Subject: A Single DLSw Switch

From: [email-masked] (Dan Profant)
Date: Wed, 14 Jul 93 19:28:35 PDT

In my review of the "Data Link Switching: Switch-to-Switch Protocol" RFC,
I was able to recognize but one reference to the use of a DLS by itself.

"
3.0 Transport Connection

Data Link Switches can be used in pairs or by themselves.  A Single
DLS internally switches one data link to another without using TCP
(DLC(1) to DLC(2) in the figure below).

    ____________________________________________________ 
   |                                                   |
   |   _____________  DLC Request       ______________ |
   |   | Data Link |<-------------------|            | |  Send
   |   |  Control  |    DLC Indication  |            | |SSP Frame
   |   |    (1)    |------------------->|            | |========>
   |   -------------                    |  Data Link | |
   |                                    |   Switch   | |
   |   _____________  DLC Request       |            | | Receive
   |   | Data Link |<-------------------|            | |SSP Frame
   |   |  Control  |    DLC Indication  |            | |<========
   |   |    (2)    |------------------->|            | | 
   |   -------------                    |            | | 
   |                                    -------------- |
   |                           Multi-protocol Router   |
   |___________________________________________________|

"
 
There seems to be no other reference to this facility.  I presume that the
packet entering the router would be through a LAN port and should not 
be presented to the DLS, if indeed the destination is not across the WAN; but 
should be routed/bridged approriately out another LAN port.   
 
The value of the DLS seems to be only when paired across the WAN.  What 
am I missing?

Hope someone can help.. 
Dan Profant
[email-masked]

---

From: [email-masked]
Date: Wed, 14 Jul 93 20:10:54 PDT

Dan -

    I think the facility you are referring to would primarily apply to
    converting between LLC2 and SDLC on the same router.  In this case,
    DLSw probably is necessary.  As you point out, perhaps it is also
    used for doing local source route bridging but there are probably
    better ways of doing this instead of using DLSw.

    Maybe someone from IBM can shed some light on this?

Regards,
-----------
Wayne Clark
cisco Systems, Inc.
[email-masked]
415/688-4627

---

From: "Shannon Nix" <[email-masked]>
Date: Thu, 15 Jul 93 09:26:14 EST

>I was able to recognize but one reference to the use of a DLS by itself.
..
>The value of the DLS seems to be only when paired across the WAN.  What 

Local data link switching can provide the following advantages:

1.  Termination of data links which affords:
    a.  A "pipe-lining" effect
    b.  Reduced hop-count limitations
    c.  Reduced sensitivity to timeouts

2.  Data link conversion for unlike local media

3.  Broadcast firewalls for NetBIOS

4.  Segmentation of large, bridged, local subnets

5.  A common means of switching data whether the destination is local or
    across the WAN.

>[email-masked]

Hope this helps,
Shannon
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