HSIM-W6 Firmware Support
HSIM-W6 Installation Guide
2-9
The ANSI standard defines a mechanism for the network to signal the existence of congestion,
called Explicit Congestion Notification (ECN) bits. Frame Relay uses FECN (Forward ECN) and
BECN (Backward ECN) bits to notify end user devices about network congestion. Although the
Frame Relay protocol does not respond to congestion, some higher layer protocols for end user
devices may respond to ECNs by recognizing that delays have increased, or that frames have been
dropped.
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.
This device supports synchronous PPP over the ISDN port. In Single Link Mode, PPP uses one
ISDN B channel for data transmission. PPP runs over each ISDN B channel for two separate
conversations (split B-channel). In Multi-Link Protocol Mode, PPP simultaneously sends and
receives data over two ISDN B-channels on the same connection to optimize bandwidth usage.
The STAC Electronics Stacker LZS Compression Protocol is supported over PPP providing up to
4:1 data compression.
PAP and CHAP Security
The HSIM-W6 supports the Password Authentication Protocol (PAP) and Challenge Handshake
Authentication Protocol (CHAP) under PPP.
PAP provides verification of passwords between devices using a 2-way handshake. One device
(peer) sends the system name and password to the other device (authenticator). Then the
authenticator checks the peer’s password against the configured remote peer’s password and
returns acknowledgment.
CHAP is more secure than PAP as unencrypted passwords are not sent across the network. CHAP
uses a 3-way handshake and supports full or half-duplex operation.
