RFC7235], and any applicable HTTP authentication schemes appear in other RFCs, such as Digest [RFC7616] and Basic [RFC7617]. The HTTP access authentication process is described in [RFC7235]. This header MUST only be used in response messages related to client- to-server requests. RFC7616]. The definition of the header is in [RFC7615], and any applicable HTTP authentication schemes appear in other RFCs. This header MUST only be used in response messages related to client-to-server requests. This header has hop-by-hop scope. RFC7235], and any applicable HTTP authentication schemes appear in other RFCs, such as Digest [RFC7616] and Basic [RFC7617].
The HTTP access authentication process is described in [RFC7235]. Unlike Authorization, the Proxy-Authorization header field applies only to the next-hop proxy. This header MUST only be used in client- to-server requests. Section 18.43 for more details on the mechanics of this message and a usage example. See discussion in the proxies section (Section 15.1) about when to consider that a feature requires proxy support. Example of use: Proxy-Require: play.basic Section 4.5. The list is the intersection of all feature tags understood by the proxies. To achieve an intersection, the proxy adding the Proxy-Supported header includes all proxy feature tags it understands. Any proxy receiving a request with the header MUST check the list and remove any feature tag(s) it does not support. A Proxy-Supported header present in the response MUST NOT be modified by the proxies. These feature tags are the ones the proxy chains support in general and are not specific to the request resource.
Example: C->P1: OPTIONS rtsp://example.com/ RTSP/2.0 Supported: foo, bar, blech User-Agent: PhonyClient/1.2 P1->P2: OPTIONS rtsp://example.com/ RTSP/2.0 Supported: foo, bar, blech Proxy-Supported: proxy-foo, proxy-bar, proxy-blech Via: 2.0 pro.example.com P2->S: OPTIONS rtsp://example.com/ RTSP/2.0 Supported: foo, bar, blech Proxy-Supported: proxy-foo, proxy-blech Via: 2.0 pro.example.com, 2.0 prox2.example.com S->C: RTSP/2.0 200 OK Supported: foo, bar, baz Proxy-Supported: proxy-foo, proxy-blech Public: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN Via: 2.0 pro.example.com, 2.0 prox2.example.com Section 18.6) MAY be used to indicate methods allowed for a particular URI. Example of use: Public: OPTIONS, SETUP, PLAY, PAUSE, TEARDOWN In the event that there are proxies between the sender and the recipient of a response, each intervening proxy MUST modify the Public header field to remove any methods that are not supported via that proxy. The resulting Public header field will contain an intersection of the sender's methods and the methods allowed through by the intervening proxies. In general, proxies should allow all methods to transparently pass through from the sending RTSP agent to the receiving RTSP agent, but there may be cases where this is not desirable for a given proxy. Modification of the Public response-header field by the
intervening proxies ensures that the request sender gets an accurate response indicating the methods that can be used on the target agent via the proxy chain. Section 13.4), PAUSE (Section 13.6), SETUP (Section 13.3), and PLAY_NOTIFY (Section 13.5) requests and responses. It MAY be included in GET_PARAMETER requests from the client to the server with only a Range format and no value to request the current media position, whether the session is in Play or Ready state in the included format. The server SHALL, if supporting the range format, respond with the current playing point or pause point as the start of the range. If an explicit stop point was used in the previous PLAY request, then that value shall be included as stop point. Note that if the server is currently under any type of media playback manipulation affecting the interpretation of the Range header, like scale value other than 1, that fact is also required to be included in any GET_PARAMETER response by including the Scale header to provide complete information. The range can be specified in a number of units. This specification defines smpte (Section 4.4.1), npt (Section 4.4.2), and clock (Section 4.4.3) range units. While octet ranges (Byte Ranges) (see Section 2.1 of [RFC7233]) and other extended units MAY be used, their behavior is unspecified since they are not normally meaningful in RTSP. Servers supporting the Range header MUST understand the NPT range format and SHOULD understand the SMPTE range format. If the Range header is sent in a time format that is not understood, the recipient SHOULD return 456 (Header Field Not Valid for Resource) and include an Accept-Ranges header indicating the supported time formats for the given resource. Example: Range: clock=19960213T143205Z- The Range header contains a range of one single range format. A range is a half-open interval with a start and an end point, including the start point but excluding the end point. A range may either be fully specified with explicit values for start point and end point or have either the start or end point be implicit. An implicit start point indicates the session's pause point, and if no pause point is set, the start of the content. An implicit end point indicates the end of the content. The usage of both implicit start
