Wiegand vs OSDP

Author: Brian Rhodes, Published on Mar 19, 2014

Wiegand has been the standard access communication protocol for decades. Despite advances in credentials, and the move to IP controllers, the connection between readers and controllers is startlingly unchanged. The Open Supervised Device Protocol (OSDP) aims to surpass Wiegand, but what advantages does it offer, and does it have industry support?

We take a deeper look in the note.

Key Contrasts

Comparing the two protocols is not difficult once their function is understood. In terms of a typical access system, the data link between credential reader and door controller is key. This link is where 'Wiegand' and 'OSDP' are most relevant.

The prime features of either protocol stack in the chart below:

******* *** **** *** ******** ****** ************* ******** *** *******. Despite ******** ** ***********, *** *** **** ** ** ***********, the ********** ******* ******* *** *********** ** *********** *********. *** **** Supervised ****** ******** (****) **** ** ******* *******, *** **** advantages **** ** *****, *** **** ** **** ******** *******?

** **** * ****** **** ** *** ****.

Key *********

********* *** *** ********* ** *** ********* **** ***** ******** is **********. ** ***** ** * ******* ****** ******, *** data **** ******* ********** ****** *** **** ********** ** ***. This **** ** ***** '*******' *** '****' *** **** ********.

*** ***** ******** ** ****** ******** ***** ** *** ***** below:

[***************]

** *******, **** ****** * '**** **********' ********* *** **** exchange ******* ****** *** **********. ****** **** ********** *** ****** access ******* *** * **** *** **, *** ******* ****** early *** ********** ********** ***** ****** ******* *** ***** * simple **************. 

Wiegand ***********

*******, ** ******* **** ********, *** ********** ** *********** **** more ******, ******* *** ***** ** **** ********** ***********. **** prominent ***** ****:

**************:******* ****** ****** *** **** ** ******** ** *** ********** and **** *** ******* *********** **** *** ****** ** ***. In ***** ** ******** **************, ********** ****** ******, ** ******** security ****, *** ****** *********** ** ** *** ****.

******* ***********: **** **** *** *** **** ***** * ***** *********** credential ** ********** ***** ** ******. ** *** **** ********** ********** *******, *** ******* ** **** *********** ** ******* ** **** limited. *** ******** ************** ** **** *** ******* ******, *** ****** ** bits **** *** ** ******* *********** ** *** ********** ** limited ** **** ***** *** ****, **** *** ********** **** itself ********* ******** **** **** ** ****. **** *** ****** ** **********, **********, *** ********** ********* *** bits, *** ****** ** **** ** **** *** ********************* ******* ** ****.

******** *********: ***** **, ******* ******* *'****' *** '******' ****** ** ************. *******, **** **** ***** sizable **********, ***** **** ********** ********* ** ***** *****, ********** finding **** ********** ****** ********** ******-*** ****** ************* *** ********** **********/** ********

ODSP *** ********

*** *** ******** ****** ** ***** ********** *** ******* ** offer:

**-***********: ******** ************* ** ****** **** **** ******* ******* ** real ****, **** ******** ****** ********* **** ****, ******* ********, or ******* ******** ** ** ******* ***********. ********* ** *** reader, ******** **** ******** **** ** **** ****** *** ****** based ** *** ****** ** *** ****** ****** *** ******. 

********* **********:** ** **** ***** ** **** *** ** ******* ** OSDP, *** ******* ***** *********** *** ** *********** ** *********  in ******. **** ***** **** *** **** **** *********** ** bit ********* *** ******** ** ******* ******** * ********** (***********, face, ** ****) ** * ****. **** *** **** ******** a ********* ****** ** *********, ** ********* *** *********** ** **** ******* ********** *** ** ****, **** ******** *** *********** ****** ** ***** ******, ********* in * ******* ***********.

******** *********:**** ********* ******** **-***, *** ** ****** *** ******** ** apply ** ***/** ** ****, ************ ********* *** *********** ***** standard ************ **********.

Cabling ********?

******* *******, ******** *** ******** ******, ********** ******* *** *** is ****'* ******* ** ***** ******** ******* ******** ** *** same ***** *** **** **** ** ********** *********. ******, **** compared ** *********** '*:*' ******, **** ****** **** ****** *** ** * **********, ***** **** **** ******* ** ******* can ** ************** **** * ****** ***** **** ** *** controller. *** ***** *****, ******* ******** (*** ****)** ******* ************* *** **********:

**** ************* ***** ***** ** *****, ******** ** **** ** a ********** ********** ** **** ********** *** ** ******** ****** of ***** ****** *** ******* ** *** ******* **** **** position ******** ** *****.

*******, **** **** **** ********** **** *******. ************* ******* **** been ********* ** *********** *** * ********* ******* **** ***** power, *** ********, ******* *******, *** ****** ** ********* **********. OSDP **** ******** * ********* ******* *** ****** *** **** range ** *********, *********** ****** * ******** **** ** *****.

