What is ppid in sctp

When the remote peer receives the reset message, it also sends unless already sent a reset message on its outgoing SCTP stream associated with the data channel. Status of This Memo This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation. SCTP Considerations 3. SDP Considerations 3. IANA Considerations 5. The application must instruct the SCTP stack to send "messages" of a given ppid. Some for reception.

The ppid of the received DATA chunk must be notified to the app somehow. I'm not saying that stack would decide PPID. SCTP was invented to support streams, and I guess for some similar reasons different media-content or sub-prorocols. Not sure if peer side browser uses streams for different PPIDs. If not, this approach will fail. But can you check?

So, in general this is not guaranteed at all. The same as in TCP streams. Browsers implement DataChannel spec. Those DataChannels are not intended to send different kind of data but just to have different identifiers and provide the app with the ability to manage different "channels" within the same WebRTC connection. So I was wrong above. I'm fine if the app is responsible to buffer and reassembly data sequential DATA chunks. In usrsctp lib the app must do it anyway. BTW I'm testing master branch and I do not see that socket.

Those are the logs in my server interactive terminal to play :. The very same happens if I use socket. PPID is always undefined. I've been thinking about this. I would just remove it and force the app to create streams via socket.

And then, when it comes to PPID stuff, stream. Well, that's not correct at all. Also, even if wrong, it's not honored PPID is always 0. Default stream is 0, by RFC, and in some cases this is what was intended. It should be clearly stated in readme, though. If reusing Duplex stream 'encoding' argument is safe, API will be socket. But what about receiving? I don't know how to handle it with standard API, yet.

Note that you are writing send instead of write. Is intended? I'd be super happy with it, but I think you meant write. What about writing data. Do you have any expectation of when this could be done? I'm super ready to test it. In fact I've my code done here. Introduction This section explains the reasoning behind the development of the Stream Control Transmission Protocol SCTP , the services it offers, and the basic concepts needed to understand the detailed description of the protocol.

However, an increasing number of recent applications have found TCP too limiting, and have incorporated their own reliable data transfer protocol on top of UDP [ RFC ]. The limitations that users have wished to bypass include the following: -- TCP provides both reliable data transfer and strict order-of- transmission delivery of data.

Some applications need reliable transfer without sequence maintenance, while others would be satisfied with partial ordering of the data. In both of these cases, the head-of-line blocking offered by TCP causes unnecessary delay. Applications must add their own record marking to delineate their messages, and must make explicit use of the push facility to ensure that a complete message is transferred in a reasonable time.

It performs this service within the context of an association between two SCTP endpoints. This section provides a consolidated list of the key terms and their definitions. Each user message occupies its own DATA chunk. Typically, message authentication codes are used between two parties that share a secret key in order to validate information transmitted between these parties.

The term "MAC" has different meanings in different contexts. Sending to different destination transport addresses does not necessarily guarantee getting separate paths.

The definition includes the source address since an implementation MAY wish to specify both destination and source address to better control the return path taken by reply chunks and on which interface the packet is transmitted when the data sender is multi-homed.

This gives the sender an indication of the space available in the receiver's inbound buffer. An association can be uniquely identified by the transport addresses used by the endpoints in the association. On a multi-homed host, an SCTP endpoint is represented to its peers as a combination of a set of eligible destination transport addresses to which SCTP packets can be sent and a set of eligible source transport addresses from which SCTP packets can be received.

In other words, a transport address is unique to an SCTP endpoint. This is the threshold that the endpoint will use to determine whether to perform slow start or congestion avoidance on a particular destination transport address. Ssthresh is in number of bytes. Note: The relationship between stream numbers in opposite directions is strictly a matter of how the applications use them. It is the responsibility of the SCTP user to create and manage these correlations if they are so desired.

One Stream Sequence Number is attached to each user message. These tags are used within a State Cookie and TCB so that a newly restarting association can be linked to the original association within the endpoint that did not restart and yet not reveal the true Verification Tags of an existing association. TCB contains all the status and operational information for the endpoint to maintain and manage the corresponding association.

