The Basics: Copper wire, D2B and MOST system differences, and what's a CAN Bus?
The first step in understanding your system is knowing how its components are connected. Mercedes vehicles have one of three basic systems interconnecting the components of their audio systems: Copper wire, the D2B fiber optics bus, or the MOST fiber optics bus. Some systems are hybrid; they may use copper wire and an amplifier in the head unit to run the front speakers, and a fiber optic connection to a separate amplifier for rear speakers and a sub woofer. The fiber optic systems are also tied into a CAN Bus, which allows control from the steering wheel and display of functions on the dashboard. All of the systems use copper wire to power individual components; and all use copper wire between the amplifier and the speakers.
Copper wire systems:
Many Mercedes vehicles before 1999 employed systems in which all of the components were connected via copper wiring. Most 3rd party head units, amplifiers, and audio processors were and are still copper wire systems. Therefore, upgrading to a new head unit, adding an amplifier, or an audio processor as simply a matter of providing power to the unit and connecting it in the proper sequence in the system. Most consumer audio shops are able to handle this kind of installation.
Fiber Optics:
Fiber optics "wiring" differs from copper wiring in that fiber optics leads ("wires") are comprised of glass or polymer (plastic) fibers that conduct light, whereas regular wiring uses metal - most often, copper - to conduct electricity. A fiber optics system will use devices that convert electrical signals to modulated light; and with different modulations, or coding, for each device, multiple devices can use the same "wire." The equipment on the fiber optic busses would include COMAND and navigation systems, Audio 10, 20, 30, and 50 units (used where the car lacks COMAND), cell phone, CD changer, satellite radio, voice control - basically anything connected to or playing through your audio system. The fiber optics system Mercedes uses are either D2B (Digital Data Bus or sometimes Domestic Data Bus) or MOST (Media Oriented Systems Transport). If you don't know which you have, see post 5, http://www.benzworld.org/forums/audio-telematics-forum/1439410-do-i-have-d2b-most.html#post3434579 or see the phone bulletins links at the bottom of this post.
D2B Bus:
Mercedes came out with its proprietary Digital Data Bus (D2B fiber optics bus) as early as 1996 in some models, and placed it in wide use for the 2000 model year (’99 in Europe). Mercedes licensed D2B to Volkswagen and Jaguar for some cars, but it was mainly used in Mercedes cars. As a result, the market is fairly small, compared to the entire auto industry, and 3rd party developers do not place a lot of effort into making upgrades for it. Any audio component in the system must connect via D2B fiber leads; equipment made for copper wire systems (and MOST fiber optics systems, discussed below) cannot be added to a D2B system; only equipment manufactured for a D2B system can be used on a D2B bus.
In addition to the requirement that the equipment be designed for D2B, each piece of equipment on or added to the bus (or “loop”) must be “version coded” in the D2B Controller. Version coding is somewhat like telling a Windows computer BIOS that a new piece of equipment has been connected, so that it will be recognized, and all of its functions enabled. Version coding is done via Mercedes DAS, a laptop computer with Mercedes-specific software that allows technicians to make settings in the many computers that control the car’s functions. If a component is removed from the fiber optic bus without connecting the fiber optic leads that went to the component (see posts 7 and 8, http://www.benzworld.org/forums/aud...399151-2000-s500-w220-chassis-how-bypass.html), the entire system will shut down.
An excellent source of information on the basic connections, and the components in the D2B loop, is in the phone bulletins in the link at the bottom of this post. Generally, Mercedes models from model year 2000 in the U.S., 1999 in Europe, through 2003, were equipped with a D2B bus. However, Mercedes began to transition to the newer, more capable MOST bus in SOME 2004 models. The first page of the phone bulletin will tell you whether you have a D2B or a MOST bus, by mentioning notes pertinent to the bus. You can also identify the type of bus in your car by looking at the fiber optic connectors – see post #2 at http://www.benzworld.org/forums/audio-telematics-forum/1439410-do-i-have-d2b-most.html#post3434579.
