Network bus bridge and system

Details Network bus bridge and system Network bus bridge and system

2000-05-26

2003-08-26

Dharia, Rupal (Department: 2189)

Electrical computers and digital data processing systems: input/

Intrasystem connection

Bus interface architecture

C710S305000, C370S395520, C370S395650, C370S401000, C370S466000, C725S012000, C725S076000, C725S077000

Reexamination Certificate

active

06611892

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a network bus bridge and a network system using the network bus bridge, and more particularly to a network bus bridge and a network system which are capable of preventing the bus bandwidth use efficiency from being lowered by the transmission delay.
2. Description of the Related Art
A network having the IEEE1394 high-speed serial bus (hereinafter simply called the “IEEE1394 bus”) has been paid attention as one of the bus type networks. The IEEE1394 bus has a number of characteristic features such as automatic setting of node IDs, hot plug and play, and isochronous mode suitable for transmission of moving-image data, and has been adopted as a bus for transmitting digital image data.
For the usual arbitration used in IEEE1394-1995, a root node issues a transmission permission. In P1394b, the transmission order of nodes is determined by a procedure called the “BOSS arbitration”. For the BOSS arbitration, a node called “BOSS” issues the transmission permission. After the node issues the transmission permission, this node is not the BOSS any more, but the node received the transmission permission becomes a new BOSS.
In other words, the BOSS arbitration is one kind of token passing. Not becoming the BOSS by giving the transmission permission to another node corresponds to “tossing a token”, and becoming the BOSS by receiving the transmission permission corresponds to “receiving a token”.
A different point of the BOSS arbitration from the general token passing is that in the token passing the circulation order of the token is predetermined, whereas in the BOSS arbitration the node becoming the BOSS (receiving a token) is determined each time through competition. Namely, in the BOSS arbitration, a node which does not desire to transmit data does not become the BOSS (i.e., does not receive a token).
Generally, a half-duplex bus type network has advantages that broadcast is easy and the network topology is flexible, but has disadvantages that other nodes cannot transmit data while one node transmits a frame of a packet. The period while a node transmits a frame is more precisely “a period from when a frame starts being transmitted to when it becomes that the next frame can be transmitted”. This period can be generally defined as a period from the time instance when a node starts transmitting a frame to when the transmitted frame extinguishes from a bus. Namely, when the bus is broadened (i.e., the maximum value of a delay between nodes is set large) for long distance transmission, the transmission delay time becomes long. As a result, the “period from when a frame starts being transmitted to when it becomes that the next frame can be transmitted” is prolonged by the transmission delay. This is apparent from the following equation [1] which indicates the time for the same size frame to be transmitted to the whole bus:
(Frame size)/(Transmission Rate)+Transmission delay  [1]
It can be understood that when the transmission delay occurs, an additional time equal to the transmission delay requires transmitting the same size frame, so that the occurrence of the transmission delay lowers the bandwidth efficiency. This problem is troublesome in that the higher the transmission rate is, the larger the influence of the transmission delay is, as seen from the equation [1].
In order to cope with this lower efficiency, a large frame is generally used. Because the influence of the transmission delay can be mitigated as the frame size becomes large, as apparent from the equation [1]. The large frame can therefore suppress the transmission efficiency from being lowered.
A network using the IEEE1394 bus is one of the half-duplex bus type networks. This network therefore has the characteristics that if the transmission distance is elongated to generate the transmission delay, the bandwidth efficiency lowers.
In the BOSS arbitration of P1394b, the BOSS can transmit a frame. After the BOSS transmits the transmission permission to another node after transmitting the frame, it is not a BOSS any more. The node received the transmission permission becomes a new BOSS and can transmit a frame immediately thereafter. Namely, in P1394b, a period while a frame cannot be transmitted is a period from the time instant when the BOSS transmits the transmission permission to the time instant when another node receives the transmission permission and becomes the new BOSS. During this period, there is no BOSS on the bus. Therefore, any frame will not be transmitted. This will be described in more detail with reference to
FIGS. 13 and 14
.
FIG. 13
is a diagram showing an example of a network system using the IEEE1394 bus, and
FIG. 14
is a diagram showing an example of the operation timing of the network system. In the network system shown in
FIG. 13
, four nodes “A”, “B”, “C” and “D” are connected to the IEEE1394 bus. The node “B” is a cycle master. In
FIG. 14
, a both-head arrow in the uppermost area indicates a transmission cycle of 125 &mgr;s. During the time duration “B”, “C”, “D”, “A”, “D”, “B”, “C” and “A” indicated by both-head arrows in the second uppermost area, nodes corresponding to these alphabets become the BOSS. Namely, they become the BOSS in the order of node “B”→node “C”→node “D”→node “A”→node “D”→node “B”→node “C”→node “A”. Idle periods caused by the transmission delay are indicated by both-head arrows (in the third uppermost area) during the period when each of the nodes becomes the BOSS. The transmission timings of nodes “A”, “B”, “C” and “D” are indicated by “A”, “B”, “C” and “D” affixed to the leftmost area in FIG.
14
.
The operation of the network system shown in
FIG. 13
will be described. After the node “B” which is the cycle master and the BOSS transmits a cycle start packet CS on the bus, it transmits a transmission permission token on the bus. The cycle start packet CS and the transmission permission token are flowing on the bus and are received by the nodes “A”, “C” and “D”. The node “C” receives the transmission permission token to become the BOSS. There-after, the node “C” transmits an isochronous packet IsC and the transmission permission token on the bus. Similarly, the nodes “D” and “A” become thereafter the BOSS in this order. The node “D” transmits an isochronous packet IsD and the transmission permission token on the bus, and the node “A” transmits an isochronous packet IsA and the transmission permission token on the bus. After the nodes “B”, “C”, “D” and “A” sequentially transmit isochronous packets on the bus in the above manner, the nodes “D” and “C” sequentially transmit asynchronous packets AD and AC. In transmitting the asynchronous packet, it is determined that the node which receives the asynchronous packet returns an acknowledgement packet to the transmitting node. Therefore, for the asynchronous packet AD, the node “B” becomes the BOSS and returns the acknowledge packet to the node “D”, and for the asynchronous packet AC, the node “A” becomes the BOSS and returns the acknowledge packet to the node “D”.
It can be understood from the above explanation that the idle time period is a period while the BOSS does not exist. In the case of the token passing, the idle period is a period while a token flows on the network. Therefore, the above-described general formula [1] becomes the following formula [2] for the BOSS arbitration:
(Frame size)/(Transmission rate)+(Transfer time of transmission permission token)  [2]
In the case of the IEEE1394 bus, a long distance such as a large bus size will not cause any deterioration of the efficiency due to the long distance transmission delay if the nodes which become the BOSS (which desire to transmit) are concentrated in a narrow area. The reason is as follows. The idle time is a time for which the transmission permission token is transferred from the current BOSS to the next BOSS. Therefore, only the transmission del

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