In other words, all periods are the same length.

Further often applies Δtxs "pxs and Δtsx" psx.

The period .DELTA.tx between the reception start of a transmission and the beginning of the next transmission on the station x results from: Δtx = txs - tsx.

The Stations are their transmission times txs or tsx, periods pxs resp. psx and the Δtx known, either by notification, by own knowledge or by derivation from known quantities.

• 1. Die Folgen tsx(k) sind explizit gegeben.
• 2. Die Folgen tsx(k)werden durch tsx(k): = tsx(0) + k·psx jeweils lokal berechnet

For example, there are several possibilities for the station s, where k ∈ {0, 1, 2, ...}:

• 1. The sequences tsx (k) are given explicitly.
• 2. The sequences tsx (k) are calculated locally by tsx (k): = tsx (0) + k · psx

• 1. Die Folgen txs(k) sind explizit gegeben.
• 2. Die Folgen txs(k) werden durch txs(k): = txs(0) + k·pxs jeweils lokal berechnet.
• 3. Die Folgen txs(k) werden durch txs(k): = tsx(k) + Δtx jeweils lokal bestimmt, wobei Δtx konstant ist und beispielsweise durch Δtx = txs(0) – tsx(0) lokal berechnet worden ist.

There are also several options at stations x, for example:

• 1. The sequences txs (k) are given explicitly.
• 2. The sequences txs (k) are calculated locally by txs (k): = txs (0) + k · pxs.
• 3. The sequences txs (k) are respectively determined locally by txs (k): = tsx (k) + Δtx, where Δtx is constant and has been locally calculated, for example, by Δtx = txs (0) -tsx (0).

in the Ideally, all possibilities are equivalent. What possibility chosen is therefore typically not a system default, but one Implementation decision.

• – Die Stationen x1, x2 wollen zeitlich überlappend nach Station s senden.
• – Die Station x1 möchte nach Station s zeitlich überlappend mit einer Sendung von Station s an Station x2 senden.

The transmission times txs of the N stations x are independent. Although each station transmits x with its period pxs, the stations are completely decoupled from each other in time. As a result, several stations can overlap to send wishes. Therefore, the following cases can occur for stations x1, x2 ∈ X:

• - The stations x1, x2 want to send time overlapping to station s.
• The station x1 would like to transmit after station s overlapping in time with a transmission from station s to station x2.

For CSMA / CD (see IEEE 802.3), a station that wants to send first checks whether the bus is free. If the station detects that the bus is busy, the program will be reset by a random period of time. This mechanism is typically carried out transparently for the applications that generate the messages (eg in a peripheral hardware component) and is not influenceable. The applications can not therefore adapt directly to it, in particular, they get no return message about bus assignments and real transmission times.

It the following definition is given: v ∈ V: = {set of send-willing Stations that are deferred because of a busy bus}.

V; bei einem Simplexbus, d.h. jede Station kann zu einer Zeit nur entweder senden oder empfangen, aber kann ebenfalls für die Station s gelten s ∈ V. Ein auf dem Standard IEEE 802.3 basierendes Ethernet wird oft als Simplexbus ausgelegt.With a duplex bus, ie each station can transmit and receive at the same time, s is guaranteed due to the above considerations

V; on a simplex bus, ie each station can only either send or receive at a time, but may also apply to the station s ∈ V. An Ethernet based on the IEEE 802.3 standard is often designed as a simplex bus.

3 shows the transmission timing for the stations s, x ∈ V, for which the broadcasts were reset due to bus occupation. Due to these provisions, the transmission times tsx and txs of 2 now on at desired times (suffix _w) to which the respective station wishes to send, and real timings (suffix _r) to which it is really sent over the bus.

Since the stations will not receive any feedback on provisions, the stations will continue to accept the following assignments: tsx_w = tsx and txs_w = txs, psx_w = psx and pxs_w = pxs, as well Δtx_w = Δtx.

