HP 3000 Manuals

COMMUNICATOR 3000/XL: XL REL. 2.2 (A.41.00)

DTC/X.25 XL Network Link Enhancement 

by Marlee Knight/Lorraine Bartlett--Information Networks Division 

PRODUCT OVERVIEW 

The DTC/X.25 XL Network Link is the HP strategic solution for HP 3000
Series 900 customers requiring access to public or private packet
switching networks.  The DTC/X.25 XL Network Link is composed of several
components, including HP OpenView DTC Manager, DTC/X.25 Network Access
and X.25 XL System Access.  X.25 XL System Access is an application
interface, which is necessary for system-to-system communication.  This
release provides an important enhancement to X.25 XL System Access, which
provides you with greater wide area network communication capabilities.


This release allows for the support of multiple DTC/X.25 cards per one
Internet Network Interface (NI) and one Protocol (IP) address for the
X.25 XL System Access.  This X.25 XL System Access enhancement provides
important benefits and features consisting of:

 *  Load Balancing
 *  Combination of Cards Supported per NI
 *  Increased Number of Virtual Circuits
 *  Increased Performance
 *  Redundancy

Load Balancing 

Load balancing can prevent a particular DTC/X.25 card from becoming a
bottleneck for X.25 networking.  There are two aspects of load balancing
to consider:  load balancing of outbound connections and load balancing
of inbound connections.

Outbound Connections 

The DTC/X.25 Network Access system software provides information to the
X.25 XL System Access software about the load of each DTC/X.25 card
configured for that system.  The algorithm to determine the load on a
DTC/X.25 card is based on the number of virtual circuits (VCs) used by
all systems accessing that DTC/X.25 card divided by the number of VCs
configured for that DTC/X.25 card.  Memory pressure on the DTC/X.25 card
is also factored into the algorithm.  The load of a DTC/X.25 card is
basically defined by the number of VCs currently open on the DTC/X.25
card and not by the overall throughput of the DTC/X.25 card.

Inbound Connections 

Load balancing of inbound connections is not the explicit responsibility
of the X.25 XL System Access software.  However, configuring multiple
DTC/X.25 cards per IP address allows for inbound load balancing.  An
inbound connection request contains a specific X.25 address.  Per this
specified address, traffic is routed to the appropriate DTC/X.25 card.
However, multiple DTC/X.25 cards can now be associated with a single IP
address of one NI on the XL system.  In this case, the inbound load
balancing of a particular DTC/X.25 card is the responsibility of either
the packet switching network (a public data network or private switch) or
the remote nodes.

Load balancing can be performed by a public data network (PDN). Since
PDNs can provide different features and different implementations of
similar feature sets, it is recommended that the PDN be contacted to
determine if the PDN can provide inbound load balancing for multiple
DTC/X.25 cards for one NI. Load balancing can also be performed by some
private X.25 switches.  In this case, the switch must be able to route
incoming calls with a given X.25 address to multiple lines.  Again, not
all X.25 switches can provide this capability.  It is recommended that
the capabilities of the switch be verified with the vendor.

Inbound load balancing can also be managed by the configuration strategy
of the remote nodes.  In this case, the remote nodes are configured with
different X.25 addresses for the same XL node.  For example, remote Node
A might contain the X.25 address of DTC 1, Card 1 for the local XL, and
remote Node B might contain the X.25 address of DTC 1, Card 2 for the
same XL node.  Therefore, calls from remote Nodes A and B to the same XL
would always be separated on different lines.

The multiple DTC/X.25 cards per single IP address enhancement provides
two inbound load balancing strategies:

 *  Same X.25 address for all DTC/X.25 cards to local XL system
 *  Different X.25 address for each DTC/X.25 card to local XL system

Configuring the same X.25 address for all DTC/X.25 cards to the local XL
system allows the X.25 XL System Access software (or PDN, in some cases)
to automatically perform the load balancing.  Whereas, configuring a
different X.25 address for each DTC/X.25 card to the local XL system
provides static load balancing by predefined separation of traffic to and
from the remote nodes.  The strategy of choice depends upon the network
environment and your specific needs.  In most situations, using the same
X.25 address for all DTC/X.25 cards to the local XL system is the
preferred choice.

Combination of Cards Supported Per NI 

For this release, DTC/X.25 XL System Access supports a maximum of 11 NIs
and 11 DTC/X.25 cards in any combination.  For example, you can configure
1 NI with 11 cards, or 11 NIs each with 1 DTC/X.25 card or 2 NIs with 5
and 6 DTC/X.25 cards, etc.  It is important to note the one-to-one
relationship between the NI and the IP address.  Each NI has one IP
address even though multiple DTC/X.25 cards can be configured for that
one IP address.  With this enhancement, you need only configure one IP
address if you need multiple DTC/X.25 card support for a given NI. You
are afforded a wide configuration scheme by the support of 11 NIs and 11
DTC/X.25 cards in any combination.  Again, the configuration strategy of
choice depends upon your network environment and your specific needs.

The figure below illustrates the case of one NI and one IP address
associated with eleven DTC/X.25 DTC/X.25 cards.


