HSCSD: An Informal FAQ Updated (long)
HSCSD FAQ
This (updated & slightly cleaned up) FAQ was compiled from a variety of sources on the web. If there are any glaring inaccuracies please advise. - EL -
I. HSCSD (High Speed Circuit Switched Data) Overview
HSCSD (High Speed Circuit Switched Data) is a high-speed, multi slot datacom platform for GSM networks. It removes the barrier to mobile datacom of low network performance, potentially bringing GSM mobile phone users the same - or even higher - performance as wireline connections.
HSCSD, is part of the evolving GSM family of standards and technologies (GSM, HSCSD GPRS, EDGE and 3GSM/W-CDMA) for digital wireless communications and is a high speed transmission technology which allows users to send and retrieve data over GSM networks at transmission speeds between 28.8kbit/sec and 43.2kbit/sec (4 times the standard GSM rate of transmission) - and theoretically up to 57.6 kbps - by enabling the concurrent usage of up to four traffic channels of a GSM network.
Transmission speeds can be even higher if combined with compression optimization and filtering products, such as the WebOnAir Filter Proxy from Ericsson, BlueKite, or other performance enhancers, and HSCSD is very well suited to data optimization.
An HSCSD bitrate of 57.6 kbps, uncompressed, is comparable to one ISDN B-channel, putting GSM data on a par with existing PSTN modem services. With end-to-end compression, for example between laptop software clients and a network server, rates of up to 200 kbit/s can be achieved.
HSCSD, being mainly a software upgrade does not entail new network elements and so the GSM operator not only avoids having to redesign the network, but can also have fast implementation.
HSCSD can be implemented at low-cost across a network in a matter of weeks, and the software now comes as a standard feature on Nokia and Ericsson switches.
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There is a downside to HSCSD, however, and that relates to network capacity
Whereas a voice call will block one time-slot on a mobile phone, HSCSD needs to block up to four time-slots in order to provide sufficiently high data speeds, for the services it will accommodate. This makes the service greedy for capacity - unacceptable on networks that are nearing saturation point, and pricey on those that are not.
As a result, during off-peak hours, when other traffic is lower, networks are beginning to offer more time slots for the data service, at reduced rates, increasing the overall usage of off-peak idle capacity.
II. The Mobile Office Goes Higher Speed With HSCSD & GPRS
Probably the most significant application for HSCSD is for corporate users accessing in-house LANs and corporate Intranets.
HSCSD Will Complement GPRS for the Corporate User
With HSCSD, faster access to the Internet becomes possible over wireless GSM. Other technologies, such as General Packet Radio Services (GPRS), will complement and enhance the value of HSCSD. since there are applications for both circuit-switched and packet-switched data in mobile wireless, and one may be better suited to a specific application or service type than the other.
If a mobile user needs to make a PSTN/ISDN connection (to corporate modem pools), only HSCSD can be used. HSCSD is ideal for real-time applications and GPRS for "always connected" applications. For example, HSCSD connections provide "active" e-mail and file transfer, while GPRS will run in the background for wireless data networking.
Mobile office applications, as well as web browsing and applications such as mobile navigation services and other features using maps and graphics will benefit greatly from the enhancements provided by this technology, making applications more attractive and easier to use. HSCSD will enable completely new applications as well, such as mobile video, and video conferencing.
Key HSCSD Applications
Applications suitable for HSCSD are real time applications where quality of service is important and high data volume transfers occur.
* Company LAN Access (Intranet Access)
* Mobile e-mail and Fax
* Internet Access
* Telemetry - Traffic surveillance, Remote control of industrial equipment, Security applications
III. HSCSD Today
GSM HSCSD is now available to more than 90 million customers on 32 networks, across 25 countries around the world. The service today offers customers access to a range of existing and new features and applications at much higher speeds than previously available on standard GSM, all with International Roaming where available.
Due to the implementation of International Roaming agreements among the networks, High Speed data services can be offered to customers of these networks while they travel to other networks that provide HSCSD service. Traveling mobile users can use HSCSD to connect to their corporate networks and e-mail service without the hassle of cables and plugs, at reasonable data rates.
For instance, a e-plus customer from Germany can use the same 38.4 kbps data link when roaming on the Luxembourg Tango network or on One in Austria, that he enjoys at home.
