Asynchronous Transfer Mode
Asynchronous Transfer Mode |
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Sometimes you establish a PVC or series of PVCs (as described in "IP over ATM" earlier in this chapter) and then discover that the PVC is not forwarding cells from one endpoint to another as expected. The roots of the problem can be diagnosed by comparing the results of ATMADM -C and ATMADM -A.
The ATMADM -A utility shows the UNI address of the ATM adapter negotiated with the switch and proofs the UNI connection.
ATMADM -C shows the addresses of both inbound and outbound calls. It also shows the attributes for SVC point-to-point and point to multipoint calls. However, in the case of PVCs, ATMADM -C shows an inbound PVC with an assigned path and channel — but without an address. ATMADM -C shows no address because no call is made to establish a PVC. To establish the connection, the UNI simply opens the PVC. The UNI attributes of the connection — including the VPI/VCI values, and the inbound and outbound bit rates — are established on the switch as part of the signaling and VP/VC setup. Once a PVC connection has been established, it remains active at the UNI level even if information is not passing through it.
Figure 14.26 shows a sample ATMADM -C result for a working PVC connection:
D:\>atmadm c
Windows ATM Call Manager Statistics
ATM Connections on Interface : Interphase 5525/5575 PCI ATM Adapter
Connection VPI/VCI Remote Address/
Media Parameters (rates in bytes/sec)
In P-P PVC 0/51 Tx: UBR, Peak 16932864, Avg 16932864, MaxSdu 9188
Rx: UBR, Peak 16932864, Avg 16932864, MaxSdu 9188
Note
The sample shown in Figure 14.26 is at full bandwidth and settings for an ATM ARP client over PVCs with no shaping as an example. Establishing traffic shaping through QoS levels at the switch can provide different up and down transmission rates, or it can lower bandwidth per VC to a much lower level than the overall bandwidth of the connection.
If ATMADM -C shows no connection but ATMADM -A and -S look okay, check your PVC settings in ATMUNI. You can do this by going to the Control Panel to the Network Connections and Local Area Connections windows; compare the values you see there for the PVC settings with the switch PVC settings. If these two VP and VC pair does not match exactly, no PVC connection can be made.
If ATMADM -A returns no address then the UNI has not established a link. If ATMADM -S is negative then the problem is probably a connection issue.
ATMADM -A results in a printout of the ATM address acquired from the switch (ILMI interaction) which is composed of 20 bytes of info. The first thirteen bytes are the switch address, the next six are the MAC address of the adapter and the last two are the selector bytes. Acquiring the address proves that you have interaction at the UNI level with the switch.
If ATMADM -A does not provide an ATM address but the ATMADM utility itself does not return an error in its output, this indicates that the utility program could not contact the call manager. The next step in this case is to dig a little deeper using ATMADM -S. In particular, study the last two figures from the ATMADM -S report, which describe transmission and reception. If only transmit is working, the adapter is up but has either no connection or only a half duplex connection. This indicates that the system has been wired improperly. Check whether the system is wired with the wrong cable (Ethernet twist instead of straight through, for instance), whether a length of bad fiber is fouling up the transmission medium, or whether some other instance of reversed polarity is plaguing the wiring. To correct the problem, check the cable type, seating, and connection.
If both transmission and reception figures are incrementing but you have no address is returned, the system is suffering from one of two possible problems: either ILMI has been disabled at the switch or the switch is running in UNI 3.0. In either case, the solution is to check the switch configuration.
If ATMADM -A indicates that you have an address and ATMADM -S indicates that ILMI is working, the next place to look is still in ATMADM -S report. In particular, check for unsuccessful outgoing calls. In LANE unsuccessful calls generally mean that the LEC cannot contact the LECS by VPI/VPI or by the well-known address — the repeated attempts to do so increment the outgoing calls.
There are several possible suspects for any failure to connect the outgoing call: LANE is not running on the switch, the switch has nodefault ELAN on the switch, or the ELAN name specified in the ATM LAN Emulation Client Properties dialog box does not exist. The last of these problems generates a warning in the event log.
IP over ATM indications are approximately the same. From the IP over ATM client side, failed calls generally mean that there is no IP over ATM Server at the ATM address you are trying to call. If this is true for IP over ATM Server, it is possible that the switch you are connected to is an early UNI 3.1 version and does not allow you to register two addresses on the same connection. In this case, you must use the actual ATM address of the server for the server's onboard client and disseminate it to all the clients you plan to connect.