PPP Working Group Craig Richards Internet Draft Shiva Corporation expires September 1996 Kevin Smith Ascend Communications, Inc. March 1996 The PPP Bandwidth Allocation Protocol (BAP) The PPP Bandwidth Allocation Control Protocol (BACP) draft-ietf-pppext-bacp-02.txt Status of this Memo This document is a submission to the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the ietf-ppp@merit.edu mailing list. Distribution of this memo is unlimited. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, ds.internic.net, venera.isi.edu, nic.nordu.net, or munnari.oz.au to learn the current status of any Internet Draft. Abstract This document proposes a method to manage the dynamic bandwidth allocation of implementations supporting the PPP multilink protocol [2]. This is done by defining the Bandwidth Allocation Protocol (BAP), as well as its associated control protocol, the Bandwidth Allocation Control Protocol (BACP). BAP can be used to manage the number of links in a multilink bundle. BAP defines datagrams to co- ordinate adding and removing individual links in a multilink bundle, as well as specifying which peer is responsible for which decisions regarding managing bandwidth during a multilink connection. Richards & Smith expires September 1996 [Page i] RFC DRAFT PPP BACP March 1996 1. Introduction As PPP multilink implementations become increasingly common, there is a greater need for some conformity in how to manage bandwidth over such links. Interoperable implementations of PPP multilink have had problems such as thrashing, when links are repeatedly brought up and torn down in a short amount of time. BACP and BAP provide a means of solving problems associated with interoperable thrashing implementations, they also provide a flexible yet robust way of managing bandwidth between 2 peers. BAP does this by defining Call- Control packets and a protocol that allows peers to co-ordinate the actual bandwidth allocation and de-allocation. Phone numbers may be passed in the Call-Control packets to minimize the end user's configuration. 1.1. Specification of Requirements In this document, several words are used to signify the requirements of the specification. These words are often capitalized. MUST This word, or the adjective "required", means that the definition is an absolute requirement of the specification. MUST NOT This phrase means that the definition is an absolute prohibition of the specification. SHOULD This word, or the adjective "recommended", means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications must be understood and carefully weighed before choosing a different course. MAY This word, or the adjective "optional", means that this item is one of an allowed set of alternatives. An implementation which does not include this option MUST be prepared to interoperate with another implementation which does include the option. 1.2. Terminology This document frequently uses the following terms: peer The other end of the point-to-point link silently discard This means the implementation discards the packet without further processing. The implementation SHOULD provide the capability of logging the error, including the contents of Richards & Smith expires September 1996 [Page 1] RFC DRAFT PPP BACP March 1996 the silently discarded packet, and SHOULD record the event in a statistics counter. BOD (bandwidth on demand) BOD refers to the ability of a system to allocate and remove links in a multilink system to change the bandwidth of a multilink bundle. This may be done in response to changing line conditions and it also may be done in response to changing resource conditions. In either case, changing bandwidth dynamically during a multilink connection is referred to as BOD. 2. New LCP Configuration Option Implementations MUST implement LCP as defined in [1]. LCP MUST be in the Network-Layer Protocol phase before BACP can be negotiated. 2.1. Link Discriminator Description This option is used to declare a unique discriminator for the link that the option is sent over. This option MUST be negotiated by LCP on every link. BAP uses the link discriminator to differentiate the various links in a multilink bundle. Each link in a multilink bundle MUST have a unique discriminator. The discriminator is independent for each peer, so each link may have 2 different LCP Link Discriminator values, one for each peer. When the Link Discriminator is sent in a BAP packet, it is the peer's Link Discriminator which is sent. A summary of the Link Discriminator LCP Option format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Link Discriminator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 23 for Link Discriminator option. Richards & Smith expires September 1996 [Page 2] RFC DRAFT PPP BACP March 1996 Length 4 Link Discriminator The Link Discriminator field is 2 octets in Length, and it contains a unique identifier used to indicate a particular link in a multilink bundle. The Link Discriminator for a link MUST be unique among the Link Discriminators assigned by this endpoint for this bundle. The Link Discriminator SHOULD be assigned in a sequential, monotonically increasing manner. 