Electrical computers and digital processing systems: multicomput – Network-to-computer interfacing
Reexamination Certificate
1999-07-09
2001-10-16
Meky, Moustafa M. (Department: 2153)
Electrical computers and digital processing systems: multicomput
Network-to-computer interfacing
Reexamination Certificate
active
06304916
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART
Use of a star type LAN for connecting a plurality of end nodes to a line concentrator which is called a hub is now widespread. In this type of LAN, the hub is connected to each end node with stranded paired cables and modular jacks.
For example, 10 Base-T which is described in the proposal of IEEE802.3 may be cited as such a LAN.
Recently in this star type LAN, developments for allowing the central line concentrator (hub) to control sending and receiving of a frame from downstream node and to arbitrate the transfer right thereof have materialized.
For example, in a system which is called a demand priority system in IEEE802.12, a medium access control (MAC) protocol provides that the hub arbitrates a frame transfer request from each downstream node which is connected to an intermediate hub, selects a downstream node, and gives permission for sending the frame.
This demand priority system will be explained hereunder.
FIG. 19
shows a configuration example of a LAN to which the demand priority system is applied. In the drawing, numerals
200
to
207
indicate end nodes and
211
,
212
, and
213
indicate hubs. When an inter-network connection device such as a bridge is used so as to connect another network, the inter-network connection device is connected to the hub as an end node. In the drawing,
207
indicates an inter-network connection device. The hubs and end nodes are nodes of the LAN. In
FIG. 19
, those indicated on the upper part are upper-stream nodes.
In this LAN, a network can be configured by connecting a plurality of hubs hierarchically. 4-pair stranded cables are used for connection between the hubs and between the hubs and end nodes, that is, between the nodes.
Each of the hubs
211
and
213
has a plurality of downstream ports and an upstream port. The end nodes or the downstream hubs
211
and
213
are connected to the respective downstream ports of the upstream hub
212
, and are regarded as downstream nodes of hub
212
. The upstream hub
212
is connected to the upstream ports of the downstream hubs
211
and
213
and is regarded as an upstream node thereof. The uppermost stream hub
212
is called a root hub.
In each hub, the downstream ports to which the nodes which are required to transfer all the frames, such as the hubs and inter-network connection device, are connected, are set in the promise cure mode beforehand and the other ports are set in the privacy mode. To each port in the privacy mode, the address which is given to the node (end node) connected to the port corresponds. The promise cure mode is a mode for sending data to all of the nodes connected in the LAN and the privacy mode is a mode for specifying the node address and sending data only to the node which is defined by the specified address.
The frame transfer operation from the end node
200
will be explained hereunder with reference to FIG.
20
.
The session for arbitrating the frame transfer right between the hub
211
and the end node
200
is executed by each using 2 pairs of the 4-pair cable for output and by alternately sending and receiving a control signal which is decided by a combination of 2 signal states on the 2-pair cable to be used for output as shown in Table 1. The same may be said with the hub
211
and the end node
201
,
202
, or others.
TABLE 1
<End node -> hub>
<Hub -> end node
Item
TP1
TP2
Item
TP3
TP4
Receivable
0
0
Permission of
0
0
(Silence)
sending (Silence)
Idle
1
1
Idle
1
1
Transfer request NP
1
2
Request for
1
2
preparation of
receiving (Incoming)
Transfer request HP
2
1
Reserve
(2
1)
Training request
2
2
Training Idle
2
2
(for connection
(for connection
check)
check)
0: Silence
1: Tone1 (938 kHz)
2: Tone2 (1.875 MHz)
NP: Normal Priority
HP: High Priority
In the table, a symbol TP indicates a pair number of the stranded cable. As a signal state, three states such as the 938 kHz tone signal output state, 1.875 MHz signal output state, and silent state are used. The transfer request NP generally indicates a priority transfer request and the sending request HP indicates a top priority transfer request.
In the initial state, the hubs
211
,
212
, and
213
and the end nodes
200
to
207
which are connected to them output a control signal IDLE.
A case that a transfer request occurs in the end nodes
200
and
202
will be considered. Specifically, it is assumed that the end node
200
sends the transfer request HP and the end node
202
sends the transfer request NP to the hub
211
. The hub
211
which recognizes it sends the control signal and the transfer request NP or the control signal and the sending request HP to the upstream hub
212
from the upstream port. When the hub
211
receives Silence from the upstream hub
212
, it arbitrates the transfer right, selects the end node
200
for giving transfer permission so that the sending request HP works preferentially to the transfer request NP, and transmits Silence to the end node
200
. The hub
211
sends the control signal and request for preparation of receiving (Incoming) to the other end nodes
201
,
202
, and
203
.
The end nodes
201
,
202
, and
203
which receive the control signal and request for preparation of receiving from the hub
211
, as shown in FIG.
20
(
2
), always put the states of the self nodes into the Silence state immediately regardless of whether or not the respective nodes send a transfer request, and transmit Silence to the hub
211
.
On the other hand, the end node
200
to which Silence is transmitted from the hub
211
recognizes permission of transfer and starts frame transfer to the hub
211
using all of the 4-pair wires. Since non-output is used as Silence in this protocol, no collision is generated during frame transfer.
The hub
211
which receives this frame sends the frame to the upstream hub
212
and checks the destination address of the inputted frame. When the end node which is the destination of this frame is connected, the hub
211
sends the frame to this end node using all of the 4-pair wires; The hub
211
also sends the frame to the node connected to the downstream port in the promise cure mode.
In the aforementioned operations, the operation of the upstream hub
212
which receives the transfer request from the downstream hub
211
is the same as the operation of the downstream hub
211
which receives the transfer request from the end node
200
. However, the upstream hub
212
is a root hub and there is no upperstream hub thereof. Therefore, the hub
212
gives transfer permission to the node connected to the downstream port without waiting for transfer permission from the upstream hub and sends the request for preparation of receiving to the other downstream nodes.
The root hub
212
gives Silence to the hub
211
as mentioned above, sends the request for preparation of receiving to the hub
213
connected to the downstream port, and sends the frame received from the hub
211
to the hub
213
connected to the downstream port in the promise cure mode using all of the 4-pair wires.
When the hub
213
receives the request for preparation of receiving from the upstream hub
212
, it sends the request for preparation of receiving unconditionally to each end node connected to the downstream port thereof. Thereafter, the hub
213
checks the destination address of the frame which is received from the upstream hub
212
. When the end node which is the destination of this frame is connected, the hub
213
sends the frame to this end node using all of the 4-pair wires. The hub
213
also sends the frame to the node (in this example, the inter-network connection device
207
) connected to the downstream port in the promise cure mode.
During the aforementioned operation, the hub
211
arbitrates the transfer right between the downstream nodes as described below. Namely, when the hub
211
receives Silence from the upstream hub, it selects one of the downstream nodes which send the transfer request by utilizing a round robin system, gives Silence to it, and sends the request for preparation
Iwatsuki Kazuko
Wada Hiroyuki
Antonelli, Terry, Stotu & Kraus, LLP
Hitachi , Ltd.
Meky Moustafa M.
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