                                             ZyXEL Communications Corporation
                                                      edited by Manfred Recla
                                                                July 12, 1996



In this addendum for the ZyXEL ISDN Terminal Adapter you will be informed
of new features and enhancements implemented in the firmware v2.03 for
the ZyXEL "Elite 2864I" or firmware v1.00 for the ZyXEL "Omni TA128"
concerning the "asynchronous PPP frames to synchronous HDLC/PPP frames
conversion"


Table of contents:
------------------
  1.  Async to Sync PPP
      1.1.  Internet and Remote Access PPP
      1.2.  making async to sync PPP calls
      1.3.  keeping a line connection during idle time
      1.4.  answering async to sync PPP calls

  2.  PPP Multilink Protocol (PPP/MP)
      2.1.  Making a call using PPP/MP
      2.2.  Dial pre-stored phone numbers
      2.3.  Endpoint Discriminator

  3.  Bandwith on Demand (BOD)
  4.  Call Bumping
  5.  Authentication (PAP or CHAP)





1.) Async to Sync PPP
======================



1.1.  Internet and Remote Access PPP:
--------------------------------------
More and more Internet Service Providers are offering their services through
dial-up ISDN lines for higher data bandwidth.  The equipment used at the
service provider's location are frequently ISDN LAN routers which, unlike
terminal adapters, do not have asynchronous capability.  For this reason,
terminal adapters that support only X.75, V.120 or asynchronous protocol will
not work with this type of equipment.

The ZyXEL ISDN Terminal Adapter (both ZyXEL "Elite 2864I" and "Omni TA128") is
able to convert the asynchronous data it receives from your computer to
synchronous format in order to communicate with ISDN LAN routers.  We call
this process "asynchronous to synchronous HDLC conversion". To simplify it,
we call it "Async to Sync PPP" protocol (PPP = Point-to Point Protocol).
(as an abbrevation you will see sometimes also "async2syncPPP").



1.2.  Making Async to Sync PPP calls:
-------------------------------------
In order to communicate with an ISDN LAN router (from vendors such as Ascend
and Cisco), you'll need to set the ZyXEL ISDN Terminal Adapter's B-channel
protocol to the following:
	ATB40<Enter>  (async2syncPPP)

You should also set the DTE speed based on the bandwidth the switches support.
(either 115.2 kbps or even higher (230 or 460.8 kbps), if channel bundeling
or bandwith on demand (BOD) is selected !)

Most of the time, you will only use this B-channel protocol for making calls
to remote sites with ISDN LAN Routers. If the remote access site you are
calling uses a terminal adapter such as the ZyXEL "Elite 2864I" or the
ZyXEL "Omni TA128", you can use X.75 or V.120 as default B-channel protocols
because they provide data compression (V.42bis).

Before making the call, check which protocol is set for the ISDN mode using
the AT&V command to view the settings.

Type:
AT&V<Enter>

The ZyXEL ISDN Terminal Adapter responds:

Current Settings...
Switch Type: DSS1
ISDN Outgoing Service: PPP Async-to-Sync Conv 64K
....

If the settings displayed match your current setup, you are ready to place
the call.
Type:
        ATDI<remote_access_number><Enter>
The ZyXEL ISDN Terminal Adapter will respond:
        CONNECT 115000/64000  PPP/None



1.3.  Keeping a Line Connection During Idle Time:
-------------------------------------------------
If you are using the PPP to access a server, more often than not, the server
will have a watchdog timer to monitor the line activity. If the idle time
exceeds some time interval (usually 1 minute), the server will release the
connection for other clients to dial in. As a user, you could be very annoyed
in some circumstances because, once disconnected, you have to dial to the
server again and repeat the login procedure. The value in register S124 (in
seconds) is used as the idle time gauge. If the idle time exceeds this
guarding period, the ZyXEL ISDN Terminal Adapter will send out a dummy PPP
packet to the server to keep it from disconnecting the line.

Example: If the server you are calling disconnects after 1 minute of
inactivity, issue the following command before connecting:
ATS124=59<Enter> (send dummy PPP packet after 59 sec of inactivity)
Setting S124=0 will disable this function.