3. BACP Operation BACP uses the same packet exchange mechanism as the Link Control Protocol defined in [1]. BACP packets MUST NOT be exchanged until PPP has reached the Network-Layer Protocol phase. BACP packets received before this phase is reached should be silently discarded. BACP is negotiated once per multilink bundle. If BACP is negotiated on any of the links in a multilink bundle, it is opened for all of the links in the bundle. The Bandwidth Allocation Control Protocol is exactly the same as the Link Control Protocol [1] with the following exceptions: Data Link Layer Protocol Field Exactly one BACP packet is encapsulated in the Information field of PPP Data Link Layer frames where the Protocol field indicates Type hex 8071 (Bandwidth Allocation Control Protocol). Code field Only Codes 1 through 7 (Configure-Request, Configure-Ack, Configure-Nak, Configure-Reject, Terminate-Request, Terminate- Ack and Code-Reject) are used. Other Codes should be treated as unrecognized and should result in Code-Rejects. Configuration Option Types BACP does not have any Configuration Options. Any options SHOULD not be sent, and any options received SHOULD be rejected using a Config-Reject packet. Richards & Smith expires September 1996 [Page 3] RFC DRAFT PPP BACP March 1996 4. BAP Operation 4.1. Link Management BAP defines packets, parameters and negotiation procedures to allow two endpoints to negotiate gracefully adding and dropping links from a multilink bundle. An implementation can: o Request permission to add a Link to a bundle (Call-Request) o Request that the peer add a link to a bundle via a callback (Callback-Request) o Negotiate with the peer to drop a link from a bundle (this implies that the peer can refuse) (Link-Drop-Query-Request) After BACP reaches the opened state, either peer MAY request that another link be added to the bundle by sending a BAP Call- or Callback-Request packet. A Call-Request packet is sent if the implementation wishes to originate the call for the new link, and a Callback-Request packet is sent if the implementation wishes its peer to originate the call for the new link. The implementation receiving a Call- or Callback-Request MUST respond with a Call- or Callback- Response with a valid Response Code. After BACP reaches the opened state, either peer MAY request that a link be dropped from the bundle. A BAP Drop-Link-Query-Request packet is sent to the peer to negotiate dropping a link. The peer MUST respond with a Drop-Link-Query-Response. If the peer is agreeable to dropping the link the implementation should then issue an LCP Terminate-Request to initiate dropping the link. If an implementation wishes to force dropping a link without negotiation, it should simply send an LCP Terminate-Request packet on the link (without sending any BAP Drop-Link-Query-Request). After an LCP Terminate-Request is sent an implementation SHOULD stop transmitting data packets on that link, but still continue to receive and process data packets normally until receipt of a Terminate-Ack from the peer. The peer SHOULD stop transmitting packets before issuing the Terminate-Ack. This procedure will insure that no data is lost in either direction. A BAP Link-Drop-Query-Request is used to inquire if the peer agrees to drop a link from the current multilink bundle. Origination of a Link-Drop-Query-Request is an optional part of BAP. A system implementing BAP MUST support the receipt of Link-Drop-Query-Request from its peer. When an implementation wants to negotiate dropping a Richards & Smith expires September 1996 [Page 4] RFC DRAFT PPP BACP March 1996 link, it MUST transmit a Link-Drop-Query-Request. When an implementation receives a Link-Drop-Query-Request, it MUST base its response on its transmit heuristics or on its configuration (e.g., if the request would cause the number of active links to fall below the allowable minimum number of links configured for the active multilink bundle). If the implementation receiving a Link-Drop-Query-Request is not monitoring its transmit data and is not configured otherwise, it MUST accept the request to drop a link. 4.2. Bandwidth Management BAP allows two peer implementations to manage the bandwidth available to the protocols using the multilink bundle by negotiating when to add and drop links (See Link Management). The Bandwidth Allocation Protocol does not include an algorithm