Copyright Inmarsat 1998 All Rights Reserved. Inmarsat-B High Speed Data Reference Manual

Transcription

1 Inmarsat-B High Speed Data Reference Manual Version 1.1 March, 1998 i

2 Table of Contents 1. SECTION ONE - SALES SUPPORT INFORMATION THE HSD MARKET Why use HSD? Inmarsat-B HSD markets and applications Positioning of the Inmarsat-B Service OVERVIEW OF INMARSAT SYSTEM ARCHITECTURE Global Coverage Network Operations Land Earth Stations Call origination Call Routing Mobile-Fixed Fixed-Mobile Mobile-Mobile Call billing Mobile-Fixed Fixed-Mobile INMARSAT-B SERVICE DESCRIPTION Inmarsat-B Service High Speed Data (HSD) Service INTRODUCTION TO ISDN APPLICATIONS AND INMARSAT-B HSD Overview of ISDN LAN routing and remote LAN access Video conferencing Multiplexing Dedicated File Transfer Systems Store-and-forward Video Audio broadcast Future Applications SALES PROCESSES Service Activation Introduction Requirements for MESs Service Activation Process Inmarsat-B HSD MES Numbering Installation and testing User familiarisation Post-sales support SECTION 2 - TECHNICAL SUPPORT INFORMATION INTRODUCTION TO ISDN ISDN Services ISDN User Interfaces Main Differences between HSD and ISDN Dialling and numbering General...32 ii

3 Fixed-to-Mobile Dialling Mobile-to-Fixed dialling Multiple Addressing General Multiple Subscriber Numbering (MSN) ISDN APPLICATIONS AND INMARSAT-B HSD - GENERAL PRINCIPLES Electrical interfaces on Inmarsat MES s Call set-up and clearing ISDN APPLICATIONS AND INMARSAT-B HSD SPECIFIC APPLICATIONS General LAN routing Background Information Cables and interface converters Video conferencing Background Information Cables and interface converters Multiplexing Background Information Cables and interface converters Dedicated File Transfer Systems Background Information Cables and Interface Converters Store-and-forward video Background Information Cables and Interface Converters Audio broadcast Background Information Cables and Interface Converters Custom solutions S/T bus adapter Intelligent router interface TROUBLE-SHOOTING TOOLS AND TECHNIQUES Basic test tools Preliminary checks Loop-back calls LES Assistance...49 Appendix 1 Synchronous Serial Data Communications Interfaces.. 53 Appendix 2 HSD Interfaces on Inmarsat-B MESs 59 Appendix 3 Serial Connector Loop-back Connectors.. 68 Annex 1 Global Implementation of ISDN 71 Annex 2 LES Services and Connnectivity Annex 3 MES Equipment and Contacts 76 Annex 4 Systems Integrators 78 iii

4 Introduction The aim of this reference manual is to improve the level of Inmarsat-B High Speed Data (HSD) market awareness and technical competence of existing Inmarsat agents, distributors, service providers and manufacturers. Section One deals with general background information on Inmarsat, Inmarsat-B High Speed Data Service, ISDN technology, and commonly used applications. Section One is intended for non-technical readers. Section Two deals with ISDN and Inmarsat HSD applications in much more detail and is intended for the technical reader. Disclaimer "This document is for the exclusive use of the recipient to whom it is addressed and the recipient shall not permit this document to be distributed to any third party at any time. Recipients are responsible for making their own decision as to the completeness, fairness or accuracy of the information and any opinions contained in this document and must rely on their own judgement in relation thereto. So far as Inmarsat is aware, the information contained in this document is true and accurate. However, no representation or warranty, express or implied, is or will be made by Inmarsat and no responsibility is or will be accepted by Inmarsat as to the accuracy or completeness of the document" The financial and sales projections given here are illustrative only and are calculated on the basis of assumptions summarised herein. Neither the projections nor the assumptions should be taken as forecasts or promises on the part of Inmarsat nor should they be taken as implying any assurance or guarantee by Inmarsat that those assumptions are necessarily correct or exhaustive." For further information contact: Inmarsat Customer Care Tel Fax Internet: or visit the Inmarsat Web site: iv