and end points is not allowed in the same Range header; however, the omission of the Range header has that meaning, i.e., from pause point (or start) until end of content. As noted, Range headers define half-open intervals. A range of A-B starts exactly at time A, but ends just before B. Only the start time of a media unit such as a video or audio frame is relevant. For example, assume that video frames are generated every 40 ms. A range of 10.0-10.1 would include a video frame starting at 10.0 or later time and would include a video frame starting at 10.08, even though it lasted beyond the interval. A range of 10.0-10.08, on the other hand, would exclude the frame at 10.08. Please note the difference between NPT timescales' "now" and an implicit start value. Implicit values reference the current pause-point, while "now" is the current time. In a time- progressing session with recording (retention for some or full time), the pause point may be 2 min into the session while now could be 1 hour into the session. By default, range intervals increase, where the second point is larger than the first point. Example: Range: npt=10-15 However, range intervals can also decrease if the Scale header (see Section 18.46) indicates a negative scale value. For example, this would be the case when a playback in reverse is desired. Example: Scale: -1 Range: npt=15-10 Decreasing ranges are still half-open intervals as described above. Thus, for range A-B, A is closed and B is open. In the above example, 15 is closed and 10 is open. An exception to this rule is the case when B=0 is in a decreasing range. In this case, the range is closed on both ends, as otherwise there would be no way to reach 0 on a reverse playback for formats that have such a notion, like NPT and SMPTE.
Example: Scale: -1 Range: npt=15-0 In this range, both 15 and 0 are closed. A decreasing range interval without a corresponding negative value in the Scale header is not valid. Section 13.4). It is sent in PLAY_NOTIFY (Section 13.5) with the end-of-stream reason to report how the PLAY request concluded, either in success or in failure. The header carries a reference to the request it reports on using the CSeq number and the Session ID used in the request reported on. This is not ensured to be unambiguous due to the fact that the CSeq number is scoped by the transport connection. Agents originating requests
can reduce the issue by using a monotonically increasing counter across all sequential transports used. The header provides both a numerical status code (according to Section 8.1.1) and a human- readable reason phrase. Example: Request-Status: cseq=63 status=500 reason="Media data unavailable" Proxies that renumber the CSeq header need to perform corresponding remapping of the cseq parameter in this header when forwarding the request to the next-hop agent. Section 18.51) is much more effective in this purpose. In case any of the feature tags listed by the Require header are not supported by the server or client receiving the request, it MUST respond to the request using the error code 551 (Option Not Supported) and include the Unsupported header listing those feature tags that are NOT supported. This header does not apply to proxies; for the same functionality with respect to proxies, see the Proxy-Require header (Section 18.37) with the exception of media-modifying proxies. Media-modifying proxies, due to their nature of handling media in a way that is very similar to a server, do need to understand also the server's features to correctly serve the client. This is to make sure that the client-server interaction will proceed without delay when all features are understood by both sides and only slow down if features are not understood (as in the example below). For a well-matched client-server pair, the interaction proceeds quickly, saving a round trip often required by negotiation mechanisms. In addition, it also removes state ambiguity when the client requires features that the server does not understand.