• 1. txs_w(k): = txs(k) sind explizit gegeben
• 2. txs_w(k): = txs(0) + k·pxs jeweils lokal berechnet (mit pxs_w = pxs)
• 3. txs_w(k): = tsx_r(k) + Δtx jeweils lokal bestimmt (dabei ist Δtx konstant und z.B. durch Δtx = txs(0) – tsx(0) lokal berechnet worden).

These equations are contradictory with each other, whereby the afore-mentioned possibilities for airtime determination are no longer equivalent. While options 1 and 2 continue to be equivalent, option 3 gives a different behavior. For the stations x results for the possibilities of the sequence determination txs_w (k):

• 1. txs_w (k): = txs (k) are given explicitly
• 2. txs_w (k): = txs (0) + k · pxs calculated locally (with pxs_w = pxs)
• 3. txs_w (k): = tsx_r (k) + Δtx are each determined locally (where Δtx is constant and has been calculated locally by Δtx = txs (0) - tsx (0)).

3 shows the behavior for options 1 and 2. Note that the two periods psx_w = psx and pxs_w = pxs refer to the desired times and remain unchanged. The time periods Δtx_w, however, are variable. These cases are called Alternative A.

On the other hand, assuming option 3 for stations x (at station s option 1 or 2), remain psx_w = psx and Δtx_w = Δtx unchanged, on the other hand, the periods pxs_w are now variable. These cases are called Alternative B.

tsx_w:

Wunschzeitpunkt einer Sendung von s nach x, d.h. s möchte zu diesem Zeitpunkt senden,

tsx_r:

Realer Zeitpunkt einer Sendung von s nach x, d.h. zu diesem Zeitpunkt wird über den Bus gesendet,

Δtx_w:

Zeit zwischen realem Empfang und Wunschzeitpunkt der nächsten Sendung auf x,

psx_w:

Periode der Wunschzeitpunkte der Sendungen von s nach x, und

pxs_w:

Periode der Wunschzeitpunkte der Sendungen von x nach s.

The following terms are also defined:

tsx_w:

Desired time of a transmission from s to x, ie s would like to send at this time,

tsx_r:

Real time of a transmission from s to x, ie at this time is sent over the bus,

Δtx_w:

Time between real reception and desired time of the next transmission on x,

psx_w:

Period of the desired times of the transmissions from s to x, and

pxs_w:

Period of the desired times of the transmissions from x to s.

Accepted, the station s can not transmit due to bus occupancy, i. s ∈ V. The from the station s with the period psx_w sent messages appear then at the stations x not with the period psx_w, but with the stochastic period psx_r (n) = tsx_r (n + 1) - tsx_r (n). It is also said that psx r has a jitter σ {psx_r).

Accepted, station x can not transmit due to bus occupancy, i. x ∈ V. The messages sent by x with the period pxs_w will then appear at the station s not with the period pxs_w, but with the stochastic one Period pxs_r (n) = txs_r (n + 1) - txs_r (n). It is therefore said that pxs_r has a jitter σ {pxs_r}.

• – Der Empfänger soll sich auf die Empfangsperiode synchronisieren, z. B. auf psx_r. Diese ist jedoch nun jitterbehaftet.
• – Der Empfänger soll die empfangenen Nachrichten seinerseits periodisch weitersenden. Dadurch entstehen Zeitpunkte, bis zu denen die weiterzusendenden Nachrichten eingetroffen sein müssen.

A problem arises when a receiver of a program is disturbed by the jittery reception for some reason. Examples for this are:

• - The receiver should synchronize to the receiving period, z. On psx_r. However, this is now jittery.
• The receiver is to forward the received messages periodically. This creates times until which the messages to be forwarded must have arrived.

• – Im Fall, daß sich der Empfänger auf die Empfangsperiode synchronisieren soll, wird eine zeitliche Mittelwertbildung durchgeführt. Nachteilig ist hierbei insbesondere die lange Regelzeit, d.h. der Empfänger braucht lange, um sich korrekt zu synchronisieren und kann eventuellen Veränderungen in der Periode nur langsam folgen.
• – Im Fall, daß der Empfänger periodisch weitersenden soll, wird ausgepuffert. Dabei wird die empfangene Nachricht zunächst gespeichert und der Speicher anschließend periodisch ausgelesen. Der mittlere Zeitraum zwischen Schreiben und Lesen muß dabei so groß gewählt werden, daß die weiterzusendende Nachricht hinreichend sicher bis zum Lesezeitpunkt eingetroffen ist. Nachteilig ist hierbei zum einen ein erhöhter Speicherbedarf im Empfänger und zum anderen die Wartezeit im Speicher, die den Jitter kompensiert.

