i-Direct satellite communication system
System architecture
iDirect produces the full-range family of the products assigned for distributed IP-networking with utilization of geostationary Artificial Earth Satellites (AES). At the moment, three models of the Central Earth Communication Stations (hubs) (CECS) are manufactured, as well as three series of modems assigned for installation on remote sites.
All iDirect products are based on the MF-TDMA principle – time-division multifrequency multiple access, on-call slotted pass-band, and present the full platform for rendering IP-services. In spite of the fact that CECS low-end models are not able of ensuring the MF-TDMA mode because only one demodulator is available, all remote modems are able of operating under MF-TDMA mode with «rapid» (up to each IP-packet) switches among carrier frequencies.
iDirect systems demonstrate high degree reliability meeting the requirements set by the force, governmental and rescue structures all over the world, as well as unsurpassed flexibility and extendibility. All critical components of the system could be reserved. 5-IF CECS allows creating any combinations from 5 AES’s of any range, and 20 transponders. While the CECS’s functionality of the medium-class (Private Hub) and economy class (Mini hub) is limited as compared to 5-IF capacity, nevertheless, the system’s software and the system management software is the same for all iDirect CECS.
Using the L-band intermediate frequency allows operating in any range applying the standard LNA’s and BUC’s. iDirect terminals ensure connecting subscriber interface units (LANs, telephony gateways, videoconference systems, SIP-telephones) under standard Ethernet interfaces.
CECS iDirect-based networks consist of one «forward» (from the CECS to remote terminals) and one or several «backward» (from remote terminals to CECS) channels. Forward channels ensure the speed range from 128 Kbit/sec to 18.2 Mbit/sec with the interval of 1 Kbit/sec. Backward channels operate at a speed from 64 Kbit/sec to 4.2 Mbit/sec.
iDirect products have been developed for rendering IP broadband services. Taking into account both technical and economic AES specificity, the iDirect products have been expressly optimized for the space segment utilization.
Data link layer (DLL). Channel level
All iDirect products support different modulation circuits поддерживают различные схемы модуляции (2, 4 and 8 PSK), and use solely the block-type noiseless coding coefficient (antijamming ability) of different capacity (from 0.433 to 0.879) that allows their efficient operation with any AES in any point of Earth. Turbocoding application allows saving up to 41% of energy as compared to Reed-Solomon codes, which makes saving on the system radiofrequency components and remote terminals possible. iDirect products are universal, and allow extremely precise regulation of forward and backward channels speed, with the interval of 1 Kbit/sec.
iDirect CECS’s possess the built-in Automatic Power Control functions that ensure reliability and optimal utilization of AES power resources.
The multiple access support system as distinct from the generally accepted approaches is not based on the stochastic access principles (Aloha), and provides for the absence of collisions in the communication link, as well as the maximal assignment speed and frequency band predictability.
There is no a «request» channel in the system as such, for ensuring the passband swift assignment on call. Each terminal reports on the queue condition re information transmission in each time interval allocated for it. Such a mechanism allows uploading the satellite resource with only effective traffic releasing it from the need to form pseudoassigned channels or separate «request» channels.
Network layer
The system represents a distributed IP-router supporting a practically unlimited number of virtual IP-networks. This allows creation of independent IP-networks above the single radiofrequency resource. Each remote modem is able of servicing several similar virtual networks.
One of the major problems related to TCP/IP traffic transmission via satellite communication channels consists in a signal passage delay that prevents TCP sessions from using the entire accessible passband. TCP traffic acceleration built-in functions allow transmitting large data bulks without installing additional software on remote PC’s, as well as special acceleration complexes from the CECS side. In case of a client’s using the means of information cryptoprotecting, iDirect produces separate units (devices) for TCP sessions acceleration.
Ensuring the quality of service (QoS)
The QoS system is based on the effective load packet classification by service classes. The classification in its turn is based on the filters operation that distribute them into different queues while analyzing the IP-packet parameters. The filters are able of analyzing any combinations of the following parameters:
- VLAN-а number.
- IP of a resource and receiver’s address.
- Prioritization parameters (DSCP, TOS).
- IP protocol (TCP, UDP, ICMP, GRE, IPSec….).
- Protocol parameters (TCP or UDP ports, or ICMP commands, etc.).
Each queue list is characterized by the priority (absolute or weight), traffic type (regular, real time with the variable passband, real time with the permanent passband), and the need for a passband urgent assignment (CIR assignment).
As in any IP-router, a packet transmission dispatcher processes push-up lines in the order of priority descending. But as the remote modem needs obtaining a passband for traffic transmission, the modem transfers its lines status with each packet transmission towards the CECS side.