for determining when to add and remove links in a multilink bundle. These algorithms are left to the implementors. It is not necessary to include such an algorithm in the protocol, and including it may limit the abilities of implementations to work optimally. Leaving out the bandwidth on demand algorithm also improves chances for interoperability and makes the protocol more flexible. This section defines two important Types of BOD: Resource BOD and Throughput BOD. This does not preclude other Types of BOD from being implemented (e.g., Time of Day). The rest of this specification refers to actions to take when implementing these types of BOD. Throughput BOD refers to BOD decisions made based on the amount of data being sent, received or queued to be sent over a multilink bundle. An example of this is when a link is added to a bundle due to a large file being transferred across the bundle. Resource BOD refers to BOD decisions based on the resources (e.g., physical port, B-channel, etc.) available to an implementation. For example, an implementation might remove a link from a multilink bundle to answer an incoming voice call, or might add a link when a line becomes free due to the termination of a separate PPP call on another port. A system implementing BACP/BAP MAY support neither, either, both or some other Type of Bandwidth On Demand. Regardless of the Type of BOD implemented, if it uses BAP it must use the procedures in this specification for adding and dropping links. Resource BOD support is an optional part of BAP. An implementation does not have to locally make resource based BOD decisions as part of BAP. However, any system implementing BAP MUST support resource BOD management by its peer. An implementation MUST use an LCP Terminate-Request to remove a link due to Resource BOD. Richards & Smith expires September 1996 [Page 5] RFC DRAFT PPP BACP March 1996 Throughput BOD support is an optional part of BAP. An implementation does not have to locally make throughput based BOD decisions as part of BAP. However, any system implementing BAP must handle throughput BOD management by its peer (i.e., receipt of Link-Drop-Query- Request). When an implementation decides that it's time to remove a link due to a throughput BOD decision, an implementation MUST transmit a Link-Drop-Query-Request to inquire if the peer agrees to drop a link from the current multilink bundle. When an implementation receives a Link-Drop-Query-Request, it MUST base its response on its transmit heuristics (if it implements Throughput BOD) or on its configuration (e.g., if the request would cause the number of active links to fall below the allowable minimum number of links configured for the active multilink bundle). If the implementation receiving a Link-Drop-Query-Request is not monitoring its transmit data and is not configured otherwise, it MUST accept the request to drop a link. It MUST NOT base its response on its receive data heuristics. By making the decision to respond to a Link-Drop-Query- Request based on transmit heuristics only, BAP maximizes interoperability of various types of throughput BOD implementations. A BAP implementation may monitor its transmit traffic, both transmit and receive traffic, or choose not to monitor traffic in either direction. Server systems SHOULD implement bi-directional monitoring and single-user dialin clients MAY implement any type of monitoring. This will allow client BOD implementations that require minimal end- user configuration. 4.3. BAP Packets All of the BAP Request and Indication packets require a Response packet in response before taking any action. An implementation MUST set a timer when sending a Request or Indication packet. The value of this timer SHOULD depend on the type and speed of the link or links in use. Upon expiration of this timer, the implementation MUST retransmit the same request or indication, with the identical identification number unless the implementation has exceeded the maximum number of retransmissions it supports for this packet. If the number of retransmissions exceeds the number supported by the implementation for this packet, the implementation MAY take appropriate recovery action. For example, if no response to a Link-Drop-Query-Request is received after 2 retransmissions, an implementation MAY initiate dropping the link by sending an LCP Terminate-Request for that link. This procedure will insure that the peer receives the proper request or indication even if a packet is lost during transmission. If a Richards & Smith expires September 1996 [Page 6] RFC DRAFT PPP BACP March 1996 Response packet is lost, this retransmission scheme will insure that the original Request or Indication will be retransmitted with the same identification number, so the peer will realize that this is not a new request or indication packet. Since BAP packets help determine the amount of bandwidth available to an implementation, PPP SHOULD give them priority over other data packets when transmitting. This will help insure the prompt addition and removal of links in a multilink bundle. This is especially important when adding links to a bundle due to bandwidth constraints. 