Industry *******

***** *******'* ******** ******* ** ********** *** *** '*******' ********, **** shares *** ******* ** *** ******* ** *** ****** ******. Notably, ****** *** ********** ***** *** ********* ******* *** ********, ***** **** **-***** **** ********** *** interface ************* ******** **** ******* *********** *********, *******, *****, ******** (******** ******** ****) *** ******. *** upcoming *** **** **** ******** ******* ******* ********* ****** ******** *******:

Does ** ******?

**** **** ******* ******* *********? **, ** **** ***. ****** Wiegand **** ****** * ****** ******** *** **** ******* *** many *****. *******, **** ***** ***** ******* *** ***** *********** advantages, ****** ** *** **** **** ******** *** ********** ****** *** basic ********* **** ** ******* ******* ** ***********.

Making *** ** ****

********* ******** ******* ** *** **** ** *** ****** * need, ****** ******** ****** ********** ** ******* ** *******. *** data ************ ******** *** ** ******** ** ***** ***********, ***-******* formats*** **-*********** ************* ******** ********** ******* (** **** *********) ** not ***** ****. **** ****-******** *********** *** **** **** ****** but *** *** **** ******** ** *******, ********* ** **** is *** ****** ********** *** *** ****.

*******, *** *** ********, ***** **** ** ********** *** *** likely *** **** ******. ** ********** ****** ** ******* *** controllers ******* *** *********** *** ****** **** ********** ** ***** *****. ***** *** *********** **********, ** ***** good ***** ** **** ******* ****** ***** *** *** ********* rather **** **** ****** ** *******.

Comments (16)

OSDP sounds like something to consider in our future migration plans.

Strangly in the few RFP's I have seen over the years that involved ACS (or EAC, take ypour pick), I have not seen one yet requiring anything progressive like OSDP or iClass or anything like that.

I believe this. In many cases, the clauses surrounding readers/credentials are performance or procurement specific, but not concerned about security, ie:

"Credentials must be non-proprietary and work with (associated system readers) HID-6005" mullion readers."

Statements like this inadvertently lock systems into one type of credential.

I strongly agree. While we do use a lot of iClass, the proposal is concerned mainly with the operability moreso than the security provided.

Another notable, although not terribly useful, difference between the two is ODSP's ability to chain multiple readers together on the same cable and have them be discretely addressed.

Brian, is the type of chaining shown in the diagram, with some spokes consisting of 8 downstream devices considered best practice?

Does the chaining create any dependencies between nodes, that are not present in a home-run model?

Are there any extra security considerations with this topology?

How would you tell if the controller has Wiegand vs. OSDP? Does it list on spec sheet?

OSDP adoption is pretty limited at this point. If the controller isn't made by Mercury (as an OEM), HID, Siemens, or Axis, there is slim chance. (Although that could change moving forward.) Those companies will overtly point out their controller supports OSDP on the spec sheet, ie:

On the other hand, I don't think I've seen a controller in the last ten years that doesn't support Wiegand. (Even Casi-Rusco and other 'proprietary' systems supported Wiegand at the controller.) It is essentially the standard protocol to talk with readers.

Why don't all new installs use odsp?

So, an OSPD installation would rely on an address rather than a direct connection from the controller to the reader? Wouldn't that make the use of composite cable obsolete? Unless you were to use the (6) conductor for an extra set. Not sure Id want to be a part of a daisy-chained reader system in an environment where there's the potential for cable damage.

Not sure Id want to be a part of a daisy-chained reader system in an environment where there's the potential for cable damage.

True.

An OSDP proponent, however, would tell you that a break in that chain would be immediately notified to the controller, while a Wiegand link would not and would rely on an additional 'tamper' line connection.

Thank you for the clarification.

Sounds like OSDP is gaining ground albeit at a slow pace. I concur the savings on cabling sounds minimal.

bytes not bites. OSDP can send multi-part messages so much more than 1024 bits can be returned. (Disclaimer: I wrote the open source OSDP implementation used in the plugfest.)

Most folks seem to use 1 or 2 devices. The image used shows 8. A small number of vendors seem to do this. You would get issues after a while because of traffic on the wire with all the polling. Yes it's just a few conductors (not "composite cable".) Yes if you cut the wire on a daisy chain you kill all the downstream readers.

There are at least half a dozen PACS vendors supporting OSDP and the number continues to increase. It's not just a Mercury thing.

" OSDP only requires 4 conductor bundles"

I'm been seeing some postings that say OSDP only requires (2) conductor cable. Has the requirement changed or does the installer trade off some functions going (2) conductor rather than (4) conductor?

OSDP requires 2 conductors for data and 2 conductors for power, so a total of 4.

I asked @Rodney Thayer to confirm this, and he did:

OSDP uses half-duplex RS-485 so that's "Tx+" and "Tx-" for data and 2 more conductors for DC power, typically +12 and ground. You need a ground wire for data also but it's usually the same conductor thus 4 conductors total.
Other devices out there use full duplex RS-485 and that would require more wires. But that's not OSDP.

That makes sense. I guess the confusion comes in when the postings are only considering the communication wires but leave off the power wires. Even this document from SIA seems to do the same thing....

2.1 Physical Interface
Half-duplex RS-485 - one twisted pair, shield/signal ground

... if I am assuming correctly...?

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