For a mobile operator HSCSD is very easy to implement and rollout as it is designed for the existing GSM structure. Since HSCSD mainly requires software upgrades, it is also a limited investment. This makes HSCSD an ideal preparation tool for future wireless datacom services, such as GPRS.
Early adoption of HSCSD gives competitive advantage to carriers by attracting the business subscriber segment of the market.In addition these operators will have important knowledge of end-user behavior and requirements as well as wireless datacom in general.
As for longevity of HSCSD, Sami Vierula of Sonera was recently quoted as saying "I think (GPRS and HSCSD will) co-exist for 2-3 years, and then HSCSD (will) slowly fade away." He is probably correct, but carriers generally feel that payback, on the low cost implementation can be very rapid.
IV. HSCSD Technology
There are several aspects to HSCSD and several variables that affect potential HSCSD performance. These include:
* Old GSM (9.6 kbps) or new more efficient HSCSD channel coding (14.4 kbps)
Maximum data rate on a time slot (of which multiples can be used) is increased by a new channel coding with altered error protection coding. The maximum data rate increases on a channel from 9.6 kbps to 14.4 kbps. and either (or both) codings (with resulting rates) can be employed on a GSM/HSCSD network.
* Time Slots
Multiple time slots combine with new coding to potentially deliver dialup modem speeds
* Transparent v. Non-Transparent (NT) mode of HSCSD operation
Discussed in more detail below, these modes are used to optimize performance under varying conditions or for various service or application types.
HSCSD Is A New Coding Pattern for GSM Data Communication.
Traditionally GSM coding has used (still uses) 22.8 kbps, with 9.6 kbps for data transmission and 13,3 kbps for error correction bits, and 13 kbps for speech transmission (voice telephony).
The new more efficient HSCSD coding pattern for channel coding, makes use of 14.4 kbps for the actual data transmission and the remainder is used for the error correction bits.
The gain of 50% in data throughput does have a small disadvantage: the cell coverage reduces easily, because the farther the base station is from the user, the more important the error correction become. If fewer corrections can be executed, the distance the base station may be from the user can not be too great.
HSCSD Provides a A New Multi-Slot Technology
During the transfer of (voice) or data by means of GSM individual time slots are assigned to users. Until now a time slot could be taken up at the same time, by only one user.
With HSCSD it is now possible to assign to each user (depending upon requirement) several time slots providing significantly improved maximum data rates.
The new multi-slot HSCSD technology functions not only with the new coding pattern, but also with the old coding pattern, so that data can be transmitted successfully and without error, when in difficult terrain, or when further removed from a base station than would be possible with the new HSCSD coding pattern, where each individual error correction bit from the old coding scheme is needed.
While the new coding scheme allowing 14.4 kbps per timeslot is only achievable when you are in an area of good coverage, the clever thing, is that if the signal does drop during a call the phone and network can drop the call to 9600bps and start using the original GSM error protection scheme (RLP) again automatically.
As a result of multi-slot HSCSD technology and new coding or a combination of old and new coding the following maximum data transmission rates can be achieved.
# Slots Old coding New coding
1 slot 9,6 kBit/s 14,4 kBit/s
2 slots 19,2 kBit/s 28,8 kBit/s
3 slots 28,8 kBit/s 43,2 kBit/s
4 slots 38,4 kBit/s 57,6 kBit/s
5 slots 48,0 kBit/s 72,0 kBit/s
Transparent V. Non-Transparent Mode For Varying Types Of HSCSD Service
HSCSD offers both transparent and non-transparent types of service so that many types of circuit switched applications can be used.
For non-transparent HSCSD calls the number of timeslots can be changed during the call, and can be allocated asymmetrically with more bandwidth in the downlink than in the uplink.
With NT HSCSD there are no hand-over problems, because the time-slots will be allocated according to availability.
Some applications such as fax and video requires transparent service, while other such Internet, e-mail work well with non-transparent services.
Non-Transparent (NT) HSCSD Data Communication
During non-transparent data communication an additional error correction is ensured by the network, but again only a variable data rate and a variable delay is utilized. This mode is generally used for web surfing or e-mailing via HSCSD.
For non-transparent HSCSD calls the number of timeslots can be changed during the call, and can be allocated asymmetrically with more bandwidth in the downlink than in the uplink. With NT HSCSD there are no hand-over problems, because the time-slots are allocated according to availability.