1.4.  Answering Async to Sync PPP calls:
----------------------------------------
There is no need to configure the ISDN mode to the protocol of an incoming
call. The ZyXEL ISDN Terminal Adapter will be able to determine the correct
protocol to use by examining the data coming in from the remote site if the
device is set to auto-answer or once an answering command is issued.  One
exception to this is when the ISDN data call is carried through Speech bearer,
(available for USA ISDN only !) in this case, you would need to set proper
MSN entry. In this case, you would need to enter the phone number that you
are expecting the Data over Speech bearer coming from into the MSN table #3
by AT&ZI3=xxx, "xxx" stands for the number that the call is expected to come
in from (i.e. "Called Party Number").

To allow the ZyXEL ISDN Terminal Adapter to answer the incoming call, you
need to set S0 to a value greater than 0 (i.e. ATS0=1). The ZyXEL ISDN
Terminal Adapter will answer the call and use asynchronous to synchronous
conversions to and from the DTE. If S0 is not set (S0=0), the DCE will report
"RING" and will also make an audible ring notification.





2.)  PPP Multilink Protocol (PPP/MP):
=====================================
PPP/MP is a protocol (RFC 1717) that allows virtual bundling of the two B
channels, for connection speeds of 128Kbps. PPP/MP support is a standard
feature of the both ZyXEL ISDN Terminal Adapter (either ZyXEL "Elite 2864I"
or "Omni TA128") models.



2.1.  Making a call using PPP/MP:
---------------------------------
A PPP/MP connection is initiated at the calling site when ATB40 (B-channel
protocol "async2syncPPP") has been selected and the PPP/MP mode has been
enabled by an AT&Jn command:
	AT&J0	Disables Multilink PPP
	AT&J1	Enables Multilink PPP in answer mode only
	AT&J2	Enables Multilink PPP in call mode only
	AT&J3	Enables Multilink PPP in both call and answer modes
By default, the ZyXEL ISDN Terminal Adapter dials the same number for both
Multilink PPP connections.

Note (for USA only !):
If the destination you are dialing requires a second telephone number to
establish a second Multilink PPP channel, then the following command can be
used: "ATDIphone_number_1+phone_number_2" where phone_number_1 and
phone_number_2 are the phone numbers of the destination.

If the destination refuses the PPP/MP during the LCP negotiation, a single
B channel PPP connection will be established. Whether or not the PPP/MP
connections have been established, the connection message will be the same.



2.2.  Dialing Pre-stored Phone Numbers:
---------------------------------------
Use ATDSn, n=0,1,..,39, to dial the (n+1)th phone number twice for both the
PPP/MP connections.

Note: (for USA only !)
Use ATDSn+Sm, (n and n=0,1,...,39) to dial the (n+1)th phone number for the
first connection and the (m+1)th phone number for the second connection.
For example, ATDIS0+S1<Enter> will dial the number stored in location '0',
and the number stored in location '1' for the PPP/MP connection.




2.3.  Endpoint Discriminator:
-----------------------------
The Endpoint Discriminator option represents identification of the system
transmitting the packet. This option advises a system that the peer on this
link could be the same as the peer on another existing link. Some PPP/MP
implementations require the use of the Endpoint Discriminator option.
The Endpoint Discriminator consists of two components: Class and Address.

-------+---------------------------------+-----------------------------------
 Class |  Address                        |  AT Command
-------+---------------------------------+-----------------------------------
   0   |  Null Class (by default)        |  ATEPD0
   1   |  Locally Assigned Address       |  ATEPD1=xxxxx
   2   |  Internet Protocol (IP) Address |  ATEPD2=<byte_1,byte_2,...,byte_n>
   3   |  IEEE 802.3 Globally Assigned   |  ATEPD3=<byte_1,byte_2,...,byte_n>
       |  MAC Address                    |
   4   |  PPP Magic-Number Block         |  ATEPD4=<byte_1,byte_2,...,byte_n>
   5   |  Public Switched Network        |  ATEPD5=xxxxx
       |  Directory Number               |
-------+---------------------------------+-----------------------------------

Each Octet_i is in the range from 0 to 255, for example:
	ATEPD2=<203,66,113,100>
Hexadecimal format is also allowable, for example:
	ATEPD2=<0xCB,0x42,0x71,0x64>
The angle brackets '<' and '>' are part of the this command !
The command ATEPD? can be used to view the current setting of the Endpoint
Discriminator Address.

Note:
The Endpoint Discriminator option is not required in most cases, thus users
don't have to change the default settings. The system administrator of your
corporate network or the Internet service provider will provide these values
if the Endpoint Discriminator option is required.





