Communcation and Invocation

Five questions to ask a DOS.

• What basic communication primitives are supplied?
• What quality of service guarantees are made?
• Which protocols are supported?
• How open is the communication implmentation?
• What steps are taken to make communication as efficient as possible?

Communication Primitives

These will mostly be based upon message passing. Either or combinations.

Systems will alos provide for group communication to allow requests to be broadcast to several possible servers.

Memory Sharing

For local process some form of memory sharing can be implemented to provide for rapid message passing within a single machine.

Quality of Service

This is becoming a major issue with the desire to be able to transmit multimedia data over the network. Within the next five years networks will be fast enough that this is a reasonable thing to do.

Protocoal and Openness

Most commercial protocols are not in fact well adjusted to RPC. One idea is to provide the network access through a server that has direct access to the network hardware.

Performance

1. A system call crosses one protection boundary, that between kernel and user and back again.
2. A local RPC crosses two, user1 to kernel to user2 and back again
3. A remote RPC corsses the network as well.

A null RPC currently takes 1000 times longer than a local system call. Argument size is an issue because one wants to use as few packets as possible.

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Last Changed: 18 October 1995