Archive-name: modems-faq

$Header: /var/news/doc/RCS/modems-faq.1,v 1.1 1993/08/26 19:13:36 rob Exp $

Here are some of the more frequently asked questions about the high
speed modem service (actually we made some of them up in an attempt to
head off anticipated  questions).  It's not designed to be a tutorial
as to how modems work, or a complete description of our setup, it's
just designed to answer 90% of the questions we get.

Here is a summary of the questions dealt with in this FAQ:

1.  What's the high speed dial in number?  What kind of modems are
    they?
2.  What is v.32bis?
3.  And the v.42 and v.42bis?
4.  What's hardware flow control?
5.  What tips do you have for setting up the modem?
6.  I am not getting the throughput I should be getting, what gives?
7.  What should I use, `telnet' or `rlogin'?
8.  I *am* using `telnet' and I *still am* not getting an eight-bit
    path, it keeps dropping characters, what is the problem?
9.  When I use telnet and my session gets messed up, I can't break out
    of it using ^] (control-right-bracket) like I can from Unix telnet.
    Why?  What should I do?
10. I tried accessing a host from the annex and got "Security Server
    is unreachable.", and couldn't access my host.  What gives?
11. How do I get to CMS or MVS?
12. Is there going to be a SLIP/PPP service?
13. So what is SLIP/PPP?
14. Why is there an hour timeout?
15. I've heard rumors that The Scholar's Workstation (TSW) is going to
    be selling high speed modems for under $200.  What's the scoop?
16. Any tips on what modems to buy?
17. Where can I complain / comment about the annex service?
18. Where can I get more help setting up my workstation and my modem? 
19. Where can I learn more about modems?

------------------------------------------------------------------------------

1.  What's the high speed dial in number?  What kind of modems are
    they?  

  Data Communications & Network Services, the campus network folks,
  have installed 96 high speed modems on ad hunt group starting at the
  phone number (510)  643-9600.  The modems are US Robotics
  v.32bis/v.42bis modems. The modems are connected to an Annex
  Terminal Server at 38.4k bps, and use hardware flow control
  (RTS/CTS) between the annex and our modems.   

2.  What is v.32bis?

  v.32bis is a CCITT standard for modems signaling at 14.4k bits per
  second (bps).  There are other standards, for other speeds, v.32 for
  9600, and v.22 for 2400.  CCITT is an international standards body
  for postal services, telephony and electronic communication.

3.  And the v.42 and v.42bis?
  
  More standards.  v.42 defines error correction, that is errors due
  to line noise will be detected and corrected.  v.42bis defines
  compression, up to 4 times compression, if the data is right.
  v.42bis is layered on top of v.42.

  Compression depends on finding patterns in data, and then
  representing them in a more unique form, so data that has more
  patterns compress better than more random data.  Text files compress
  well, as do executable programs, but random data or previously
  compressed data does not fair well. 

  The modems will also do MNP Levels 2-5.  Though if you can do
  v.42bis, it's preferable to MNP Level 5.  MNP Level 5 is another
  compression protocol, but with MNP Level 5 has the misfeature where
  random uncompressable data takes  longer to send than if it were
  sent without MNP level 5 compression turned on.  

4. What's hardware flow control?

  Well, if you did your math, you've realized that the modems have a
  potential to peak at data rates up to 57.6k bps.  That's where flow
  control comes in, if your computer is hooked up like:

   annex <-----> modem <---/\/\/---> modem <-----> your computer
          38.4k           PacBell           57.6k

  Flow control is the way the annex or your computer signals to your 
  modem (and vice versa) that they have enough data to process and
  would like to halt the flow of data until they have caught up.
  Hardware flow control is done by using extra wires in the cable
  between your modem and the computer, it allows each device to signal
  if they are Ready-To-Send or if it is Clear-To-Send (RTS/CTS).

  There is another kind of flow control called software flow control,
  or XON/XOFF which uses characters (Control-S and Control-Q) in the
  data stream to signal the remote end that it should stop sending
  data, or resume sending data.  This is considered bad form by many,
  as it removes two possible characters that can be sent as data, and
  makes file transfer a little bit more difficult.

