PPP Working Group Craig Richards Internet Draft Shiva Corporation expires July 1996 Kevin Smith Ascend Communications, Inc. January 1996 The PPP Bandwidth Allocation Protocol (BAP) The PPP Bandwidth Allocation Control Protocol (BACP) draft-richards-bacp-00.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 [1]. This is done by defining the Bandwidth Allocation Protocol (BAP), as well as its associated control protocol, the Bandwidth Allocation Control Protocol (BACP). BAP will manage the number of links in a multlink bundle. This includes defining 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 July 1996 [Page i] INTERNET DRAFT PPP BACP January 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 may have 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, as well as providing a flexible yet robust way of managing bandwidth between 2 peers. BAP does this by defining rules governing bandwidth on demand allocation and by defining Call-Control packets that co-ordinate the actual bandwidth allocation and de- allocation. Phone numbers may be passed in the Call-Control packets to improve dynamic bandwidth decisions, as well as minimizing 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 Richards & Smith expires July 1996 [Page 1] INTERNET DRAFT PPP BACP January 1996 capability of logging the error, including the contents of 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 - Link Discriminator Description This option is used to declare a unique discriminator for the link that the option is sent over. This option may be in an LCP configure request packet. The link discriminator is used to differentiate the various links in a multilink bundle. If this option is used, 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. 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 ?? for Link Discriminator option. Length The Length field is one octet, and indicates the length of this LCP Option including the Type, Length, and Link Discriminator fields. Richards & Smith expires July 1996 [Page 2] INTERNET DRAFT PPP BACP January 1996 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. 3. BACP Packet Format BACP uses the same packet exchange mechanism as the Link Control Protocol [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 80?? (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 has a distinct set of Configuration Options, which are defined in the next section. 4. BACP Configuration Options BACP Configuration Options allow negotiation of desirable BACP parameters. These options are used in Config-Request, Config-Ack, Config-Nak, and Config-Reject packets. BACP uses the same Configuration Option format defined for LCP [1], with a seperate set of Options. Richards & Smith expires July 1996 [Page 3] INTERNET DRAFT PPP BACP January 1996 Current values of BACP Configuration Options are assigned as follows: 1 Datagrams-Supported 2 Base-Phone-Number 4.1. Datagrams-Supported Description This option is used to inform the peer of which Bandwidth Allocation Protocol datagrams this implementation supports. This option MUST be included in every BACP Configure-Request packet. An implementation MUST NOT send its peer any packets which it does not support, as indicated by this option. If an implementation receives a packet that it does not support, it MUST silently discard it. Since this configuration option is used to inform the peer, and can not be negotiated, an implementation SHOULD NOT transmit a Config-Nak or a Config-Rej in response to this configuration option. A summary of the Datagrams-Supported 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 | Datagrams Supported | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 1 for Datagrams-Supported. Length The Length field is one octet, and indicates the length of this BACP Option including the Type, Length and Datagrams Supported fields. Datagrams Supported The Datagrams Supported field is a bit mask. It is 2 octets long. If a bit is set, it indicates support of both a Bandwidth Allocation Protocol Request or Indication datagram as well as the Richards & Smith expires July 1996 [Page 4] INTERNET DRAFT PPP BACP January 1996 corresponding Response datagram. Bit 0 of the Datagrams Supported field corresponds to bit 31 of the Datagrams-Supported Option as diagrammed above. Bit Datagram Supported --- ------------------ 0 Call-Request & Call-Response 1 Callback-Request & Callback-Response 2 Link-Drop-Request & Link-Drop-Response 3 Link-Drop-Query-Request & Link-Drop-Query-Response 4 Bundle-Drop-Request & Bundle-Drop-Response 5 Link-Type-Request & Link-Type-Response 6 Available-Link-Indication & Available-Link-Response 7 Call-Fail-Indication & Call-Fail-Response 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. 4.2. Base-Phone-Number Description This Configuration Option provides a way to inform the peer of an implementation's base phone number. The base phone number can be used in conjunction with the unique-digits sub-option of the phone-number BAP option to create a valid phone number string to be dialed. This option would be needed if an answering implementation wishes to make a callback call to initiate a subsequent link in a bundle. By default, the answerer's base phone number is the original number used to make the call that creates the first link in a multilink bundle, and the originator does not have a base phone number. However, if a callback protocol is used during link establishment of the first link of a bundle, then the callback phone number would be the default base number for the originator's implementation. Since this configuration option is used to inform the peer, and can not be negotiated, an implementation SHOULD NOT transmit a Config-Nak or a Config-Rej in response to this configuration option. A summary of the Base-Phone-Number Option format is shown below. The fields are transmitted from left to right. Richards & Smith expires July 1996 [Page 5] INTERNET DRAFT PPP BACP January 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 | Base Phone Number... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 2 for Base-Phone-Number. Length The Length field is one octet, and indicates the length of this BACP Option including the Type, Length and Base Phone Number fields. Base Phone Number The Base Phone Number field is an ASCII phone number string. It will contain the complete set of digits that must be dialed by the calling implementation to reach the called implementation. This might include a code to reach an outside line, long distance prefix, area code, country prefix and/or country code, as well as the phone number to be dialed. It should be similar to the format of a phone number used when performing a callback connection. 5. BAP Overview 5.1. Link Management 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 to answer the call for the new link. The implementation receiving Call- and Callback-Requests must respond with the appropriate Request-Ack or Request-Nak Response Code. 5.2. Bandwidth Management In order to discuss bandwidth management, it is first necessary to define some terms. For the purposes of this specification, Bandwidth on Demand (BOD) is divided into 2 different types - throughput BOD and resource BOD. Throughput BOD refers to BOD decisions made based Richards & Smith expires July 1996 [Page 6] INTERNET DRAFT PPP BACP January 1996 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 dynamic bandwidth decisions based on the equipment available to an implementation. For example, a link might be removed from a multilink bundle to allow an incoming voice call to be answered, or a link might be added when a line becomes free due to the termination of a seperate PPP call on another port. A system implementing BACP may be capable of implementing neither, one or both types of dynamic bandwidth management. 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 handle resource BOD management by its peer. When links are removed due to resource BOD decisions, an implementation MUST use a Link-Drop-Request. A Link- Drop-Request is used to inform the peer that the implementation is going to drop a link from the multilink bundle. The peer MUST reply to this request with a Link-Drop-Response with the Response Code set to Request-Ack. No other response is allowed. The peer that decides to drop a link MAY choose to drop the link even if a Request-Ack has not been received. This SHOULD only be done if there is a time critical quality to dropping the link. An example of this is when there is an incoming call on a line in use by the multilink bundle, and the line must be dropped quickly before the incoming call goes away. 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. 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. A Link- Drop-Query-Request is used to inquire if the peer agrees that it is okay 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 (unless it is not monitoring its transmit data, in which case it MUST accept the request to drop a link.) It MUST NOT base its response on its receive data heuristics. It MAY base its decision on its configuration, for example 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. 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. An implementation may monitor its transmit traffic, both transmit and receive traffic, or choose not to monitor traffic in either direction Richards & Smith expires July 1996 [Page 7] INTERNET DRAFT PPP BACP January 1996 when implementing BACP. It is recommended that server systems implement at least transmit monitoring, and that single-user dialin servers implement bi-directional monitoring. This will allow clients implementations that require a minimum amount of end-user configuration in order to implement BOD successfully. The Bandwidth Allocation Protocol does not include an algorithm for determining when to add and remove links in a multilink bundle. 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. 6. BAP Packets All of the BAP Request and Indication packets require a Response packet in response before taking any action, except the Link-Drop- Request packet. The sender of the Link-Drop-Request packet is not required to receive a response to this packet before dropping a link, because there may be a time critical event depending on dropping the link. However, when possible, the sender of a Link-Drop-Request packet SHOULD wait for a response before dropping the link. With the exception of the Link-Drop-Request packet, an implementation MUST set a timer when sending a request or indication packet. Upon expiration of this timer, the implementation MUST retransmit the same request or indication, with the identical identification number. This will insure that the peer receives the proper request or indication even if it is lost during transmission. If a 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 the response was lost, and that this is not a new request or indication packet. Since BAP packets help