One TSN is attached to each chunk containing user data to permit the receiving SCTP endpoint to acknowledge its receipt and detect duplicate deliveries. Or in the opposite case, for a packet that has been sent but no acknowledgement has been received. Stewart Standards Track [Page 9] RFC Stream Control Transmission Protocol September o Unordered Message: Unordered messages are "unordered" with respect to any other message; this includes both other unordered messages as well as other ordered messages.

An unordered message might be delivered prior to or later than ordered messages sent on the same stream. The Verification Tag provides a key that allows a receiver to verify that the SCTP packet belongs to the current association and is not an old or stale packet from a previous association. These are depicted in Figure 2 and explained in the remainder of this section. A cookie mechanism, similar to one described by Karn and Simpson in [ RFC ], is employed during the initialization to provide protection against synchronization attacks.

The cookie mechanism uses a four-way handshake, the last two legs of which are allowed to carry user data for fast setup. The startup sequence is described in Section 5 of this document. SCTP provides for graceful close i. SCTP also allows ungraceful close i. Section 9 describes both the graceful and the ungraceful close procedures.

SCTP does not support a half-open state like TCP wherein one side may continue sending data while the other end is closed. When either endpoint performs a shutdown, the association on each peer will stop accepting new data from its user and only deliver data in queue at the time of the graceful close see Section 9. Sequenced Delivery within Streams The term "stream" is used in SCTP to refer to a sequence of user messages that are to be delivered to the upper-layer protocol in order with respect to other messages within the same stream.

This is in contrast to its usage in TCP, where it refers to a sequence of bytes in this document, a byte is assumed to be 8 bits. The SCTP user can specify at association startup time the number of streams to be supported by the association. This number is negotiated with the remote end see Section 5. However, while one stream may be blocked waiting for the next in-sequence user message, delivery from other streams may proceed.

SCTP provides a mechanism for bypassing the sequenced delivery service. User messages sent using this mechanism are delivered to the SCTP user as soon as they are received. On receipt, fragments are reassembled into complete messages before being passed to the SCTP user. The receiving end acknowledges all TSNs received, even if there are gaps in the sequence.

In this way, reliable delivery is kept functionally separate from sequenced stream delivery. Stewart Standards Track [Page 12] RFC Stream Control Transmission Protocol September The acknowledgement and congestion avoidance function is responsible for packet retransmission when timely acknowledgement has not been received.

Packet retransmission is conditioned by congestion avoidance procedures similar to those used for TCP. See Section 6 and Section 7 for a detailed description of the protocol procedures associated with this function. Chunk Bundling As described in Section 3 , the SCTP packet as delivered to the lower layer consists of a common header followed by one or more chunks.

Each chunk may contain either user data or SCTP control information. The user's disabling of bundling only affects SCTP implementations that may delay a small period of time before transmission to attempt to encourage bundling. When the user layer disables bundling, this small delay is prohibited but not bundling that is performed during congestion or retransmission.

The Verification Tag value is chosen by each end of the association during association startup. Packets received without the expected Verification Tag value are discarded, as a protection against blind masquerade attacks and against stale SCTP packets from a previous association.

The CRC32c checksum should be set by the sender of each SCTP packet to provide additional protection against data corruption in the network. The SCTP path management function chooses the destination transport address for each outgoing SCTP packet based on the SCTP user's instructions and the currently perceived reachability status of the eligible destination set.

The path management function monitors reachability through heartbeats Stewart Standards Track [Page 13] RFC Stream Control Transmission Protocol September when other packet traffic is inadequate to provide this information and advises the SCTP user when reachability of any far-end transport address changes.

The path management function is also responsible for reporting the eligible set of local transport addresses to the far end during association startup, and for reporting the transport addresses returned from the far end to the SCTP user. On the receiving end, the path management is responsible for verifying the existence of a valid SCTP association to which the inbound SCTP packet belongs before passing it for further processing.