4.4. Race Conditions A race condition can occur if both implementations send a Call- Request, Callback-Request or Link-Drop-Query-Request at the same time. These race conditions should be solved as follows: If each implementation sends a Call-Request (or Callback-Request) at the same time, the implementation with the lowest username value SHOULD be favored. A username value is compared by converting the ASCII bytes of the username used by the peer during authentication into hexadecimal octets to create a number. If both implementations are using the same username, then the lowest Multilink Endpoint Discriminator SHOULD be favored. Once again, each Multilink Endpoint Discrininators is first converted into hexadecimal octets starting with the Class octet, before being compared. This means that the favored peer's request SHOULD be acked by its peer, and the unfavored peer's request SHOULD be naked by the favored peer. If each implementation sends a Link-Drop-Query-Request at the same time, the same scheme SHOULD be used as for Call-Requests. 4.5. BAP Datagram Format Description Before any BAP packets may be communicated, PPP MUST reach the Network-Layer Protocol phase, and BACP MUST reach the opened state. Exactly one BAP packet is encapsulated in the Information field of PPP Data Link Layer frames where the Protocol field indicates type hex 0071 (Bandwidth Allocation Protocol). The maximum length of a BAP packet transmitted over a PPP link is the same as the maximum length of the Information field of a PPP data link layer frame. Richards & Smith expires September 1996 [Page 7] RFC DRAFT PPP BACP March 1996 Bandwidth Allocation Protocol datagrams can be catagorized as either Request, Indication or Response packets. Every Request and Indication datagram has a corresponding Response packet. Request and Indication datagrams have a slightly different format from Response datagrams, as the Response datagrams include a Response Code octet. All of the BAP datagrams MUST be supported by an implementation. A summary of the Bandwidth Allocation Protocol datagram Request and Indication packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data ... +-+-+-+-+-+-+-+-+ A summary of the Bandwidth Allocation Protocol datagram Response packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Response Code | Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type The Type field is one octet and identifies the type of BAP datagram packet. Datagram types are defined as follows. This field is coded in binary coded hexadecimal. Richards & Smith expires September 1996 [Page 8] RFC DRAFT PPP BACP March 1996 01 Call-Request 02 Call-Response 03 Callback-Request 04 Callback-Response 05 Link-Drop-Query-Request 06 Link-Drop-Query-Response 07 Call-Status-Indication 08 Call-Status-Response The various types of BAP datagrams are explained in the following sections. Identifier The Identifier field is one octet and is binary coded. It aids in matching Requests and Indications with Responses, as well as which links are added or removed. Call-Status-Indication packets MUST use the same Identifier as was used by the original Call-Request or Callback-Request that was used to initiate the call that failed. All other Request or Indication packets MUST use a unique Identifier for each new Request or Indication. All Response packets MUST use the same identifier as the Identifier in the Request or Indication packet being responded to. When re- transmitting a request or indication, the Identifier MUST be the same as the Identifier used on the previous transmission of the request or indication. Length The Length field is two octets and indicates the length of the packet including the Type, Identifier, Length and Options fields. It is binary encoded. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception. Response Code The Response Code is only present in Response datagrams. It is binary coded and can have the following values: 00000000 Request-Ack 00000001 Request-Nak 00000010 Request-Rej 00000011 Request-Full-Nak The Request-Ack Response Code is sent to indicate that the Request or Indication command is valid and was successfully received by an Richards & Smith expires September 1996 [Page 9] RFC DRAFT PPP BACP March 1996 implementation. The Request-Nak Response Code is sent to indicate that the Request command was received, but an implementation does not want the requested action performed at this time. If a Response containing a Request-Nak Response Code is received, the original Request MAY be retried after an implementation determines that sufficient time has elapsed. The Request-Rej Response Code is sent to indicate that the Request command received by an implementation is not implemented (i.e., if receiving a callback is not implemented by the peer.) The Request-Full-Nak Response Code is sent to indicate that the Request command was received, but an implementation does not want the requested action performed. The Request-Full-Nak is used to indicate that an implementation has reached the maximum (for a Call- or Callback- Request) or the minimum (for a Link-Drop-Query-Request) bandwidth configured or available for this multilink bundle. If a Response containing a Request-Full-Nak Response Code is received, the original Request SHOULD NOT be retried until the total bandwidth of the multilink bundle has changed. Data The Data field is variable in length, and will usually contain the list of zero or more BAP Options that the sender desires to transmit. The format of BAP Options is described in a later chapter. 4.5.1. Call-Request Before originating a call to add another link to a multilink bundle, an implementation MUST transmit a Call-Request packet. This will inform the peer of the request to add another link to the bundle and give the peer a chance to inform the implementation of the phone number of a free port that can be called. The options field MUST include the Link-Type option. The options field MAY include the No-Phone-Number and/or the Reason options. Upon reception of a Call-Request, a Call-Response datagram MUST be transmitted. 4.5.2. Call-Response An implementation MUST transmit a Call-Response datagram in response to a received Call-Request datagram. If the Call-Request is acceptable, the Call-Response MUST have a Response Code of Request- Ack; otherwise the Response Code MUST be Request-Nak or Request- Full-Nak. The Phone-Number option MUST be included in a Call-Response packet with a Response Code of Request-Ack unless the Call-Request Richards & Smith expires September 1996 [Page 10] RFC DRAFT PPP BACP March 1996 included the No-Phone-Number option. The options field MAY include the Reason and/or Link-Type options. 4.5.3. Callback-Request An implementation that wants its peer to originate another link to add to the multilink bundle MUST transmit a Callback-Request packet to its peer. This will inform the peer of the request to add another link to the bundle and will also inform the peer of the number to be called. The options field MUST include the Phone-Number option. The Link- Type and Reason options MAY also be included. Upon reception of a Callback-Request, a Callback-Response datagram MUST be transmitted. 4.5.4. Callback-Response An implementation MUST transmit a Callback-Response datagram in response to a received Callback-Request datagram. If the Callback- Request is acceptable, the Callback-Response MUST have a Response Code of Request-Ack. A Callback-Response packet MAY include the Link-Type option. 4.5.5. Link-Drop-Query-Request An implementation that determines that a link is no longer needed and wishes to negotiate dropping it (e.g., based on a throughput BOD decision), MUST transmit a Link-Drop-Query-Request packet. The options field MUST include the Link-Discriminator option, and MAY include the Reason option. Upon reception of a Link-Drop-Query-Request, an implementation MUST transmit a Link-Drop-Query-Response datagram. The Response-Code will be Request-Ack if it agrees to drop the link; if it does not agree to drop the link the Response-Code will be Request-Nak or Request-Full- Nak. After the receipt of a Link-Drop-Query-Response with a Response Code of Request-Ack, the transmitter of the Link-Drop-Query-Request MUST initiate tear down of the indicated link by sending an LCP Terminate-Request packet on the designated link. 4.5.6. Link-Drop-Query-Response An implementation transmits a Link-Drop-Query-Response datagram in response to a received Link-Drop-Query-Request datagram. If the implementation agrees (e.g., based on its throughput BOD algorithm) to reduce the bandwidth of the multilink bundle, then the Response Richards & Smith expires September 1996 [Page 11] RFC DRAFT PPP BACP March 1996 Code MUST be set to Request-Ack. Otherwise, the Response Code MUST be set to either Request-Nak or Request-Full-Nak. The Reason option MAY be included in the Link-Drop-Query-Response packet. 