Example (Not complete): C->S: SETUP rtsp://server.com/foo/bar/baz.rm RTSP/2.0 CSeq: 302 Require: funky-feature Funky-Parameter: funkystuff S->C: RTSP/2.0 551 Option not supported CSeq: 302 Unsupported: funky-feature In this example, "funky-feature" is the feature tag that indicates to the client that the fictional Funky-Parameter field is required. The relationship between "funky-feature" and Funky-Parameter is not communicated via the RTSP exchange, since that relationship is an immutable property of "funky-feature" and thus should not be transmitted with every exchange. Proxies and other intermediary devices MUST ignore this header. If a particular extension requires that intermediate devices support it, the extension should be tagged in the Proxy-Require field instead (see Section 18.37). See discussion in the proxies section (Section 15.1) about when to consider that a feature requires proxy support.
Section 13.3. The RTP-Info header and the Range header MAY be included in a GET_PARAMETER request from client to server without any values to request the current playback point and corresponding RTP synchronization information. When the RTP-Info header is included in a Request, the Range header MUST also be included. The server response SHALL include both the Range header and the RTP-Info header. If the session is in Play state, then the value of the Range header SHALL be filled in with the current playback point and with the corresponding RTP-Info values. If the server is in another state, no values are included in the RTP-Info header. The header is included in PLAY_NOTIFY requests with the Notify-Reason of the end of stream to provide RTP information about the end of the stream. The header can carry the following parameters: url: Indicates the stream URI for which the following RTP parameters correspond; this URI MUST be the same as used in the SETUP request for this media stream. Any relative URI MUST use the Request-URI as base URI. This parameter MUST be present. ssrc: The SSRC to which the RTP timestamp and sequence number provided applies. This parameter MUST be present. seq: Indicates the sequence number of the first packet of the stream that is direct result of the request. This allows clients to gracefully deal with packets when seeking. The client uses this value to differentiate packets that originated before the seek from packets that originated after the seek. Note that a client may not receive the packet with the expressed sequence number and instead may receive packets with a higher sequence number due to packet loss or reordering. This parameter is RECOMMENDED to be present.
rtptime: MUST indicate the RTP timestamp value corresponding to the start time value in the Range response-header or, if not explicitly given, the implied start point. The client uses this value to calculate the mapping of RTP time to NPT or other media timescale. This parameter SHOULD be present to ensure inter-media synchronization is achieved. There exists no requirement that any received RTP packet will have the same RTP timestamp value as the one in the parameter used to establish synchronization. A mapping from RTP timestamps to NTP format timestamps (wallclock) is available via RTCP. However, this information is not sufficient to generate a mapping from RTP timestamps to media clock time (NPT, etc.). Furthermore, in order to ensure that this information is available at the necessary time (immediately at startup or after a seek), and that it is delivered reliably, this mapping is placed in the RTSP control channel. In order to compensate for drift for long, uninterrupted presentations, RTSP clients should additionally map NPT to NTP, using initial RTCP sender reports to do the mapping, and later reports to check drift against the mapping. Example: Range:npt=3.25-15 RTP-Info:url="rtsp://example.com/foo/audio" ssrc=0A13C760:seq=45102; rtptime=12345678,url="rtsp://example.com/foo/video" ssrc=9A9DE123:seq=30211;rtptime=29567112 Lets assume that Audio uses a 16 kHz RTP timestamp clock and Video a 90 kHz RTP timestamp clock. Then, the media synchronization is depicted in the following way. NPT 3.0---3.1---3.2-X-3.3---3.4---3.5---3.6 Audio PA A Video V PV X: NPT time value = 3.25, from Range header. A: RTP timestamp value for Audio from RTP-Info header (12345678). V: RTP timestamp value for Video from RTP-Info header (29567112). PA: RTP audio packet carrying an RTP timestamp of 12344878, which corresponds to NPT = (12344878 - A) / 16000 + 3.25 = 3.2 PV: RTP video packet carrying an RTP timestamp of 29573412, which corresponds to NPT = (29573412 - V) / 90000 + 3.25 = 3.32