5 1. Section One - Sales Support Information 1.1 The HSD Market Why use HSD? The Inmarsat-B High Speed Data (HSD) service provides a global, satellite-based extension of the terrestrial ISDN network to users who would otherwise be unable to access ISDN. As urban-based organisations become more familar to the features and capabilities of ISDN they will come to expect the same communications features and capabilities at their remote sites and offices. Many established Inmarsat customers already use Inmarsat systems for transferring data from remote locations. As terrestrial ISDN is made available by their telephone service providers they too will wish to take advantage of the higher speeds and lower costs of the Inmarsat-B HSD service for their Inmarsat data communications needs. One can see then that demand for the Inmarsat-B HSD service is clearly linked to the availability and growth of ISDN applications and services. Because of the global growth of ISDN a whole range of telecommunications applications that were once the domain of large corporations have now become cost-effectively available to even the smallest of businesses. Dial-up networking using ISDN enables any number of Local Area Networks (LANs) to be quickly and easily linked; the establishment of global video-conferencing standards for use over ISDN has led to the widespread availability of desk-top PC-based video conferencing systems; the development of audio coding (compression and digitisation) techniques and standards for the transmission of broadcast quality audio over ISDN has eliminated the need for dedicated audio transmission circuits for broadcasters - to mention but a few applications. Anyone who uses modems over traditional analogue telephone circuits will be only too familiar with the clicking and buzzing of two modems handshaking and trying to connect for seconds of chargeable telephone time. An ISDN call typically takes 3-10 seconds to connect - a factor which becomes even more significant when one is making a call over a satellite communications system such as Inmarsat. While the use of Inmarsat-B HSD to implement ISDN applications in remote locations is a major benefit, it should not be forgotten that the Inmarsat-B HSD service is also the most cost-effective means of transferring data over Inmarsat. Inmarsat-B supports medium speed data service which provides a 9600bps circuit through the terrestrial PSTN to normal dial-up modems. So while there is an additional equipment cost incurred by the user in implementing Inmarsat-B HSD (due to ISDN termination equipment and line rental charges, and in some cases, additional equipment at the mobile terminal end), the reduced call charges per kilobit will normally cover this cost many times over the life-span of the terminal and in many cases will have covered the additional equipment cost within a matter of months. With the introduction of the Inmarsat-B HSD service there is no longer any reason why persons working in remote locations should not enjoy any of the sophisticated IT solutions that are taken for granted in today s modern office. 1

6 1.1.2 Inmarsat-B HSD markets and applications Inmarsat-B HSD services are designed to accommodate the needs of a wide range of users with large amounts of data to transmit such as broadcast journalists, oil exploration and production companies, mining companies, government agencies, international organisations, foreign service offices and merchant shipping. Some typical high speed data applications: Multiplexed voice, data and fax A duplex 64 kbit/s data channel may be used to carry two to ten multiplexed (or combined) telephone, fax and medium-speed data circuits. This capability will interest companies, banks and other organisations located in areas where it is difficult to obtain telephone lines. Multiplexed HSD can also allow national authorities to quickly and economically augment or restore their communications infrastructure in the event of a disaster. Broadcast quality audio uplink Broadcasters can use 7.5 and 15 khz audio codecs to supply broadcast-quality reports from the field or the high seas directly to the studio. Store and Forward Video Broadcasters also use store-and-forward video applications to take high quality video clips (captured at rates from 512kbps to 3Mbps), transfer them to the studio using 56/64kbps HSD, then play them back at their original rate. Videoconferencing Businesses can use Inmarsat-B HSD for videoconferencing and application sharing from remote and semi-mobile locations worldwide. LAN interconnections Operators of Local area networks (LANs) on board ships and in remote hotels and financial institutions increasingly require connections with other LANs. It is possible to interconnect different networks transparently via duplex HSD, using, for example, TCP/IP-based protocols. Telepresence Telepresence can bring expert assistance to the most remote or mobile sites, avoiding the expense of transporting and accommodating specialists. Inmarsat-B HSD can support telepresence applications such as the repair of ship engines on the high seas. Telemedicine Inmarsat-B HSD can provide rapid access to shared and remote medical expertise, using interactive audio-visual and data communications. 2

7 Tele-education Inmarsat-B HSD can support tele-education applications such as the training of staff in remote locations in installation, maintenance and emergency procedures. The resulting savings in expenses and travel can be significant Positioning of Inmarsat-B HSD Inmarsat-B HSD will be of greatest benefit to users working in locations with a basic or nonexistent telecommunications infrastructure and who either have a need to use ISDN-type applications or who have large volumes of data to transmit back to an urban head office or data processing centre. For such users, if a terrestrial ISDN service exists in the area of operation then this would normally be the first choice of communications link. However, in the absence of a terrestrial ISDN service or in areas where the ISDN service is unreliable or uncompetitively priced, then the satellite-delivered option becomes attractive. Figure 1.1 below shows how the Inmarsat services (including Inmarsat-B HSD) are competitively positioned against other telecommunications services. Figure 1.1 Positioning of Inmarsat within the Global Telecommunications Infrastructure There are three key features of the Inmarsat-B HSD service that currently make it unique amongst other satellite communications service providers as follows:- on-demand satellite capacity seamless global coverage direct-dialled access to the global ISDN network 3