4.5.7. Call-Status-Indication After an implementation attempts to add a link to a bundle as the result of a Call-Request or a Callback-Request, it MUST send a Call- Status-Indication packet to its peer. The Call-Status option MUST be included to inform the peer of the status of the call and the action the implementation will take in case of call failure. The reason option MAY also be included in the Call-Status-Indication packet. Upon reception of a Call-Status-Indication packet, an implementation MAY log the failure and reason code, and a Call-Status-Response datagram MUST be transmitted. 4.5.8. Call-Status-Response An implementation transmits a Call-Status-Response datagram in response to a received Call-Status-Indication datagram. The Response Code field MUST be set to Request-Ack in this packet. The Reason option MAY be included in this packet. 5. BAP Datagram Options BAP Datagram Options are used in various BAP packets. Their use in various packets is as defined below. The format of these options loosely follows the formatting conventions of LCP Configuration Options. When there are multiple BAP Options in one BAP packet, the options MAY be transmitted in any order. A summary of the BAP Option format is shown below. The fields are transmitted from left to right. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Richards & Smith expires September 1996 [Page 12] RFC DRAFT PPP BACP March 1996 Type The type field is one octet, and indicates the type of the BAP Datagram Option. This field is binary coded Hexadecimal. The following options are currently defined: 01 Link-Type 02 Phone-Number 03 No-Phone-Number-Needed 04 Reason 05 Link-Discriminator 06 Call-Status Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length, and Data fields. Data The Data field is zero or more octets, and contains information specific to the BAP Option. The format and length of the Data field is determined by the Type and Length fields. 5.1. Link-Type Description This option indicates the general type of link indicated for the operation being performed. This option does not indicate a specific link type, rather it gives some general characteristics of the desired link type. This option MAY be used along with other knowledge (i.e., the type of the other link(s) in the bundle or user configuration) to determine the type of link desired to be used in the operation. It MUST be included in a Call- or Callback-Request, and MAY be included in a Call- or Callback- Response. A summary of the Link-Type BAP Option format is shown below. The fields are transmitted from left to right. Richards & Smith expires September 1996 [Page 13] RFC DRAFT PPP BACP March 1996 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Link Speed (kbps) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Type | +-+-+-+-+-+-+-+-+ Type 01 for Link-Type. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length and Link Type fields. Link Speed The Link Speed field is 2 octets, and indicates the requested speed of the desired link in kilobits per second. This field is coded as 2 binary coded hexadecimal octets, with the most significant octet sent first. Link Type The Link Type field is a bit mask. It is 1 octet in length. Bit 0 of the Link Type field corresponds to bit 32 of the Link-Type BAP Option as described above. If a bit is set, it indicates support of the corresponding link type (more than one bit MAY be set): Bit Link type --- ------------- 0 ISDN 1 X.25 2 analog 3-7 reserved If the Length field contains more bits than are defined by this specification, then any bits that are not defined should be ignored. If the Length field is shorter than the number of bits defined, then the implementation should set all bits not received to 0. Richards & Smith expires September 1996 [Page 14] RFC DRAFT PPP BACP March 1996 5.2. Phone-Number Description This option is used to transmit an implementation's phone number to its peer. For example, this phone number could be either the phone number of a hunt group for this device, or the specific phone number of a free port on this device. An implementation MAY include more than one Phone-Number option in a response. This indicates that there is more than one phone number that can be used for the requested operation. The Phone-Number option MUST appear in a Callback-Request if the Response Code is set to Request-Ack. It also MUST appear in a Call-Response with a Response Code set to Request-Ack if the Call-Request did not contain the No-Phone-Number option. It MAY be included in the Call-Status-Indication packet. A summary of the Phone-Number BAP Option format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |Sub-Option Type| Sub-Option Len| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Option... +-+-+-+-+-+-+-+-+ Type 02 for Phone-Number. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length, and Sub-Option fields. Sub-Option Type The following Sub-Options Types are defined for the Phone-Number option. 