Appendix C.1 for description on how RTP handles this. The transmitted-data rate SHOULD NOT be changed by selection of a different scale value. The resulting bitrate should be reasonably close to the nominal bitrate of the content for scale = 1. The server has to actively manipulate the data when needed to meet the bitrate constraints. Implementation of scale changes depends on the server and media type. For video, a server may, for example, deliver only key frames or selected frames. For audio, it may time-scale the audio while preserving pitch or, less desirably, deliver fragments of audio, or completely mute the audio. The server and content may restrict the range of scale values that it supports. The supported values are indicated by the Media-Properties header (Section 18.29). The client SHOULD only indicate request values to be supported. However, as the values may change as the content progresses, a requested value may no longer be valid when the request arrives. Thus, a non-supported value in a request does not generate an error, it only forces the server to choose the closest value. The response MUST always contain the actual scale value chosen by the server. If the server does not implement the possibility to scale, it will not return a Scale header. A server supporting scale operations for PLAY MUST indicate this with the use of the "play.scale" feature tag. When indicating a negative scale for a reverse playback, the Range header MUST indicate a decreasing range as described in Section 18.40. Example of playing in reverse at 3.5 times normal rate: Scale: -3.5 Range: npt=15-10
Section 4.7.1): RAP: Random Access Point (RAP) is the behavior of requesting the server to locate the closest previous random access point that exists in the media aggregate and deliver from that. By requesting a RAP, media quality will be the best possible as all media will be delivered from a point where full media state can be established in the media decoder. CoRAP: Conditional Random Access Point (CoRAP) is a variant of the above RAP behavior. This policy is primarily intended for cases where there is larger distance between the random access points in the media. CoRAP uses the RAP policy if the condition that there is a Random Access Point closer to the requested start point than to the current pause point is fulfilled. Otherwise, no seeking is performed and playback will continue from the current pause point. This policy assumes that the media state existing prior to the pause is usable if delivery is continued. If the client or server knows that this is not the fact, the RAP policy should be used. In other words, in most cases when the client requests a start point prior to the current pause point, a valid decoding dependency chain from the media delivered prior to the pause and to the requested media unit will not exist. If the server searched to a random access point, the server MUST return the CoRAP policy in the Seek-Style header and adjust the Range header to reflect the position of the selected RAP. In case the random access point is farther away and the server chooses to continue
from the current pause point, it MUST include the "Next" policy in the Seek-Style header and adjust the Range header start point to the current pause point. First-Prior: The first-prior policy will start delivery with the media unit that has a playout time first prior to the requested time. For discrete media, that would only include media units that would still be rendered at the request time. For continuous media, that is media that will be rendered during the requested start time of the range. Next: The next media units after the provided start time of the range: for continuous framed media, that would mean the first next frame after the provided time and for discrete media, the first unit that is to be rendered after the provided time. The main usage for this case is when the client knows it has all media up to a certain point and would like to continue delivery so that a complete uninterrupted media playback can be achieved. An example of such a scenario would be switching from a broadcast/multicast delivery to a unicast-based delivery. This policy MUST only be used on the client's explicit request. Please note that these expressed preferences exist for optimizing the startup time or the media quality. The "Next" policy breaks the normal definition of the Range header to enable a client to request media with minimal overlap, although some may still occur for aggregated sessions. RAP and First-Prior both fulfill the requirement of providing media from the requested range and forward. However, unless RAP is used, the media quality for many media codecs using predictive methods can be severely degraded unless additional data is available as, for example, already buffered, or through other side channels.
