Significance of ":23" on ISDN PRI interfaces

Significance of ":23" on ISDN PRI interfaces

Post by Keith » Thu, 16 Aug 2001 11:58:33



I realize that a PRI circuit contains 23B+1D channels. When
configuring this type of interface on a router, I believe the serial
interface is generated after configuring the "pri-group timeslots
1-24" command (i.e. under controller T1 1/0). So, the following
interface is now available for configuration
"interface Serial1/0:23". I know that the ":23" is the D channel, but
is this representation only to signify that this serial interface is
indeed a PRI.

Although I know it works, it looks misleading when you see an IP
address configured for "int s1/0:23" when in essence it's the D
channel. You see this when there is typically only one dialer profile
configured in contrast to multiple "int DialerX" interfaces used with
dialer pools.

Just curious,
Keith

 
 
 

Significance of ":23" on ISDN PRI interfaces

Post by Ian » Fri, 17 Aug 2001 04:47:28



Quote:> I realize that a PRI circuit contains 23B+1D channels. When
> configuring this type of interface on a router, I believe the serial
> interface is generated after configuring the "pri-group timeslots
> 1-24" command (i.e. under controller T1 1/0). So, the following
> interface is now available for configuration
> "interface Serial1/0:23". I know that the ":23" is the D channel, but
> is this representation only to signify that this serial interface is
> indeed a PRI.

> Although I know it works, it looks misleading when you see an IP
> address configured for "int s1/0:23" when in essence it's the D
> channel. You see this when there is typically only one dialer profile
> configured in contrast to multiple "int DialerX" interfaces used with
> dialer pools.

> Just curious,
> Keith

Keith,

ISDN PRI is delivered to you over a channelised T1 in north America, or
channelised E1 most other places.  You must tell your serial controller to
divide timeslots into channels on this line, and this then lets you set up a
serial sub-interface for each.  One of these is the D-channel, the rest are
B-channels.  The B-ch sub-i/fs inherit the properties of the D-ch sub-i/f so
this is the only one you need to configure, and the only one that shows up
in configs.

Making sure you've got the right timeslot (channel) for the D-ch is
important, ie 'int sX/Y:23' for a T1, or 'int sX/Y:15' for an E1.

HTH,
Ian
--


 
 
 

Significance of ":23" on ISDN PRI interfaces

Post by Aaron Leona » Wed, 22 Aug 2001 09:18:34


~ I realize that a PRI circuit contains 23B+1D channels. When
~ configuring this type of interface on a router, I believe the serial
~ interface is generated after configuring the "pri-group timeslots
~ 1-24" command (i.e. under controller T1 1/0). So, the following
~ interface is now available for configuration
~ "interface Serial1/0:23". I know that the ":23" is the D channel, but
~ is this representation only to signify that this serial interface is
~ indeed a PRI.
~
~ Although I know it works, it looks misleading when you see an IP
~ address configured for "int s1/0:23" when in essence it's the D
~ channel. You see this when there is typically only one dialer profile
~ configured in contrast to multiple "int DialerX" interfaces used with
~ dialer pools.
~
~ Just curious,
~ Keith

Your curiosity is perspicacious.  Indeed, the semantics of our ISDN
D channel interfaces are rather recondite, and have confused even
some of our development engineers.

SOME commands that are entered on the D channel interface are
actually applicable to the D channel itself, and not to the
applications running on the B channels.  For the most part,
these commands are prefixed with "isdn".

But MOST of the commands on the D channel interface are NOT
applicable to the D channel.  Rather, the D channel interface
is used as a kind of legacy dialer (a la "dialer rotary-group")
via which the sync data calls are configured.  For example,
"encapsulation ppp" on the D channel doesn't actually mean
that PPP is used on the D channel (which would be absurd as
D channels always use LAP-D encapsulation), but rather that
the *B* channels would use PPP.

Aaron