01 Unique Digits 02 Subscriber Number 03 Phone Number Sub Address Richards & Smith expires September 1996 [Page 15] RFC DRAFT PPP BACP March 1996 5.2.1. Phone-Number Sub-Options Unique Digits This byte is a count of the number of unique digits in the phone number. The Unique Digits byte indicates the number of rightmost digits of the complete phone number that are different from port to port on the given device. (For example, if all phone numbers on a given device are 617/555-89XX, the Unique Digits byte is 2, if all phone numbers are 617/55X-XXXX, then the Unique Digits byte will be 5). This field is required. The purpose of the unique digits sub-option is to aid the originating implementation in phone number parsing. With this information, the implementation that originates a call does not have to know which combination of access codes, country codes, dialing codes, area codes and extension numbers are necessary. It just takes the digits contained in the original phone number dialed, and replaces the rightmost unique digits with the rightmost unique digits of the new phone number. For example, if the original number dialed is 9,16175512345, and the new phone number has an area code of 617, a phone number of 5598765, and a unique digits value of 5, then the number to be dialed will be created by replacing the rightmost 5 digits of the original number (12345) with the rightmost 5 digits of the new number (98765), which results in a new phone number to be dialed of 9,16175598765. Subscriber Number This field is the phone number of the port that should be called by the peer. It MAY include the National Destination and Country Codes. This field is an ASCII string and MUST contain only ASCII characters 0-9 inclusive (valid phone number digits). This field is required. Phone Number Sub Address This field is the sub address of the port to be called by the peer. This sub-option SHOULD only be used for an ISDN call. This field is an ASCII string and only contains valid phone number digits. This field is optional. 5.3. No-Phone-Number-Needed Description The No-Phone-Number option indicates that the calling implementation is already configured with the phone number of its Richards & Smith expires September 1996 [Page 16] RFC DRAFT PPP BACP March 1996 multilink peer and the peer MUST NOT include the Phone Number option in the response. This may be for security reasons, for configuration reasons, or for any other reason. This option MAY be used in a Call-Request packet. A summary of the No-Phone-Number BAP Option format is shown below. The fields are transmitted from left to right. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 03 for No-Phone-Number. Length 2 5.4. Reason Description This option is used to indicate a reason for the Request or Response. It is meant to be used for informational purposes only. This option MAY be used in any BAP packet. A summary of the Reason BAP Option format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Reason String... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 04 for Reason. Richards & Smith expires September 1996 [Page 17] RFC DRAFT PPP BACP March 1996 Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length and Reason String fields. Reason String This is an ASCII string. The content of the field is implementation dependent. An implementation MAY ignore the Reason String field. 5.5. Link-Discriminator Description The Link-Discriminator option MUST be used in a Link-Drop-Query- Request datagram. This option is used to inform the peer of which link will be dropped. A summary of the Link-Discriminator BAP Option format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Link Discriminator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 05 for Link-Discriminator Length 4 Link Discriminator The Link Discriminator field is 2 octets in length. It contains the Link Discriminator that was contained in the LCP Link- Discriminator Configuration Option sent by the peer. 5.6. Call-Status Description The Call-Status option MUST be used in a Call-Status-Indication Richards & Smith expires September 1996 [Page 18] RFC DRAFT PPP BACP March 1996 datagram. This option is used to inform the peer of the status of the completed call attempt, as well as a possible action that will be taken (if the call failed). A summary of the Call-Status BAP Option format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Status | Action | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 06 for Call-Status. Length 4 Status The Status field is 1 octet in length. If the call was successful, the value MUST be set to 0. A non-zero value indicates a call failure. A value of 255 indicates a non-specific failure, and a more specific call status MAY be indicated by using the