If the response is being forwarded through a proxy, the proxy application MUST NOT modify the Server response-header. Instead, it SHOULD include a Via field (Section 18.57). If the response is generated by the proxy, the proxy application MUST return the Server response-header as previously returned by the server. Section 4.3) and MUST be returned in the SETUP response. Once a client receives a session identifier, it MUST be included in any request related to that session. This means that the Session header MUST be included in a request, using the following methods: PLAY, PAUSE, PLAY_NOTIFY and TEARDOWN. It MAY be included in SETUP, OPTIONS, SET_PARAMETER, GET_PARAMETER, and REDIRECT. It MUST NOT be included in DESCRIBE. The Session header MUST NOT be included in the following methods, if these requests are pipelined and if the session identifier is not yet known: PLAY, PAUSE, TEARDOWN, SETUP, OPTIONS SET_PARAMETER, and GET_PARAMETER. In an RTSP response, the session header MUST be included in methods, SETUP, PLAY, PAUSE, and PLAY_NOTIFY, and it MAY be included in methods TEARDOWN and REDIRECT. If included in the request of the following methods it MUST also be included in the response: OPTIONS, GET_PARAMETER, and SET_PARAMETER. It MUST NOT be included in DESCRIBE responses. Note that a session identifier identifies an RTSP session across transport sessions or connections. RTSP requests for a given session can use different URIs (Presentation and media URIs). Note, that there are restrictions depending on the session as to which URIs are acceptable for a given method. However, multiple "user" sessions for the same URI from the same client will require use of different session identifiers. The session identifier is needed to distinguish several delivery requests for the same URI coming from the same client. The response 454 (Session Not Found) MUST be returned if the session identifier is invalid.
The header MAY include a parameter for session timeout period. If not explicitly provided, this value is set to 60 seconds. As this affects how often session keep-alives are needed, values smaller than 30 seconds are not recommended. However, larger-than-default values can be useful in applications of RTSP that have inactive but established sessions for longer time periods. The 60-second value was chosen as the session timeout value as it results in keep-alive messages that are not too frequent and low sensitivity to variations in request/response timing. If one reduces the timeout value to below 30 seconds, the corresponding request/response timeout becomes a significant part of the session timeout. The 60-second value also allows for reasonably rapid recovery of committed server resources in case of client failure.
Example: Speed: 1.0-2.5 Use of this header changes the bandwidth used for data delivery. It is meant for use in specific circumstances where delivery of the presentation at a higher or lower rate is desired. The main use cases are buffer operations or local scale operations. Implementers should keep in mind that bandwidth for the session may be negotiated beforehand (by means other than RTSP) and, therefore, renegotiation may be necessary. To perform Speed operations, the server needs to ensure that the network path can support the resulting bitrate. Thus, the media transport needs to support feedback so that the server can react and adapt to the available bitrate. Section 4.5, that are understood by the client or server. These feature tags are the ones the server or client supports in general and are not specific to the request resource. Example: C->S: OPTIONS rtsp://example.com/ RTSP/2.0 Supported: foo, bar, blech User-Agent: PhonyClient/1.2 S->C: RTSP/2.0 200 OK Supported: bar, blech, baz
Section 17.4.25). In case more than one transport specification was present in the request, the server MUST return the single transport specification (transport- spec) that was actually chosen, if any. The number of transport-spec entries is expected to be limited as the client will receive guidance on what configurations are possible from the presentation description. The Transport header MAY also be used in subsequent SETUP requests to change transport parameters. A server MAY refuse to change parameters of an existing stream. The transport protocol identifier defines, for each transport specification, which transport protocol to use and any related rules. Each transport protocol identifier defines the parameters that are required to occur; additional optional parameters MAY occur. This flexibility is provided as parameters may be different and provide different options to the RTSP agent. A transport specification may only contain one of any given parameter within it. A parameter consists of a name and optionally a value string. Parameters MAY be given in any order. Additionally, a transport specification may only contain either the unicast or the multicast transport type parameter. The transport protocol identifier, and all parameters, need to be understood in a transport specification; if not, the transport specification MUST be ignored. An RTSP proxy of any type that uses or modifies the transport specification, e.g., access proxy or security proxy, MUST remove specifications with unknown parameters
