Cabletron Systems HSIM-W6 Installationsanleitung PDF herunterladen (Seite 18)

Chapter 2: About the HSIM-W84

2-6 HSIM-W84 Installation Guide

The NAT method (that is supported only on interface T1-1) allows several DHCP clients on a

sub network to connect to WAN clients by allowing the DHCP clients to share a single public IP

address. When the HSIM-W84 uses NAT, the NAT method modiﬁes the IP headers and addresses,

and the selected ﬁelds in upper layer protocol headers. This is done to replace the hidden local IP

addresses from the sub network with one or more public InterNic assigned IP addresses that can be

sent over the outside network on the HSIM-W84 T1-1 WAN interface. Once the HSIM-W84 is

assigned at least one public IP address, over 250 IP clients can share this address simultaneously

using NAT. This public IP address is assigned statically by the Internet Service Provider (ISP), or

equipment installer.

Point-to-Point Protocol

PPP is a data link layer industry standard WAN protocol for transferring multi-protocol data trafﬁc

over point-to-point connections. It is suitable for both high-speed synchronous ports as well as

lower speed asynchronous dial-up ports. With this protocol, options such as security and network

protocols can be negotiated over the connection.

The STAC Electronics Stacker LZS Compression Protocol is supported over PPP providing up to

4:1 data compression.

Frame Relay Protocol

Frame Relay can be deﬁned as a “packet mode” service, organizing data into individually

addressed units known as “frames”. Frame Relay eliminates all Layer 3 processing. Only a few

Layer 2 functions are used, such as checking for a valid, error free frame, but not requesting

retransmission if an error is found. Frame Relay uses a variable length framing structure, which,

depending on user data, can range from a few to more than a thousand characters.

A Frame Relay Network will often be depicted as a cloud, because the Frame Relay Network is

not a single physical connection between one endpoint and another. Frame Relay protocol is based

on the concept of Virtual Circuits (VCs). VCs are two-way, software deﬁned data paths between

two ports that take the place of private lines in the network. There are two types of Frame Relay

connections; Switched Virtual Circuits (SVCs), and Permanent Virtual Circuits (PVCs).

Permanent Virtual Circuits, or PVCs, are set up via a network management system, and initially

deﬁned as a connection between two sites, or endpoints. PVCs may be added as the demand arises

for more bandwidth, alternate routing, or more sites. PVCs are ﬁxed paths, not available on

demand, or on a call-by-call basis. Although the actual path through the network may change from

time to time, such as when automatic rerouting takes place, the beginning and end of the circuit

will not change.

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Cabletron Systems HSIM-W6 Installationsanleitung Seite 18