[Sis-csi] 2:30 Eastern it is
Dave Israel
dave.israel at nasa.gov
Thu Jan 25 16:17:07 EST 2007
The TDRSS channel is capable of providing a 25 Mbps forward link. I think
current hardware limitations at the ground station keep the current usage
lower. The C3I spec currently specifies a 25 Mbps maximum forward link.
If Will is asking "What is 'uplink'?" because the term doesn't make as much
sense when you have space-to-space crosslinks, the short answer is that
space-to-space crosslinks are not in Phase 1. One of the end points of any
space link is on Earth and the uplink or forward link is the data path from
the Earth to the user.
Also, I should have mentioned that the CANDOS picture I sent out is
probably not the final version. It shows all the basics, but I'm sure
there's some subtle things that aren't captured exactly right yet.
Dave
At 03:41 PM 1/25/2007, Scott, Keith L. wrote:
>People I heard on the call:
> Keith Scott
> Howie
> Keith H.
> Scott B.
> Ed Criscuolo
> Will Ivancic
> Larry Schneider
> Ed Greenberg
>
>** Request from the high-rate uplink WG
>
>Current TDRSS uplink rate is 25Mbps (Dave?)
>There seemeed to be some confusion about what the real rate(s) were:
> S-band is 2-4 mbps
> Ku ~3Mbps up and down
>
>Scott: to estimate the required uplink data rate, find out the maximum
>rate at which you can forward packets, and use that. If the first
>spacecraft on orbit has to serve 3 others or 60 others, doesn't matter,
>they get what they get but at least we'll be able to get the data up as
>fast as we can forward it. For this exercise, assume a dedicated
>processor for packet handling. Keith H. notes that several years ago
>i386 class machines could saturate a 10Mbps Ethernet, so even rad hard
>things nowadays should be able to do that.
>
>What rates can VxWorks forward at over the past N years?
>VxWorks -- how fast can the network stack forward.
>Scott and/or flight software people at Goddard may have some VxWorks
>machines.
>Larry Schneider has a lot of VxWorks machines to handle the ISS
>high-rate uplink
> VxWorks expert is off this week but email out questions to
>Larry (to give to
> Alex).
>
>Ed -- driver for uplink may be HD uplink video (~5mbps)
>Cap everything by about 30-50Mbps because we don't think uplink radios
>can do more.
>
>Will sent email
>"What is 'uplink'?"
>
>
> --keith
>
>-----Original Message-----
>From: sis-csi-bounces at mailman.ccsds.org
>[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Scott, Keith L.
>Sent: Thursday, January 25, 2007 12:35 PM
>To: sis-csi at mailman.ccsds.org
>Subject: [Sis-csi] 2:30 Eastern it is
>
>Ok, we're on for 11:30 pacific, 1:30 central, 2:30 eastern on
>Thursdays, starting today.
>
>Phone Number:
> 703 983 6338 (x31550) in Washington
> 781-271-6338 (x16338) in Bedford
> 866-648-7367 (866-MITRE-MP) Toll Free
>
>Meeting ID: 55555
>
>Today's Agenda:
> Recap from Colorado Springs Meeting
> Request for requirements info from High-Rate Uplink WG
> Red Book 1 Items:
> Collect information and distribute
> GPM (Jane)
> CANDOS (Dave/Keith H.)
> SNIS (Dave)
> Shuttle&ISS (Larry)
> Surrey satellite (Loyd/Will)
> Mash these against requirements
> From the 'assumptions' slide, list possible solutions
>to each of the requirements
> Downselect possible solutions
> Assign people to write text
> Publish book
>
> --keith
>
>-----Original Message-----
>From: sis-csi-bounces at mailman.ccsds.org
>[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Scott, Keith L.
>Sent: Thursday, January 25, 2007 9:34 AM
>To: sis-csi at mailman.ccsds.org
>Cc: Greg.J.Kazz at jpl.nasa.gov
>Subject: [Sis-csi] Telecon scheduling and request for requirements
>
>========== Telecon scheduling
>
>I apologize for this but we're going to need to reschedule our weekly
>telecons, starting with today's. Hopefully this will be the last time
>we'll have to do this for a while. I'll start off by proposing one
>hour earlier on Thursdays (11:30 pacific, 1:30 central, 2:30 eastern).
>Please let me know if this works for you and, if not, what would. If
>we can't come to consensus quickly we'll wave off this week's telecon,
>but please see below on a request for requirements from the High Rate
>Uplink WG in SLS; I'd like to hash this out over email and get them an
>answer by next week.
>
>========== Request for Requirements from High-Rate Uplink WG
>
>Following up from the Colorado Springs meetings, we've received a
>request for requirements from the High Rate Uplink WG (CWE at
>http://public.ccsds.org/sites/cwe/sls-hru/default.aspx?RootFolder=%2fsi
>tes%2fcwe%2fsls%2dhru%2fPublic%2fCharters&View=%7bED7A93D1%2d1BB1%2d403
>3%2d8432%2dD7382F71947D%7d). In particular they want to know what
>kinds of uplink rates the cislunar architecture would require. I think
>that our DOWNLINK requirements should at least cover current shuttle
>and station rates of ~150Mbps, but I don't think we require full
>symmetry on the uplink.
>
>The largest driver for the uplink rate might be crew accommodation of
>live HDTV events, which would be on the order of 5-10Mbps, if they were
>actually provided. If we had that then we should be able to cover most
>or all of the operational uplink traffic in the margin! :) Just as
>another point of reference, 150Mbps of TCP downlink would require
>~2Mbps of TCP ACK traffic. We also need to remember that in a
>networked world such as we've proposed, one uplink may be serving
>several spacecraft.
>
>In any case, we need to provide them with a number that:
> 1) Is large enough to cover our requirements for a reasonable
>amount of time
> 2) Is not so large that they roll on the floor laughing at us
>
>Regardless of the rate requirement, RFC3819 (Advice for Internet
>Subnetwork Designers) and maybe rfcs RFC3155 (End-to-end Performance
>Implications of Links with Errors) and RFC3366 (Advice to link
>designers on link Automatic Repeat reQuest (ARQ)) seem relevant.
>
> --keith
>
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______________________________________________________________
Dave Israel
Leader, Advanced Technology Development Group
Microwave & Communication Systems Branch
NASA Goddard Space Flight Center Code 567.3
Greenbelt, MD 20771
Phone: (301) 286-5294 Fax: (301) 286-1769
E-mail: dave.israel at nasa.gov
"Without deviation from the norm, progress is not possible." -Frank Zappa
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