User`s guide

XSR User’s Guide 109
Chapter 6 PPP Features
Configuring PPP
IP Address Assignment
In PPP, IPCP configuration option type 3 corresponds to IP address
negotiation. This configuration option provides a way to negotiate the IP
address to be used on the local end of the link.
It allows the sender of the Configure-Request to state which IP address is
desired, or to request that the peer provide the information. The peer can do
this by NAKing the option, and returning a valid IP address. If the host wants
the peer to provide the IP address, it will mark the IP address field as
configuration option 0.
Upon receiving an IP-address Configure-Request with IP address field 0,
IPCP may allocate a valid IP address to the peer by sending a Configure-Nak
to the received Configure-Request or it may reject the Configure-Request.
PPP Bandwidth Allocation/Control Protocols (BAP/BAPC)
The XSR supports the PPP Bandwidth Allocation/Control protocols
(BAP/BACP) as a means of managing individual links of a multilink bundle
as well as specifying which peer is responsible for managing bandwidth
during a multilink connection.
This ability to dynamically change bandwidth during a multilink connection is
referred to as Bandwidth-on-Demand (BoD). For more information on BoD,
refer to “Configuring Integrated Services Digital Network (ISDN)” on
page 187 and “Configuring Dialer Services” on page 135.
BAP/BACP, as defined by RFC-2125, is a flexible, robust method of managing
bandwidth between two peers. BAP does this by defining Call-Control
packets and a protocol that allows peers to co-ordinate actual bandwidth
allocation and de-allocation. Phone number values may be passed in the Call-
Control packets to minimize user configuration.
BAP/BACP provides the following benefits:
 Allows multilink implementations to interoperate by providing call
control through the use of link types, speeds, and telephone numbers.
 Controls thrashing caused by frequent raising/tearing down links.
 Ensures that both ends of a link are told when links are
added/dropped from a multilink bundle.