  This service does *not* do software flow control.  It does hardware 
  flow control, and by using telnet, we provide an eight-bit clean
  path.  By eight-bit clean path, we mean that all characters get
  passed unmolested from your modem to the host you are connecting to, 
  and vice versa.

5.  What tips do you have for setting up my modem at home?

    o set it eight bits, no parity, one stop bit, 
    o make sure that hardware flow control (RTS/CTS) is on.
    o that software flow control (XON/XOFF) is turned off.
    o make sure your cable is OK.  It should be a modem cable, and
      have at least five wires hooking up the pins.

  I'd also recommend that your home computer should probably be
  communicating with your modem at as high a speed as possible, if you
  can do 57.6k bps, without flow control problems or buffer overflows,
  go for it.  There should be no harm in keeping the pipe as full as
  possible.  If you have problems, decrease your speed.

  It's been suggested that if you use Eudora to only allow your modem
  to establish error-corrected connections.  This will help reduce the 
  chance that you get line noise for mail.  Many modems will by
  default negotiate to a non-error-corrected state if the phone line
  is bad. 

6.  I am not getting the throughput I should be getting, what gives?

  There are many variables that can affect throughput, here some I can
  think of off the top of my head.

  If you are using compression in your modem, and are sending already
  compressed data like compressed files, or ZIP archives, *don't*
  expect to get better than your link speed, 1400 characters/sec for
  v.32bis and 960 characters/sec for v.32.  As a general rule,
  compressing files before transferring, then uncompressing them
  after is better, because your computer can compress them *much*
  better than the modem ever can.  

  Phone line quality can also be a problem.  v.32bis modems will
  retrain to lower data rates if they detect too many errors.

  It also maybe that your serial card or computer is not fast enough
  or to busy to keep up.  You probably won't be loosing any data, but
  using hardware flow control, your computer might be signalling the
  modem to halt the data rate for a while, while it processes the
  characters it just received.  A symptom of this, is that uploads go
  fast, and downloads are slow, as it is much more of a load on the
  CPU to receive characters, than to send characters.  As far as PC's
  go, if you have a fairly fast PC (386/486) and a older/cheaper
  serial card, you might consider buying a newer, faster one.

  If you are doing heavy disc accesses, or are using an AppleTalk(tm)
  you might also experience a slow down. 

7.  What should I use, `telnet' or `rlogin'?

  If you are going to be doing file transfers, or need an eight-bit 
  clean path, we recommend you use `telnet', as it will provide an
  eight-bit clean path.  

  `rlogin' *almost* provides an eight-bit path, but unfortunately the 
  way a client tells the server that the window size has changed, by
  sending a \255\255ss sequence upstream screws it up.  

8.  I *am* using `telnet' and I *still am* not getting an eight-bit
    path, it keeps dropping characters, what is the problem?

  We've had a couple of reports of this, tinkered with buffering on
  the annex, and *think* we have fixed it.  If you are currently
  experiencing problems, *PLEASE* send mail to annex@nic.berkeley.edu, 
  describing your woes.

  From personal experience, I have run a SLIP connection through an 
  annex to another host on the network using `telnet' for several 
  months, with no problem.  I transferred a lot of data, doing 200 meg 
  dumps over the SLIP line without telnet misbehaving, or dropping
  characters.

9.  When I use telnet and my session gets messed up I can't break out
    of it using ^] (control-right-bracket) like I can from Unix telnet.
    Why?  What should I do?

  We do not define a "telnet escape" character by default.  This is so
  that you get an eight-bit path to your host.  You can override the
  default if you want, but you may not need to. 
 
  There are two things you can do:

    a)  You can always get back to the annex prompt by using then
        BREAK key of your terminal (or BREAK function of your terminal
        emulation program). 

    b)  Initially at the Annex prompt, type the command:

           stty tesc ^]

        This sets the telnet escape character to be control-].  Be
        careful, as this can screw up file transfers.  To undefine the
        escape character, at the Annex prompt, type the command: 

                stty tesc undef

10. I tried accessing a host from the annex and got "Security Server 
    is unreachable.", and could not access the host I wanted.  What
    gives? 

