Transaction based technology

Transaction based technologies can provide cost effective support for applications with low data transmission requirements. Generally, these applications send requests/information in form of small packages (couple of hundred bytes) to a central server, that responds to these requests, stores the information and acknowledges these with also small packages (couple of hundred bytes). The terminal equipment can connect to the network through serial port or 10 Base-T Ethernet interface.

Hungaro Digitel Ltd. supports the transaction type low data transmission requirements through its Skystar Advantage system.

Skystar Advantage rendszer

The Skystar Advantage system – representing a high level VSAT technology – has been developed and is manufactured by Gilat Satellite Networks Ltd. It has been designed for continuous operation, its availability is high, the MTBF value of the equipment is the highest in the industry (10 years). The system can be expanded easily, quickly and efficiently. The network management system is capable of managing systems containing 3,000 VSATs.

STRUCTURE OF OUR SKYSTAR ADVANTAGE SYSTEM

The central terrestrial station (HUB) includes

• the central antenna (3.7 m),
• the RF and baseband equipment,
• the NMS (Network Management System) system.

For reasons of high reliability, the equipment of the central terrestrial station are duplicated.

The terminal point VSAT equipment set includes

• a 1.2 m diameter parabolic antenna,
• an outdoor unit (ODU) with the RF terminal equipment,
• an indoor unit (IDU) with the RF and baseband equipment.
  
  The equipment use one or more outbound channels (HUB-VSAT direction) and an inbound channel (VSAT-HUB direction) with the necessary bandwidth for the actual traffic for data transmission.
  
  Hungaro DigiTel Ltd. uses a satellite (AMOS) operating in the Ku band (from 10.95 GHz to 14.50 GHz).

Channel access

HUB-VSAT direction

TDM type (statistical multiplexing), the packets are addressed and put in a common queue, the system sends them from here through the appropriate outbound channel to the VSATs. The channel speed can be centrally configured (set).

VSAT-HUB direction

The VSATs use a channel set (2-4 MHz) accessible for each terminal point. The channel set operates with an efficient and flexible TDMA and FDMA combination (time and frequency division ALOHA access). This channel access protocol is ideal for interactive traffic using short messages and provides a couple of seconds response time. Beyond this, in case of heavy traffic, dedicated access can be provided (fixed frequency assignment), so the high traffic terminal points do not increase the possibility of collision. Transmission speed of VSATs is 38.4 kbit/s.

The network management system (NMS)

The network management system (NMS) provides network monitoring and equipment control. The NMS software consists of client/server applications running with UNIX operating system and operates on SUN Ultra 10 stations. Network configuration, logging of error events and alarms, collection of statistical data is provided also in the management system.

The internal protocol (backbone) of the system realizes levels 1, 2 and 3 of the OSI model, and provides reliable connection between VSAT equipment and the HUB. Parameters of the internal protocol can be configured in the management system.

Supported protocols

• X25 (SVC and PVC)
• SDLC
• Asynchronous X3/X28/X29
• Token Ring
• Ethernet
• TCP/IP
• Bisynchronous

The system is capable of supporting several protocols simultaneously, so the user can apply the same satellite system for its different applications.

Hungaro DigiTel Ltd. – for reasons of fully meeting its partners’ requirements – has also purchased and installed the Skystar Advantage system, further enhanced by GILAT.

Features of the NG SSA system

Outbound (64 kbps - 2 Mbps)

• 64, 128 kbps BPSK
• 256, 384, 512, 768, 1024, 2048 kbps QPSK
• Viterbi: 1/2 +Reed Solomon
• Statistical TDM access

Inbound (76,8 - 153,6 kbps)

• 76.,8, 153,6 kbps MSK
• Viterbi
• Dual Inbound Rate: 153 kbps MSK
• Inbound access:

RA (random access); interactive applications.
DA (dedicated access); applications with higher bandwidth requirement.
ADA (RA/DA dynamic transitions); combined type applications.
On demand resource allocation. According to the user’s needs, higher bandwidth can be allocated to the DA channels, (Dual Inbound Rate), or a DA channel can be divided between several terminal points (PDA).
Protocol spoofing (local production of TCP/IP acknowledgement).

Further possibilities in the NG SSA system

• Broadcast/Multicast technologies (simultaneous download of identical information – prices, inventory records, restriction lists, etc. – at multiple locations).
  
  
• Reliable Data Broadcast (with end-end acknowledgement mechanism).
  
  
• X25 Broadcast (no end-end acknowledgement).
  
  
• Teletext type service.
  
  
• UDP Broadcast/Multicast and IGMP Internet applications, software update.
  
  
• Audio Broadcast.
  
  
• Video Broadcast.
  
  
• When using high speed outbound, real time transmission of digitalized voice and video signals, so, for example – supplemented with studio equipment –, the system can be used for implementation of a full remote education network.
  
  
• Protection possibility with Hayes modem (Dial Backup function).
  
  
• The NG SSA system provides special possibilities in cases when the user has a special interest in having a disruption free data transmission. To assure this, the VSAT terminal equipment of the NG SSA system can be supplemented with Dial Backup modems. With this protection, no operator intervention is required in case of disruption of the satellite link, it automatically swaps to the modem connection.
  
  
• Widened X.25 Hunt Group possibilities for 255 Hunt Groups, max. 48 ports can be assigned to each of them.
  
  
• Enhanced data security.
  
  
• The NG SSA system supports integrated encryption in both outbound and inbound direction.
  
  
• Port priority function.
  
  
• Four level priorities can be assigned to the user’s ports. This assures the short response time required by interactive applications, even in case of higher traffic load.