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HP 3000/iX Network Planning and Configuration Guide: HP 3000 MPE/iX Computer Systems > Chapter 2 Networking Concepts
Network Environment Design Considerations |
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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 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. 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. 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 3000s 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. The following sections describe certain design requirements for special situations, such as shared dial links, personal computers, and using non-HP 3000 minicomputers on an NS network. 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, shared dial links cannot be used as gateway halves. LAN, Token Ring, FDDI, 100VG-AnyLAN, 100Base-T, and X.25 networks can access non-HP 3000 nodes. Point-to-Point networks must be composed of only HP 3000s. 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. 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.
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