Asynchronous vs synchronous vs isochronous communication

Hey all,

Just wanted to know if understand these things correctly.
To my knowledge asynchronous communiction is where the sender starts the transmission with a startbit and the receiver will have to figure out the clock rate of this transmision. In a synchronous communication the sender and the receiver will synchronise their clock rates witch each other, and to make sure that their own clock rate is correct they will individually synchronise with an external source. In an isochronous communication the sender and the receiver will synchronise their clock rate with an external source, wich will have some time slots in wich you are able to send and receive data.

If you have any corrections or more information, please let know - thanks

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pinkiaiii

depends of devices your speaking suppose and situations,routers would have issue if not synchronized on clock rate properly and bandwidth-cant think of any scenarios yet,but suppose it wouldn't go well if one device was operating at 100mb/s while another at 10,so that's really up to devices and protocols in place where some of them are able to adapt other have to be manually synchronized to work as in one end has to be dce-dte and all other links with same values,or be able to update from others like some server or router clocks etc.

So its a broad field from routing ospf protocols,SPT,to hardware where in some cases it works without need of synchronization but results are sort of default and might give you issues,in examples where you need one switch to be main root bridge,or changing value/cost of a link to make it more preferable.

same with switches you can plug hosts in and they synchronize out of the box,make vlans routing protocols and then you need manual synchronization in place-be it same vlan or ip range.

clarson

asynchronous is like the rs232 transmissions on the console cable.
both the sender and receiver have their clocks set seperately. the sender will transmit a bit with a start bit at the front and a stop bit at the end. When the receiver reads a start bit it will start reading the byte at it's clock rate till it reads the stop bit. So, in this case the clocks could be off as much as 5% and still have successfull transmission. But by adding the start bit and stop bit there is a 25% overhead on the data that is transmitted.
So, asynchronous, nothing to keep the clocks in sync. if the clock are far enough apart, communication in inaccurate or stops.

synchronous transmission is like sending a ethernet frame. the clock rate has already been established by the protocol. There is a start or flag byte at the start of the frame for synchronization. And a few more such as the address, control, crc, and finish byte are added for proper transmission. This results in a lot less over head for the frame transmission vs asynchronous.
So, synchronous, there is method to keep the clocks in sync to keep from dropping data from the clocks being to far apart.

isochronous transmission is designed to provide a steady bit flow for multimedia applications. Delivering such data at a steady rate is essential. An isochronous network is designed to accept and send data at a fixed rate. As an example, an isochronous mechanism designed to transfer voice operates at 64,000 bits/s. The sender must generate digitized audio continuously at exactly 64000 bit/s. A receiver must be able to accept and play the stream.
So, isochronous, not only is the clock rate synchronous but so is the data rate

niel4575 wrote: »

Hey all,

Just wanted to know if understand these things correctly.
To my knowledge asynchronous communiction is where the sender starts the transmission with a start bit and the receiver will have to figure out the clock rate of this transmision. In a synchronous communication the sender and the receiver will synchronise their clock rates witch each other, and to make sure that their own clock rate is correct they will individually synchronise with an external source. In an isochronous communication the sender and the receiver will synchronise their clock rate with an external source, wich will have some time slots in wich you are able to send and receive data.

If you have any corrections or more information, please let know - thanks