same number as the Q.931 cause value (i.e., 1 is unassigned number, 17 is user busy, etc.) Action The Action octet indicates what action the calling implementation is taking after a failed call. If the call was sucessful, the Action octet MUST be set to 0. The Action octet can have the following values: 0 - No retry 1 - Will retry same number 2 - Will retry next number in list Richards & Smith expires September 1996 [Page 19] RFC DRAFT PPP BACP March 1996 Appendix List of BAP datagrams and associated fields. datagram mandatory fields allowed options -------- ----------------- --------------- Call-Request Link-Type No-Phone-Number Call-Response Phone-Number Link-Type Callback-Request Link-Type Phone-Number Callback-Response Link-Type Link-Drop-Query-Request Link-Discriminator Link-Drop-Query-Response Call-Status-Indication Call-Status Phone-Number Call-Status-Response The Reason option is allowed to be included with any BAP datagram. History of BACP The first version of BACP was written by Craig Richards of Shiva Corporation. This version was enhanced and improved by the MPCP Working Group, a collaborative effort of 3Com, Ascend, Bay Networks, Cisco, Microsoft, Shiva, US Robotics and Xylogics. Acknowledgements Kevin Smith of Ascend for his contributions based on his work on the MP+ Specification. Gerry Meyer and Robert Myhill of Shiva for their early comments and improvements. Andy Nicholson of Microsoft for his improvements to the bandwidth management scheme. Dana Blair and Andy Valencia of Cisco, Cheng Chen and Dan Brennan of 3Com for their good ideas as part of the MPCP Working Group. All of the members of the MPCP working group for their ability to work with their competitors with enthusiasm to produce a better protocol for the industry. Security Considerations Security issues are not discussed in this memo. References [1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, Daydreamer, July 1994. Richards & Smith expires September 1996 [Page 20] RFC DRAFT PPP BACP March 1996 [2] Sklower, Lloyd, McGregor & Carr, "The PPP Multilink Protocol", RFC 1717, PPP Extensions Working Group, Work in Progress. Chair's Address The working group can be contacted via the current chair: Fred Baker Cisco Systems 519 Lado Drive Santa Barbara, California 93111 VOICE +1 408 526 4257 FAX +1 805 681-0115 EMail: fred@cisco.com Editors' Addresses Craig Richards Shiva Corporation 28 Crosby Drive Bedford, MA 01730 VOICE +1 617 270 8419 FAX +1 617 270 8599 EMail: crich@us.shiva.com Kevin Smith Ascend Communications, Inc. 1275 Harbor Bay Parkway Alameda, CA 94501 CA EMail: kevin@ascend.com Richards & Smith expires September 1996 [Page 21] RFC DRAFT PPP BACP March 1996 Table of Contents 1. Introduction .......................................... 1 1.1 Specification of Requirements ................... 1 1.2 Terminology ..................................... 1 2. New LCP Configuration Option .......................... 2 2.1 Link Discriminator .............................. 2 3. BACP Operation ........................................ 3 4. BAP Operation ......................................... 4 4.1 Link Management ................................. 4 4.2 Bandwidth Management ............................ 5 4.3 BAP Packets ..................................... 6 4.4 Race Conditions ................................. 7 4.5 BAP Datagram Format ............................. 7 4.5.1 Call-Request .................................... 10 4.5.2 Call-Response ................................... 10 4.5.3 Callback-Request ................................ 11 4.5.4 Callback-Response ............................... 11 4.5.5 Link-Drop-Query-Request ......................... 11 4.5.6 Link-Drop-Query-Response ........................ 11 4.5.7 Call-Status-Indication .......................... 12 4.5.8 Call-Status-Response ............................ 12 5. BAP Datagram Options .................................. 12 5.1 Link-Type ....................................... 13 5.2 Phone-Number .................................... 15 5.2.1 Phone-Number Sub-Options ........................ 16 5.3 No-Phone-Number-Needed .......................... 16 5.4 Reason .......................................... 17 5.5 Link-Discriminator .............................. 18 5.6 Call-Status ..................................... 18 Appendix - List of BAP datagrams and associated fields ....... 20 ACKNOWLEDEMENTS .............................................. 20 SECURITY CONSIDERATIONS ...................................... 20 REFERENCES ................................................... 20 CHAIR'S ADDRESS .............................................. 21 EDITORS'S ADDRESSES .......................................... 21 Richards & Smith expires September 1996 [Page ii]