8 If the customer needs a systems that has to fulfil all of these requirements (for example, a flyaway Satellite News Gathering (SNG) system) then the Inmarsat-B HSD service is the perfect choice for the customer. However, in practice, the decision will not be so clear cut and it will be necessary to consider whether the customers needs will be best addressed by Inmarsat-B HSD or by a VSAT solution. Several factors need to be considered in making this choice as follows:- Satellite traffic charges VSAT services are generally arranged and charged on an annual basis as opposed to the Inmarsat on-demand, per-minute charge. On this basis the VSAT charge per minute can look very attractive if the link is to be used on an almost continuous basis (for example, the transmission of geophysical data from a seismic survey ship). However, if the link is to be used on a less than full time basis (for example, on-demand routing, video conferencing, live audio news broadcasts) careful calculations need to be done to determine the data volume break-even point for the fixed VSAT annual cost. It should also be remembered that several Inmarsat Service Providers will provide long term lease arrangements at competitive prices for customers with high volumes of traffic. Equipment costs Inmarsat-B HSD land-mobile terminals cost in the region of $30-40KUS. A typical VSAT system would cost in the region of $50-100KUS depending upon the antenna size and type of system (C-band or Ku-band). Obviously these equipment costs need to be taken into account in carrying out the traffic break-even analysis as discussed above. Equipment size Two important factors are determined by the size of the satellite communications system - the portability of the system and the complexity of installation. Inmarsat-B HSD systems weigh typically 18-30kgs with an antenna size of 1 metre. They are highly portable which makes them as well suited for rapid deployment in temporary situations as for permanent installation. Systems can be checked as hold luggage or transported in a light aircraft. Deployment is typically done in a matter of minutes by untrained personnel with permanent installations carried out in a matter of a few hours. VSAT systems weigh typically up from 100-1,000kgs with antenna sizes ranging from 1-3 metres. The physical size of the equipment requires that special transport arrangements need to be made for the equipment. Installation has to be carried out by a specialist technician or technicians and can take several hours or even days for larger systems. Licensing Inmarsat-B terminals, like VSAT terminals, must be licensed (or exempted from licensing requirements) in each country in which they operate. Inmarsat has successfully encouraged many countries to reduce or remove regulatory barriers for market access and it continues intense efforts on a daily basis through contacts with regulators to facilitate access where barriers remain. Data rates Inmarsat-B HSD supports 64 and 56kbps. VSAT system support data rates from 300bps to 2Mbps depending upon antenna size and satellite capacity. 4

9 1.2 Overview of Inmarsat system architecture Global Coverage Inmarsat, the International Mobile Satellite Organisation, operates a system of 4 geostationary satellites. Figure 1.2 below shows the Inmarsat satellite system, and the areas of global coverage of each of the four satellite regions: Figure 1.2 Inmarsat Global Coverage Each of the four ocean regions operates as a separate network. In areas where regions overlap, as shown on the map, the separate networks are defined by either mobile antenna discrimination (for Inmarsat-A, -B and high gain Aero) or by frequency (for Inmarsat-C, -M and low gain Aero). Mobile antenna discrimination means that antennas with sufficient size can receive and transmit to one satellite without causing interference to or receiving interference from another satellite. The user of a mobile earth station with a small antenna, however, must determine which satellite to use by its frequency (frequencies are not re-used between overlapping regions) Network Operations In each ocean region there is a Network Co-ordination Station (NCS), which manages and coordinates the telecommunications traffic in that region. The NCS assigns available communication channels to the Mobile Earth Stations (MESs). When a channel is no longer required, it is released to be allocated to another MES for use. Typically, the NCS function is performed at a particular Land Earth Station (LES) under contract to Inmarsat. Each of the Inmarsat systems (A, B/M and C) requires a separate NCS for each of the four ocean regions. The systems Inmarsat-M, Inmarsat-B and mini-m all use the same NCS in each ocean region. Overall co-ordination of the network is performed 24 hours a day, every day, by the Network Operations Centre (NOC) at Inmarsat s headquarters in London, England. The NOC 5

10 maintains contact via dedicated satellite and terrestrial links with the NCSs and LESs in all four ocean regions Land Earth Stations The Land Earth Stations (LESs) are the gateways which provide the link between the satellites and public terrestrial telecommunications networks. Each LES communicates with just one of the four Inmarsat satellites and is thus said to serve a particular Ocean Region. Often several LESs are situated together thus offering multiple ocean region coverage from a single location. LESs are owned and operated by national telecommunications operators and other authorised private telecommunications organisations. LES operators compete with each other for Inmarsat customers traffic. Thus, customers will find it beneficial to shop around to determine which LES offers the best services and most economic traffic charges for their particular communications needs. Figure 1.3 Inmarsat System Overview Call origination Telephones calls over the Inmarsat satellites can be made from either the mobile satellite terminal (mobile-to-fixed calling) or from a normal terrestrial telephone line (fixed-to-mobile calling). The point of origination of the call (i.e. from the satellite terminal or from a terrestrial line) determines the manner in which the call is routed and billed as discussed below in sections Call Routing and Call Billing. 6

11 1.2.5 Call Routing Mobile-Fixed LES selection is made by the Mobile Earth Station (MES) operator by either using the default LES programmed into the MES for each ocean region or by entering the LES code in the dialling string for a particular call in accordance with the MES manufacturers instructions. Terrestrial routing of the call to its final destination is carried out by the LES operator using its own national or international routing arrangements Fixed-Mobile When a land-based fixed subscriber wishes to make a call to an MES, the terrestrial network needs to be able to recognise the dialled number, route the call and bill the call at the correct tariff. The subscriber s telephone service provider therefore needs to have put into place appropriate routing arrangements with one or more LES operators in order to handle Inmarsat fixed to mobile calls. Some telephone service providers have their own LES or LESs. However, they will still have to make routing arrangements with LES operators in other ocean regions as very few countries can see more than two Inmarsat satellites. There will always therefore be a need to route traffic through other LESs in order to provide global access for customers in all four ocean regions. These routing arrangements require that the telephone service providers exchange recognises not only the ocean region dialled but also the type of call to be made so that the call can be routed to an LES offering the desired service in the correct ocean region. This information is also required so that the call can be charged at the correct tariff. In summary then, the routing of calls made in the fixed-to-mobile direction cannot be determined by the fixed subscriber but is dependant upon the routing arrangements made by the telephone service provider Mobile-Mobile Mobile to Mobile calling is supported for High Speed Data Services. There is additional end-to-end delay because of the double satellite hop, which is likely to reduce the throughput and performance of nearly all user applications Call billing Mobile-Fixed When a call is made from an Inmarsat Mobile Earth Station (MES) the call charge is composed of two elements - the satellite portion comprising the call from the MES to the LES via one of the Inmarsat satellites and the terrestrial portion (or back-haul) 1 which is the delivery of the call from the LES to the final destination. An MES user can make a call using any LES within the ocean region of operation that supports the Inmarsat service required. 1 The terrestrial delivery or back-haul is normally carried on copper or fibre links to it s final destination. Where no alternative routing exists it may be carried on a second satellite link such as Intelsat. Despite the fact that the back-haul may be carried on a satellite circuit it is still referred to as the terrestrial delivery to distinguish it from the Inmarsat mobile satellite portion of the call. 7

