The information in this article applies to:
SYMPTOMS
When two sites are connected by a T1 wide area network (WAN) link, you may be unable to map a drive or gain access to resources across the WAN. In some cases, Windows NT Server-based or Windows NT Workstation-based computers in the workgroup may be unable to join the domain.
CAUSEThis behavior occurs because the telephone company has improperly configured the coding for the T1 circuit at the Channel Switching Unit (CSU). RESOLUTIONTo resolve this problem, contact the telephone company to test the T1 line and correct the configuration settings. MORE INFORMATION
It is important to match the input signal line code with the line code characteristics of the transmission path.
Not all equipment in a B8ZS circuit injects a B8ZS code. For example, line repeaters typically do not enforce the B8ZS code and simply pass whatever signal they receive. Because of the difference in consecutive zeros, a pattern may not be successful if the test point is on the "span side" using AMI encoding, but is successful if transmitted from a central office or end point where B8ZS is used. This situation indicates that the circuit probably works for customer traffic as long as the B8ZS encoding is maintained. However, the circuit is marginal and is not suitable for AMI encoding. B8ZS is bipolar AMI with a difference. In bipolar AMI, 0 indicates no line signal and 1 indicates a positive or negative level, alternating for successive ones. Note that a long string of zeros results in a constant signal. With B8ZS, if eight zeros occur in the message and the last pulse is positive, the eight zeros are encoded as 000+-0-+. If eight zeros occur in the message and the last pulse is negative, the eight zeros are encoded as 000-+0+-. Normally, the difference between base-band coding prevents any application layer protocol from functioning properly. Problems arise because AMI and B8ZS are so similar. AMI code may lose synchronization during a long string of zeros. This behavior does not occur, using the new rules for B8ZS. Ping.exe works across a T1 connection because it pads the Internet Control Message Protocol (ICMP) 32-byte data field with alphabetic characters. No packet sent across a T1 connection contains a string of eight zeros. Tracert.exe pads the ICMP 64-byte data field with all zeros. Packets sent across a T1 connection do contain a string of eight zeros, which invokes the B8ZS code. If equipment is not configured to invoke the B8ZS code, the transmission is not successful. Additional query words:
Keywords : kbnetwork |
Last Reviewed: January 25, 2000 © 2000 Microsoft Corporation. All rights reserved. Terms of Use. |