vaf@Valinor.Stanford.EDU (Vince Fuller) (01/24/91)
Has anyone tried testing the cisco gateway synchronous PPP implementation against that done for the Sun by Torben Nielsen? We (Sun and BARRNet) have found that the two interoperate without problem using 56KB lines but do not work at all using a T-1 line. When we tried connecting the two over a T-1 line, the Sun end sees a CRC error for every packet that the cisco sends while the cisco sees nothing in return. Can someone describe the T1 PPP framing used by the cisco implementation? Any hints or suggestions would be appreciated. Thanks, --Vince
forster@cisco.com (Jim Forster) (01/24/91)
Vince,
We put the same bits out on the V.35 or RS-449 line no matter what the
speed. We neither off nor accept options. Given that it works at 56k but
not T-1, possibilities that come to mind (which you've probably tried but
which are worth repeating) are:
- CSU/DSU configuration: 1.54 vs. 1.35 mb/sec, inverted/non-inverted
data, SCTE signal usage
- V.35 cable length
- twisted pair cable length & twists per foot
- run through the various loop back modes
- cisco sending packets too quickly together. Unlikely if not
impossible during LCP bringup, but can be ruled out by
slowing us down with the "transmitter delay" command.
I hope someone with more Digital Telecom expertise will correct me or
add on.
Have fun and good luck!
-- Jimmelohn@eng.sun.com (Bill Melohn) (01/24/91)
What size CRC does the Cisco interface use at T1 speeds? The default for the Sun HSI interface is 32 bits, but this can be configured. If this were the problem though, we would have A) expected reconfiguring the Sun side to solve the problem [it didn't] and B) we would have expected the Cisco to notice the incoming packets and count them as CRC errors (or something) as well.
vaf@Valinor.Stanford.EDU (Vince Fuller) (01/25/91)
Jim, Does the cisco PPP implementation put raw PPP packets out onto the T-1? I believe (and Bill Melohn can correct me if I'm mistaken) that the Sun PPP implementation puts HDLC framing around the PPP packets. Bill - can you tell me if this is done for both the T1/RS449 and 56KB/RS232 Sun synchronous interfaces? The fact that things work using 56KB/RS232 but not with T1/RS449 implies that the encapsulations may be different. Thanks, --Vince
melohn@eng.sun.com (Bill Melohn) (01/25/91)
PPP is defined as having HDLC framing (no LAPB) surrounding the data portion of each packet. The HDLC should be identical between the various Sun communications processors, since they interoperate.
forster@cisco.com (Jim Forster) (01/25/91)
The PPP spec for synchronous mode calls for PPP packets to be put in an HDLC frame. We always use a 16-bit CRC. Bill mentioned that the Sun T-1 rate card defaults to 32-bit CRC, so this should be adjusted, although I agree with him that a mismatch on 16 vs. 32 bit CRC's should show up as both systems seeing only CRC errors. -- Jim