3.)  Bandwidth On Demand (BOD)
==============================
The BOD function will monitor data traffic over the ISDN line. If both
B-channels are connected and the traffic is low, PPP/MP will drop one of the
B-channels. On the other hand, if only one B-channel is currently connected
and the data traffic is high, PPP/MP will adaptively try to establish another
B-channel to increase the bandwidth of the data link.

For PPP/MP to make a decision as whether the data traffic is high or low, you
have to specify the criteria as follows:

--------+----------+-----------+---------+------+----------------------------
        |  Command | Parameter | Default | Unit | Remark
--------+----------+-----------+---------+------+----------------------------
high    |  ATJAn   |  n=0-255  |   48    | Kbps | Add-threshold for BOD.
traffic |          |           |         |      | If the line utility is
        |          |           |         |      | higher than this threshhold
        |          |           |         |      | for Add-persist time
        |          |           |         |      | interval, PPP/MP will add
        |          |           |         |      | second B-channel.
        +----------+-----------+---------+------+----------------------------
        |  ATKAMn  |  n=0-63   |    0    | Min  |
        +----------------------+---------+------+  Add-persist
        |  ATKASn  |  n=0-63   |    0    | Sec  |
--------+----------------------+---------+------+----------------------------



--------+----------+-----------+---------+------+----------------------------
        |  Command | Parameter | Default | Unit | Remark
--------+----------+-----------+---------+------+----------------------------
low     |  ATJSn   |  n=0-255  |   32    | Kbps | Sub-threshold for BOD.
traffic |          |           |         |      | If the line utility is
        |          |           |         |      | lower than this threshhold
        |          |           |         |      | for Sub-persist time
        |          |           |         |      | interval, PPP/MP will drop
        |          |           |         |      | one of the B-channels.
        +----------+-----------+---------+------+----------------------------
        |  ATKSMn  |  n=0-63   |    0    | Min  |
        +----------------------+---------+------+  Sub-persist
        |  ATKSSn  |  n=0-63   |    0    | Sec  |
--------+----------------------+---------+------+----------------------------

If the Add-persist is ZERO, then BOD function is disabled. The BOD function
can only be effective when the ZyXEL ISDN Terminal Adapter is in the calling
site (i.e. the client site).





4.)  Call Bumping:
==================
You can place or answer a voice call (and only one !) from a device that is
attached to one of the POTS ports while a PPP/MP call is active. The ZyXEL
ISDN Terminal Adapter automatically removes one of the PPP/MP connections and
uses it for the voice call. Once the voice call ends, the ZyXEL ISDN Terminal
Adapter automatically reestablishes that channel for PPP/MP operation. The
Call Bumping function is effective only when the ZyXEL ISDN Terminal Adapter
is in the calling site (i.e. the client site).

The following command can be used to select the Call Bumping function:
	ATCE0		Disable the Call Bumping function
	ATCE1		Enable the Call Bumping function (default)





5.)  Authentication:
====================
The PPP provides for an optional Authentication phase before the internet
connection is established. As the default setting (S118.3=0), the ZyXEL ISDN
Terminal Adapter (both ZyXEL "Elite 2864I" and ZyXEL "Omni TA128") enables
the PAP authentication protocol only, all other authentication protocol
received from the server will be NAKed by the ZyXEL ISDN Terminal Adapter.
But if the bit 3 of S118 is set (S118.3=1), the ZyXEL ISDN Terminal Adapter's
PPP will support all the authentication protocols that application software
can work with. Because the password is stored in the application software but
the ZyXEL ISDN Terminal Adapter, the ZyXEL ISDN Terminal Adapter does not
guarantee the connection of the second link of PPP/MP if the authentication
protocol is different from PAP.

For example, the implementation of the CHAP protocol of the Windows95 system
causes trouble for the second link of PPP/MP. But for the WindowsNT v3.51 RAS
system, the second link of the PPP/MP using CHAP protocol can be established
without any problem. To detour the problem in Windows95, you can set S118.3=0
to disable the CHAP option as follow :

ATS118.3=0	Accept PAP only, all other authentication protocol request
                received from the server will be NAKed (default).
ATS118.3=1	Accept all kinds of authentication protocol that application
                software can work with, but does not guarantee the connection
                of the second link of the PPP/MP if the authentication
                protocol is different from PAP.