before forwarding the RTSP message. If that results in no remaining transport specification, the proxy SHALL send a 461 (Unsupported Transport) (Section 17.4.25) response without any Transport header. The Transport header is restricted to describing a single media stream. (RTSP can also control multiple streams as a single entity.) Making it part of RTSP rather than relying on a multitude of session description formats greatly simplifies designs of firewalls. The general syntax for the transport protocol identifier is a list of slash-separated tokens: Value1/Value2/Value3... Which, for RTP transports, takes the form: RTP/profile/lower-transport. The default value for the "lower-transport" parameters is specific to the profile. For RTP/AVP, the default is UDP. There are two different methods for how to specify where the media should be delivered for unicast transport: dest_addr: The presence of this parameter and its values indicates the destination address or addresses (host address and port pairs for IP flows) necessary for the media transport. No dest_addr: The lack of the dest_addr parameter indicates that the server MUST send media to the same address from which the RTSP messages originates. The choice of method for indicating where the media is to be delivered depends on the use case. In some cases, the only allowed method will be to use no explicit address indication and have the server deliver media to the source of the RTSP messages. For multicast, there are several methods for specifying addresses, but they are different in how they work compared with unicast: dest_addr with client picked address: The address and relevant parameters, like TTL (scope), for the actual multicast group to deliver the media to. There are security implications (Section 21) with this method that need to be addressed because an RTSP server can be used as a DoS attacker on an existing multicast group.
dest_addr using Session Description Information: The information included in the transport header can all be coming from the session description, e.g., the SDP "c=" and "m=" lines. This mitigates some of the security issues of the previous methods as it is the session provider that picks the multicast group and scope. The client MUST include the information if it is available in the session description. No dest_addr: The behavior when no explicit multicast group is present in a request is not defined. An RTSP proxy will need to take care. If the media is not desired to be routed through the proxy, the proxy will need to introduce the destination indication. Below are the configuration parameters associated with transport: General parameters: unicast / multicast: This parameter is a mutually exclusive indication of whether unicast or multicast delivery will be attempted. One of the two values MUST be specified. Clients that are capable of handling both unicast and multicast transmission need to indicate such capability by including two full transport-specs with separate parameters for each. layers: The number of multicast layers to be used for this media stream. The layers are sent to consecutive addresses starting at the dest_addr address. If the parameter is not included, it defaults to a single layer. dest_addr: A general destination address parameter that can contain one or more address specifications. Each combination of protocol/profile/lower transport needs to have the format and interpretation of its address specification defined. For RTP/AVP/UDP and RTP/AVP/TCP, the address specification is a tuple containing a host address and port. Note, only a single destination parameter per transport spec is intended. The usage of multiple destinations to distribute a single media to multiple entities is unspecified. The client originating the RTSP request MAY specify the destination address of the stream recipient with the host address as part of the tuple. When the destination address is specified, the recipient may be a different party than the originator of the request. To avoid becoming the unwitting perpetrator of a remote-controlled DoS attack, a server MUST perform security checks (see Section 21.2.1) and SHOULD log
such attempts before allowing the client to direct a media stream to a recipient address not chosen by the server. Implementations cannot rely on TCP as a reliable means of client identification. If the server does not allow the host address part of the tuple to be set, it MUST return 463 (Destination Prohibited). The host address part of the tuple MAY be empty, for example ":58044", in cases when it is desired to specify only the destination port. Responses to requests including the Transport header with a dest_addr parameter SHOULD include the full destination address that is actually used by the server. The server MUST NOT remove address information that is already present in the request when responding, unless the protocol requires it. src_addr: A general source address parameter that can contain one or more address specifications. Each combination of protocol/profile/lower transport needs to have the format and interpretation of its address specification defined. For RTP/AVP/UDP and RTP/AVP/TCP, the address specification is a tuple containing a host address and port. This parameter MUST be specified by the server if it transmits media packets from an address other than the one RTSP messages are sent to. This will allow the client to verify the source address and give it a destination address for its RTCP feedback packets, if RTP is used. The address or addresses indicated in the src_addr parameter SHOULD be used both for the sending and receiving of the media stream's data packets. The main reasons are threefold: First, indicating the port and source address(s) lets the receiver know where from the packets is expected to originate. Second, traversal of NATs is greatly simplified when traffic is flowing symmetrically over a NAT binding. Third, certain NAT traversal mechanisms need to know to which address and port to send so-called "binding packets" from the receiver to the sender, thus creating an address binding in the NAT that the sender-to-receiver packet flow can use. This information may also be available through SDP. However, since this is more a feature of transport than media initialization, the authoritative source for this information should be in the SETUP response.