Note: Path Management and Packet Validation are done at the same time, so although described separately above, in reality they cannot be performed as separate items. Serial Number Arithmetic It is essential to remember that the actual Transmission Sequence Number space is finite, though very large.

There are some subtleties to computer modulo arithmetic, so great care should be taken in programming the comparison of such values. Doing so will cause problems in comparing TSNs. All other arithmetic and comparisons in this document use normal arithmetic. Readers interested in the details of the various changes that this document incorporates are asked to consult [ RFC ]. A chunk contains either control information or user data. See Section 6. If a user data message doesn't fit into one SCTP packet it can be fragmented into multiple chunks using the procedure defined in Section 6.

It can be used by the receiver in combination with the source IP address, the SCTP destination port, and possibly the destination IP address to identify the association to which this packet belongs. For details see Section 8. Its calculation is discussed in Section 6. Each chunk is formatted with a Chunk Type field, a chunk-specific Flag field, a Chunk Length field, and a Value field. It takes a value from 0 to The value of is reserved for future use as an extension field.

Chunk Flags: 8 bits The usage of these bits depends on the Chunk type as given by the Chunk Type field. Unless otherwise specified, they are set to 0 on transmit and are ignored on receipt. Therefore, if the Chunk Value field is zero-length, the Length field will be set to 4. The Chunk Length field does not count any chunk padding. The Chunk Length value does not include terminating padding of the chunk.

However, it does include padding of any variable-length parameter except the last parameter in the chunk. The receiver MUST ignore the padding. Note: A robust implementation should accept the chunk whether or not the final padding has been included in the Chunk Length. Chunk Value: variable length The Chunk Value field contains the actual information to be transferred in the chunk. The usage and format of this field is dependent on the Chunk Type. If the length of the chunk is not a multiple of 4 bytes, the sender MUST pad the chunk with all zero bytes, and this padding is not included in the Chunk Length field.

The receiver MUST ignore the padding bytes. SCTP-defined chunks are described in detail in Section 3. The optional and variable-length parameters contained in a chunk are defined in a Type-Length-Value format as shown below.

It takes a value of 0 to The value of is reserved for IETF-defined extensions. Thus, a parameter with a zero-length Parameter Value field would have a Length field of 4. The Parameter Length does not include any padding bytes.

Chunk Parameter Value: variable length The Parameter Value field contains the actual information to be transferred in the parameter. If the length of the parameter is not a multiple of 4 bytes, the sender pads the parameter at the end i. The length of the padding is not included in the Parameter Length field.

The Parameter Types are encoded such that the highest-order 2 bits specify the action that must be taken if the processing endpoint does not recognize the Parameter Type. In the 00 or 01 case, the processing of the parameters after the unknown parameter is canceled, but no processing already done is rolled back. Note that a parameter type MUST be unique across all chunks. For example, the parameter type '5' is used to represent an IPv4 address see Section 3.

If an unordered user message is fragmented, each fragment of the message MUST have its U bit set to '1'. B bit: 1 bit The B eginning fragment bit, if set, indicates the first fragment of a user message. E bit: 1 bit The E nding fragment bit, if set, indicates the last fragment of a user message. Length: 16 bits unsigned integer This field indicates the length of the DATA chunk in bytes from the beginning of the type field to the end of the User Data field excluding any padding. TSN wraps back to 0 after reaching Stream Identifier S: 16 bits unsigned integer Identifies the stream to which the following user data belongs.

Stream Sequence Number n: 16 bits unsigned integer This value represents the Stream Sequence Number of the following user data within the stream S. Valid range is 0 to Payload Protocol Identifier: 32 bits unsigned integer This value represents an application or upper layer specified protocol identifier.

This value is passed to SCTP by its upper layer and sent to its peer. This identifier is not used by SCTP but can be used by certain network entities, as well as by the peer application, to identify the type of information being carried in this DATA chunk. This field must be sent even in fragmented DATA chunks to make sure it is available for agents in the middle of the network. The upper layer is responsible for any byte order conversions to this field. The value 0 indicates that no application identifier is specified by the upper layer for this payload data.

