Is it possible for SA540 to work in transparent bridge mode?

Question

Hi all,
I've been considering to use a Cisco SA540 in an industrial project; please consider Scenario 1 and 2 files attached (bear with me - I'm an engineer, not an artist).
All networks mentioned in both scenarios are regular and well known Ethernet TCP/IP networks. The Corporate Network and Automation Network (including the DMZ) are in different subnets. The Corporate Network is the biggest one, similar to any company's corporate network you all know. The Automation Network exists for the purpose of operating and maintaining the industry process; it's smaller but highly critical. Only specific staff (automation staff and dedicated operators) have access to it. Although many devices and networks in the Automation Network are industry specific - not so well known, a small segment of it is plain Ethernet TCP/IP, as I've already stated. The Automation Network has a DMZ, where we lay servers that provide industry process information for the Corporate Network.
Scenario 2 may look at a first glance the best option, since it's simpler, doesn't require another router and benefits from Cisco SA540 support for both a LAN and a DMZ. The problem with Scenario 2 is the following:
Since both networks are maintained by different teams under different management, TI staff would have absolute control over the Cisco SA540. This way automation staff could not grant that the Automation Network is really protected from the Corporate Network.
TI staff may even demand for another device to interface with the Automation Network - which is not Cisco SA540, since they rule everything that lives in the Corporate Network. In this case, I have my hands tied!
Scenario 1 solves the above problems. Since automation would have absolute control over the Cisco SA540, they could grant security for the Automation Network (except for DMZ, but that's the reason why it is called a DMZ!). TI staff could ask for any router they prefer to interface with the DMZ, I would never mind about it.
Considering the above, I will probably be forced to adopt Scenario 1 instead of Scenario 2. So here comes my question: is it possible for Cisco SA540 to work with the same subnet for both WAN and LAN interfaces (in Scenario 1, no DMZ interface is required)? In other words, is it possible for Cisco SA540 to work in transparent bridge mode? I've been through all of the Cisco SA540 Administration Manual and as far as I could understand, routing is not an option - it is demanding.
Although I understand I could adopt Scenario 1 and still have different subnets for DMZ and the rest of the Automation Network by connecting the DMZ to the WAN interface and the rest of the Automation Network to the LAN interface in the Cisco SA540, I believe it's not worth the effort. The Automation Network is so small and we do all we can to keep it as simple as possible.

Answer 1

Adriano, there is a RV042G, which supports the gig ports and a 800 mbps nat throughput. Here is the datasheet
http://www.cisco.com/en/US/prod/collateral/routers/ps10907/ps9923/ps12262/data_sheet_c78-706724.html
If you are using a DSL connection, the SRP527/547 models may be an alternative. These models support the RFC 1483 Bridges EOA Please note the SRP547 should be 10/100/1000. Also note the SRP521/541 are Fast Ethernet units and they do differ from the SRP527/547. The main selling point of these devices are the FXS/FXO ports. So this may also be a bit of an "unfocused" solution. But it's worth throwing the idea out there!
Here is the admin guide;
http://www.cisco.com/en/US/docs/voice_ip_comm/unified_communications/srp540_series/administration/srp500_AG_2567701.pdf
Here is the datasheet;
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6790/gatecont/ps10500/data_sheet_c78-550705.pdf