DACNET: An Intranet of DAC connecting Directorates & Field Units

Requirement: Dialup for Field UnitsDedicated Link for Directorates

While finalizing on the network design aspects regarding topology, other networking module requirements and network protocol usage, it is essential to keep the bandwidth requirements in perspective. Some of the factors which influence the required bandwidth are:

Type of application Type of transaction (interactive/batch) No. of simultaneous users on the network Transaction size Response time expected

Network Design

VSAT (Very Small Aperture Terminal)

• Outdoor Unit: Antenna & RFT

Antenna: Reflector, Feedhorn & Mount

RFT: LNA, Down Converters

Upconverters, HPA

Indoor Unit: Functions as a modem and also interfaces with end user equipment

VSAT Applicationso Superior quality full mesh telephony with fax o High volume file transfers o Video conferencing on demand o Internet access o Point-of-sale credit card and check verification o Electronic funds transfer for debit cards, pharmacy

adjudication, and electronic benefits o High volume, secure automatic teller machine (ATM)

transactions o "Back office" applications such as accounting, time

and attendance, and e-mail o Wireless local loop (WLL) connectivity

Advantages of VSATs• Last Mile Problem: Guarantee seamless

communication even across the last mile• Reach• Reliability: (99.5 %, 80-85% in case of Lease Line)• Support for mission-critical applications: ERP,

Billing & finance and data broadcast• Time: Less deployment time)• Flexibility: Enormous expansion capabilities• System Integration: Single point of contact• Network Management• Maintenance: Low Mean Time Repair (MTTR)• Cost: Pay-by-mile concept in case of lease line

VSAT System Architecture

Consists of:

Space Segment: Satellite transponder

Ground Segment:

Central HUB or MES

Remote VSATs

Topologies:

Star

Mesh

Hybrid

Access Technologies

• Time Division Multiple Access(TDMA) • Frequency Division Multiple Access(FDMA) • Code Division Multiple Access(CDMA) • Demand Assigned Multiple Access(DAMA) • Pre-Assigned Multiple Access(PAMA) • Frequency-Time Division Multiple

Access(FTDMA)

Frequency bands

Band Uplink (GHz) Downlink (GHz)

C

Ext.-C

5.925 – 6.425

6.725 – 7.025

3.7 – 4.2

4.5 – 4.8

Ku 14.0 – 14.5 10.95 – 11.7

Why Ku Band?• Capable of offering up to 45 Mbps• Hardware Economics• Very small Antenna sizes up to 0.75 m• Very strong satellite traponders• Most suitable for web eanabled applications

without any bottlenechs in terms of bandwidth/availability

• Offering broadcasting and Multicasting Turbo Internet Appliactions

• Internet connectivity without any legacy bottlenecks

When designing a WAN using satellite as a transmission medium, planning for the right band of operation is imperative. Any band of operation whether C, Ext-C or Ku band has to be looked at from following perspectives:

• Availability over Indian Sub-continent• Long term perspective• Commercial & Technical Issues• Ku band statistics

Since Ku band frequency of operation is very high, the size of ground equipment such as antenna reduces to quite an extent. Also since most of the Ku band transponders are high power (typically EIRP of 44 DBW as against 32 DBW in C Band) even the radio frequency terminals (RFT) required are small, hence overall sizes for ground equipment go down considerably. For example, if it needs 3.8 meter antenna with a 5W RF to uplink 64 Kbps SCPC carrier in C/Ext-C band, the same carrier can be uplinked using 1.8/2.4 Meter antenna with 0.5W RFT.

Availability: Ku band is very standard band for operation all over the world. Large no. of satellites with Ku band transponders are available. Over Indian sub-continet also Ku band is available through INTELSAT, INSAT 3B and PANAMSAT. Moving from one satellite to another is not an issue, since availability is universal.

Disaster recovery of transponder and satellite is taken care of due to the flexibility to change to another satellite. Long Term Perspective: Operation in Ku band are brighter in term of availability of transponders, Economics of scale in terms of bulk production of the H/W electronics globally.

Commercial & Technical Issues: Ku band transponders have higher EIRP, the cost of hiring a transponder is higher than that of either C or Ext-C Band. However it is more than offset by lower capital expenditure on the ground equipment. Besides, as contracted bandwidth increases, economics of scale come into play and it becomes even more viable.

The only technical issue that needs to be taken care of with Ku band is rain fade that can be taken care of by Installing Uplink Power Control (UPC) at the hub siteBy building the rain fade margins into the link calculations and selecting appropriate RFT 

Response of SkyBlaster and DirecWay VSATs 

Upload/Download speed and Round Trip Time(RTT) were observed for DirecWay 4020 and SkyBlaster 360E VSAT systems. The results are summarized below:

A file of 3.5 MB was uploaded to ALPHA server on NIC LAN and ICAR server on RF Link. The upload speed of SkyBlaster is better. There is a difference of the order 4.54 Kbytes/Sec. in upload.

A file of 3.5 MB was downloaded from ALPHA and ICAR servers. The download speed of DirecWay VSAT is found to be better than SkyBlaster. There is a significant difference in the speed if content server (ALPHA) is in NIC LAN. The difference is of order 14.7 Kbytes/Sec. if content server (ICAR) is on RF Link.

A file of 1.16 MB and 1.5 MB was downloaded from Internet sites. The difference is nominal in both the VSAT systems.The analysis of Round Trip Time reveals that the SkyBlaster is more consistent.

Both the VSAT systems have maintained 8/32 Kbps connectivity.

Direcway (Hughes)

Skyblaster 360E (Gilat)

Upload (FTP)Alpha Time (sec) 393.22 263.66

Speed (KBytes/sec) 9.34 13.97

ICAR Time (sec) 419.95 278.28Speed (KBytes/sec) 8.75 13.2

Download (FTP)Alpha Time (sec) 15.28 37.27

Speed (KBytes/sec) 240.42 98.59

ICAR Time (sec) 45.16 55.13Speed (KBytes/sec) 81.35 66.65

Download (Email)3.5 MB Time (sec) 29 102

Speed (KBytes/sec) 123 35.1

Download (Internet)1.16 MB Time 8 Min. 3 Sec.7 Min. 45 Sec.

Speed (KBytes/sec) 2.47 2.56

1.5 MB Time 7 Min. 9 Sec.7 Min. 56 Sec.Speed (KBytes/sec) 3.48 3.14

Round Trip TimeGateway Min (ms) 571 703

Max (ms) 991 813Average (ms) 623 761

Remote1 Min (ms) 1222 1484Max (ms) 3996 2704Average (ms) 1564 1771

Remote2 Min (ms) 1443 1531Max (ms) 4119 3016Average (ms) 2198 1658

Remote3 Min (ms) 1259 1468Max (ms) 1978 1594Average (ms) 1418 1520

File Size 3.5 MB 3.5 MB

Response of VSATs