How Remote Access Service Processes Datagram Traffic

• March Release of Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Server version 4.0
• Microsoft Windows NT Workstation version 4.0

SUMMARY

This article discusses how Remote Access Service (RAS) uses datagrams under Windows NT. The article is divided into the following subjects:

• Remote RAS Workstation Posts NCB_Add_Group_Name



• LAN System Sends a Burst of Multicast Datagrams to a Group Name



• RAS Client Sends a Datagram



• Remote RAS Workstation Posts NCB_Add_Name



• LAN System Sends a Datagram to a Unique RAS Client Name

Remote RAS Workstation Posts NCB_Add_Group_Name

1. The RAS server checks to see if the group name registered locally already.
   
   
   • If the name is already registered (because another workstation has posted NCB_Add_Group_Name), the RAS server flags the name as registered and does not post NCB_Receive_Datagram.
   
   
   
   • Otherwise, the group name is not registered and the following steps are performed.
   
   
   



2. The RAS server posts NCB_Add_Group_Name on all available transports (NBF, TCP/IP, etc.).
   
   
   • MaxNames for RAS: There must be enough names to accommodate all the remote clients add request. The default is 255 (the maximum) which should leave plenty of room.
   
   
   
   • MaxNames for transport: Each transport has a MaxNames entry that may need tuning. It should be set high enough to handle all of the local server names plus all of the remote client NetBIOS names. The NBF transport can be configured in Control Panel using the "Maximize Throughput and Connections" setting. This allows names and sessions to be tuned high without any realistic limit. See the Windows NT documentation for information on default names in the section covering RemoteListen.
   
   
   
   • If NCB_Add_Group_Name fails on any transport because another system responds with an AddNameResponse frame (meaning that another system has the group name registered as a unique name), then the group is not added on the server or the client workstation.
   
   
   



3. The RAS server posts RcvDgSubmittedperGroupName number of NCB_Receive_Datagrams for the group name.
   
   
   • This has nothing to do with how many NCB_Receive_Datagrams are posted by the remote client. This is handled by the server only. When a client posts NCB_Add_Group_Name or NCB_Add_Name, the RAS server automatically posts NCB_Receive_Datagram for each name, regardless of what the client posts (even if the client does not post anything).
   
   
   
   • RcvDgSubmittedperGroupName controls how many NCB_Receive_Datagrams are posted by the server for each group name. This is a resource- intensive parameter. Each one takes 1.5K of physical RAM. As soon as one is completed the server automatically posts a new one.
   
   
   

LAN System Sends a Burst of Multicast Datagrams to a Group Name

1. Check EnableBroadcast. Default is 0, disabled. (This datagram is not broadcast in example.)
   
   

   
       0 Yes. Drop broadcast (not multicast) datagram and do not forward
         to remote clients.
   
       1 No. Continue. 




2. Check MulticastForwardRate. Default is 5.
   
   

   
      -1 Drop datagram. Do not forward any broadcast or multicast. This
         setting is useful to filter out LAN Manager server announcements
         that use multicast datagrams for domain group names. If you
         have a large LAN Manager network with many servers, this can use
         up asynchronous bandwidth.
   
       0 Guarantees delivery of datagram to client.
   
      >0 (1 to 32767) Works as a gate. After the designated number of
         seconds, the gate opens and all datagrams arriving at the server
         are forwarded to remote clients. When the gate is closed, all
         datagrams are dropped.
   
      NOTE: This parameter is useful for reducing LAN Manager server
      announcement traffic. On a large network, all the server
      announcements can look like a steady stream of data flowing over
      the asynchronous line. 




3. Check DisableMcastFwdWhenSessionTraffic. Default is 1, enabled.
   
   

   
       1 When a client is busy transferring data during a session (a file
         copy, for example), multicast datagrams are dropped.
   
      -1 Broadcast datagrams are dropped even if EnableBroadcast is set
         to 1.
   
       0 Datagrams are always forwarded. This may slow session traffic. 

1. Check MaxDgBufferedPerGroupName. Default is 10.
   
   Because of the difference between the LAN speed and the asynchronous line speed, datagram traffic must be buffered. The maximum number of datagrams that the RAS server can buffer per group name is controlled by MaxDgBufferedPerGroupName. In the default (10) is used, every 11th datagram is dropped. The maximum is 255. This is a virtual memory parameter, so it is a relatively minor drain on system resources.



2. The RAS server checks to see which clients have the group name registered. It then multiplexes the datagram to each of these remote clients. RAS clients that have NCB_Receive_Datagram posted for that group name receive the datagram.

RAS Client Sends a Datagram

1 All datagrams sent by remote clients are forwarded onto all transports. The default is all valid networks.

0 Datagrams can only be received by the RAS server if it has an NCB_Receive_Datagram posted for the given name.

Remote RAS Workstation Posts NCB_Add_Name

1. The RAS server posts NCB_Add_Group_Name on all available transports (NBF, TCP/IP, etc.).
   
   
   • MaxNames for RAS: There must be enough names to accommodate all the remote clients add request. The default is 255 (the maximum) which should leave plenty of room.
   
   
   
   • MaxNames for transport: Each transport has a MaxNames entry that may need tuning. It should be set high enough to handle all of the local server names plus all of the remote client NetBIOS names. The NBF transport can be configured in Control Panel using the "Maximize Throughput and Connections" setting. This allows names and sessions to be tuned high without any realistic limit. See the Windows NT documentation for information on default names in the section covering RemoteListen.
   
   
   
   • If NCB_Add_Group_Name fails on any transport because another system responds with an AddNameResponse frame (meaning that another system has the group name registered as a unique name), then the group is not added on the server or the client workstation.
   
   
   



2. The RAS server posts RcvDgSubmittedperGroupName number of NCB_Receive_Datagrams for that unique name. This has nothing to do with how many NCB_Receive_Datagrams are posted by the remote client. This is handled by the server only. When a client posts NCB_Add_Group_Name or NCB_Add_Name. the RAS server automatically posts NCB_Receive_Datagram for each name regardless of what the client posts (even if the client does not post anything).

LAN System Sends a Datagram to a Unique RAS Client Name

1. The RAS Server receives the datagram, and places it in a buffer. (There is no parameter to control this buffer: all datagrams are buffered.)



2. A new NCB_Receive_Datagram is posted on the server.



3. The RAS Server forwards the datagram from the buffer to the remote client with the unique name posted.
   
   NOTE: Unique name datagrams take priority over group name datagrams. They are forwarded to the client before pending group datagrams. NET LOGON uses unique name, directed datagrams that are given priority over group datagrams.

Reference(s):

Additional query words: prodnt advanced server serial comm modem

Keywords : kbnetwork ntras ntnetserv NTSrvWkst
Version : 3.1 4.0
Platform : winnt
Issue type :