12 However, different LESs will have different tariffs for both the Inmarsat portion of the call and for the terrestrial delivery and it makes good economic sense to spend some time looking at different traffic routings and perhaps even entering into a direct agreement with a particular LES operator to benefit from the most economic traffic charges for a particular service. Calls made in the mobile-fixed direction are billed either by the Radio Traffic Accounting Authority (Accounting Authority for short), direct by the LES or by the Inmarsat Service Provider (ISP). See section Service Activation for more detail Fixed-Mobile Call charges for fixed subscriber originated calls are fixed by the telephone service provider and cannot be influenced by the subscriber. However, in countries where the telecommunications service has been deregulated there will normally be a choice of telephone service providers thus enabling a fixed subscriber to have a choice of tariffs. Calls made in the fixed-mobile direction are billed by the telephone service provider. 8

13 1.3 Inmarsat-B Service Description Inmarsat-B Service The Inmarsat-B service was launched in 1993 as the digital successor to Inmarsat-A. Like Inmarsat-A, Inmarsat-B supports voice telephony, Group 3 fax, medium speed data (9.6kbps), telex and High Speed Data (56/64Kbps). But by the use of digital coding and modulation schemes it provides all of these services with a more efficient use of the available power and bandwidth of both the Inmarsat-3 satellites and the mobile earth stations. This has provided the opportunity for lower tariffs and higher quality of service to the end-user. Inmarsat-B is available to land-mobile customers as a suitcase-sized, portable system weighing as little as 18kg or as a maritime version with a stabilised tracking antenna unit housed in protective radome High Speed Data (HSD) Service The Inmarsat-B High Speed Data service provides a duplex, 56 or 64Kbps (user-selectable) data service with terrestrial delivery via ISDN. The service became commercially available in all Inmarsat Ocean Regions in July Like all Inmarsat services, the Inmarsat-B HSD service is a demand-assigned service and so all elements of the link - both satellite and terrestrial - need to be allocated on a demand basis. It follows then that an LES can only offer Inmarsat-B HSD if a 56 or 64Kbps demand assigned terrestrial service is available at the LES such as ISDN or Switched-56. If a terrestrial 56/64Kbps service is not available at the LES then the LES will only be able to offer a mobile-to-mobile service. 9

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15 1.4 Introduction to ISDN Applications and Inmarsat-B HSD Overview of ISDN ISDN or Integrated Services Digital Network is the ITU-T (formerly CCITT) term for the digital public telecommunications network. It is offered in two packages - Basic Rate and Primary Rate. Basic Rate, also known as 2B+D, provides two 64Kbps (B) data channels and one 16Kbps (D) signalling channel. It is intended to provide service for individual users and business applications such as LAN data links or high quality audio feeds for broadcast media applications. It is provided as a dial-up service by the local telephone service provider and is charged for, like a normal telephone service, on the basis of a standing (monthly or quarterly) charge and a usage charge per minute. The usage charge per channel is similar to normal telephony rates. Primary Rate provides up to 30 x 64Kbps (B) data channels and 1 x 64 Kbps (D) signalling channel. It is aimed at high band-width business applications such as video-conferencing and high capacity on-demand LAN bridge/router links. Because the Inmarsat-B HSD service operates at only 64Kbps it is normally used with the Basic Rate ISDN service but can be used on Primary Rate with applications that can operate on a single B-channel. For example, a remote video-conferencing user is able to dial into a high capacity group video-conferencing system using just a single Inmarsat-B HSD channel, albeit with reduced video quality. At an ISDN subscriber s premises the point at which the ISDN telephone line terminates is known as the U-interface. The ISDN connection is terminated at the U-interface by a Network Termination device known as NT1. This is normally permanently wall mounted. In the US the customer is responsible for providing the NT1, in the rest of the world it is provided by the ISDN service provider as part of the ISDN service. Figure 1.4 ISDN Physical Line Configurations The ISDN subscriber interface at the NT1 is known as the T point or T-Interface. If a second network termination device such as an ISDN switchboard is connected to the NT1 at the T- interface this is designated the NT2 and the ISDN subscriber interface is then the S point or S-interface. The physical and electrical characteristics of the S-Interface and T-Interface are identical and they are usually referred to as the S/T-interface or S/T bus (also S0 interface 11

