[zeromq-dev] EPGM Congestion Control

[Martin Sustrik]

Michael,

> 2. Correct me if I am wrong but I thought EPGM was PGM implemented over
> UDP. If this is correct then after you create the datagram socket you
> can set the option IP_MULTICAST_TTL via setsockopt. I do not believe
> this is currently available in 0MQ. Is that correct?

It's up to Steve to decide here. Does it make sense to set TTL in 
context of PGM? What does the spec say? Is it exposed in OpenPGM API?

If so, there's no problem in adding it to 0MQ API.

> 3. Yes, I could provide a patch. I plan on using 0MQ to distribute
> multiple prices feeds. It’s not realistic to batch prices until you have
> a full UDP packet before sending them. This would add latency where it’s
> not desired. I am assuming there is a timer tied to the queue which is
> performing this limit. Is that timer configurable and what is the
> default time interval?

Ah. I thought you want the interoperability rather than low latency.

No there's no timer. The messages are pushed to the network immediately, 
if possible. The only case when message batching happens is when 
publisher publishes them faster then the network is able to accept them. 
In such case there's no latency impact. Thus, sending one message per 
packet is unlikely to improve the performance.

Martin