The system allows transmitting several packets within one time interval, which in case of transmitting a large number of small packets (for instance, VoIP) allows an even more effective utilizing of the satellite resource.
Classification and traffic transmission diagram
System components description
CECS iDirect Hub
At present, iDirect produces 3 basic CECS models: 5-IF, Private Hub and Mini Hub. All iDIrect CECS’s possess the similar architecture. The radiofrequency part, protocol processor servers, management system servers and master router are separated within the range of any decision. The iDirect CECS differs in various extendibility capacity, the number of remote maintained terminals and redundancy potential.
CECS iDirect 5-IF and Private Hub support operation in the «star» mode and fully connected MESH-mode when the 5000 and 7000-series terminals transfer information directly to each other avoiding the CECS. A Mini Hub supports only the «star» mode.
All CECS’s support only the following functions:
- P routing.
- Full system of the traffic prioritization and service quality assurance.
- RTP (cRTP) headlines compression.
- TCP flow acceleration.
- Ethernеt VLANs.
- Portable and mobile remote modems.
- L-band for any range and frequency compatibility.
5-IF CECS
Except those listed above, the following functions are accessible at 5-IF CECS:
- MF-TDMA support.
- Creation of several networks with a single CECS.
- Simultaneous operation with several (up to 5) AES.
- Simultaneous operation with several ranges.
- Simultaneous operation for 20 transponders.
- Creation of completely independent satellite networks on a single CECS.
- Fully reserved solution.
- Opportunity for SCPC organization.
5-IF mounting rack’s appearance
ЦСЗС 5IF CECS represents a mounting rack for installing linear planes (modems or demodulators), with the individual reserved power supply, reserved synchronization resources of 10 MHz, and reserved forced cooling fans. The 5-IF mounting rack is supplied with built-in splitters and 5 pairs of inputs/outputs, thus allowing simultaneous operation with different AES, ranges, transponders.
CECS Private Hub
CECS Private Hub represents a single reserved modem linear plane in a separate body. The Private Hub allows organizing one forward and one backward channel. The opportunity for CECS Private Hub modernization up to 5-IF is accessible.
CECS with Mini Hub
Opportunities of a Mini Hub are even more restricted as compared to those of a Private Hub model. Networks with the maximal number of remote terminals up to 30 could be organized basing on the Mini Hub.
All CECS’s possess similar architecture differing only in the number of modems and level of reserving. The following table presents consolidated parameters of all CECS’s:
CECS consolidated parameters
Parameter 5IF Private Hub Mini Hub
Network topologies STAR, MESH, SCPC STAR, MESH STAR
Number of forward channels (networks) Not limited 1 1
Number of backward channels Up to 20 per each network 1 1
IP speed in a forward channel From 128 Kbit/sec to 18Мbit/sec
IP speed in a backward channel From 64 Кbit/sec to 4,2 Мbit/sec
Modulation types BPSK, QPSK, 8PSK
Character speeds From 64 Кsim/sec to 11,5 Мsim/sec in a forward channel
From 64 Кsim/sec to 2,875 Мsim/sec in a backward channel
FEC Turbo 0.879, 0,793, 0.533, 0.431 in a forward channel
Turbo 0,793, 0.66, 0.533, 0.431 in a backward channel
Protocol processors
Protocol processors present the system’s main part. Their role includes collection of data on the required passband, forming the intervals and frequencies occupation schedule by remote stations, service quality assurance, mounting rack linear planes and remote modems control, collection and delivery of statistics to the management system, etc.
Standard 1U servers by IBM are used as a platform for NMS servers under OC Linux control. The servers are adjusted to maximal reliability with the help of both OC Linux means or basic components hardware redundancy. From the point of view of the onshore IP-network, Protocol Processors (PP) look as a router supporting the routing information protocol RIP-2.
PP gate the entire traffic through themselves assuring its prioritization, acceleration, etc. As for the control system (console) servers, the servers manufactured by IBM and OC Linux are used for PP, ensuring high capacity and reliability. It will possibly be needed to equip CECS with additional PP’s because PP’s let pass the traffic through themselves in case of networking with a big number of terminals (more than 1000). This happens without CECS stopping and service breaking; simply one more server is added, the software is installed, and the control system is reported that one more PP is available and ready to process the traffic. PP’s operate in the hot reserve.
Control system servers
Control system servers present the central storage for configurations and statistical data of all networks serviced by a certain CECS.