User Data: variable length This is the payload user data. The implementation MUST pad the end of the data to a 4-byte boundary with all-zero bytes. A sender MUST never add more than 3 bytes of padding. The absence of this parameter indicates that the sending endpoint can support any address type. The Chunk Flags field in INIT is reserved, and all bits in it should be set to 0 by the sender and ignored by the receiver.

The sequence of parameters within an INIT can be processed in any order. The Initiate Tag is allowed to have any value except 0. See Section 5. Note: There is no negotiation of the actual number of streams but instead the two endpoints will use the min requested, offered. The valid range is from 0 to It is binary encoded. That is, during the life time of this association, this IP address can appear in the source address field of an IP datagram sent from the sender of the INIT, and can be used as a destination address of an IP datagram sent from the receiver of the INIT.

Moreover, a multi- homed endpoint may have access to different types of network; thus, more than one address type can be present in one INIT chunk, i. This optional parameter should be added to the INIT chunk by the sender when it reattempts establishing an association with a peer to which its previous attempt of establishing the association failed due to a stale cookie operation error. The receiver MAY choose to ignore the suggested cookie life-span increase for its own security reasons.

The peer is responsible for resolving the name. Using this parameter might make it more likely for the association to work across a NAT box. The method for resolving the host name is out of scope of SCTP.

The other fields are defined the same as their counterparts in the INIT chunk. Parameter Value: This parameter is returned to the originator of the INIT chunk when the INIT contains an unrecognized parameter that has a value that indicates it should be reported to the sender. This parameter therefore acknowledges receipt of all TSNs less than or equal to its value.

The duplicate count is reinitialized to zero after sending each SACK. The parameter field contains the Heartbeat Information, which is a variable-length opaque data structure understood only by the sender. Heartbeat Length: 16 bits unsigned integer Set to the size of the chunk in bytes, including the chunk header and the Heartbeat Information field. Heartbeat Information: variable length Defined as a variable-length parameter using the format described in Section 3. The parameter field contains a variable-length opaque data structure.

Heartbeat Ack Length: 16 bits unsigned integer Set to the size of the chunk in bytes, including the chunk header and the Heartbeat Information field. T bit: 1 bit The T bit is set to 0 if the sender filled in the Verification Tag expected by the peer. Reflecting means that the sent Verification Tag is the same as the received one. Note: Special rules apply to this chunk for verification; please see Section 8.

Length: 16 bits unsigned integer Set to the size of the chunk in bytes, including the chunk header and all the Error Cause fields present. See Section 3. This chunk has the following format. Length: 16 bits unsigned integer Indicates the length of the parameter. Set to 8. It contains one or more error causes.

Cause-Specific Information: variable length This field carries the details of the error condition. Section 3. Reserved: 16 bits This field is reserved. It is set to all 0's on transmit and ignored on receipt. The sender of this error cause MAY choose to report how long past expiration the State Cookie is by including a non-zero value in the Measure of Staleness field. If the sender does not wish to provide this information, it should set the Measure of Staleness field to the value of zero.

Out of Resource 4 Cause of error Out of Resource: Indicates that the sender is out of resource. Unresolvable Address 5 Cause of error Unresolvable Address: Indicates that the sender is not able to resolve the specified address parameter e. Unrecognized Chunk Type 6 Cause of error Unrecognized Chunk Type: This error cause is returned to the originator of the chunk if the receiver does not understand the chunk and the upper bits of the 'Chunk Type' are set to 01 or The new addresses are listed in the error code.

An implementation MAY provide additional information specifying what kind of protocol violation has been detected. It is sent by the initiator of an association to its peer to complete the initialization process. Length: 16 bits unsigned integer Set to the size of the chunk in bytes, including the 4 bytes of the chunk header and the size of the cookie. Note: Special rules apply to this chunk for verification, please see Section 8. The events that may potentially advance an association's state include: o SCTP user primitive calls, e.

