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Space Transport Protocols TCP, SCPSTP

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The Space Communications Protocol Standards (SCPS) project was developed to ... include GEO, HEO, and LEO (including constellations such as SDI and Teledesic) ... – PowerPoint PPT presentation

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Title: Space Transport Protocols TCP, SCPSTP


1
Space Transport Protocols (TCP, SCPS-TP)
  • Fred Brosi
  • February, 2001

2
What is SCPS?
  • The Space Communications Protocol Standards
    (SCPS) project was developed to improve
    communications performance in a satellite
    environment
  • Intended environments include GEO, HEO, and LEO
    (including constellations such as SDI and
    Teledesic)
  • SCPS extended the internet protocol suite

3
SCPS extends the internet protocol suite
Internet Stack
OSI Stack
Sample Protocols
7
Application
FTP, SCPS-FP
Application
Presentation
6
Session
5
TCP, SCPS-TP
End-to-End
Transport
4
IPSEC, SCPS-SP
3.5
IP, SCPS-NP
Internetwork
Network
3
Network Access
Various protocols (e.g., CCSDS commercial,
military)
Data Link
2
1
Physical
4
SCPS Capabilities
Record read record update
Core
File record Integrity
Automatic restart
Interoperable
/-
User suspend/resume
Internet FTP
Suppress ASCII reply codes.
SCPS FILE TRANSFER PROTOCOL
7
Congestion control appropriate formixed-loss
environments (congestion, corruption,
outage) Selective negative acknowledgment Robust
header compression Window scaling (long/fat
pipes) Partial Reliability service
(BETS) Delimitation of record boundaries Timesta
mping for high ratesequencing, delay measurement.
(SCPS-FP)
(Optional)
Core
Interoperable
SCPS TRANSPORT PROTOCOL
/-
Internet
4
(SCPS-TP)
TCP/UDP
SCPS SECURITY PROTOCOL
3.5
(SCPS-SP)
(Optional)
Authentication guarantee of the identity of a
source Access Control prevention of
unauthorized access Integrity protection
against modification Confidentiality protection
from disclosure.
SCPS NETWORK PROTOCOL
3
(SCPS-NP)
(Optional)
Provide both connectionless and managed-
connection routing Support precedence
(priority) based handling Offer multiple routing
options Signal errors to the layer
above Support packet lifetime control Scaleable
- tailor capability to need, e.g.,
highcommunications efficiency in
constrainedbandwidth conditions.
2
Underlying Link Protocol
SCPS sits on top of existing link capabilities,
and augments them
5
When does the Internet stack have problems?
  • When there is loss due to sources other than
    congestion
  • When there are shorter round trip times in the
    network than yours (other users recover fast and
    get first in line)
  • When sessions span spacecraft contacts or require
    handovers between ground stations (intentionally
    or unintentionally)
  • When systems support varying bandwidthdelay
    products
  • When there is significant bandwidth asymmetry
  • When there is limited bandwidth, CPU, or memory

6
What basic extensions to TCP does SCPS make?
  • Selective NACK for faster, bit-efficient loss
    recovery
  • Loss-tolerant congestion control
  • Rate control (with or in lieu of congestion
    control)
  • Loss-tolerant header compression
  • Partial reliability service
  • Ability to use SCPS-SP and/or SCPS-NP and/or IP
  • Retains interoperability with standard TCP
    its extensions

7
The SCPS Transport Protocol (SCPS-TP)
  • Transport protocols support end-to-end
    communication only active at end points
  • SCPS-TP is Internet TCP and UDP, plus extensions
  • SCPS extensions improve operation in the space
    environment
  • Result end-to-end communication and reliability
    to suit mission requirements

8
Requirements for Reliable Data Transfer
  • Support for end to end data transfer
  • Transfer with full reliability (complete,
    correct, in sequence, no duplication)
  • Uplink for command and table loads
  • Downlink for compressed data transfer
  • Transfer with best effort reliability (correct,
    in sequence, no duplication, possibly with gaps)
  • For transfer of telemetry, image data, etc.
  • Transfer with minimal reliability (correct,
    possibly incomplete, possibly out of sequence)
  • Minimal reliability must support multicast
    operation
  • Other requirements address priority, etc.

1993 SCPS Exploratory Study
9
Factors affecting use of TCP in terrestrial and
spacecraft communication environments
10
Modifications to TCP to support spacecraft
communication environments
11
Things to remember about SCPS-TP
  • SCPS-TP is TCP and UDP with modifications to suit
    the spacecraft communications environment
  • Depending on configuration options selected,
    SCPS-TP can be less than TCP, identical to TCP,
    or a super-set of TCP
  • Mission requirements dictate which options are
    selected
  • A few profiles (2 or 3) will cover the majority
    of mission classes

12
SCPS File Transfer Protocol (SCPS-FP)
  • Files are named collections of data - could be
    in memory, mass storage, etc.
  • File transfer protocols coordinate movement of
    files (or parts of files) between systems
  • SCPS-FP is derived from FTP
  • Extensions support movement of file records,
    addition of integrity checking, and
    interrupt/restart support

13
SCPS-FP is Internet FTP With Extensions
  • SCPS-FP extensions to Internet FTP include
  • Record Read
  • Record Update
  • Autorestart
  • Manual Interrupt
  • Suppression of Reply Text
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