Transparent HSCSD Data Communication
During transparent data communication there is no additional error correction by the network, but a constant data rate and a constant delay is maintained. Fax and video require transparent service.
For transparent HSCSD calls, the number of timeslots cannot be changed during a call. With transparent bit-rates, HSCSD offers constant bit-rates and transmission delay, which is very useful for video applications requiring a constant rate of transmission.
Other HSCSD Capabilities
These capabilities are discussed in more detail in section VI (D2-Netz network).
- Flexible Channel Allocation
- Blocking
- Handover
- Asymmetrical v. Symmetrical Channel Allocation
V. Nokia Terminals for HSCSD
The Nokia Card Phone 2.0 was the world's first PC Card with a built-in GSM phone that turned a notebook computer or other portable devices into a complete high-speed mobile office with voice calls made hands free via a headset. As a multislot terminal, the card supports data transmission speeds up to 43.2 kbps.
nokia.com
Other Nokia terminals that have supported HSCSD include the Nokia 7110 and Nokia 9110.
The new Nokia 9210 Communicator is now shipping:
nokia.com
More HSCSD capable terminals will be available in the near future. These will include:
* The Nokia 6310 HSCSD with GPRS & Bluetooth (Q4):
nokia.com
Look for a HSCSD with GPRS 9210 Communicator early in 2002 and there may be another Nokia surprise under the Christmas tree this year (or worse case, shortly after).
VI. A Real Life HSCSD Example - D2 Vodafone D2-Netz Network
d2mannesmann.de
Available Data Rates
Depending upon number of the combined channels and the used channel coding different data rates are available. The max. number of combined channels or the max. data rate determines you. The actually used number depends on the availability of free channels. By the flexible channel allocation of the D2-Netzes this number can vary during the data link. Additionally for the receiving of data more channels are combined if necessary than for transmitting data (see asymmetrical channel allocation).
The following table shows the maximum data rates currently available with HSCSD in the German D2 Vodafone, D2-Netz network during non-transparent data communication.
Using multiple time slot in combination with the new channel coding (14,4 kbit/s) the data rates can be increased.
The new channel coding has been available since May 2001 in the entire D2-Netz
Channels Channel coding 9.6 kbps Channel coding 14.4 kbps
1 9,6 kbit/s 14,4 kbit/s
2 19,2 kbit/s 28,8 kbit/s
3 28,8 kbit/s 43,2 kbit/s * / 38.4 kbit/s **
4 38,4 kbit/s ** 57,6 kbit/s * / 38.4 kbit/s **
* theoretical value, which is achieved on the air interface in the D2-Netz
** only with connections to ISDN receiving stations, which support the V.110-Standard
D2-Netz Notes:
- The currently available terminals can combine and support max. 3 channels for receiving of data only in the non transparent operating mode. Future D2 terminals will support both modes.
- During the non-transparent data communication to transmit-strain an additional error protection log is applied. This log guarantees that data, which transmit-strains on was falsified (?) are requested again. Thus the data rate can vary during non-transparent data communication.
D2 Netz Terminals
HSCSD requires new mobile terminals, which are able to use several channels for a data link. The new devices differ by the number of combinable channels and the data rates attainable thereby.
These models are, or will be, available for HSCSD & GSM Voice and SMS
* Nokia Card Phone 2.0 Now
* Ericsson R520m (Q2) with GPRS/Bluetooth
* Nokia 6210 Now
* Nokia 6310 (Q4) with GPRS/Bluetooth & SyncML
* Nokia 8310 Now
* Nokia 9210 Now with PersonalJava & SyncML
* Siemens S40 (Q3) with GPRS
Flexible Channel Allocation (UP-/Downgrading)
In the following cases the number of combined channels can be reduced by the D2-Netz during the active data link:
- Blocking: In a radio cell, which is fully occupied by HSCSD data links among other things, a language connection is to be structured. The data link is reduced by a channel, in order to create capacity for the language connection. If the language connection is terminated, the channel is assigned to the data link again.
- Handover: When changing from one radio cell into another, in which sufficient channels are not free, in order to maintain the data link on all combined channels, the HSCSD connection is maintained in each case on at least one channel.. As soon as sufficient channels are available, the number of the combined channels is again increased.
