Network and internetwork design must take many factors into consideration: the
desired physical location of the computers comprising the network, the volume
of projected communications traffic between nodes, communications traffic
patterns, and the possibility of connections to other types of nodes (such as
those in a public data network) are just some of the criteria to consider.
These factors will affect your choice of NS network type (LAN, Token Ring,
FDDI, 100VG-AnyLAN, 100Base-T, Point-to-Point, X.25) as well as choice of
specific links. They will also affect how you design your network layout. You
may want to create subnetworks within your network by configuring IP subnet
addresses. You may, on the other hand, need to join several networks together
to form an internetwork or internet.
Line Speed
Line Speed is a measure of the rate at which data is transmitted
by a physical link (usually measured in kilobits or megabits per
second). The maximum line speed varies among different NS links.
Line speed may therefore influence your choice of link. Although
line speed does not indicate the exact throughput of a particular
link, it can be used on a comparative basis to indicate relative
throughput.
In general, an IEEE 802.3/Ethernet LAN or Token Ring
network will be faster than a Point-to-Point or X.25 network because
the bus or ring topology provides a faster routing mechanism than
a series of Point-to-Point hops. FDDI, 100VG-AnyLAN, and 100Base-T
links will be an order of magnitude faster than LAN or Token Ring.
Links using leased lines will have a higher line speed than links
using normal telephone lines.
Consult your Hewlett-Packard representative for line speeds and the most
up-to-date performance data for various links.
Geographical Location
The geographical location of the computers that will be part
of your network or internet will be an important factor in deciding
both the physical topology and the link types that you should use.
If all of the nodes you want to connect are located relatively
close to each other (in the same building, for example) you might
choose to connect them via a LAN, Token Ring link, 100VG-AnyLAN,
or 100Base-T.
Another option for nodes located in the same geographic location
is to use hardwired (direct-connect) Point-to-Point links. You might
wish to use a Point-to-Point network if the distance between some
nodes on the network will be greater than the maximum distance allowed
between nodes on a LAN. Bridges, hubs and routers are commonly implemented to
extend LANs.
FDDI networks also offer greater distances than LAN, Token
Ring, 100VG-AnyLAN, or 100Base-T networks. FDDI networks can be
up to 200 kilometers in length, with nodes up to 2 kilometers apart.
If you need to connect nodes that are geographically distant
(for example, HP e3000s located in different cities) you might choose
to connect them via a dial link. For NS dial links, you can use
the Point-to-Point 3000/iX Network Link.
Finally, if you need to use satellite transmission because
of the large geographical distance between nodes, or if you need
to have access to other nodes on a public or private X.25 network,
you might wish to use the DTC/X.25 iX Network Link.
Special Cases
The following sections describe certain design requirements for special
situations, such as shared dial links, personal computers, and using non-HP
e3000 minicomputers on an NS network.
Shared Dial Links
Shared dial links have two limitations that must be
considered when designing a network. First, a shared dial link cannot
be used as an intermediate link in a Point-to-Point network. Any
other kind of dial link can be used for intermediate links, but
shared dial links can be used only to connect leaf nodes (that is,
nodes that receive messages targeted only for themselves, also referred
to as end nodes). Second, cannot dial out on SMUX, shared dial links
cannot be used as gateway halves.
Non-HP e3000 Nodes (Including PCs)
LAN, Token Ring, FDDI, 100VG-AnyLAN, 100Base-T, and X.25 networks can access
non-HP e3000 nodes. Point-to-Point networks must be composed of only HP e3000s.
Applicable SYSGEN Parameters
VT terminals are not physical devices, instead they are virtual
devices created dynamically at remote logon, header entries are
created for the maximum number of VT terminals at system boot time.
The exact number of head entries created for VT terminals will depend
on the value of MAXDYNIO (which is configurable in SYSGEN).
The exact number of remote sessions which can be supported
on a given system will depend on the exact mix of jobs and sessions
(remote and local, active and inactive) on that system.
The maximum number of concurrent processes may limit the number
of remote logons before the maximum number of dynamic I/O devices does.
Dynamic Ldevs
This is actually a system parameter that can be configured
to 999 in SYSGEN. The default is 332, but the actual number that
can be in use may be limited by the IDD/ODD limits. VT and NS use
one dynamic ldev per remote session and one per LAN link and one
per Point-to-Point link.
NOTE: The result of having DYNAMIC IO DEVS configured too low for NS
VIRTUAL TERMINAL connections is VTERR 8 or VT INFORM 050.
Likewise the dynamic I/O device limit may be reached before the concurrent
process limit.