determine the amount of bandwidth available to an implementation, they SHOULD be given 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. A race condition can occur if both implementations send a Call- Request at the same time, or if both implementations send a Link- Drop-Request at the same time. A race condition SHOULD be solved by favoring the implementation with the lowest username value. If both implementations are using the same username, then the lowest Multilink Endpoint Discriminator SHOULD be favored. This means that Richards & Smith expires July 1996 [Page 8] INTERNET DRAFT PPP BACP January 1996 the favored peer's request should be acked by its peer, and the unfavored peer's request should be naked by the favored peer. 6.1. BAP Datagram Format Description Before any BAP packets may be communicated, PPP must reach the Network-Layer Protocol phase, and the BA Control Protocol 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 00?? (Bandwidth Allocation Protocol). The maximum length of a BAP packet transmitted over a PPP links is the same as the maximum length of the Information field of a PPP data link layer frame. 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. 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. Richards & Smith expires July 1996 [Page 9] INTERNET DRAFT PPP BACP January 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 | 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: 00 Call-Request 01 Call-Response 02 Callback-Request 03 Callback-Response 04 Link-Drop-Request 05 Link-Drop-Response 06 Link-Drop-Query-Request 07 Link-Drop-Query-Response 08 Bundle-Drop-Request 09 Bundle-Drop-Response 0A Link-Type-Request 0B Link-Type-Response 0C Available-Link-Indication 0D Available-Link-Response 0E Call-Failure-Indication 0F Call-Failure-Response The various types of BAP datagrams are explained in the following sections. Identifier The Identifier field is one octet and aids in matching Requests and Indications with Responses, as well as which links are added or removed. Call-Failure-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 Richards & Smith expires July 1996 [Page 10] INTERNET DRAFT PPP BACP January 1996 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. 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 can have the following values: 0 Request-Ack 1 Request-Nak 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. 6.1.1. 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 intention 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 Call-Add-Code options. Upon reception of a Call-Request, a Call-Response datagram MUST be transmitted. 6.1.2. Call-Response An implementation transmits a Call-Response datagram in response to a received Call-Request datagram. If the Call-Request is acceptable, the Call-Response will have a Response Code set to Request-Ack, otherwise the Response Code will be Request-Nak. The Phone-Number option MUST be included in a Call-Response packet with a Response Code of Request-Ack unless the Call-Request included the No-Phone- Richards & Smith expires July 1996 [Page 11] INTERNET DRAFT PPP BACP January 1996 Number option. The Nak-Code option MUST be included in a Call- Response packet with a Response Code of Request-Nak, and the Time- Until-Retry and Link-Types options MAY be included in such a packet. 6.1.3. 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 intention 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 Link-Type and Phone-Number options. The Call-Add-Code option MAY also be included. Upon reception of a Callback-Request, a Callback-Response datagram MUST be transmitted. 6.1.4. Callback-Response An implementation transmits a Callback-Response datagram in response to a received Callback-Request datagram. If the Callback-Request is acceptable, the Callback-Response will have a Response Code of Request-Ack, otherwise the Response Code will be Request-Nak. The Nak-Code option MUST be included in a Callback-Response packet with a Response Code of Request-Nak, and the Time-Until-Retry option MAY also be included in such a packet. 6.1.5. Link-Drop-Request An implementation that requires that a link be removed from the current multilink bundle MUST transmit a Link-Drop-Request packet. This will usually be due to resource BOD decisions. If an implementation wants to remove a link due to a throughput BOD decision, it MUST send a Link-Drop-Query-Request (see section below) The options field MUST include the Link-Type option and MAY include the Drop-Code option and MAY include the Link-Discriminator option. Upon reception of a Link-Drop-Request, a Link-Drop-Response datagram with a Response Code of Request-Ack MUST be transmitted. After the receipt of the Link-Drop-Response datagram, the transmitter of the Link-Drop-Request MUST initiate tear down of the indicated link by sending an LCP Terminate-Request packet. The Link-Drop-Request is the only BAP Request packet that does not require a response before an action is taken. If there are time constaints, an implementation may go ahead and drop a link from the multilink bundle without receiving a response from its peer. Richards & Smith expires July 1996 [Page 12] INTERNET DRAFT PPP BACP January 1996 6.1.6. Link-Drop-Response An implementation transmit a Link-Drop-Response datagram in response to a received Link-Drop-Request datagram. The Response Code MUST be set to Request-Ack in this packet. 