[MS-WMSP] Real time in WMSP

Question

As I know, streaming is action that transfer of real-time data. And UDP is usually used for transfer of real-time data. While MS-WMSP used TCP, so how do it ensure real-time ?

Answer 1

TH1912,

 

Thank you for your question.  An engineer from the Protocols team will contact you soon.

 

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Bryan S. Burgin Senior Escalation Engineer Microsoft Protocol Open Specifications Team

Answer 2

Hi, TH1912

You can’t with [MS-WMSP], by design.  See [MS-WMSP] 1.4 “Relationship to Other Protocols”, which states:

 

“The Windows Media HTTP Streaming Protocol depends on HTTP 1.0, as specified in [RFC1945]. The pipelined mode of the protocol can only be used if the client, the server, and any intermediate HTTP proxy servers support the pipelining feature of HTTP 1.1, as specified in [RFC2616].

“This protocol can be used instead of the Microsoft Media Server (MMS) Protocol as specified in [MS-MMSP]. This protocol can also be used instead of the Real-Time Streaming Protocol Extensions as specified in [MS-RTSP]. However, it should be noted that although these two other protocols allow the multimedia data to be transmitted over either User Datagram Protocol (UDP) or TCP, the Windows Media HTTP Streaming Protocol only allows multimedia data to be transmitted over TCP (because HTTP always uses TCP).

“Implementations of the client role of the protocol are able to share cookies with implementations of the client role of the Real-Time Streaming Protocol (RTSP) Windows Media Extensions [MS-RTSP] that are running on the same machine.”

Therefore, you may want to look at [MS-RTSP].

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Bryan S. Burgin Senior Escalation Engineer Microsoft Protocol Open Specifications Team

Answer 3

Thank you for answering me. I know what you mean but in this description : "This protocol can also be used instead of the Real-Time Streaming Protocol Extensions as specified in [MS-RTSP]".  If it can be used instead of [MS-RTSP], i think it can do what [MS-RTSP] do. I know [MS-RTSP] uses UDP and [MS-WMSP] uses TCP.  UDP is usually used in Real-Time applications because it is not a reliable protocol. But TCP's different. Because TCP's reliable protocol, it is not usually used in Real-Time applications. And Streaming is action that transfer of Real-Time data. So i want to know how [MS-WMSP] ensures Real-Time when it use TCP as transport protocol. 

Answer 4

TH1912,

 

[MS-RTSP] and [MS-WMSP] are similar in purpose, so either can be used in many situations.  Thus, “This protocol can also be used instead of the Real-Time Streaming Protocol Extensions as specified in [MS-RTSP]” is true.  However, they are not exactly the same in every respect and one of the key differentiators is that [MS-RTSP] is better suited for Real Time because of its use of UDP.  TCP is a reliable protocol because it adds a lot of chatter and overhead between the endpoints to make it reliable: packet sequencing, acknowledgements, retries, re-ordering, etc.  The strength of TCP (reliability), however, is at discord with the goal of Real Time; you can’t have both.  Accordingly, if Real Time is your goal, then [MS-WMSP], because it’s TCP-based, is a poor choice for your application and you should examine [MS-RTSP].  The answer to your question “While MS-WMSP used TCP, so how do it ensure real-time” is: you can’t and look to [MS-RTSP] instead

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Bryan S. Burgin Senior Escalation Engineer Microsoft Protocol Open Specifications Team

Answer 5

Hi Bryan S.Burgin

I agree with you that [MS-WMSP] cannot ensure real-time. But i want to ask you one more question is "Streaming is a real-time action. If [MS-WMSP] cannot ensure real-time, why is it used in Streaming action ?"

Answer 6

Hi, PenguiSh,

 

Let me research this for you and I'll reply soon.

 

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Bryan S. Burgin Senior Escalation Engineer Microsoft Protocol Open Specifications Team

Answer 7

Hi Bryan S.Burgin

I'm still waiting an answer from you. Thank you for trying to helping me.

Answer 8

PenguiSh,

 

The term “Real Time” is being overloaded in this discussion.  In my previous replies, I was using it in more of the traditional context of Real Time, which TCPIP cannot provide and for which the protocol [MS-RTSP] is better suited because it uses UDP.

 

[MS-WMSP] also uses the term Real Time in the phrase “real-time multimedia data” as pointed out in [MS-WMSP] 1.6 “The Windows Media HTTP Streaming Protocol is suitable for streaming delivery of __real-time multimedia data__. The term streaming means that the data is transmitted at some fixed rate or at some rate that is related to the rate at which the data will be consumed (for example, displayed) by the receiver.”

 

I believe it is in this second context that is the term real time is being used in connection with “streaming”.

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Bryan S. Burgin Senior Escalation Engineer Microsoft Protocol Open Specifications Team