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Link management
options define how PPP establishes, maintains and monitors a communications
link. These factors, and the condition of the link, help PPP decide
when to bring a link up and down in situations other than on-demand
dialups. Active vs. Passive PPP Negotiations | |
HP-UX
PPP, like most PPP implementations, expects to actively initiate
the negotiation process. By default, when a line is connected, pppd
immediately sends PPP messages, anticipating that a PPP implementation
on the other end is ready to negotiate. In auto mode, this directly
follows completion of a Systems chat script login procedure. When
pppd is not in auto mode, messages
are sent when the daemon starts. The default behavior works correctly in almost all situations.
However, sometimes it is better to let the other end send its messages
first when calling another system's dial-up modem. A few PPP implementations
get confused when a peer speaks first and negotiations may be slow
if both ends are active. In these situations, assign pppd
the passive option. The passive option makes pppd
wait until the other end communicates before it sends messages. This is an example of the pppd
command line for outbound passive connection: pppd hostname:peer auto passive |
When a PPP implementation that gets confused by the other
end's active negotiations dials an HP-UX PPP system, it would be
wise to make the calling pppd passive
if possible. However, if it is not possible, negotiations may proceed
faster if the Login script invokes
the passive option on the receiving pppd. Idle Timer Link Control | |
The idle option allows you to limit
the number of seconds that can pass without receiving or transmitting
the type of packets specified in the filter file's keepup field.
The timer shuts down the link when the specified number of seconds
elapse. The idle option works on both the calling and the answering
pppd. If both have the idle option
set, the end that specifies the shorter interval shuts down the
line first. The default is to never shut down the link. Do not invoke the idle option when pppd
is talking to a system that runs PPP software that does not implement
on-demand auto-dialing. The session may not stay intact if the
link is taken down by the idle timer. These systems include those
running most free PPP implementations, or MS-DOS PCs running FTP
Software's PC/TCP. Setting Idle Timer ValuesThe two criteria for determining idle timer values are: the cost of maintaining a connection the scarcity of resources
Limits for Outbound CallsSet a relatively brief idle timeout for the system placing
a call if the connection costs per minute, for example, a long-distance
telephone call. On the other hand, if the telephone billing scheme
is based on the number of calls rather than duration, set a longer
idle timer (or none at all), on the calling system's pppd.
Keep in mind that it can take 25 seconds or more to allocate a
modem, dial out, complete the call, login to the remote system,
and negotiate PPP connectivity. The minimum idle timer setting
should be 30 seconds to accommodate the connection and negotiations.
All ABORT and TIMEOUT strings must be written with the same thought
in mind. Set a relatively brief timeout for an answering system if
it has too few modems to accommodate a large number of incoming
connections. The answering system might also benefit from a shorter
idle timeout value if it acts as a hub and provides its services
via a toll-free WATS (800) number. On the other hand, if it provides
its services via a 976 or 900 number scheme, you may not want to
specify any timeout interval since each unit of connection time
increases the answering system's revenue. |
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