# callback on createSendTransport

**URL:** <https://mediasoup.discourse.group/t/callback-on-createsendtransport/866>\
**Category:** mediasoup libraries\
**Created:** [April 24, 2020, 9:15am UTC](https://mediasoup.discourse.group/t/callback-on-createsendtransport/866 "2020-04-24T09:15:04Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![OG-RTC](https://avatars.discourse-cdn.com/v4/letter/o/f475e1/32.png) [@OG-RTC](https://mediasoup.discourse.group/u/OG-RTC)\
**Post date:** [April 24, 2020, 9:15am UTC](https://mediasoup.discourse.group/t/callback-on-createsendtransport/866/1 "2020-04-24T09:15:05Z")

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Hello, on client side I see that the transport takes the below params:

createSendTransport({ id, iceParameters, iceCandidates, dtlsParameters, sctpParameters, iceServers, iceTransportPolicy, additionalSettings, proprietaryConstraints, appData }: TransportOptions): Transport;

In an example I see the the transport is having a callback on it to provide the server side producer id.

transport.on(‘produce’, async ({ kind, rtpParameters }, callback, errback) =\> {  
try {  
const { id } = await socket.request(‘produce’, {  
transportId: transport.id,  
kind,  
rtpParameters,  
});  
callback({ id });

My question is, is the producerId needed/mandatory by the transport because we can have multiple producers on the same transport unlike the plainRTPTransport that can have only 1 producer/consumer ?

Is it an optional field or mandatory?

Thanks

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<div class="post-metadata">

**Author:** ![ibc](https://yyz2.discourse-cdn.com/free1/user_avatar/mediasoup.discourse.group/ibc/32/1540_2.png) [@ibc](https://mediasoup.discourse.group/u/ibc)\
**Post date:** [April 24, 2020, 9:28am UTC](https://mediasoup.discourse.group/t/callback-on-createsendtransport/866/2 "2020-04-24T09:28:44Z")

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Oh, this **exact** question was already answered last week, please check the forum. Also this is a mediasoup-client category topic, not mediasoup one. Changing it.

> [@OG-RTC](#):
>
> My question is, is the producerId needed/mandatory by the transport because we can have multiple producers on the same transport unlike the plainRTPTransport that can have only 1 producer/consumer ?

Where in the docs you read that a `PlainTransport` can have only 1 producer/consumer?

> [@OG-RTC](#):
>
> Is it an optional field or mandatory?

Fix your signaling and get a proper requet/response mechanism.