In order to avoid the effects of jittery reception, previous solutions attempt to compensate for the jitter, with different approaches:

• - In the case that the receiver is to synchronize to the receiving period, a temporal averaging is performed. The disadvantage here is in particular the long control time, ie the receiver takes a long time to sync correctly and can follow any changes in the period only slowly.
• - In the case that the receiver is to send periodically, is buffered. The received message is first stored and the memory is then read out periodically. The mean time between writing and reading must be chosen so large that the message to be forwarded has arrived safely enough until the time of reading. The disadvantage here is on the one hand an increased memory requirements in the receiver and on the other hand, the waiting time in the memory, which compensates for the jitter.

Out US 5,852,723 A method for handling prioritized traffic in so-called "half-duplex" networks is known, whereby a so-called "network device" for transmitting prioritized data uses a so-called "Truncated Binary Exponential Backoff" (TBEB) algorithm during a first Access attempt to determine a first so-called "collision delay interval". When the network device encounters a collision, a random integer multiple of a timeslot is multiplexed with a fractional coefficient to ensure that the network device successfully accesses a network media.

Out US 6,078,591 Another method for collision-free transmission in "half-duplex" networks is known.

Of the Invention is based on the object, an improved method to compensate for jitter in the transmission of messages over a bus structure to accomplish.

These The object is achieved by a method according to claim 1. preferred Embodiments and developments of the invention are the subject the dependent claims.

The basic idea of the invention is the fact that the desired Transmission times tsx_w (k + n), txs_w (k + n), n ∈ {1, 2, 3, ...} following Broadcasts are shifted so that the difference between the desired Transmission time tsx_w (k + n), txs_w (k + n) and the actual transmission time tsx_r (k + n), txs_r (k + n) is each below a threshold.

• 1. Station s muß Jitter in Empfangsrichtung und Senderichtung erkennen können. Während die Erkennung von jitterbehaftetem pxs_r trivial für Station s ist, ist eine Jittererkennung der psx_r für Station s offen.
• 2. Station s muß die Sendezeiten direkt oder indirekt verschieben können.

Here are two sub-problems:

• 1st station s must be able to detect jitter in the receive direction and send direction. While the detection of jittery pxs_r is trivial to station s, jitter detection of psx_r is open to station s.
• 2. Station s must be able to move the transmission times directly or indirectly.

The solution of the first partial problem preferably takes place in that a station x ∈ X, which receives jittery, also sends jittery. Station s can use the jitter of pxs_r to detect if psx_r might have jitter. Conversely, it follows
pxs_r has no yittter ⇒ psx_r also has no jitter

• – txs_w(k) explizit gegeben sind oder
• – txs_w(k): = txs(0) + k·pxs lokal auf den Stationen x

berechnet werden.With respect to alternatives A and B described above, the following distinctions are made:
Alternative A is given if

• - txs_w (k) are given explicitly or
• - txs_w (k): = txs (0) + k · pxs locally on the stations x

be calculated.

In alternative A, if a station x detects a jitter at station s sending period psx_r, it intentionally provides its transmission times txs_w (k + n) with a stochastic deviation d: txs_w: = txs_w + d, where σ {d}> 0, From which follows: σ {txs_w} = σ {d}, and further σ {pxs_w} = σ {d}> 0.

alternative B is given if txs w (k): = tsxr (k) + Δtx locally on the stations x is determined. Where Δtx constant and can for example be calculated locally by Δtx = txs (0) - tsx (0).

Alternative B inherits any jitter from tsx_r to txs_w: σ {txs_w} = σ {tsx_r}, and further σ {pxs_w) = σ {psx_r}, since Δtx is constant.

