[181386] in North American Network Operators' Group
Re: Residential VSAT experiences?
daemon@ATHENA.MIT.EDU (Fred Baker (fred))
Mon Jun 22 18:36:54 2015
X-Original-To: nanog@nanog.org
From: "Fred Baker (fred)" <fred@cisco.com>
To: William Herrin <bill@herrin.us>, Nicholas Oas <nicholas.oas@gmail.com>
Date: Mon, 22 Jun 2015 22:35:45 +0000
In-Reply-To: <CAP-guGWod0ayQMq31ajL1Bq3cR3gS9uhh8i6Q9XwwEmnycOa9Q@mail.gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
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> On Jun 22, 2015, at 3:11 PM, William Herrin <bill@herrin.us> wrote:
>=20
> Two-way satellite systems based on SV's in geostationary orbit (like
> the two you're considering) have high latency. 22,000 miles out,
> another 22,000 miles back and do it again for the return packet.
> You'll start around 500ms latency and go up from there. Any kind of
> interactive session (like SSH and RDP) will be excruciating.
It is indeed. This is first-hand in the sense that I once worked for an =
earth station manufacturer and did a fair bit of work related to this =
environment, and second-hand in that my sister, for a while, used VSAT =
connectivity to her home.
The trick in the context is what's called a "performance-enhancing =
proxy", or PEP. What it does, in concept, is terminate a TCP connection =
at each earth station and use some form of private protocol over the =
bird. Cisco RBSCP (which maps TCP connections to SCTP sessions over the =
bird, =
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/configuration/1=
5-sy/ir-15-sy-book/ir-rt-bsd-sat.html) is an example of such a =
technology. The obvious benefit of a PEP is that it can convince a TCP =
sender to keep enough data in flight to make good use of the throughput =
rate of the satellite - you have a start-up issue with the first RTT, =
but after that it has essentially figured out what the effective window =
should be and makes that happen. The downside of a PEP is when the =
application is itself interactive (it's not about rate, it's about =
responsiveness clocked by end-to-end RTT) or the protocol in question =
isn't TCP (noting that TCP in IPsec ESP isn't TCP to the PEP - it's =
IPsec ESP, and can't be goosed along).
In my sister's case, her description of the service was somewhat =
colorful, and included the word "slow".
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