mode: The mode parameter indicates the methods to be supported for this session. The currently defined valid value is "PLAY". If not provided, the default is "PLAY". The "RECORD" value was defined in RFC 2326; in this specification, it is unspecified but reserved. RECORD and other values may be specified in the future. interleaved: The interleaved parameter implies mixing the media stream with the control stream in whatever protocol is being used by the control stream, using the mechanism defined in Section 14. The argument provides the channel number to be used in the $ block (see Section 14) and MUST be present. This parameter MAY be specified as an interval, e.g., interleaved=4-5 in cases where the transport choice for the media stream requires it, e.g., for RTP with RTCP. The channel number given in the request is only a guidance from the client to the server on what channel number(s) to use. The server MAY set any valid channel number in the response. The declared channels are bidirectional, so both end parties MAY send data on the given channel. One example of such usage is the second channel used for RTCP, where both server and client send RTCP packets on the same channel. This allows RTP/RTCP to be handled similarly to the way that it is done with UDP, i.e., one channel for RTP and the other for RTCP. MIKEY: This parameter is used in conjunction with transport specifications that can utilize MIKEY [RFC3830] for security context establishment. So far, only the SRTP-based RTP profiles SAVP and SAVPF can utilize MIKEY, and this is defined in Appendix C.1.4.1. This parameter can be included both in request and response messages. The binary MIKEY message SHALL be Base64-encoded [RFC4648] before being included in the value part of the parameter, where the encoding adheres to the definition in Section 4 of RFC 4648 and where the padding bits are set to zero. Multicast-specific: ttl: multicast time-to-live for IPv4. When included in requests, the value indicates the TTL value that the client requests the server to use. In a response, the value actually being used by the server is returned. A server will need to consider what values that are reasonable and also the authority of the user to set this value. Corresponding functions are not needed for IPv6 as the scoping is part of the IPv6 multicast address [RFC4291].
RTP-specific: These parameters MAY only be used if the media-transport protocol is RTP. ssrc: The ssrc parameter, if included in a SETUP response, indicates the RTP SSRC [RFC3550] value(s) that will be used by the media server for RTP packets within the stream. The values are expressed as a slash-separated sequence of SSRC values, each SSRC expressed as an eight-digit hexadecimal value. The ssrc parameter MUST NOT be specified in requests. The functionality of specifying the ssrc parameter in a SETUP request is deprecated as it is incompatible with the specification of RTP [RFC3550]. If the parameter is included in the Transport header of a SETUP request, the server SHOULD ignore it, and choose appropriate SSRCs for the stream. The server SHOULD set the ssrc parameter in the Transport header of the response. RTCP-mux: Used to negotiate the usage of RTP and RTCP multiplexing [RFC5761] on a single underlying transport stream/flow. The presence of this parameter in a SETUP request indicates the client's support and requires the server to use RTP and RTCP multiplexing. The client SHALL only include one transport stream in the Transport header specification. To provide the server with a choice between using RTP/RTCP multiplexing or not, two different transport header specifications must be included. The parameter setup and connection defined below MAY only be used if the media-transport protocol of the lower-level transport is connection oriented (such as TCP). However, these parameters MUST NOT be used when interleaving data over the RTSP connection. setup: Clients use the setup parameter on the Transport line in a SETUP request to indicate the roles it wishes to play in a TCP connection. This parameter is adapted from [RFC4145]. The use of this parameter in RTP/AVP/TCP non-interleaved transport is discussed in Appendix C.2.2; the discussion below is limited to syntactic issues. Clients may specify the following values for the setup parameter: active: The client will initiate an outgoing connection. passive: The client will accept an incoming connection.