For actions execution related to configuration or reviewing statistics, the client’s control software is used, being performed on any PC under the OC Windows control. Architecture of the (management) control «client-server», and enhanced fault tolerance of control servers allow installing the iDirect CECS in unattended premises. There are scripts for control servers’ geographical distribution (spacing) to ensure even higher level of fault tolerance. The control servers loss does not effect the clients’ servicing.
As well, the «Client-Server» architecture allows ensuring a remote access to the system via Virtual Private Networks that enables effective control by the CECS group from the remote SCC. The following figures illustrate the iMonitor SW appearance (network monitoring).
iMonitor SW
Remote terminals
All modems manufactured by iDirect (series 3100, 5100, 5300 and 7000) possess the following basic functions:
- Operation with forward physical channels up to 18 Mbit/sec with modulations (2, 4 and 8 PSK).
- Operation with backward physical channels up to 4.2 Mbit/sec (2.4 PSK).
- Operation in a multifrequency mode.
- Prioritization and service quality assurance.
- Allocation of the band for determined applications.
- Support of virtual LANs (VLAN).
- TCP Protocol acceleration for effective transmission via AES.
- Power and 10 MHz reference (pedestal) frequency supply for SHF equipment.
Series 5100, except general characteristics, supports traffic compression, operation in the «point-point» (iSCPC) mode, and possesses 8-port in-built Ethernet switch board. Series 5300 has all functions of the series 5100, and is able to operate in the fully connected mode (MESH).
Series 7000 modems possess all functions of the 5300 series, plus the enhanced processor throughput, the body integrated in the rack, and are positioned as the units for mobile communication systems.
| Series | 3100 | 5100 | 5300 | 7000 |
| Topology | STARSTAR, SCPC | STAR, SCPC, MESH | STAR, SCPC, MESH | |
| SHF interface | L-band | |||
| BUC power | +24 V (up to 4 Watt Ku or to 5 Watt С-band) | +48 V (up to 8 Watt Ku or to 10 Watt C) | ||
| LNB power | +19.5В | |||
| SHF interfaces | Ethernet | 8 Ethernet | ||
| Data compression | Only headlines | Headlines and data | ||
| IP functions | Firewall, QoS, DHCP server/helper, DNS cache, cRTP | |||
System power parameters
All system components (both from the side of CECS and modems) possess identical power parameters. The system power parameters for different systems of modulation and coding are presented in the following table:
| Parameter | Value | ||||
| Character speed | |||||
| Forward channel | |||||
| Minimal | 0.064 Мсим/с | ||||
| Маximal | 11.5 Мсим/с | ||||
| Backward channel | |||||
| Minimal | 0.064 Мсим/с | ||||
| Маximal | 2,875 Мсим/с | ||||
| Demodulation threshold | Modulation | FEC | Block size | Eb/No for BER 10E-9 | C/N |
| Forward channel | 8PSK | 0,879 | 16K | 7,9 | 12,1 |
| 8PSK | 0,793 | 4K | 7,0 | 10,8 | |
| QPSK | 0,879 | 16K | 4,81 | 7,25 | |
| QPSK | 0,793 | 4K | 4,6 | 6,6 | |
| QPSK | 0,533 | 1K | 3,9 | 4,2 | |
| QPSK | 0,495 | 4K | 4,0 | 3,95 | |
| BPSK | 0,879 | 16K | 4,76 | 4,2 | |
| BPSK | 0,793 | 4K | 3,91 | 2,9 | |
| BPSK | 0,533 | 1K | 4,23 | 1,5 | |
| BPSK | 0,495 | 4K | 4,0 | 1,0 | |
| Backward channel | QPSK | 0,793 | 4K | 4,6 | 6,6 |
| QPSK | 0,66 | 1K | 5,4 | 6,6 | |
| QPSK | 0,533 | 1K | 3,9 | 4,2 | |
| BPSK | 0,793 | 4K | 3,91 | 2,9 | |
| BPSK | 0,66 | 1K | 4,9 | 3,1 | |
| BPSK | 0,533 | 1K | 4,23 | 1,5 | |
In conclusion it seems possible to state that the principle «the single system – all services» is implemented on the basis of the iDirect platform. At that, the platform ensures variety of services depending on a customer’s demand. In case if it is required to renew a service or application using the architecture with the voice gateways and capacity of the iDirect platform itself, the range of required services could be extended, for example: increase of the DF speed in an IP channel; increase of the number of voice ports or number of envelopes in the E1 flow while connecting to a customer’s PBX. The unified types of terminals and flexibility regarding the used equipment will allow making an offer meeting any customer’s demands.