6.1.7. Link-Drop-Query-Request An implementation that determines that a link is no longer needed based on a throughput BOD decision MUST transmit a Link-Drop-Query- Request packet. The remote implementation will respond with a Response Code of Request-Ack if it agrees that there is too much bandwidth in the current multilink bundle based on a throughput BOD algorithm, or a Request-Nak if its own throughput BOD management determines that current load conditions warrent keeping all links of the bundle. The options field MUST include the Link-Type option and MAY include the Drop-Code option and MAY include the Link- Discriminator option. Upon reception of a Link-Drop-Query-Request, a Link-Drop-Query- Response datagram MUST be transmitted. After the receipt of a Link- Drop-Query-Request 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. 6.1.8. 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 determines, based on its BOD algoritm, that it would be acceptable to reduce the bandwidth of the multilink bundle, then the Response Code should be set to Request-Ack. Otherwise, the Response Code should be set to Request-Nak. If the Response Code is Request-Nak, the Nak-Code option MUST be included, and the Time-Until-Retry option MAY be included. 6.1.9. Bundle-Drop-Request An implementation that wishes to terminate a multilink bundle MAY transmit a Bundle-Drop-Request to its peer. This packet indicates that the peer is going to terminate all the links in the current bundle. This packet can be used instead of sending Link-Drop- Requests for each link in a multilink bundle. The options field MAY include a Drop-Code option. Upon reception of a Bundle-Drop-Request, a Bundle-Drop-Response with a Response Code of Request-Ack MUST be transmitted. After the receipt Richards & Smith expires July 1996 [Page 13] INTERNET DRAFT PPP BACP January 1996 of the Bundle-Drop-Response, the transmitter of the Bundle-Drop- Request MUST initiate tear down of all links in the bundle by sending an LCP Terminate-Request packet on each link. 6.1.10. Bundle-Drop-Response An implementation transmits a Bundle-Drop-Response datagram in response to a received Bundle-Drop-Request datagram. The Response Code MUST be set to Request-Ack in this packet. 6.1.11. Link-Type-Request If an implementation desires to know which types of links its peer supports for the current multilink bundle, it MAY send a Link-Type- Request to its peer. Upon reception of a Link-Type-Request, a Link-Type-Response datagram MUST be transmitted. 6.1.12. Link-Type-Response An implementation transmits a Link-Type-Response datagram in response to a received Link-Type-Request datagram. The Response Code MUST be set to Request-Ack in this packet. The Link-Types option MUST be included in this datagram, so the peer will be informed of which link types this implementation supports. 6.1.13. Available-Link-Indication Whenever an implementation transmits a Call-Response or a Callback- Response with the Response Code set to Request-Nak and the Nak Code set to "link not currently available", that implementation enters a link denied state. While an implementation is in a link denied state and a link of the type previously requested becomes available, and if the implementation and its peer both support the Available-Link packets, then the implementation MUST send an Available-Link- Indication packet to the peer. When an Available-Link-Indication packet is sent to the peer, the link denied state is cleared for that link type. Each independent link type has an independent link denied state. When an implementation receives an Available-Link-Indication packet, it MUST transmit an Available-Link-Response packet in response so that the peer knows that the indication was received. The Link-Type option MUST be included in the Available-Link-Indication datagram. Richards & Smith expires July 1996 [Page 14] INTERNET DRAFT PPP BACP January 1996 6.1.14. Available-Link-Response An implementation transmits an Available-Link-Response datagram in response to a received Available-Link-Indication datagram. The Response Code MUST be set to Request-Ack in this packet. 6.1.15. Call-Failure-Indication After an implementation fails an attempt to add a link to a bundle as the result of a Call-Request or a Callback-Request, it MUST send a Call-Failure-Indication packet to its peer. The options field MUST include the Call-Failure-Code option to indicate why the call failed as well as whether or not the implementation will retry the call. The Link-Type option MAY be included and the Phone-Number option indicating the phone number of the attempted call MAY be included. Upon reception of a Call-Failure-Indication packet, an implementation MAY log the failure and reason code, and a Call-Failure-Response datagram MUST be transmitted. 6.1.16. Call-Failure-Response An implementation transmits a Call-Failure-Response datagram in response to a received Call-Failure-Indication datagram. The Response Code field MUST be set to Request-Ack in this packet. 7. 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. 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 ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type The type field is one octet, and indicates the type of the BAP Richards & Smith expires July 1996 [Page 15] INTERNET DRAFT PPP BACP January 1996 Datagram Option. The following options are currently defined: 0 Link-Type 1 Link-Types 2 Phone-Number 3 No-Phone-Number-Needed 4 Call-Add-Code 5 Nak-Code 6 Drop-Code 7 Call-Failure-Code 8 Time-Until-Retry 9 Link-Discriminator 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. 