16 and S0 bus). Physically the S/T interface is an RJ-45 connector. It is to the S/T-interface that the subscriber equipment is connected. Interface conversion between the S/T bus and the serial communications interface on the subscriber Data Terminal Equipment (DTE) is carried out using an ISDN Terminal Adapter (TA). Nowadays most equipment capable of being used with ISDN can be supplied with an integral ISDN Basic Rate Interface (BRI). The DTE can be any type of data equipment such as a video-conferencing system, bridge/router or audio codec. The TA is also known as the Data Communications Equipment or DCE. Stand-alone TA s can be ordered with either a dual channel 2B+D BRI or a simple single channel B+D BRI. As an Inmarsat-B HSD channel is equivalent to a single B-channel consideration may be given to using a single channel TA for use with Inmarsat-B HSD applications as the single channel TA will normally be less expensive than a 2B+D unit. However, a dual channel TA will permit communication with two separate Inmarsat-B applications in different locations simultaneously (see section Multiple Addressing below) and will also facilitate testing and fault-finding (see section Troubleshooting below). Inmarsat is aware that in the USA, only very few terminal adapters will split the ISDN to provide a single DTE connection. There are several differing implementations of ISDN worldwide. Protocol conversion between differing ISDN standards is carried out transparently by the national telephone service providers. However, ISDN BRIs differ with the different ISDN standards and so care should be taken to specify the correct country of use, and hence ISDN BRI, for the base station equipment. The DTE to be used with the Inmarsat-B HSD terminal uses a serial communications port ( e.g. V.35, X.21, RS.232) and so is independent of any ISDN standard. 12

17 1.4.2 LAN routing and remote LAN access The concept of linking or networking computers within a single site thus creating a Local Area Network or LAN is familiar to most of us and these LANs are becoming increasingly common in remotely located hotels, offices and financial institutions around the globe. There is also an increasing demand for these remote LANs and individual remote users to access a central or headquarters LAN to deposit or retrieve data such as thus creating a Wide Area Network or WAN. Remote access of this nature is normally and most effectively implemented using LAN routers or bridges. Routers and bridges manage the transfer of data between LANs and are manufactured as individual units or as combined bridge/routers. Though routers and bridges differ in mode of operation, the implementation of each is similar and so the term bridge/router is used within this manual to refer to either a bridge or router or hybrid. When the amount of data to be transferred between two LANs or a central LAN and a remote user is large then a dedicated or leased circuit, whether terrestrial or satellite, will provide the most economically attractive communications solution. However, in many instances the amount of traffic is insufficient to economically justify a leased circuit. The use of an ISDN dial up connection, either Basic Rate or Primary Rate, can be an attractive solution to provide the telecommunications link required. With a dial-up connection the bridge/router has no dedicated connection to the central LAN. Instead, the bridge/router automatically connects to the other bridge/router when there is data to be transmitted. Figure 1.5 Remote LAN Access Two automated dialling modes are possible - DTR dialling and V.25bis dialling In DTR dialling mode, the DTR signal in the bridge/router serial communications interface triggers the Data Communications Equipment (DCE), which may be an ISDN Terminal 13

18 Adapter or Inmarsat-B HSD terminal, to automatically dial-up another LAN. The ISDN telephone number of the other LAN is pre-programmed into the DCE by the user. In V.25bis dialling the user configures the bridge/router with a table of different ISDN telephone numbers corresponding to different LANs so that the bridge/router can send data not just to one pre-programmed LAN destination as in DTR dialling but to several different LANs. Obviously this is a more flexible mode of operation and should be the preferred option if this facility is supported by the DCE. In both modes, once a connection has been established it will be held open for traffic. When there has been no traffic for a pre-determined length of time, selected by the user, the bridge/router will automatically clear the call. Some bridges/routers will take a fixed minimum time to disconnect, in which case it is recommended that there is a guarding function in the application However, not all mobile users will have access to ISDN. The Inmarsat-B HSD service is ideally suited to this application in circumstances where no terrestrial ISDN connection is available. Using an Inmarsat-B HSD terminal a user can connect a remote user or LAN from anywhere within the Inmarsat global coverage area. 14

19 1.4.3 Video conferencing Video conferencing solutions are normally supplied either as dedicated systems specifically designed for installation in a dedicated video conferencing room or as PC hardware and software kits intended for installation in a desk top PC. Both implementations are suitable for use with the Inmarsat-B HSD service. The international standard for video conferencing over ISDN is the ITU-T recommendation H.320 which governs video conferencing over narrow-band (64Kbps to 1920Kbps) networks. Most video conferencing systems in general use worldwide are compliant with this standard and so H.320 is used as the basis for discussion in this manual. Other proprietary standards are equally capable of being used over an Inmarsat-B HSD channel and the same principles will apply for their use as discussed below. Figure 1.6 Video Conferencing H.320 is a suite of specifications which define how video conferencing systems communicate over ISDN. The most important aspect to consider in respect of using a H.320 compliant system with the Inmarsat-B HSD service is that of the audio codec to be used. H.320 defines three audio compression standards to handle a broad range of applications - G.711, G.722 and G.728 (see para below for more detail). G.711 and G.722 both require 64Kbps channels and are therefore unsuitable for Inmarsat-B HSD video conferencing applications as they would each consume all of the available bandwidth. It is therefore important to use the G.728 algorithm which only consumes 16Kbps of bandwidth, thus leaving 48Kbps for video and signalling. This applies to both the terrestrial and remote systems. In modern systems this is not generally an issue, however some older systems do not support G.728 and so are not suitable for use with the Inmarsat-B HSD service. 15