actpass: The client is willing to accept an incoming connection or to initiate an outgoing connection. If a client does not specify a setup value, the "active" value is assumed. In response to a client SETUP request where the setup parameter is set to "active", a server's 2xx reply MUST assign the setup parameter to "passive" on the Transport header line. In response to a client SETUP request where the setup parameter is set to "passive", a server's 2xx reply MUST assign the setup parameter to "active" on the Transport header line. In response to a client SETUP request where the setup parameter is set to "actpass", a server's 2xx reply MUST assign the setup parameter to "active" or "passive" on the Transport header line. Note that the "holdconn" value for setup is not defined for RTSP use, and MUST NOT appear on a Transport line. connection: Clients use the connection parameter in a transport specification part of the Transport header in a SETUP request to indicate the client's preference for either reusing an existing connection between client and server (in which case the client sets the "connection" parameter to "existing") or requesting the creation of a new connection between client and server (in which cast the client sets the "connection" parameter to "new"). Typically, clients use the "new" value for the first SETUP request for a URL, and "existing" for subsequent SETUP requests for a URL. If a client SETUP request assigns the "new" value to "connection", the server response MUST also assign the "new" value to "connection" on the Transport line. If a client SETUP request assigns the "existing" value to "connection", the server response MUST assign a value of "existing" or "new" to "connection" on the Transport line, at its discretion. The default value of "connection" is "existing", for all SETUP requests (initial and subsequent). The combination of transport protocol, profile and lower transport needs to be defined. A number of combinations are defined in the Appendix C.
Below is a usage example, showing a client advertising the capability to handle multicast or unicast, preferring multicast. Since this is a unicast-only stream, the server responds with the proper transport parameters for unicast. C->S: SETUP rtsp://example.com/foo/bar/baz.rm RTSP/2.0 CSeq: 302 Transport: RTP/AVP;multicast;mode="PLAY", RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/ "192.0.2.5:3457";mode="PLAY" Accept-Ranges: npt, smpte, clock User-Agent: PhonyClient/1.2 S->C: RTSP/2.0 200 OK CSeq: 302 Date: Fri, 20 Dec 2013 10:20:32 +0000 Session: rQi1hBrGlFdiYld241FxUO Transport: RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/ "192.0.2.5:3457";src_addr="192.0.2.224:6256"/ "192.0.2.224:6257";mode="PLAY" Accept-Ranges: npt Media-Properties: Random-Access=0.6, Dynamic, Time-Limited=20081128T165900 Section 18.37), if there is a proxy on the path between the client and the server, the proxy MUST send a response message with a status code of 551 (Option Not Supported). The request MUST NOT be forwarded. See Section 18.43 for a usage example.
For organizations that have strong privacy requirements for hiding internal structures, a proxy MAY combine an ordered subsequence of Via header field entries with identical sent-protocol values into a single such entry. Applications MUST NOT combine entries that have different received-protocol values. RFC7235]; its usage depends on the used authentication schemes, such as Digest [RFC7616] and Basic [RFC7617]. The WWW-Authenticate response-header field MUST be included in 401 (Unauthorized) response messages. The field-value consists of at least one challenge that indicates the authentication scheme(s) and parameters applicable to the Request-URI. This header MUST only be used in response messages related to client to server requests. The HTTP access authentication process is described in [RFC7235] with some clarification in Section 19.1. User agents are advised to take special care in parsing the WWW-Authenticate field-value as it might contain more than one challenge, or if more than one WWW-Authenticate header field is provided, the contents of a challenge itself can contain a comma-separated list of authentication parameters.