For a detailed technical discussion of the D2B bus, see https://web.archive.org/web/2012022...Telematics/416 HO D2B (CooksonI) 03-09-04.pdf
MOST bus:
The D2B Bus was succeeded by the MOST (Media Oriented Systems Transport) fiber optics bus beginning with Model Year '04 (later in some models). MOST is a more capable bus, and rather than being proprietary, is an automotive industry standard used by many manufacturers. As a result, there are far more options manufactured for it, and MOST is still in use in the newest Mercedes cars. You cannot use equipment designed for one type of bus with the other. Again, the phone bulletins at Phone Bulletins will help you identify which system your car has by model year. All Mercedes passenger cars since MY 2005 have had the MOST bus. If you are inclined, you can also read a great deal of technical information on the MOST bus (and comparisons with D2B) at https://web.archive.org/web/2006090...elematics/416 HO MOST (CooksonI) 07-01-04.pdf and once again, if you wonder which type of system you have, you can determine it from the fiber optic connectors – post #2 at http://www.benzworld.org/forums/audio-telematics-forum/1439410-do-i-have-d2b-most.html#post3434579. Just as with the D2B system, leaving a fiber optic loop open when equipment is removed will cause the entire system to shut down. The loop must be closed with a coupler (bypass) - posts 7 and 8, http://www.benzworld.org/forums/aud...399151-2000-s500-w220-chassis-how-bypass.html.
Again, for a detailed discussion of the MOST bus, see https://web.archive.org/web/2006090...elematics/416 HO MOST (CooksonI) 07-01-04.pdf
CAN (Controller Area Network) bus:
Among many other functions, the CAN-B bus allows your steering wheel buttons to control components of your audio system, and also relays the information from the equipment on the fiber optic loop to the instrument cluster, so that it can be shown (usually on a multifunction display). It is used in cars with both the D2B bus and the MOST bus. Other CAN busses exist - CAN B is the interior bus, and is connected to the audio system; CAN C is for the engine; and CAN D is the diagnostics bus. These are copper wire electronics busses, and they communicate with each other and with the fiber optics bus when necessary through devices called "gateways." In simplest terms, CAN busses help various controls, sensors and displays operate. When you replace an original equipment Mercedes head unit with a 3rd party unit, that unit will probably not have CAN-B connections, and you will lose steering wheel button control and instrument cluster audio, navigation, and phone displays. There are 3rd party devices that can be installed to restore some of these functions, but they must be matched to the car’s CAN-B bus and to the head unit as well.
For a detailed technical discussion of the various CAN busses, see https://web.archive.org/web/2014081...507 Systems I/507 HO CAN B (ICC) 10-28-02.pdf and https://web.archive.org/web/2013041...isor/219 HO Networking (ACB-ICC) 09-03-02.pdf
The first step in understanding your system is knowing how its components are connected. Mercedes vehicles have one of three basic systems interconnecting the components of their audio systems: Copper wire, the D2B fiber optics bus, or the MOST fiber optics bus. Some systems are hybrid; they may use copper wire and an amplifier in the head unit to run the front speakers, and a fiber optic connection to a separate amplifier for rear speakers and a sub woofer. The fiber optic systems are also tied into a CAN Bus, which allows control from the steering wheel and display of functions on the dashboard. All of the systems use copper wire to power individual components; and all use copper wire between the amplifier and the speakers.
Copper wire systems:
Many Mercedes vehicles before 1999 employed systems in which all of the components were connected via copper wiring. Most 3rd party head units, amplifiers, and audio processors were and are still copper wire systems. Therefore, upgrading to a new head unit, adding an amplifier, or an audio processor as simply a matter of providing power to the unit and connecting it in the proper sequence in the system. Most consumer audio shops are able to handle this kind of installation.
Fiber Optics:
Fiber optics "wiring" differs from copper wiring in that fiber optics leads ("wires") are comprised of glass or polymer (plastic) fibers that conduct light, whereas regular wiring uses metal - most often, copper - to conduct electricity. A fiber optics system will use devices that convert electrical signals to modulated light; and with different modulations, or coding, for each device, multiple devices can use the same "wire." The equipment on the fiber optic busses would include COMAND and navigation systems, Audio 10, 20, 30, and 50 units (used where the car lacks COMAND), cell phone, CD changer, satellite radio, voice control - basically anything connected to or playing through your audio system. The fiber optics system Mercedes uses are either D2B (Digital Data Bus or sometimes Domestic Data Bus) or MOST (Media Oriented Systems Transport). If you don't know which you have, see post 5, http://www.benzworld.org/forums/audio-telematics-forum/1439410-do-i-have-d2b-most.html#post3434579 or see the phone bulletins links at the bottom of this post.