20 1.4.4 Multiplexing Multiplexing is defined as the simultaneous transmission of two or more channels within a single communications circuit. The component channels can be the same, as in a multichannel telephony multiplexer, or from a variety of different sources such as phone, fax and data. The number of channels which can be multiplexed onto a single communications circuit depends upon the capacity of the communications circuit and the bandwidth requirements of the individual channels to be multiplexed. Figure 1.7 Multiplexing Early multiplexers allocated fixed bandwidth slots within the communications circuit for each multiplexed signal. However, modern statistical multiplexing techniques permit the dynamic allocation of bandwidth on an as needed basis. For example, a device such as a network router may be attached to a data port on a multiplexer and assigned the full bandwidth of the communications link. When a phone or fax, also attached to the multiplexer, goes off-hook the multiplexer will automatically reduce the bandwidth available to the router in order to assign bandwidth to the phone or fax. When the phone or fax call is complete and goes on-hook the bandwidth is automatically re-assigned to the router on the data port. Obviously statistical multiplexing techniques make much more efficient use of a fixedbandwidth channel and should be the preferred multiplexing technique in Inmarsat-B HSD applications. 16

21 1.4.5 Dedicated File Transfer Systems The use of bridge/routers with the Inmarsat-B HSD service provides a means of using widely available, off-the-shelf equipment, with a familiar user interface for transparently and automatically connecting two or more LANs. It sounds ideal but in some circumstances an alternative solution for the transfer of data over the Inmarsat-B service can be more attractive. While TCP/IP is a robust protocol and very suitable for satellite communication, there is a lot of overhead associated with network protocols such as TCP/IP. Actual data throughputs can be quite variable between 30-60Kbps. This means that if large data file transfer is the primary requirement of the Inmarsat-B HSD service (for example, geophysical applications) then the bridge/router solution with associated network overhead may not be the most economic means of transmitting data back to base. Further, conventional file transfer software packages designed for terrestrial circuits may not adapt very well to the delays of a satellite communications channel which are typically of the order of 250ms. The user should be aware that the total round trip delay is much more important to communications protocols. This can vary per LES between 500 to 1400ms depending on the call and terrestrial portion of the link. A Mobile to Mobile call can see a round trip delay of up to two seconds. To address this requirement several specialist manufacturers have produced file transfer solutions specifically designed for the fastest possible data throughput on an Inmarsat-B satellite link. Figure 1.8 File Transfer System Several systems are available and all have unique characteristics but do share some common features such as:- Proprietary s/w and h/w required at each end of the link - no interchangeability between systems. Lap top or PC-based Synchronous communications interfaces Full duplex data transfer capability 17

22 Very robust file transfer protocols offering full error correction, data recovery following link failure and high data throughput - typically averaging 60Kbps on a 64Kbps link. Do not offer interactive operation All systems were originally written to be run from within the DOS environment to maximise the data throughput but most are now offered with an optional Windows interface albeit with a small sacrifice in data throughput. Hardware implementation solutions vary with options of internal ISA bus cards, PCMCIA cards and in-line devices. 18

23 1.4.6 Store-and-forward Video A live video link of a quality suitable for transmission by a news network would require a communications channel, whether terrestrial or satellite, with a capacity of 2-8 Mbps. Clearly this capacity is not available with the Inmarsat-B HSD service and to achieve this in a remote location, away from fixed high capacity terrestrial circuits, would require the use of a VSAT Satellite News Gathering (SNG) system. However, imagine the logistical effort required to transport a typical VSAT Satellite News Gathering (SNG) system to the scene of a breaking news story. These systems typically consist of 5-10 flight cases weighing up to 1,000kg in total - not a very portable solution! Figure 1.9 Store-and-Forward Video System The highly portable Inmarsat-B HSD service is clearly a much more attractive option but, with data rates of 56 and 64Kbps, it is simply not capable of providing sufficient channel capacity for a live video feed as discussed above. But suppose the high quality video was encoded (digitised and compressed) at the higher bit rate and then stored on a computer hard disk or other mass storage medium. The data could then be later transmitted, at whatever data rate was available, 56 or 64Kbps, through the Inmarsat-B HSD system back to the studio for later transmission. This solution is the essence of store-and-forward video applications and gives users the ability to transmit high quality video at lower data rates that would normally be considered poor or unacceptable for TV transmission. Though the video is no longer live it need not be more than an hour old and the trade off in terms of portability - 30kg in total compared to up to 1000kg for a VSAT system - makes it a very attractive and practical alternative. In addition, conventional VSAT solutions require prior scheduling of satellite time and visibility of a suitable satellite from the required location. Inmarsat-B HSD overcomes both of these issues because the channels are demand assigned and are available globally. Video file sizes, and hence transmission times and cost, are determined by three factors - data channel rate (56 or 64Kbps for the Inmarsat-B HSD service), video coding rate (which can range from 512kbps to 3Mbps) and video sequence length. Some typical transmission times for one minute of broadcast quality video are given 19