Asymmetrical v. Symmetrical Channel Allocation
In a High Speed Circuit Switched Data network, you can make use of multiple slots at the same time. When you are sending and receiving e-mail you can choose to use two slots in, two slots out, doubling the speed. When you are downloading Internet pages you can choose to use three slots in, one slot out, tripling the download speed to 43.2 kb/s. (from Nokia site)
The data rates attainable with HSCSD are for transmitting data (Uplink) and for the receiving of data (Downlink). The first HSCSD terminals are able to combine only four channels, however in the total, 2 channels each are used for UP and Downlink during a symmetrical channel allocation.
In order to combine up to 3 channels, for transmitting data at another data rate than that used for receiving data the user can select e.g. 3 channels for the Downlink, but only one channel for the Uplink (asymmetrical channel allocation 3+1).
This is meaningful for Internet surfing as opposed to sending and receiving e-mail, since when downloading files from the Internet or an Intranet more data will transfer compared to transmitting the instructions for downloading.
VII. HSCSD (High-Speed Circuit-Switched Data) - Specification & Standard
Standard Type: Mobile Cellular (data)
Location: Worldwide
Completion: Phase 1 1997 - Phase 2 1999
Controlling body GSM Association & (now) 3GPP
Developers European Telecommunication Companies
Phase 1 - supported a bundling of four time slots (this corresponds to a net data transmission rate of 38.4 kbps).
Phase 2 - supports up to eight time slots and new channel coding scheme
VIII. Circuit-Switched v. Packet-Switched in the 2G to 3G Transition
A very good article called "3G Costs can be read here:
Message 15973613
I think there is a takeaway related to the HSCSD discussion that has been taking place on this thread and it also relates to the fact that at BT Manx, WCDMA is currently implemented in circuit-switched mode only at 64 kbps, and at DoCoMo, FOMA has (or will be) implemented(ing) video (streaming and still) applications using circuit-switched mode at 64 kbps, while i-mode and e-mail use 384 kbps packet-switched data.
A key point:
"For networks requiring a high degree of latency control, packet switching is no more efficient than cell or circuit switching. This is particularly true when applied to wireless networks."
IX. Networks That Have So Far Launched HSCSD
Europe:
Connect, Austria
KPN Orange, Belgium;
Eurotel Praha, Czech Republic;
Tele Denmark, Denmark;
Sonofon, Denmark;
Sonera, Finland;
DNA Finland, Finland;
Cosmote, Greece;
Stet Hellas, Greece;
'E-plus' Mobilfunk ,Germany;
Mannesmann Mobilfunk GmbH, Germany;
Pannon GSM, Hungary;
Eircell, Ireland;
BiteGSM, Lithuania; LMT, Latvia;
Tango, Luxemburg;
Telenor, Norway;
Polkomtel, Poland;
Telecel Vodafone, Portugal;
Connex,Romania;
Mobitel d.d., Slovenia;
Telia, Sweden;
Europolitan Vodafone, Sweden;
Swisscom Mobile, Switzerland;
Orange, Switzerland;
Turkcell, Turkey;
Orange, UK
Asia Pacific:
CSL Limited, Hong Kong;
SmarTone, Hong Kong;
SingTel Mobile, Singapore;
M1,Singapore
Middle East and Africa:
Partner Communications Company, Israel;
MTN, South Africa <<
X. Errata
* Good article by Joanne Taaffe called Mobile: HSCSD - Bird in the hand is worth two in the bush?
Message 15891672
* Article: Internet Spoofing Software (iOra) Tested Over UK HSCSD Service ... "20-fold reduction in download times and 20-fold cost saving on the Orange HSCSD service costs"
Message 15918859
* The knowledge and wisdom of Ilmarinen (from whom I have learned a thing or two):
- HSCDS has always been the technology which bridges the gap between single slot, switched circuit GSM data and GPRS.
Message 15971746
- 1. channel coding is NOT an error correction ... 8. Just to be sure, for packet networks the issue of error correction is slightly different, but not the (basic) issue of channel coding, which is the same. (I'm sure one can make some optimization of channel coding to make it slightly better for packet transmission)
Message 15972625
- Channel coding and error correction, history.
Message 15972699
- Error correction v, "error reduction"
Message 15972958
- Eric - |
