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DLSw+ performance adequate on DSL?

 
 
Doug Simpson
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      10-19-2004
We have a brand new MPLS VPN network from a major provider. We then
resell these VPNs (VRFs) to our customers.

We are considering rolling out 300 to 600 legacy SNA/SDLC sites via
DLSw+ over MPLS/IP. Provider would manage the entire package,
including both core and edge DLSw+ peer routers. A single MPLS VPN
(VRF) would be used for the entire DLSw+ network. In all that
follows, therefore, just read "MPLS" as "IP."

To speed this migration, we are considering using a null modem serial
cable to connect the edge router directly to the IBM controller at
each site. This is an interim step to be followed by slower-paced
conversion to IP LAN at each site.

Most customers at these sites are poor government agencies who are
salivating at the lower cost and higher bandwidth of DSL. Most
agencies care less about SLA than price/bandwidth. No doubt they will
change their tune at trouble-time.

Provider is recommending against DSL for DLSw+ because of latency and
reliability concerns. They also mentioned the tendency of some
provider's DSL to timeout during zero traffic conditions. Provider
says this might cause chronic DLSw+ session drops, though I would
think that DLSw+ hello packets would prevent zero traffic conditions.

Provider is concerned about sites that might limp along with existing
but poor SNA service because of DLSw+ session issues. Stealth
troubles are indeed bad news and we want to make sure we avoid them.

Provider recommends a 64K frame circuit to each site. Frame is a
comfort factor for provider. DSL connection is at arm's length to
MPLS network, but frame comes straight into the provider's MPLS PE
router. Problem is that 64K is twice the cost and a fraction of the
bandwidth of DSL. 64K is ample for SNA traffic, but would need to be
increased with the advent of IP and real applications.

With sufficient testing and planning, can DSL serve as an adequate
transport for DLSw+ at the scale of 300 to 600 sites?

Options considered:

o Limit DSL to native IP (tn3270).
Offer DLSw+ only on 64K frame circuits.

o Scale up DLSw+/DSL in careful, stepwise pilots.
Switch trouble sites to 64K frame.

Vendor uses a mix of Cisco and Juniper in the core and all Cisco at
the edge. All DLSw+ routers would be Cisco.

Advice and anecdotes are welcome!

Doug Simpson
Network Design Engineer
 
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stephen
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      10-19-2004
"Doug Simpson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> We have a brand new MPLS VPN network from a major provider. We then
> resell these VPNs (VRFs) to our customers.
>
> We are considering rolling out 300 to 600 legacy SNA/SDLC sites via
> DLSw+ over MPLS/IP. Provider would manage the entire package,
> including both core and edge DLSw+ peer routers. A single MPLS VPN
> (VRF) would be used for the entire DLSw+ network. In all that
> follows, therefore, just read "MPLS" as "IP."
>
> To speed this migration, we are considering using a null modem serial
> cable to connect the edge router directly to the IBM controller at
> each site. This is an interim step to be followed by slower-paced
> conversion to IP LAN at each site.
>
> Most customers at these sites are poor government agencies who are
> salivating at the lower cost and higher bandwidth of DSL. Most
> agencies care less about SLA than price/bandwidth. No doubt they will
> change their tune at trouble-time.
>
> Provider is recommending against DSL for DLSw+ because of latency and
> reliability concerns. They also mentioned the tendency of some
> provider's DSL to timeout during zero traffic conditions. Provider
> says this might cause chronic DLSw+ session drops, though I would
> think that DLSw+ hello packets would prevent zero traffic conditions.
>
> Provider is concerned about sites that might limp along with existing
> but poor SNA service because of DLSw+ session issues. Stealth
> troubles are indeed bad news and we want to make sure we avoid them.
>
> Provider recommends a 64K frame circuit to each site. Frame is a
> comfort factor for provider. DSL connection is at arm's length to
> MPLS network, but frame comes straight into the provider's MPLS PE
> router. Problem is that 64K is twice the cost and a fraction of the
> bandwidth of DSL. 64K is ample for SNA traffic, but would need to be
> increased with the advent of IP and real applications.


i have recently looked at a network using both frame and DSL where there is
DLSw / SDLC to a local device.

512k ADSL works better than Frame - the higher speed links lower
serialisation delay compensates for the latency through the DSL / ATM
network.

however this is private DSL - ADSL is used as an access line rather than for
an internet feed with IPsec style VPN.

most of the scaling issues seem to occur with central DLSw engines - use
some meaty routers here, allow for backups, and limit the number of peers.

email me offline if you want to discuss.

i strongly suggest you ask for QoS for the DSLw with either solution.
>
> With sufficient testing and planning, can DSL serve as an adequate
> transport for DLSw+ at the scale of 300 to 600 sites?


Yes - so long as the DSL is predictable and you control the traffic to some
extent.
>
> Options considered:
>
> o Limit DSL to native IP (tn3270).
> Offer DLSw+ only on 64K frame circuits.
>
> o Scale up DLSw+/DSL in careful, stepwise pilots.
> Switch trouble sites to 64K frame.


you may end up with some locations where you cant get ADSL, so you need a
backstop anyway.

>
> Vendor uses a mix of Cisco and Juniper in the core and all Cisco at
> the edge. All DLSw+ routers would be Cisco.
>
> Advice and anecdotes are welcome!
>
> Doug Simpson
> Network Design Engineer

--
Regards

Stephen Hope - return address needs fewer xxs


 
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