24 in the table below. Times and costs are based on a 64Kbps Inmarsat-B HSD channel. A similar transmission using a 56Kbps channel would increase transmission times and costs by about 10%. Coding rate Picture Quality File Size Tx Time 64Kbps Tx Cost (est.) 1.0Mbps Low 7.5MB 16.6mins $200US 1.5Mbps Medium 11.25MB 24.9mins $300US 2.0Mbps High 15MB 33.3mins $400US Table 1.1 Transmission times and costs for one minute of broadcast quality video on Inmarsat-B HSD Assumptions 1. Transmission times are for one minute of video. 2. Actual data throughput on the 64Kbps channel is 60Kbps. 3. HSD indicative costs are assumed to be $12US/min. Transmission of the video files over the Inmarsat-B HSD is carried out using a file transfer system of the type described in the previous section. Commercially available Store-and Forward video systems are supplied with an integral File Transfer System. 20

25 1.4.7 Audio broadcast Several international standards and proprietary systems exist for the coding (digitisation and compression) of audio signals all of which use different techniques to apply differing degrees of compression to the audio input - music or speech. The degree of compression applied determines the amount of bandwidth required for the coded audio data stream The compression process also introduces a time delay which becomes greater as the degree of compression increases. Both of these factors - required bandwidth and coding delay - have to be taken into account in determining the most suitable coding algorithm for a particular applications for use over the Inmarsat-B HSD 64Kbps service. Figure 1.10 High Quality Audio Transmission Given that satellite propagation delays are of the order of 250ms the need for greater audio bandwidth (i.e. greater compression) has to be balanced against a desire to keep any coding delays to a minimum. The three international recognised coding standards in common use and suitable for use over the Inmarsat-B HSD service are summarised in the table below. 21

26 Coding Standard Audio bandwidth Coding delay Typical application on 64Kbps link G.711 3KHz Negligible Rarely used over Inmarsat as audio bandwidth is too narrow for most commercial applications. G KHz 6ms Particularly suited to live or interactive interviews because of short coding delay. ISO MPEG Layer II 10-15KHz 500ms Wide audio bandwidth is very suitable for transmission of music. Long coding delay makes it difficult to use for interactive voice applications. Several different implementations of the MPEG Layer II standard, such as Musicam, are in commercial use all of which implement the MPEG Layer II standard in differing ways, hence the range of audio bandwidths given. Other proprietary audio compression algorithms, such as TDAC developed by CNET in France, are also successfully used for high quality broadcast over Inmarsat-B HSD. 22

27 1.4.8 Future Applications MES ISDN Interface Inmarsat is developing a specification for an ISDN Interface to be supported by Mobile Earth Station equipment. The MES ISDN Interface will connect to off-the-shelf ISDN terminal adapter equipment. This MES ISDN Interface connect only to the Inmarsat-B 64kbit/s service. The objective is to provide mobile ISDN applications with a compatible interface to that used on the terrestrial network. User costs will be reduced eliminating the need for customised HSD peripheral equipment and support. The MES ISDN S/T bus shall support up to eight user Terminal Equipment (TE1) devices, each of which may be able to support a number of user terminals. At the MES, a representation of ISDN Multiple Subscriber Numbering (MSN) of up to 10 numbers will allow selection of user terminal equipment for Terrestrial originated calls. The system overview is shown below: App App App App Application ISDN Terminal Equipment ISDN Terminal Equipment ISDN S/T Bus Inmarsat System Customer Premises Equipment (CPE) Satellite ISDN NT1 Interface Inmarsat ISDN NT1 Interface MES LES IWF ISDN Figure 1.11 MES ISDN Interface Overview The ISDN functionality to be supported over the Inmarsat network is termed 1B+s. 1B+s is a subset of 2B+D: the standard terrestrial ISDN Basic Rate Interface (BRI) offering two 64kbit/s user channels and one 16kbit/s channel for call setup. The term 1B+s refers to the Inmarsat-B MES implementation of only one ISDN-B 64kbit/s channel, and the necessary subset of ISDN-D channel messages used for Layer 3 signalling, which, after protocol conversion, will be mapped to the Inmarsat-B ACSE. 23

28 Applications Any application protocol capable of in-band negotiation may use the Inmarsat 64kbit/s service via the MES ISDN interface. For example, PPP connections to an internet service provider will be possible from a Laptop PC connected to the MES (via a PC Card ISDN Terminal Adapter). PPP enables good throughput over Inmarsat connections; but inherent satellite delays expose V.120 connections to lower throughput when the default V.120 window size of 7 (and frame size of 256 bytes) is used. 24

