Message Header Fields

The format of the MyRTP control message header is as shown in Figure 5. The fields in the header are aligned as shown.

  
Figure 5: MyRTP Message Header

The header has a fixed size of 16 bytes while the size of the payload depends upon the type of the packet. The fields have the following meaning:

• MyRTP Protocol ID This field indicates that this message is a MyRTP message. This is in order to isolate MyRTP messages from other misdirected messages received by the establishment controllers at their well known ports.
• Version Num This field indicates the current version number of the MyRT protocol being implemented.
• Length of Packet This field indicates the length of the payload in the message. The size of the payload depends on the type of the message and is used to verify that the correct number of bytes are received as part of the payload. As seen from the header format, the size of this field is 2 bytes, so the maximum payload possible in a MyRTP message is bytes.
• Message Type This field identifies the contents and format of the MyRTP payload and determines its interpretation by the controller process. Connection management distinguishes 15 types of MyRTP messages. The different messages are described a little later in this section.
• Sequence Number This field indicates the current sequence number of the MyRTP control message. This is used by MyRTP to detect packet loss and verify correct sequencing. This is particularly important if the underlying layers are unreliable or connectionless (for e.g. UDP).
• LCID This field stands for the Local Connection Identifier. Since one connection extends over multiple switches, each switch assigns a unique connection identifier to the connection. This field helps identify the particular connection the message is meant for.
• Immediate Sender This field identifies the immediate previous sender of the message. Together with the LCID in the message, the connection can be uniquely identified.

Table 1 lists all the MyRTP control messages and their function in the protocol.

  
Table 1: MyRTP Messages