The state diagram in the figures below illustrates state changes, together with the causing events and resulting actions. Note that some of the error conditions are not shown in the state diagram. Full descriptions of all special cases are found in the text. Note: Chunk names are given in all capital letters, while parameter names have the first letter capitalized, e.

State Cookie parameter. Or, if the received State Cookie is expired see Section 5. Retransmits' times. Once the association is established, unidirectional streams are open for data transfer on both ends see Section 5.

Otherwise, "Z" will be vulnerable to resource attacks. It may also notify its ULP about the successful establishment of the association with a Communication Up notification see Section Note: T1-init timer and T1-cookie timer shall follow the same rules given in Section 6. Subsequent acknowledgements should be done as described in Section 6. After receiving the stream configuration information from the other side, each endpoint MUST perform the following check: If the peer's MIS is less than the endpoint's OS, meaning that the peer is incapable of supporting all the outbound streams the endpoint wants to configure, the endpoint MUST use MIS outbound streams and MAY report any shortage to the upper layer.

The upper layer can then choose to abort the association if the resource shortage is unacceptable. After the association is initialized, the valid outbound stream identifier range for either endpoint shall be 0 to min local OS, remote MIS Handle Address Parameters During the association initialization, an endpoint shall use the following rules to discover and collect the destination transport address es of its peer.

If the receiver of an INIT resolves the host name upon the reception of the chunk, and the mechanism the receiver uses to resolve the host name involves potential long delay e. The receiver should use only these transport addresses as destination transport addresses when sending subsequent packets to its peer.

When this parameter is present, the receiver of INIT initiate MUST either use one of the address types indicated in the Supported Address Types parameter when responding to the INIT, or abort the association with an "Unresolvable Address" error cause if it is unwilling or incapable of using any of the address types indicated by its peer.

The other addresses MAY be ignored. Inside this State Cookie, the sender should include a MAC see [ RFC ] for an example , a timestamp on when the State Cookie is created, and the lifespan of the State Cookie, along with all the information necessary for it to establish the association. The use of a MAC is mandatory to prevent denial-of-service attacks. Retransmits' see Section 15 is reached causing the peer endpoint to be marked unreachable and thus the association enters the CLOSED state.

If these values do not match, the packet MUST be silently discarded. This shall be repeated Max. The receiver shall treat such a setup chunk as a duplicate and process it as described in this section. Note: An endpoint will not receive the chunk unless the chunk was sent to an SCTP transport address and is from an SCTP transport address associated with this endpoint. Therefore, the endpoint processes such a chunk as part of its current association.

The rules in the following sections shall be applied in order to identify and correctly handle these cases. For a normal association INIT i. M - Tag matches the existing TCB. A - All cases, i. Note: For any case not shown in Table 2, the cookie should be silently discarded. Action A In this case, the peer may have restarted. All the congestion control parameters e. B In this case, both sides may be attempting to start an association at about the same time, but the peer endpoint started its INIT after responding to the local endpoint's INIT.

Thus, it may have picked a new Verification Tag, not being aware of the previous tag it had sent this endpoint. C In this case, the local endpoint's cookie has arrived late. The cookie should be silently discarded.

An Example of a Association Restart In the following example, "A" initiates the association after a restart has occurred. Endpoint "Z" had no knowledge of the restart until the exchange i. B An old State Cookie was processed after setup completed.

When processing an ERROR chunk with a "Stale Cookie" error cause an endpoint should first examine if an association is in the process of being set up, i. Other Initialization Issues 5. It is very important that the Initiate Tag value be randomized to help protect against "man in the middle" and "sequence number" attacks.

Careful selection of Initiate Tags is also necessary to prevent old duplicate packets from previous associations being mistakenly processed as belonging to the current association. A new Verification Tag value MUST be used each time the endpoint tears down and then reestablishes an association to the same peer. Path Verification During association establishment, the two peers exchange a list of addresses. In the predominant case, these lists accurately represent the addresses owned by each peer.

However, it is possible that a misbehaving peer may supply addresses that it does not own. Burst parameter.