29 1.5 Sales Processes Service Activation Introduction Service Activation is the term used by Inmarsat to define the process of formal registration which must be carried out before bringing each new or modified Mobile Earth Station (MES) into service. In the past the most important part of Service Activation was the technical testing of the equipment. However, with the increased reliability of MESs and greater number and variety of users, Service Activation has moved from being a technical process to being a largely administrative procedure centred on the customer. Like an application for a telephone or service, it consists mainly of setting up an account for the user. The first stage in Service Activation is the administrative registration of customers and their equipment. For the majority of MESs, nothing further is required. Only for Inmarsat-A MESs will some testing be necessary. In all other instances, as soon as the MES is registered and the details transmitted to the Land Earth Stations (LESs) it can be used Requirements for MESs All operational Mobile Earth Stations (MESs) must satisfy four basic requirements as follows:- Financial The customer must be able to pay the bills and must select either an Inmarsat Service Provider (ISP) or Accounting Authority (AA) that will liaise with LESs for billing purposes. Maritime customers who will use the MES for distress and safety purposes must be registered with an Accounting Authority. Legal The MES must meet all national licensing requirements The Routing Organisation is responsible for the enforcement of the national licensing requirements. Contractual The MES operator or owner must agree to the Inmarsat Terms and Conditions for the Utilisation of the Space Segment, and realise that any violation of these terms and conditions could result in the suspension of or permanent withdrawal of access to the space segment. Technical The MES must be a model type approved by Inmarsat and must have passed any Service Activation tests (Inmarsat-A only) Service Activation Process Service Activation can be initiated by the owner of an MES or anyone who is acting on behalf of the owner. However, an applicant who is not the owner (for example, an agent) must pass the Service Activation Registration Form to the owner for signature. The applicant selects the Inmarsat Service Provider or Accounting Authority who will be responsible for processing the traffic charges associated with the terminal. The details of the 25

30 owner, MES and billing arrangements are recorder on the Service Activation Registration Form which is then signed by the owner of the MES and forwarded to the relevant national Routing Organisation (RO) or Inmarsat Service Provider (ISP) for approval and allocation of Inmarsat Mobile Number. After processing and approving the application the RO or ISP passes the information on to the Inmarsat Service Activation Unit in London, England who ensure that the details of the MES are transmitted to all Land Earth Stations so that access may be granted. The Inmarsat-B Service Activation process is automated and normally takes about 24 hours providing there are no queries related to the application Inmarsat-B HSD MES Numbering The Inmarsat Mobile Number (IMN) is the subscribers number, which is used for calling a Mobile Earth Station (MES). It performs exactly the same function as a PSTN or PSDN number. The exact form of the IMN varies from one Inmarsat service to another and so can be used to verify the type of service associated with the number. The Inmarsat Mobile Number (IMN) for an Inmarsat-B HSD user takes the following form where T 1 T 2 T 1 T 2 D X 1 X 2 X 3 X 4 X 5 X 6 3 for Inmarsat-B 9 for Inmarsat-B HSD D HSD service required Maritime* 1 Duplex HSD 2 One-way forward HSD 3 One way return HSD Land-mobile* 4 Duplex HSD 5 One way forward HSD 6 One way return HSD X 1 -X 6 Identification of MES and individual HSD service * Currently only the Duplex HSD service is available. Inmarsat-B IMNs are assigned by Inmarsat and are distributed in batches to Routing Organisations and Inmarsat Service Providers for allocation to their customers Installation and testing No customer will thank you for running up his satellite communications bill for carrying out testing, configuration and trouble-shooting that could have been done on an ISDN line back at the office. It is good practice to check any Inmarsat-B HSD application first on an ISDN line. This can be done on a single Basic Rate line as only one 64Kbps (B) channel is used for the application. Calls can therefore be made from one B channel to the other. An ISDN to ISDN test will verify that the application works in the office environment. The next test should include the satellite delay. Many off the shelf applications will not have 26

31 been tested with a round-trip delay on the order that can be expected with the Inmarsat-B Service (i.e ms). Each end of the application can be connected to the ISDN BRI either directly, if the equipment is fitted with a BRI, or through the ISDN Terminal Adapter (TA) if only the serial interface is available using interface converters as necessary (see Section 2.4.1, Basic Test Tools, below). If required both ends of the application can be connected to the dual channel TA and calls made from one DTE to the other. If the DTE equipment does not have dialling features calls can be initiated from the TA either via the front panel or from a PC connected to the control port on the TA. A typical pre-installation check-list may comprise the following checks: Has the MES been upgraded to HSD? Is the MES commissioned for HSD? What is the MES HSD IMN? (Leave a note of this at the ISDN equipment for fixedmobile dialling). Does the chosen LES support HSD? (Check for all Ocean Regions). Is the ISDN number valid and functioning and not being used for another application? (This is a common installation problem. Always check the ISDN number using a terrestrial link first) Does the ISDN number have international access if connected to a PABX (for fixedmobile dialling)? Is ISDN configured for satellite transit delay? Is the application configured for satellite transit delay (widow size, maximum delay)? User familiarisation The main objective of an Inmarsat HSD system provider should be to provide an HSD application that is as simple to use as its ISDN equivalent In practice this is determined by the extent to which the Inmarsat-B Premium HSD MES has automated dialling features and the extent to which the HSD application can use these features. (Once the call has been set-up, the actual operation of the application will be as on an ISDN circuit and the user may refer to the relevant operators manual for guidance.) If the application can be installed with fully automated call set-up (e.g. routers with DTR dialling) then user familiarisation will be simple and no different to using the application in an ISDN terrestrial environment. However, if the application or MES does not support automated dialling then the call set-up will have to be done manually via the MES hand-set and the user will have to be instructed in this simple procedure. In either case the actual operation of the equipment should be done whenever possible using an ISDN line in the first instance so that the user can become familiar with the operation of the equipment without running up an unnecessary satellite traffic bill Post-sales support Once installed it would be reasonable to expect the equipment to function reliably for its working life. Modern IT equipment has a high degree of reliability and equipment failures 27