Increased Number of Virtual Circuits 

For this release, the number of VCs supported for one NI for DTC/X.25 XL
System Access increases from 256 to 1024.  This enhancement is important
for a customer taking advantage of the multiple DTC/X.25 cards per IP
enhancement.  In this situation, the customer can increase the maximum
VCs configured for the X.25 NI and distribute the traffic load over the
multiple DTC/X.25 cards configured for that NI and IP address.  Note that
the limit of VCs per DTC/X.25 card remains at 256.  Therefore, to obtain
1024 VCs, the customer needs at least 4 DTC/X.25 cards.  (And, there is
also a limit of 3 DTC/X.25 cards per DTC.)

Increased Performance 

Another benefit of the multiple DTC/X.25 cards per NI is increased
overall X.25 throughput.  If the customer's X.25 throughput is limited by
line bandwidth, the use of multiple DTC/X.25 cards for one IP address
increases the bandwidth resulting in greater overall throughput.

Redundancy 

The multiple DTC/X.25 cards per single IP address also allows for
redundancy for X.25 traffic in case of DTC/X.25 card failure.  If a
DTC/X.25 card or link fails, it is possible for its traffic to be
rerouted to another DTC/X.25 card or link.  Given the two methods of
configuring the DTC/X.25 cards and their X.25 address for the local XL
system, there are two aspects to link redundancy.

In the case where the DTC/X.25 cards all have the same X.25 address for
the local XL system, traffic can be redirected from a DTC/X.25 card/link
that has failed to one of the other cards with the same X.25 address for
the local XL system.  Although existing connections routed through the
failed DTC/X.25 card/link may be aborted, new connections can be
re-established to the local XL system without operator intervention.

In the other case, where the DTC/X.25 cards have different X.25 addresses
for the local XL system, traffic cannot be redirected from a DTC/X.25
card/link that has failed to one of the other cards without operator
intervention.  Under these circumstances, configuration changes may be
required.  However, the capability of having multiple DTC/X.25
cards/links for one XL system does provide more redundancy than was
previously available with X.25 XL System Access.

Features of the specific PDN or private X.25 switch may also assist in
providing this redundancy feature.  The PDN or X.25 switch vendor should
be contacted to determine the exact role either can support for
redundancy.

USER INTERFACE CHANGES 

In order to accommodate the DTC/X.25 XL Network Link enhancement of
supporting multiple DTC/X.25 cards per one NI and one IP address, changes
were made to the user interface.  The following areas are affected:

 *  Guided HP X.25 configuration
 *  NI and link management
 *  Migration

Guided HP X.25 Configuration 

With this release, the appropriate NMMGR screens were changed to
configure the multiple links enhancement.  Also, with this release,
Guided Configuration for the HP X.25 NI configuration is enhanced.  The
customer need only select the Guided HP X.25 NI task to go through the
necessary screens to enter data for both the configuration file
(NMCONFIG) as well as the network directory file (NSDIR). A single screen
is now used to configure the remote nodename, IP Address, X.25 Address,
X.25 Address Key, Facility Set, Security Class and PVC Number for X.25
VCs.

NI and Link Management 

Issuing the NETCONTROL START/STOP; NET=<niname> command for an X.25 NI
configured with multiple links starts or stops the X.25 NI and all of its
configured links.  It is not necessary (or possible) to issue multiple
NETCONTROL START/STOP commands to start or stop the multiple links for a
single NI.

The NETCONTROL NET=<niname>;ADDLINK/DELLINK=<linkname> command is much
more meaningful in the multiple link environment.  Using combinations of
the DELLINK and ADDLINK options of the NETCONTROL command, it is possible
to have various links up/down without bringing up/down the X.25 NI. It is
important to note that with multiple links per NI, it is possible for one
link of an X.25 NI to be up while all the other links are down.  This
situation requires that all inbound and outbound connections be on that
specified link or DTC/X.25 card.

Migration 

NS X.25 3000/V Network Link (HP24405A) also supports multiple X.25 links
for a single IP address.  However, there are differences between the NS
X.25 3000/V Network Link implementation and the DTC/X.25 XL Network Link
implementation.  NS X.25 3000/V supports multiple links for a single IP
address, but each one of these X.25 links is managed by its own NI.
Whereas, with DTC/X.25 XL Network link, each DTC/X.25 card/link is
managed by a single X.25 NI. This implementation difference results in
different requirements to start/stop these multiple links and also
requires different approaches to programmatic level 3 X.25 access of
these links.

For NS X.25 3000/V Network Link, each of the multiple links for the one
IP address is started/stopped by starting/stopping the NI each link is
associated with.  Whereas, for the DTC/X.25 XL Network Link, each of the
links for the one IP address can be started/stopped by using the
ADDLINK/DELLINK parameter of the NETCONTROL command.  Or, to start/stop
all links, the one NI is just started/stopped.

Programmatic level 3 X.25 access with the NS X.25 3000/V Network Link
implementation requires the programmer to accommodate for all links
available for the one IP address.  However, with the DTC/X.25 XL Network
Link, link selection is transparent to the level 3 X.25 access programmer
and no special programming is necessary for the multiple cards per IP
address feature.  More specifically, when programming level 3 X.25 access
with multiple links per IP address with NS X.25 3000/V, one call socket
must be created for each NI, for each link.  Whereas, programmatic level
3 X.25 access with DTC/X.25 XL requires only one call socket to be
created for the one NI (with the multiple X.25 links).

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