Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1998-07-14
2004-05-04
Vanderpuye, Ken (Department: 2661)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S238100
Reexamination Certificate
active
06731604
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transmission apparatus for connecting a plurality of LANs (Local Area Network) to each other and constructing a fast and high-capacity back bone network, a network transmission system for constructing a plurality of routes by connecting a plurality units of the transmission apparatus to each other, and to a transmission method for realizing a relay as a backbone with those transmission apparatus.
BACKGROUND OF THE INVENTION
FIG. 30
is a block diagram showing a network transmission system in a building for an ordinary business organization. Constructed in the building shown in
FIG. 30
is a LAN using floors from a first basement to a third floor. Routers RT
1
, RT
2
, and RT
3
are installed in the third floor, second floor, and first floor respectively, and those routers RT
1
, RT
2
, and RT
3
are connected to a transmission apparatus
100
as a backbone for the routers installed in the first basement.
As for a system in each floor, a plurality of hubs HB
1
. . . HBi (i: a natural number) are connected to the router RT
1
. A plurality of hubs, not shown through, are connected to each of the other routers RT
2
, and RT
3
similarly to the router RT
1
. Terminals TL
1
. . . TLj (j: a natural number) for a server or a work station or the like are connected together onto the hub HB
1
, and terminals PC
1
. . . PCk (k=a natural number) connected together onto the hub HB
2
. It should be noted that the same system as the relation among the router, the hubs, and the terminals shown in the third floor is installed also in the first floor and the second floor.
The transmission apparatus
100
has also a plurality of hubs and terminals connected thereto under controls by its own like the routers RT
1
, RT
2
, and RT
3
on each floor and also connects other transmission apparatus thereto.
Description is made for a case, as an example of operations in the network transmission system shown in
FIG. 30
, where the terminal TL
1
in the third floor transmits data to any terminal in the second floor. A protocol to be used is a TCP (Transmission Control protocol)/IP (Internet Protocol) protocol as one example.
FIG. 31
is a view schematically showing a format of a frame (also called as a packet) used in the TCP/IP protocol. The frame comprises, as shown in
FIG. 31
, from the header to the end thereof, a start flag indicating a start of the frame, a MAC (Media Access Control) header for defining a destination MAC address and a source MAC address or the like, a type value for defining a protocol type, an IP header for defining a destination IP address and a source IP address or the like, a frame check sequence (FCS) for data and a checksum, and an end flag indicating an end of the frame.
Herein a MAC address and an IP address of a source terminal TL
1
are MACA and IPA, and a MAC address and an IP address of a destination terminal are MACB and IPB, respectively. Further MAC addresses of the router RT
1
, the transmission apparatus
100
and the router RT
2
provided for relaying data between the terminal TL
1
and a destination terminal are MACC, MACD, and MACE respectively.
At first, the terminal TL
1
prepares a frame according to the format shown in FIG.
31
. Defined in the MAC header of the frame, during the preparation, is a MAC address (MACC) of the router RT
1
through which the frame passes first of all when transferred to the destination terminal as a destination MAC address together with the MAC address (MACA) of the source terminal. Defined also in the IP header thereof is an IP address (IPB) of a destination terminal together with the IP address (IPA) of the source terminal.
When the frame is sent out onto a network by the terminal TL
1
, the frame is first received by the router RT
1
. This router RT
1
extracts the IP header as well as the MAC header from the received frame. Further the router RT
1
confirms from the IP header that the source terminal is the terminal TL
1
(IPA) and the destination is a terminal having an IP address of IPB, and then rewrites the MAC header to MACD for the transmission apparatus
100
as the following MAC address. As described above, the router RT
1
transmits the frame with the updated MAC header to the transmission apparatus
100
as a backbone.
The rewriting operation of the MAC header is also executed in the following transmission apparatus
100
and the router RT
2
. Namely, the MAC address is rewritten from MACD to MACE in the transmission apparatus
100
, and the MAC address is rewritten from MACE to MACB in the router RT
2
. As described above, the MAC header is updated each time data passes through the router in data transmission through the router.
A large amount of traffic generated in each floor is concentrated to the transmission apparatus
100
in this network transmission system, which makes it necessary to select a transmission apparatus having a large capacity and high-speed capability.
There is, as a transmission apparatus with a large capacity capable of connecting a plurality of routers to each other, a combination of a switching hub with a router and a combination of an ATM (Asynchronous Transfer Mode) switch with a router other than the transmission apparatus
100
(router).
FIG. 32
is a block diagram schematically showing a transmission apparatus constructed by a combination of a switching hub with a router, and
FIG. 33
is a block diagram schematically showing a transmission apparatus constructed by a combination of an ATM switch with a router.
A transmission apparatus
200
shown in
FIG. 32
has a router
201
and a switching hub
202
connected to each other. The switching hub
202
executes bridging among transfer paths a, b, c as well as among transfer paths d, e, f, and also performs switching between the transfer paths a, b, c and the transfer paths d, e, f. This switching hub
202
relays, if applied in an OSI (Open Systems Interconnection) layer, a layer corresponding to the layer
2
thereof. Namely, the switching hub
202
transparently relays, by selecting a route according to the MAC address, the frame flowing on the LAN.
Also, the router
201
receives the frame from the switching hub
202
, rewrites data such as the MAC address, TTL (Time to Live), and a checksum to new ones, and returns the frame to the switching hub
202
(e.g., rewriting the MAC address from MACX to MACY). This router
201
relays, if applied an OSI layer, a layer corresponding to the layer
3
thereof. The router
201
receives, by selecting a route according to the IP address, the frame running on the LAN, rewrites the frame to new one, and then relays the rewritten frame to other LAN.
A transmission apparatus
300
shown in
FIG. 33
has a server
302
and routers
303
,
305
connected to an ATM switch
301
. In
FIG. 33
, the router
303
positioned in the input side of the ATM switch
301
divides the frame into data units each called as a cell having a short fixed length by an ATM board
304
incorporated therein and transmits the units to the ATM switch
301
. On the other hand, the router
305
positioned in the output side of the ATM switch
301
returns each cell to the frame by an ATM board
306
incorporated therein and then transmits the frame.
The ATM switch
301
relays, if applied in the OSI layer, layer corresponding to the layer
1
thereof according to the cells running between the routers
303
and
305
. This ATM switch
301
selects a destination router (route) with a support by the server
302
in which the destination information is stored. Namely, a route is selected by an identifier unitrarily allocated thereto and specific to the ATM in the ATM switch
301
. In this example, the destination router is the router
305
.
In the transmission apparatus
200
shown in
FIG. 32
, however, the frame is rewritten at the router
201
when passing therethrough even if the switching hub
202
can transparently pass the frame therethrough. For this reason, it is satisfactory in the functional aspect that the layer as far as the layer
3
can be covere
Baba Hidekazu
Chugo Akira
Fujitsu Limited
Staas & Halsey , LLP
Vanderpuye Ken
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