A Brief Introduction fo msnslp and Analysis of File Transfer

Introduction of msnslp

[Abstract]

Msnslp is based on SIP (Session Initiation Protocal ). msnslp looks much similar with SIP while it support less methods. with MSN Messenger 6.0 or higher, it supports to use msnslp to transfer files instead of msnftp used under version 5.

Keywords: SIP, msnslp, file transfer, display picture, emoicon

 

1. What is msnslp?

Msnslp looks much like sip but it supports less methods than sip. mostly we only use invite/Bye/as methods in msnslp. MSN Messenger 6.0 or later can transfer files/display pictures and show emoicons via msnslp protocol.

 

2. msnslp message

A msnslp message always has structures as below:

 

Start line

Message Header

CRLF

Message Body

Message footer

 

3. Start line

Msnslp has 2 kinds start line, one is request line, the other is status line.

1), request line has such structures:

Method space msnmsgr: buddy@mail.com space msnslp-version CRLF

 

Method: Invite/Bye

The invite method is used to start a initial session, and bye to end a session.

If you got a second invite message with the same session, than it only means to change parameters of the session.

Msnslp-version: "msnslp/ 1.0"

Now msnslp only have one version.

 

2), status line:

A status line tells the response of the other client, for example 200 OK, 603 decline etc.

Structure:

Msnslp-version space status-code space reason CRLF

 

Status-code:

200 OK: Everything is expected.

603 decline: the other client declined the request

500 internal error: Something is wrong with the request

404 Not found: usually happened when a wrong buddy mail was send

 

4. Message Header:

The message header contains mostly the following fileds: "to", "from", "via", "CSeq", "Call-ID", "Max-forwards ", "Content-Type" and Content-Length;

 

To: The one who is the sender of the message.

From: The one who sends the message

Via: shows the Protocol (msnslp/1.0/TLP) and branch ID which is the identifier of the message.

CSeq: command sequence. The initial invite shoshould be 0, and the ACK of IT shoshould be 1 and so on.

Call-ID: this field identifier a certain invitation, usually a guid value shocould assign to it.

Max-forwards:

Always 0. Used to limit the number of proxies and other ways, it was not used till now.

Content-Type:

For requests: Application/X-msnmsgr-sessionreqbody

For transfer: Application/X-msnmsgr-transreqbody

 

5. Message Body:

The content of message body depends on the type of message.

 

 

Well, in the next sector, lets see how msnslp works during a file transfer process.

 

Contact:

Email: fangzhengzhu@kingsoft.com

MSN: windows2000d@163.com