Both alternatives solve subproblem 1, where Alternative B offers the advantage that stations x do not require any special mechanism. However, the cause of a jittery pxs_r in both alternatives can no longer be determined unambiguously, the jitter may already be present at transmission (intentionally generated or inherited), or may be due to the transmission of x to s. But this is not a problem.

subproblem 2 can be solved in which station s have their own transmission times tsx_w (k) can move yourself. To the transmission times txs (k) of the stations x has to move to station s inform the stations x of the desired displacement. This is for example possible in one system, in which all broadcast times are centrally managed and communicated.

Further the alternative B (txs_w (k): = tsx_r (k) + Δtx with constant Δtx) can always be used become. This shifts txs_w (k) indirectly Shifts of tsx_w (k) achieved.

• – Die Bedingung pxs_r hat keinen Jittter ⇒ psx_r hat ebenfalls keinen Jitter wird erfüllt.
• – Station s überprüft die pxs_r auf Jitter. Sind alle pxs_r jitterfrei, sind folglich auch die psx_r jitterfrei. Es ist nichts zu tun. Ansonsten wird folgende Schleife durchlaufen, bis ein befriedigendes Ergebnis vorliegt:
• – Station s selektiert eines der jitterbehafteten psx_r.
• – Für Alternative A:
• – Station s verschiebt die dazugehörigen Wunschsendezeiten tsx_w und txs_w mit den Zielen: a) Jitter von psx_r reduzieren, b) Jitter der anderen pxs_r nicht vergrößern, c) Verschiebung der tsx_w(k+n) und txs_w(k+n) möglichst gering halten.
• - Für Alternative B: Station s verschiebt die dazugehörigen Wunschsendezeiten tsx_w mit den Zielen: a) Jitter von psx_r reduzieren, b) Jitter der anderen pxs_r nicht vergrößern, c) Verschiebung der tsx_w(k+n) möglichst gering halten.

The overall algorithm for achieving jitter-free data exchange is therefore:

• - The condition pxs_r has no Jittter ⇒ psx_r also has no jitter is fulfilled.
• - Station s checks the pxs_r for jitter. If all pxs_r are jitter-free, the psx_r are jitter-free as well. There is nothing to do. Otherwise, the following loop is run until a satisfactory result is obtained:
• - Station s selects one of the jittery psx_r.
• - For alternative A:
• - Station s shifts the corresponding desired send times tsx_w and txs_w with the goals: a) reduce jitter of psx_r, b) do not increase the jitter of the other pxs_r, c) minimize the shift of tsx_w (k + n) and txs_w (k + n) ,
• - For alternative B: station s shifts the corresponding desired send times tsx_w with the targets: a) reduce jitter of psx_r, b) do not increase the jitter of the other pxs_r, c) minimize the shift of tsx_w (k + n).

The Advantages of Alternative B, i. txs_w: = tsx_r + Δtx are: The whole mechanism is running autonomous on s.

through a suitable algorithm can achieve an optimal result be the disadvantages of the known compensation method of the Jitters avoids. Furthermore, the jitter measurements are often already for others Purposes needed anyway, i.e. they are often already present.

A preferred embodiment The invention will be explained below with reference to the drawings.

1 shows a schematic representation of a CSMA / CD bus,

2 shows the ideal transmission timing between a station s and an arbitrarily selected station x of the bus,

3 shows the transmission timing for stations s and x, where for both s and x the transmissions are reset when the bus is busy, and

The 1 to 3 serve to explain the problem and have already been dealt with in the introduction in the introduction.

4 shows the transmission timing of an application example from the GSM mobile radio with a base station controller BSC (with integrated TRAU and PCU) and several base stations BTS connected thereto, wherein 4 only one base station BTS is shown. Each base station BTS can communicate with at least one mobile station MS. The BSC corresponds to the station s, the BTS correspond to the stations x. The CSMA / CD bus is an IEEE 802.3 Ethernet LAN.

The BSC sends voice data to the BTS, which forward it to mobile terminals MS. Conversely, the MSs send to the BTSs, who forward them to the BSC. The transfer BTS to MS and vice versa is subject to a strict perodic Timing. We have psx = pxs and Δtxs ≅ Δtsx «psx for all x. Picture 4 shows the situation with jitter (the send durations) are not shown).

