Termination causes
The Value field is four octets, containing an integer specifying
the cause of session termination, as follows:
1 User
Request
2 Lost Carrier
3 Lost Service
4 Idle Timeout
5 Session Timeout
6 Admin Reset
7 Admin Reboot
8 Port Error
9 NAS Error
10 NAS Request
11 NAS Reboot
12 Port Unneeded
13 Port Preempted
14 Port Suspended
15 Service Unavailable
16 Callback
17 User Error
18 Host Request
The termination causes are as follows:
User Request---------------------- User requested termination of service, for
example with LCP Terminate or by logging out.
Lost Carrier---------------DCD was dropped on the port.
Lost Service---------------Service can no longer be provided; for example, user's connection to a host was interrupted.
Idle Timeout---------------Idle timer expired.
Session Timeout-------------------Maximum session length timer expired.
Admin Reset----------------------Administrator reset the port or session.
Admin Reboot--------------------Administrator is ending service on the NAS, for
example prior to rebooting the NAS.
Port Error------------------------NAS detected an error on the port which required
ending the session.
NAS Error------------------------NAS detected some error (other than on the port)
which required ending the session.
NAS Request----------------------NAS ended session for a non-error reason not
otherwise listed here.
NAS Reboot----------------------The NAS ended the session in order to reboot
non-administratively ("crash").
Port Unneeded----------------------NAS ended session because resource usage fell
below low-water mark (for example, if a bandwidth-on-demand algorithm decided that
the port was no longer needed).
Port Preempted----------------------NAS ended session in order to allocate the
port to a higher priority use.
Port Suspended---------------------NAS ended session to suspend a virtual session.
Service Unavailable------------------NAS was unable to provide requested service.
Callback----------------------------NAS is terminating current session in order
to perform callback for a new session.
User Error-------------------------Input from user is in error, causing
termination of session.
Host Request-----------------------Login Host terminated session normally.
PPP intiation sessions are of 2 phases
1. LCP Link Control Protocol
2. NCP Network Control Protocol
LCP as the first phase protcol during PPP connection initialization, it takes care of
configuration parameters such as negotiating authentication, link speed, stop bit,
etc...then it terminates leaving it to the NCP.
NCP as the second phase protocol takes care of the L3 Network Layer protcol related
stuffs like getting an ip address from the DHCP server for the dialing host etc...Note
you also got IPX on this layer3....IP here is called as IPCP which uses the DNS & WINS
services.
DTR, DSR and DCD
If the voltage on pin 20 drops, it tells the modem that the computer is unable to
transmission, perhaps because it is down. The modem will hang up the phone if a call
is in progress. If the voltage on pin 8 drops, it tells the computer that the modem no
longer has a connection. In both cases, these pins give a simple yes/no report on the
state of the transmission. This form of handshaking is sometimes referred to as modem
control.
There is a further level of handshaking that is used to control the rate of data
transmission. When transmitting large amounts of data at high speed, it is possible
that one end of a link may try to send data faster than the other can receive it. To
keep this from happening, there is a flow-control handshake that allows either end to
prevent the other from sending any more data until it gets the go-ahead.
When a DTE device is ready to send data, it asserts pin 4 (Request to Send or RTS). If
the DCE is ready to receive it, it gives the go ahead by asserting pin 5 (Clear to
Send or CTS). Data transmission then begins. If the voltage on CTS drops at any time,
this tells the sending system that the receiver isn?t ready for more data. Since this
flow control handshake is implemented in the serial port hardware, it is considerably
more efficient and reliable than the CTRL S/CTRL Q (XON/XOFF) handshake that can be
performed in software.
If both types of handshaking are used, the entire conversation between computer and
modem might look like this (where a plus sign signifies raising the voltage on the
line, and a minus sign signifies dropping the voltage):
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