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Based on the SCPS-NP agreement OPNET Simulation Design

In Electronic Infomation Category: B | on April 20,2011

Abstract: To analyze the Advisory Committee on Space Data Systems (CCSDS, CONsultative Committee for Space Data SySTems) Series protocol features. To verify the CCSDS space data communication features based on a series of recommendations put forward proposals in the network layer (SCPS-NP, Space CommunicationsProtocol Specification-Network Protocol) performance. Communication through OPNET simulation software for modeling, the basic realization of the SCPS-NP agreement requires the function of the performance of the protocol analysis of Chinas development of space communication protocol recommendations.

0 Introduction

As countries continue to explore outer space resources, development and P3100SB datasheet and use of Internet technology and P3100SB price and the continuous development of the ground maturity. The world Internet traffic into the ground, create a unified data network world become a new hotspot. This requires a unified space efficient communication protocol for security. In this request, the system by the national space research organization composed of the Advisory Committee on Space Data Systems (CCSDS) has done a lot of work to develop a series of agreements.

1 CCSDS protocol architecture

CCSDS series of protocols can be modeled TCP / IP, classification hierarchy to the physical layer, data link layer, network layer, transport layer and P3100SB suppliers and application layer. Each layer contains multiple protocols. Specifically described as follows:

(1) Physical Layer

At the physical layer, CCSDS has developed the "Radio frequency and modulation systems" proposal. Provides communications needs of medium and deep space missions to near-Earth radio frequency and modulation system.

(2) data link layer

Data link layer includes the data link layer protocol and channel coding. The main development of the sub-protocol telemetry and remote sub-agreements for conventional spacecraft data system, the business is simple; advanced on-orbit data system protocol (AOS), for large spacecraft, many types of business; close-space link, close to each other for the space link between the spacecraft, mainly point to point communication. Channel coding in the development of BCH codes, convolutional codes, RS codes and data link the various data structures, etc. [2].

(3) network layer

At the network layer, transport layer and application layer, CCSDS has developed a TCP / IP protocol features a series of parallel proposals photogenic, that Space Communications Protocol Specification SCPS. The starting point is the need to adapt to space communications and the Internet as much as possible on the basis of compatibility and interoperability protocol. The Internet Protocol as the basis for the improvement of the space environment. SCPS-NP is one of the network layer protocol. Compared with the IP protocol, the major improvements in the following points: A guide of different lengths and head for the user in the functional trade-offs between efficiency; offers a variety of routing patterns, increased flooding addressing; provided by the configuration management system end to end routing; in the SCPS Control Message Protocol (SCMP), the increase in channel quality due to disruption caused by the signaling link.

(4) Transport Layer

At the transport layer, in addition to the corresponding SCPS-TP transport layer outside, CCSDS has developed a protocol for file transfer CFDP, CFDP provides both a transport layer function, but also provides application-level file management function [2]. In addition, end to end data protection with a proposed capacity of the SCPS Security Protocol (SCPS-SP), is an Internet IPsec protocol improvements have been made.

(5) Application layer

In the application layer, CCSDS developed the text of the File Transfer Protocol SCPS-FP, lossless data compression, spatial sub-agreements.

2 SCPS-NP Protocol Modeling

Order to verify the performance of SCPS-NP agreement, this uses the OPNET software to model testing. OPNET modeling using three mechanisms: the top layer of the network, reflecting the characteristics of the network topology; followed by the node level, by the appropriate protocol modules, reflecting the characteristics of the device; the bottom layer for the process to the state machine form to describe the proposal, reflecting the specific features of the agreement is how to achieve [6]. Three-tier system based on modeling, simulation used in the satellite - ground station communication scenario, Figure 1 node model for the satellite ground station with a similar node model, in which agreement on the part of the SCPS-NP are:

scps_np_encap module, SCPS-NP agreement guided the first package module, the data package decapsulation;

scps_np module, SCPS-NP protocol module, the specific realization of SCPS-NP the required functions;

router_map module, routing table update module provides static or dynamic routing table updates the routing table.

node simulation model in Figure 1.

2.1 scps_np_encap process module design

Main task of the module is to guide the data package SCPS-NP header or decapsulation remove lead head, the process design shown in Figure 2.

the process of Figure 2 scps_encap module structure

First set INIT to initialize state to enter the WAIT state, then according to different packet streams, the packet encapsulation or decapsulation. SCPS-NP header package lead length and format of the user to select the node properties. Subcontracting agreements with the space provided similar services, the guide head length is 4 bytes, with the IPv4 protocol to provide similar services, the lead head and a length of 20 bytes.

2.2 scps_np process module design

Scps_np module main function is to SCPS-NP agreement implementation. The process design shown in Figure 3.

First set INIT to initialize state to enter the WAIT state, when the data came from the upper module, the access to deliver state, sending data to the network. When the data came from the network, the access toup state, the received data for testing, will meet the protocol standards and the destination address data into the upper node for further processing, the destruction does not meet the conditions of the package and return to WAIT state. If the node has routing and forwarding packets need to enter the router state. In the router state, according to protocol requirements, routing control process, then the user selects the different routing methods. There are static, dynamic, Hong routing three ways. Forward, go back to WAIT state. Routing information provided by the module router_map.

the process of Figure 3 scps_np module structure

2.3 router_map process module design

Router_map modules main task is to maintain and update the routing table, the process design shown in Figure 4.

First set INIT to initialize state to enter the WAIT state, when the user selects a static route in the WAIT to remain intact. Static routing information has been set.

Dynamic routing mode when you select to create a self-interruption, every once in a routing table update interval. When the interrupt arrives, enter the update state, according to location information at this time to recalculate routes.

the process of Figure 4 router_map module structure

3 Simulation Results Analysis This simulation model

SCPS-NP agreement implemented the basic elements can be combined to do a variety of other agreements simulation test simulation, the SCPS-NP agreement with the main features of the first length of the different leads of control for the protocol overhead, and space is limited, The following guide describes only the first length of the different under the same conditions in the other, the impact of the throughput.

Throughput is defined as a node in unit time, the effective user successfully received bytes (bit / s), ie throughput = (successfully received the total number of bytes of data - the number of overhead bytes) / total time . Its performance depends on the data transmission business unit of proportion used in overhead and channel bit error rate and other factors.

IPv4 protocol for similar lead of 20-byte header and a simple protocol similar to sub-space 4-byte header lead the first two guided modes, in the 10-5 bit error rate, the flow of the upper FTP 1 MB file size satellite downlink transmission using AOS case is apparent from Figure 5, the first derivative can be simplified to bring greater network throughput and reduce the protocol overhead. Speed ??up file transfer.

Figure 5 under different leads in the first length of the throughput compared

4 Conclusion

With the development of Chinas air and space, between the network of spacecraft, spacecraft and ground network integration is the current direction of development of urgently needed. Integrated network in the world of research, CCSDS made many valuable suggestions, to deepen the understanding and study of these proposals on Chinas space construction of the network protocol has a good sense of reference. A Rough studied here, one proposal SCPS-NP, to achieve its basic functions. However, agreement is a huge CCSDS Series architecture, the need for the joint force in order to thoroughly understand.

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