The Period psx is generated by the BSC. The BTS sends to the MS with the same period, to which the BTS applies accordingly to the BSC must synchronize. Here comes the synchronization problem mentioned above in the introduction on.

Of the Period Δtx_r contributes to Speech delay, which is already relatively high in GSM anyway and the voice quality impaired. By Δtx r To keep it minimal, jitter freedom is also sought here. The however, the known method of buffering to compensate for the jitter would increase Δtx_r.

• a. Alle BTS setzen ihre Sendezeitpunkte (zur BSC) auf txs_w: = tsx_r + Δtx.
• b. Die BSC ermittelt die Jitter aller Perioden pxs_r.
• c. Die BSC wählt die pxs_r mit maximalem Jitter aus.
• d. Die BSC verschiebt die Sendezeitpunkte tsx_w(k+n) mit dem Ziel der Jitterminimierung. Die Verschiebung sollte dabei möglichst gering sein, z.B. k·Δtsx, mit 0 < k < 10.
• e. Die Schritte werden solange wiederholt, bis alle Jitter ausreichend gering sind, d.h. unter einem Schwellwert liegen.

For example, to eliminate or minimize the jitter by the new method, the following algorithm can be used:

• a. All BTS set their transmission times (to BSC) to txs_w: = tsx_r + Δtx.
• b. The BSC determines the jitter of all periods pxs_r.
• c. The BSC selects the pxs_r with maximum jitter.
• d. The BSC shifts the transmission times tsx_w (k + n) with the goal of jitter minimization. The shift should be as low as possible, eg k · Δtsx, with 0 <k <10.
• e. The steps are repeated until all jitter is sufficiently low, ie below a threshold.

For a 100 Mbps Ethernet, approximately: psx = 20 ms Δtsx = 8 μs

The expected shifts are so small.

Claims (8)

Method for transmitting messages over a bus structure, with a station s and several stations x ∈ X: = {a, b, c, ...}, where the messages can be transmitted from the station s to a station x and vice versa, and wherein a station (x, s) before transmitting a message at a desired transmission time (txs_w (k), tsx_w (k), k ∈ {0, 1, 2, ...}) checks whether the bus is already from a other station (x, s) is used for message transmission and the station (x, s) transmits the message only if the bus is not used, and in the other case the transmission time of the message by a random period to a transmission time (txs_r ( k), tsx_r (k)), and wherein the desired transmission times (txs_w (k + n), tsx_w (k + n), n∈ {1, 2, 3, ...}) of subsequent transmissions are thus shifted in that the difference between the desired transmission time (txs_w (k + n), tsx_w (k + n)) and the actual transmission time (txs_r (k + n ), tsx_r (k + n)) is each below a threshold, characterized in that a station x∈ X which receives a jittery signal from the station s also sends a jittery signal to the station s such that the station x their transmission times txs_w with a stochastic deviation d, if the station x detects a jitter at the actual transmission period psx r station s, if for the station x, the sequence determination for the k-th transmission time, k ∈ {0, 1, 2, ...} is either explicitly given by txs_w (k) = txs (k) or is calculated locally by txs_w (k): = txs (0) + k · pxs. Method according to claim 1, characterized in that the existence Jitter in the period psx r or at the transmission time tsx r of the station s is inherited at the transmission time txs r of the station x. Method according to one of the preceding claims, characterized characterized in that Station s have their own transmission times tsx_w (k) for the kth transmission, k ∈ {0, 1, 2, ...}, shifts itself. Method according to claim 3, characterized that the Station s the stations x for shifting their transmission times txs (k) prompts. Method according to one of the preceding claims, characterized characterized in that all Broadcasting times are managed centrally and communicated to the stations. Method according to claim 5, characterized in that that the Management of the transmission times is perceived by the station s. Use of the method according to one of the preceding claims in a mobile radio system with at least one base station controller (BSC) and several connected base stations (BTS). Use according to claim 7, characterized the existence GSM mobile radio system is used.