  The annex, before it allows a connection, checks to see if the IP
  address / port number is `authorized', to avoid people from using
  our terminal servers to telnet off campus. 

  This should *not* happen if your are attempting to access an on
  campus host.  Please let us know if it is.

11.  How do I get to CMS or MVS?

  Telnet to cmsgate to access CMS or mvsgate for MVS.  This service 
  connects you to a 7171 connected to the 3090.

12. Is there going to be a SLIP/PPP service?

  Yes, that's the plan.  We are planning to implement a dialup
  SLIP/PPP service using these modems.  We plan to start testing with
  a small group of people starting around the middle of September.  
  Look at ucb.net.announce then for announcements for testers if you 
  are interested.  

  CSLIP will be supported.

13. So what is SLIP/PPP?

  SLIP stands for Serial Line/IP, PPP for Point-to-Point Protocol.
  They are basically protocols that allow remote computers to enjoy
  the same network connectivity via a phone line that machines
  directly connected to the campus network enjoy.  Albeit at *much*
  lower speeds. 

14. Why is there an hour timeout?

  With other modem services, we've experienced problems with people 
  logging in and leaving themselves idle for hours at a time.  It's 
  frustrating to have received a busy signal for hours upon a time and 
  then upon finally logging in, seeing that a substantial number of
  people are idle. 

15. I've heard rumors that The Scholar's Workstation (TSW) is going to
    be selling high speed modems for under $200.  What's the scoop?

  US Robotics is is allegedly negotiating with TSW to sell the modems.
  I've heard that the price is going to be under $200 for a
  v.32bis/v.42bis Fax modem.  I wouldn't hold your breath though.
  This is the University remember. 

16. Any tips on what modems to buy?

  Buy something that does v.32bis/v.42bis.  We've had very good
  success in interacting with alot of different brands of modems.
  If you are conservative, you should probably opt for the US Robotics
  modems.  Don't buy anything with HST/HST+/PEP or other proprietary
  protocols, as our modems don't handle them, and they usually add
  to the cost.

  One can purchase a no-name brand v.32bis/v.42bis modem for under
  $180 if you look around.  I've seen brand name US Robotics external 
  Sportster's v.32bis/v.42bis modems in `Computer Currents' for around 
  $180, I've heard that one can buy them at a computer store off of
  Telegraph for about $190.  Prices are dropping, so check around.  If
  you buy a no-name brand, make sure you can return it if it doesn't
  work with our modems (or doesn't work at all).

17. Where can I complain / comment about the annex service?

  Send mail to annex@nic.berkeley.edu.  Please include this
  information (if applicable):

        a) port number of the annex you were dialed into (this is
           contained in the prompt).  This enables us to find a bad
           annex port / modem pair.
        b) type of computer you are using (or terminal).
        c) type of modem you are using, does it do v.32bis/v.42bis?
        d) speed your connection from your computer to  your modem is
           at. 

  plus anything you think might help. 

  If you are experiencing problems, call the Trouble Desk (642-4920), 
  giving the information noted in items a-d.

18. Where can I get more help setting up my workstation and my modem? 

  You might try the people who sold you the modem, but failing that,
  Workstation Services is very experienced in helping people with  
  Macintosh, PC and Unix workstations problems.  They should be able
  to help you if you run into any problems hooking up your modem and 
  configuring it and your computer. They can be reached electronically 
  as drmicro@garnet.berkeley.edu, or between the hours of 10-4
  weekdays, in person at 264 Evans or by phone at 642-8899. 

19. Where can I learn more about modems?

  There is an excellent article, by Seth Novogrodsky, on modems in the
  May-June issue of `Berkeley Computing'.  It's entitled `A Practical
  Guide to Selecting a Modem'.  Subscriptions are free to
  universities, colleges, departments, faculty, staff and students.
  Send mail to avante@garnet.berkeley.edu for a subscription, with
  your postal address, and university affliation (student/staff/faculty).