$a device=x2700
$d1 :cosmos12b:
$d2 :cosmos14:
$a tab=1",3.5",4.5",4.8",5.7"
$a left=5
$5
$l0
Intro
     Nature of Edinburgh University
        Data Network                - slide 1
          Based on 3 x gec packet switches (CPSEs) - central circles
        Voice Network               - slide 2

     Early exposure to PABX & LANs
        ICL/DTI - Investigate Interconnection
        Project Diagram             - slide 3

     + University in progress of procuring new PABXs


Potential Advantages                  - slide 4

     1.   Common wiring
          2835 telephones  - static
          1520 data ports  - +20%/tear

            But - wiring owned by BT
                  (those with private PBX ok)
            So rewiring anyway  (3 pairs)

     2.   Direct Connection

          Explain OUR situation re Networks
          PABX solves

     3.   Multiple Terminal prots

          3270, co3, asynch etc
          NOTE: call mechanisms are different

     4.   Large number of infrequently used terms
          GOOD at 15:1

     5.   Single exch. management
          PACX can do most of the above BUT two boxes.

     6.   Synchronous X.25 Traffic
          - its ok up to 19.2
          Advantages of connecting a PAD at exchange through
          Only 1 circuit (1 erlang)  - all way through
          permnanent circuit
          easy for telephone planners

Disadvantages                               - slide 5

     1. Non - Blocking
          In theory lots of capacity (univ. only?) - 200 erlangs
          In practice - features use up capacity
                      - h/w can be blocking - depends on act. con.
                        ie peripheral racks etc

          Situation much worse with multiple exchanges
          Explain 2mb trunk usage

     2. Cost
          This is difficult
            Depends on whether - totally new
                                 integeration with existing
                                 type of existing configuration
            Look at typical methods of connection      - slide 6
               PABX - #800 - #1000
               X.25 - #200 - #250                      - slide 7
               PACX - #105        (includes 3:1 allocation)

          Total cost (from scratch)
            X.25 cheapest
            PACX next
            PABX much, much more


     3. Limitations of 64k                   Back to  - slide 5 ?

          More a myth than a reality

          Terminals at 9.6  (or 19.2?)

          Ethernet/Cambridge Ring  run at 10Mb BUT

          our experiences with Ring & ethernet

          Host i/o packet limitations

          Vax 750 40pk/sec  128 bytes  41 kb/s
                                256 bytes  82

          Vax 780 100pk     128        102
                                256        204

          (L3 figs only !!!!)
          More powerful machines, do better, seperate network ?

     4. Interference with speech
         Telephone managers v worried about speech service
         Likes the IDEA of data using slack (if there is)
         Guarentee ?

     5. Network Management

        Call monitoring difficulties
        (Not quite as bad as in paper)
        Still based on external
        extremely clumsy on DNX for all calls (circ files, 10 mins)

     6. Name directory
        none  - PACX learnt earlier

FUTURE                                  - slide 8 (nb: from 5)

       Data port
           call is more complex  DTRX, hotlining etc
           demand is lower
           hence cost unlikely to be less than voice
           - difficult to get incremental costs

       DIU
          codec chips should reduce costs
          integrated into 'feature phone' #40 ?

       Alternatives

          Micro/telephone

          Data Network Gateways


PABX/LAN Gateways

          Current method of attachment                - slide 10

               host requires multiple DIUs
               (DNX) Wiring, racks, space, power

               Peak usage problems

          LAN + DIUs Connection                  - slide 11

              (DNX) Hunt group problems - Linear/circular
                       - not as flexible as voice !!!

               OSLUs, pads, hosts etc


FUTURE

              Trunk G/W                   - slide 12

                 Gives intelligence between PABX & GW
                    speeds, asy/syn, parity etc

                 Interesting terminal char. (echoing etc)

              Integerated G/W

                 X.25  - Ferranti (check blurb)


CONCLUSION                               - slide 13

              Too Expensive

              BUT, if DIU cheaper:-

                 Single exchange  OK vs PACX

                 Multiple "       Trunk problems


              PABX is Voice orientated, saw a market
                   didn't really consider needs

              - PACX much more advanced in data handling

              - Manufacturers should think again about DATA requirements

$e