There are two different issues here that people tend to get confused
about. Remember the OSI 7-layer model, particularly the lower two layers?
OK. Physical layer. The clocking on the wire is a physical-layer
function. If you have a back-to-back cable between 2 routers (no csu/dsu),
then one needs to take teh place of the csu/dsu with respect to providing
clocking on the wire. That would be the router with the DCE end of the
cable attached. That's where you put the "clock rate" statement.
Let's move up to layer two, the data-link layer. The data link layer has
no awareness of how that cable works or who is providing clock. This is
where frame relay lives. So, if frame relay has no awareness of clock
rate, which implies physical-layer DCE/DTE issues, it stands to reason
that the frame-relay DCE function can be assigned to either of the router
interfaces attached to a back-to-back cable. And indeed, this is the
case.
Frame relay user-to-network interface has a "user" side and a
"network" side. The "network" side (where the "cloud," or the
frame-relay switch, would normally be) has the frame-relay DCE function to
perform in terms of LMI. What you're saying with the "frame-relay
intf-type dce" statement is, "this interface is on the network side of
this UNI connection and needs to perform LMI functions just as a switch
would. I am expecting the device connected to me to act as a router (user
side)."
So, to sum up, if you have a back-to-back serial cable connection between
two routers, the "clock rate" statment MUST go on the interface where the
DCE side of the cable is attached. If you are using frame-relay
encapsulation with one router acting as a frame-relay switch, the
"frame-relay intf-type dce" statment MUST be on the switch interface. The
frame-relay and physical-layer DCE functions do not relate to each other
in any way.
Pamela
On Thu, 15 Mar 2001, Bob Timmons wrote:
> If you're using a back-to-back cable, the DCE will ALWAYS be the router with
> the DCE side
> of the cable. If you're doing frame-relay, and using 1 router to be the
> frame-relay switch, you'd
> typically use the DCE side of the back-to-back on the frame-switch for all
> routers connected
> to the frame-relay switch. You would then set your desired clock rate on
> each serial interface.
>
> ""sanjay"" <[EMAIL PROTECTED]> wrote in message
> 96ibeu$3f1$[EMAIL PROTECTED]">news:96ibeu$3f1$[EMAIL PROTECTED]...
> > On the frame-relay switch router, just make sure you specify "frame-relay
> > intf-type dce" command. On point to point serial connection between 2
> > routers, you will need to setup clock rate on one of the routers. Which
> ever
> > router you put the clock rate, it becomes the DCE.
> >
> >
> > ""CiScO"" <[EMAIL PROTECTED]> wrote in message
> > 96i57s$bpl$[EMAIL PROTECTED]">news:96i57s$bpl$[EMAIL PROTECTED]...
> > > Do I need to config the serial as a DCE or does it automatically become
> a
> > > DCE when I specify a clock rate?
> > >
> > > Will this type of connection work even if I'm not running Frame Relay,
> for
> > > instance setting up OSPF single area or multiple area, using ppp encap?
> > >
> > > Thanks!
> > >
> > >
> > > ""John Neiberger"" <[EMAIL PROTECTED]> wrote in message
> > > sa8c04a1.091@fsutil01">news:sa8c04a1.091@fsutil01...
> > > > Each serial link needs to have some sort of clocking at the physical
> > > > layer, regardless of your choice of datalink layer protocol. In
> > > > addition, each serial link is entirely separate from the others and
> can
> > > > have differing clockrates.
> > > >
> > > > Be sure that you set your clockrate on the DCE side only. The DTE
> side
> > > > does not need to be specified because it is, by definition, listening
> to
> > > > the clock from the DCE.
> > > >
> > > > >>> "." <[EMAIL PROTECTED]> 2/15/01 4:09:37 PM >>>
> > > > DCE to DTE no CSU/DSUs
> > > >
> > > > If I connect my routers via serial interfaces using a crossover serial
> > > > cable
> > > > , do I need to set a clock rate even if I'm running fame relay? If I
> do
> > > > need
> > > > to use a clock rate do all the routers need to be set for the same
> > > > clock
> > > > rate?
> > > >
> > > > Thanks!
> > > >
> > > >
> > > > _________________________________
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