 Hello and welcome to the session on packet format of stream control transmission protocol sctp part 2. At the end of this session, students will be able to list and describe different packet types used in the sctp. Students will be able to discuss the purpose and of each field in each packet. In it, Chung that is initiation Chung is the first Chung sent by an endpoint to establish an association. The packet that carries this Chung cannot carry any other control or data chunks. The value of the verification tag for this packet is 0, which means no tag has yet been defined. The format is shown in the figure. The three common fields are type, flag and lengths are as before. The value of the type field is 1, the value of the flag field is 0 that is no flags and the value of the length field is minimum of 20. The other fields are initiation tag. This 32-bit field defines the value of the verification tag for packets travelling in opposite direction. All packets have a verification tag in the general header. This tag is the same as for all packets travelling in one direction in an association. The value of this tag is determined during association establishment. The endpoint that initiates the association defines the value of this tag in the initiation tag field. This value is used as the verification tag in the rest of the packets sent from the other direction. For example, when endpoint A starts an association with endpoint B, A defines an initiation tag value say X, which means that which is used as a verification tag for all packets sent from B to A. The initiation tag is a random number between 0 and 2 raise to 32 minus 1. The value of 0 defines no association and is permitted only by the general header of the init chunk. Advertise receiver window credit. This 32-bit field is used in flow control and defines the initial amount of data in bytes that the sender of the init chunk can allow. It is the receiver window value that will be used by the receiver to know how much data to send. Outbound stream. This 16-bit field defines the number of streams that the initiator of the association suggests for stream in the outbound direction. Maximum inbound stream. The 16-bit field defines the maximum number of streams that the initiator of the association can support in the inbound direction. Initial TSN. This 32-bit field initializes the transmission sequence number that is TSN in the outbound direction. Here note that each data chunk in an association has one TSN. The value of this field is also a random number less than 2 raise to 32. Variable length parameters. These optional parameters may be added to the init chunk to define the IP address of sending endpoint. The number of IP addresses, the endpoint can support multi-home. The preservation of the cookie state and the type of addresses and support of explicit congestion notification that is ECN. No other chunk can be carried in a packet that carries an init chunk. Init ACK chunk. The init ACK chunk initiation acknowledgement chunk is the second chunk sent during association establishment. The packet that carries this chunk cannot carry any other control or data chunks. The value of the verification tag for this packet is the value of the initiation tag defined in the received init chunk. The format is shown in this figure. The main part of the chunk are as same as those defined in the init chunk. However, a mandatory parameter is required for this chunk. The parameter of type 7 defines the state cookie sent by the sender of this chunk. Remember note that the initiation tag field in this chunk initiates the value of the verification tag for future packets traveling from the opposite direction. No other chunks can be carried in a packet that carries an init ACK chunk. Cookie echo. The cookie echo chunk is the third chunk sent during association establishment. It is sent by the endpoint that receives an init ACK chunk. The packet that carries this chunk can also carry user data. The format is shown in the figure. Here note that this is a very simple chunk of type 10. In the information section, it echoes the state cookie that the endpoint has previously received in the init ACK. The receiver of the init ACK cannot open the cookie. Cookie ACK. The cookie ACK chunk is the fourth and the last chunk sent during association establishment. It is sent by an endpoint that receives a cookie echo chunk. The packet that carries this chunk can also carry user data. The format is shown in the figure. Here note that this is a very simple chunk by type 11. The length of the chunk is exactly 4 bytes, sac that is selective acknowledgement chunk which acknowledges the receipt of the data packets. Figure shows the format of the sac chunk. The common fields are the same as discussed previously. The type of field that has value 3. The flag bits are all set to 0s. Cumulative TSN acknowledgement. This 32-bit field defines the TSN of the last data chunk received in sequence. Advertise Receiver window credit. This 32-bit field is the updated value for receiver window sites. Number of gap ACK blocks. This 16-bit field defines the number of gaps in the data chunk received after the cumulative TSN. Number of duplicates. This 16-bit field defines the number of duplicate chunks following the cumulative TSN. Gap ACK block start offset. For each gap block, this 16-bit field gives the starting TSN relative to cumulative TSN. Gap ACK block end offset. For each gap block, this 16-bit field defines the ending TSN relative to the cumulative TSN. Duplicate TSN. For each duplicate chunk, this 32-bit field gives the TSN of the duplicate chunk. Heartbit and Heartbit ACK. The Heartbit chunk and the Heartbit ACK chunk are similar except for the type field. The first has a type of 4 and the second a type of 5. Figure shows the format of these chunks. These two chunks are used to periodically probe the condition of an association. An endpoint sends the Heartbit chunk. The peer responds with the Heartbit ACK if it is alive. The format has common three fields and mandatory parameter fields that provide sender specific information. This information in the Heartbit chunk includes the local time and the address of the sender. It is copied without change into the Heartbit ACK chunk. Shutdown, shutdown ACK and shutdown complete. These three chunks are similar. The shutdown chunk type 7 is 8 bytes in length. The second 4 bytes define the cumulative TSN. The shutdown ACK chunk type 8 is 4 bytes in length. The shutdown complete chunk type 14 is also 4 bytes long and has a 1-bit flag, the T-flag. The T-flag shows that the sender does not have a TCB table. Figure shows the format error. The error chunk is sent when an endpoint finds some error in a received packet. Here note that the sending of an error chunk does not imply the aborting of the association. Figure shows the format of the error chunks. The errors are defined in the table abort. The abort chunk is sent when an endpoint finds a fertile error needs to abort the association. The error types are the same as those for the error chunk. The figure shows the format of an abort chunk. Forward TSN. This is a chunk recently added to the standard RFC 375 to inform the receiver to adjust its cumulative TSN. It provides partial reliable service. Here pause the video, think and answer. The answer is B, different chunks. Again pause the video, think and answer. The answer is C, no other chunks. Here is the reference. Thank you.