Subject: [pcp] discuss: multiple port allocations

From: "Dan Wing" <[email-masked]>
Date: Tue, 7 Dec 2010 11:18:24 -0800

This is one of the PCP discussion points.

(This repeats a thread from earlier this week, but encloses it into
the set of things we need to resolve so I can successful edit 
pcp-base-01.)

http://tools.ietf.org/html/draft-wing-softwire-port-control-protocol-02
included the ability to request multiple ports.  Requesting multiple
mappings is an optimization to reduce PCP request/response messages.
PCP is trying to stay as simple as possible to finish the specification
soon and to keep implementations as simple as possible to meet the
basic needs for port mapping -- and keeping it similar to how TCP
and UDP create mappings in NATs (which is done one port at a time) 
goes a long ways towards that goal.

I haven't found many protocols that would have much benefit from
this optimization, though.  Web servers need two ports (HTTP and 
HTTPS), IMAP and POP servers also need two ports (for their 
unencrypted and encrypted variants) -- but getting a webserver 
or mail server running is not time- or bandwidth-critical.  RTP
needs two ports (RTP+RTCP; separate issue if they need to 
be adjacent) and it is time critical.  However, an application
using RTP can pre-allocate its ports (at application startup)
using PCP so this is not important, either.  And the 4 PCP
messages (to allocate two ports at application startup) are not 
significant compared to the RTP traffic (when a call is active) 
or to the application-level SIP (or Skype) keepalive traffic.

Is there an application protocol that would benefit from the
ability to get 2, 3 or 10 ports in one PCP message?  If so,
let's talk about that application protocol and understand how
it could benefit.

---

From: Lars Eggert <[email-masked]>
Date: Wed, 8 Dec 2010 12:27:02 +0200

Hi,

> mappings is an optimization to reduce PCP request/response messages.

packets are cheap. Keep PCP simple, and do one mapping per transaction.

Lars

---

From: Tina Tsou <[email-masked]>
Date: Thu, 09 Dec 2010 09:56:21 -0800

In my mind, this feature can be fulfill the function as an IPv4 address
sharing scheme, treating some of the port number bits as part of an extended
address.
Perhaps PCP WG can consider it jointly with softwire WG.

Best Regards,
Tina TSOU
http://tinatsou.weebly.com/contact.html

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Dan
Wing
Sent: Tuesday, December 07, 2010 11:18 AM
To: [email-masked]
Subject: [pcp] discuss: multiple port allocations

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