7.1. Link-Type Description This option indicates the type of link supported for the operation being performed. Exactly one bit MUST be set in the Link Type field. This option MUST be included in all Bandwidth Allocation Protocol datagrams except Bundle-Drop- Request/Response and Link- Type- Request/Response datagrams. A summary of the Link-Type 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 Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 0 for Link-Type. Richards & Smith expires July 1996 [Page 16] INTERNET DRAFT PPP BACP January 1996 Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length and Link Type fields. Link Type The Link Type field is a bit mask. It is 2 octets in length. Bit 0 of the Link Type field corresponds to bit 31 of the Link-Type BAP Option as described above. If a bit is set, it indicates support of the corresponding link type: Bit Link type --- ------------- 0 Sync ISDN 64K 1 Sync ISDN 56K 2 Sync ISDN Data over voice 3 V.120 on Sync ISDN 64K 4 V.120 on Sync ISDN 56K 5 V.120 on Sync ISDN Data over voice 6 V.110 on Sync ISDN 64K 7 V.110 on Sync ISDN 56K 8 V.110 on Sync ISDN Data over voice 9 ISDN PRI H0 Channel 10 X.25 11 Asynchronous analog modem 12 Synchronous analog modem 13 Analog modem over ISDN 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. 7.2. Link-Types Description This option indicates the types of links capable of being supported in this multilink bundle. This option has a similar format to the Link-Type option, except that the Link Type field is a bit mask instead on having exactly one bit set. This option MUST be included in the Link-Type-Response datagram. A summary of the Link-Types BAP Option format is shown below. The fields are transmitted from left to right. Richards & Smith expires July 1996 [Page 17] INTERNET DRAFT PPP BACP January 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 Types | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 1 for Link-Types. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length and Link Types fields. Link Types The Link Types field is a bit mask. It is 2 octets long. See the bit definitions in the previous section (Link-Type Option) for a definition of the bits in the Link Types field. If a bit is set, it indicates support of the corresponding link type. 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. 7.3. Phone-Number Description This option is used to transmit an implementation's phone number to its peer. This phone number should be either the phone number of a hunt group for this device, or the specific phone number of a free port on this device. If there are no free ports on this device, a Response with a Response Code of Request-Nak should be sent, and this option would not be used. Note that an implementation may include more than one Phone-Number option in a response. This means 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. It also MUST appear in a Call-Response if the Call-Request did not contain the No-Phone-Number option. It MAY appear in the Call-Failure- Richards & Smith expires July 1996 [Page 18] INTERNET DRAFT PPP BACP January 1996 Indication datagram. 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 2 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. 0 Unique Digits 1 Phone Number 2 Area Code 3 Country Code 4 Phone Number Sub Address 7.3.1. 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 Richards & Smith expires July 1996 [Page 19] INTERNET DRAFT PPP BACP January 1996 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. Phone Number This field is the phone number of the port that should be called by the peer. It MUST NOT include the area code and country code fields IF they are defined in seperate sub-options. This field is an ASCII string and only contains valid phone number digits. This field is required. Area Code This field is the area code of the port that should be called by the peer. This field is an ASCII string and only contains valid phone number digits. This field is optional. Country Code This field is the country code of the port that should be called by the peer. This field is an ASCII string and only contains valid phone number digits. This field is optional. Phone Number Sub Address This field is the sub address of the port to be called by the peer. This sub-option will only be used for an ISDN call. This field is an ASCII string and only contains valid phone number digits. This field is optional. 7.4. No-Phone-Number-Needed Description The No-Phone-Number option is used to indicate that the calling peer is already configured with the phone number of its multilink peer. This may be for security reasons, for configuration Richards & Smith expires July 1996 [Page 20] INTERNET DRAFT PPP BACP January 1996 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 3 for No-Phone-Number. Length The Length field is one octet, and indicates the length of this BAP Option including the Type and Length fields. 7.5. Call-Add-Code Description This option is used to indicate the primary reason for requesting that a link be added to a bundle. This option MAY be used in a Call-Request or a Callback-Request packet. A summary of the Call-Add-Code 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 | Description +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String (Optional)... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 4 for Call-Add-Code. Richards & Smith expires July 1996 [Page 21] INTERNET DRAFT PPP BACP January 1996 Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length, Reason and optional Description String fields. Reason The reason code byte can have the following values: 0 - unlisted reason 1 - link has been freed up 2 - other resources freed up 3 - transmit queue length exceeds limit 4 - receive traffic exceeds limit 5 - transmit traffic exceeds limit Description String The Description String field is optional. If the length field indicates that the option continues past the Reason field, then the remaining octets in the option are the Description String. This is an ASCII string. The content of the field is implementation dependent. An implementation MAY ignore the Description String field. 7.6. Nak-Code Description This option is used to transmit a Nak code to the peer. This option MUST be included in every Call-Response and Callback- Response with a Response Code of Request-Nak. A summary of the Nak-Code 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 | Description +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String (Optional)... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Richards & Smith expires July 1996 [Page 22] INTERNET DRAFT PPP BACP January 1996 Type 5 for Nak-Code. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length, Reason and optional Description String fields. Reason The reason code byte can have the following values: 0 - unlisted reason 1 - link not currently available 2 - multilink bundle has reached its maximum capacity 3 - invalid phone number 4 - no resources 5 - peer does not have sufficient privilege Description String The Description String field is optional. If the length field indicates that the option continues past the Reason field, then the remaining octets in the option are the Description String. This is an ASCII string. The content of the field is implementation dependent. An implementation MAY ignore the Description String field. 7.7. Drop-Code Description This option is used to indicate the primary reason for requesting that a link be removed from the bundle. This option MAY be used in a Link-Drop-Request, Link-Drop-Query-Request or a Bundle-Drop- Request packet. A summary of the Drop-Code BAP Option format is shown below. The fields are transmitted from left to right. Richards & Smith expires July 1996 [Page 23] INTERNET DRAFT PPP BACP January 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 | Reason | Description +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ String (Optional)... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 6 for Drop-Code. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length, Reason and optional Description String fields. Reason The reason code byte can have the following values: 0 - unlisted reason 1 - incoming call 2 - outgoing call 3 - transmit data dropped below threshold 4 - receive data dropped below threshold 5 - transmit queue dropped below threshold 6 - higher priority connection requested line 7 - user initiated disconnect Description String The Description String field is optional. If the length field indicates that the option continues past the Reason field, then the remaining octets in the option are the Description String. This is an ASCII string. The content of the field is implementation dependent. An implementation MAY ignore the Description String field. 7.8. Call-Failure-Code Description This option is used to indicate the action that will be taken Richards & Smith expires July 1996 [Page 24] INTERNET DRAFT PPP BACP January 1996 after a call failed, as well as a reason code for the failure. This option MUST be included in a Call-Failure-Indication packet. A summary of the Call-Failure-Code 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 | Action | Reason | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Description String (Optional)... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 7 for Call-Failure-Code. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length, Action, Reason and optional Description String fields. Action The Action octet indicates what action the calling implementation is taking after a failed call. The Action octet can have the following values: 0 - No retry 1 - Will retry same number 2 - Will retry next number in list Reason The reason code byte can have the following values: 0 - unlisted reason 1 - no dial tone 2 - no answer 3 - no carrier 4 - unable to negotiate LCP 5 - unable to authenticate 6 - call canceled Richards & Smith expires July 1996 [Page 25] INTERNET DRAFT PPP BACP January 1996 Description String The Description String field is optional. If the length field indicates that the option continues past the Reason field, then the remaining octets in the option are the Description String. This is an ASCII string. The content of the field is implementation dependent. An implementation MAY ignore the Description String field. 7.9. Time-Until-Retry Description The Time-Until-Retry option MAY be used in Nak's of Call-Response, Callback-Response, and Link-Drop-Query-Response datagrams with the Response Code set to Request-Nak. This option is used to inform the peer that the previous Request will not be accepted until the time indicated by the option. This retry time only applies to the link type or types being requested. A summary of the Time-Until-Retry 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 | Time (seconds) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Time (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 8 for Time-Until-Retry. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length and Time fields. Time The Time field is 4 octets in length (network byte order), and indicates the time in seconds before the Request being Nak'd may be retried. Richards & Smith expires July 1996 [Page 26] INTERNET DRAFT PPP BACP January 1996 7.10. Link-Discriminator Description The Link-Discriminator option MAY be used in a Link-Drop-Request or a Link-Drop-Query-Request datagram. This option is used to inform the peer of which link will be dropped. If the peer did not send the LCP Link Discriminator Configuration Option during the LCP link negotiation phase, then this option MUST NOT be sent. 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 9 for Time-Until-Retry. Length The Length field is one octet, and indicates the length of this BAP Option including the Type, Length and Link Discriminator fields. 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. Richards & Smith expires July 1996 [Page 27] INTERNET DRAFT PPP BACP January 1996 Appendix List of BAP datagrams and associated options. datagram mandatory options possible options -------- ----------------- ---------------- Call-Request Link-Type No-Phone-Number Call-Add-Code Call-Response Phone-Number Nak-Code Time-Until-Retry Link-Types Callback-Request Link-Type Phone-Number Call-Add-Code Callback-Response Nak-Code Time-Until-Retry Link-Types Link-Drop-Request Link-Type Link-Discriminator Drop-Code Link-Drop-Response Link-Drop-Query-Request Link-Type Link-Discriminator Drop-Code Link-Drop-Query-Response Bundle-Drop-Request Drop-Code Bundle-Drop-Response Link-Type-Request Link-Type-Response Link-Types Available-Link-Indication Link-Type Available-Link-Response Call-Failure-Indication Call-Failure-Code Phone-Number Link-Type Call-Failure-Response 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 Richards & Smith expires July 1996 [Page 28] INTERNET DRAFT PPP BACP January 1996 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. [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: fbaker@cisco.com Editors' Addresses Craig Richards Shiva Corporation 63 Third Avenue Burlington, MA 01803 VOICE +1 617 270 8419 FAX +1 617 270 8599 EMail: crich@shiva.com Kevin Smith Ascend Communications, Inc. Richards & Smith expires July 1996 [Page 29] INTERNET DRAFT PPP BACP January 1996 1275 Harbor Bay Parkway Alameda, CA 94501 CA EMail: kevin@ascend.com Richards & Smith expires July 1996 [Page 30] INTERNET DRAFT PPP BACP January 1996 Table of Contents 1. Introduction .......................................... 1 1.1 Specification of Requirements ................... 1 1.2 Terminology ..................................... 1 2. New LCP Configuration Option - Link Discriminator ..... 2 3. BACP Packet Format .................................... 3 4. BACP Configuration Options ............................ 3 4.1 Datagrams-Supported ............................. 4 4.2 Base-Phone-Number ............................... 5 5. BAP Overview .......................................... 6 5.1 Link Management ................................. 6 5.2 Bandwidth Management ............................ 6 6. BAP Packets ........................................... 8 6.1 BAP Datagram Format ............................. 9 6.1.1 Call-Request .................................... 11 6.1.2 Call-Response ................................... 11 6.1.3 Callback-Request ................................ 12 6.1.4 Callback-Response ............................... 12 6.1.5 Link-Drop-Request ............................... 12 6.1.6 Link-Drop-Response .............................. 13 6.1.7 Link-Drop-Query-Request ......................... 13 6.1.8 Link-Drop-Query-Response ........................ 13 6.1.9 Bundle-Drop-Request ............................. 13 6.1.10 Bundle-Drop-Response ............................ 14 6.1.11 Link-Type-Request ............................... 14 6.1.12 Link-Type-Response .............................. 14 6.1.13 Available-Link-Indication ....................... 14 6.1.14 Available-Link-Response ......................... 15 6.1.15 Call-Failure-Indication ......................... 15 6.1.16 Call-Failure-Response ........................... 15 7. BAP Datagram Options .................................. 15 7.1 Link-Type ....................................... 16 7.2 Link-Types ...................................... 17 7.3 Phone-Number .................................... 18 7.3.1 Phone-Number Sub-Options ........................ 19 7.4 No-Phone-Number-Needed .......................... 20 7.5 Call-Add-Code ................................... 21 7.6 Nak-Code ........................................ 22 7.7 Drop-Code ....................................... 23 7.8 Call-Failure-Code ............................... 24 Richards & Smith expires July 1996 [Page ii] INTERNET DRAFT PPP BACP January 1996 7.9 Time-Until-Retry ................................ 26 7.10 Link-Discriminator .............................. 27 Appendix - List of BAP datagrams and associated options ...... 28 ACKNOWLEDEMENTS .............................................. 28 SECURITY CONSIDERATIONS ...................................... 29 REFERENCES ................................................... 29 CHAIR'S ADDRESS .............................................. 29 EDITORS'S ADDRESSES .......................................... 29 Richards & Smith expires July 1996 [Page iii]