D2B Bus:
Mercedes came out with its proprietary Digital Data Bus (D2B fiber optics bus) as early as 1996 in some models, and placed it in wide use for the 2000 model year (’99 in Europe). Mercedes licensed D2B to Volkswagen and Jaguar for some cars, but it was mainly used in Mercedes cars. As a result, the market is fairly small, compared to the entire auto industry, and 3rd party developers do not place a lot of effort into making upgrades for it. Any audio component in the system must connect via D2B fiber leads; equipment made for copper wire systems (and MOST fiber optics systems, discussed below) cannot be added to a D2B system; only equipment manufactured for a D2B system can be used on a D2B bus.
In addition to the requirement that the equipment be designed for D2B, each piece of equipment on or added to the bus (or “loop”) must be “version coded” in the D2B Controller. Version coding is somewhat like telling a Windows computer BIOS that a new piece of equipment has been connected, so that it will be recognized, and all of its functions enabled. Version coding is done via Mercedes DAS, a laptop computer with Mercedes-specific software that allows technicians to make settings in the many computers that control the car’s functions. If a component is removed from the fiber optic bus without connecting the fiber optic leads that went to the component (see posts 7 and 8, http://www.benzworld.org/forums/aud...399151-2000-s500-w220-chassis-how-bypass.html), the entire system will shut down.
An excellent source of information on the basic connections, and the components in the D2B loop, is in the phone bulletins in the link at the bottom of this post. Generally, Mercedes models from model year 2000 in the U.S., 1999 in Europe, through 2003, were equipped with a D2B bus. However, Mercedes began to transition to the newer, more capable MOST bus in SOME 2004 models. The first page of the phone bulletin will tell you whether you have a D2B or a MOST bus, by mentioning notes pertinent to the bus. You can also identify the type of bus in your car by looking at the fiber optic connectors – see post #2 at http://www.benzworld.org/forums/audio-telematics-forum/1439410-do-i-have-d2b-most.html#post3434579.
For a detailed technical discussion of the D2B bus, see https://web.archive.org/web/2012022...Telematics/416 HO D2B (CooksonI) 03-09-04.pdf
MOST bus:
The D2B Bus was succeeded by the MOST (Media Oriented Systems Transport) fiber optics bus beginning with Model Year '04 (later in some models). MOST is a more capable bus, and rather than being proprietary, is an automotive industry standard used by many manufacturers. As a result, there are far more options manufactured for it, and MOST is still in use in the newest Mercedes cars. You cannot use equipment designed for one type of bus with the other. Again, the phone bulletins at Phone Bulletins will help you identify which system your car has by model year. All Mercedes passenger cars since MY 2005 have had the MOST bus. If you are inclined, you can also read a great deal of technical information on the MOST bus (and comparisons with D2B) at https://web.archive.org/web/2006090...elematics/416 HO MOST (CooksonI) 07-01-04.pdf and once again, if you wonder which type of system you have, you can determine it from the fiber optic connectors – post #2 at http://www.benzworld.org/forums/audio-telematics-forum/1439410-do-i-have-d2b-most.html#post3434579. Just as with the D2B system, leaving a fiber optic loop open when equipment is removed will cause the entire system to shut down. The loop must be closed with a coupler (bypass) - posts 7 and 8, http://www.benzworld.org/forums/aud...399151-2000-s500-w220-chassis-how-bypass.html.
Again, for a detailed discussion of the MOST bus, see https://web.archive.org/web/2006090...elematics/416 HO MOST (CooksonI) 07-01-04.pdf
CAN (Controller Area Network) bus:
Among many other functions, the CAN-B bus allows your steering wheel buttons to control components of your audio system, and also relays the information from the equipment on the fiber optic loop to the instrument cluster, so that it can be shown (usually on a multifunction display). It is used in cars with both the D2B bus and the MOST bus. Other CAN busses exist - CAN B is the interior bus, and is connected to the audio system; CAN C is for the engine; and CAN D is the diagnostics bus. These are copper wire electronics busses, and they communicate with each other and with the fiber optics bus when necessary through devices called "gateways." In simplest terms, CAN busses help various controls, sensors and displays operate. When you replace an original equipment Mercedes head unit with a 3rd party unit, that unit will probably not have CAN-B connections, and you will lose steering wheel button control and instrument cluster audio, navigation, and phone displays. There are 3rd party devices that can be installed to restore some of these functions, but they must be matched to the car’s CAN-B bus and to the head unit as well.
For a detailed technical discussion of the various CAN busses, see https://web.archive.org/web/2014081...507 Systems I/507 HO CAN B (ICC) 10-28-02.pdf and https://web.archive.org/web/2013041...isor/219 HO Networking (ACB-ICC) 09-03-02.pdf