General questions about the power of Erlang

Ulf Wiger etxuwig@REDACTED
Tue Dec 12 11:41:04 CET 2000

On Tue, 12 Dec 2000, Karel Van Oudheusden wrote:

>It is exactly the scheduling which I am concerned about.  In Ada
>(what about Erlang?) the programmer is for instance allowed to
>specify certain scheduling desires.  These are however not similarly
>executed on the different platforms (which is of course not
>surprising to some extent).

It appears as if Ada has more in common with Java than with Erlang in
this respect. Erlang's scheduling semantics are carefully preserved on
all platforms.

>Another question I have is the following.  Erlang has had a lot of
>success in ATM switches.  Are these hard real-time (embedded)
>applications?  Is there a good mathcing between the ATM hardware and
>the Erlang code?  Or is this the same application domain as what
>Erlang is now made open source for: general purpose programming
>(regardless of platform) for Internet applications?

The common way to build robust and scalable datacom and telecom
switches is to divide the system in to control processors and device
processors, where the device processors perform simple, hard 
real-time (or "wire-speed") tasks, and the control processors take
care of the more complex (soft real-time) functions. Typical control
processor functions would be:

- Starting, stopping, monitoring, blocking, deblocking, and 
  upgrading system components

- Serving operators with a management interface 
  (HTTP, CORBA, SNMP or other in various combinations)

- Ensuring high availability through redundancy and load sharing

- Handling signalling protocols and performing address and route

Erlang shines on the control system functions. There is some work on
moving Erlang closer to the "fast-path", but in today's systems, we
implement this in C.

Ulf Wiger                                    tfn: +46  8 719 81 95
Senior System Architect                      mob: +46 70 519 81 95
Strategic Product & System Management    ATM Multiservice Networks
Data Backbone & Optical Services Division      Ericsson Telecom AB

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