*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* -=[SD]=- Sepulchral Darkness -=[SD]=- presents : Cableless Local Area Networks Brought to you by : ---=[AZTECH]=--- Sepulchral Darkness '95 All Rights Worth Shit *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* By Frank Booty ~~~~~~~~~~~~~~ With the increasing demand for mobile services, technology has provided the market with the Cordless or Cableless Local Area Network (CLAN) to bring mobility to to the fixed LAN enviroment. Indeed there is a very definite trend in the public telecommunications market towards cordless transmission. It has been a proven succes in the voice market with the great demand for mobile services, but in the field of data communications, cordless solutions have not always been satisfactory. Figure 1 shows an example of a CLAN. Figure 1 ~~~~~~~~ * An Example of a CLAN | +---+ * | | | | <----+ | * +---+ +---+ * | | * | | | | | | | +------+ +---+ +---+ <----+--- Consoles | +---+ |SERVER| | | | |-------| |-------| | * +---+ | | +---+ | | | <----+ | +------+ +---+ | | | | Wired * +---+ | Backbone | +---+ * | | | = Ariel +---+ Only now is the market seeing the advent of Wide Area Networks (WANs) designed specifically for mobile data services. Several Organisations (Cognito, Hutchinson and RAM for example) who currently operate mobile data networks are set to lead a significant growth in the transmission of data by mobile users. There are also cordless telecommunications in offices and residential enviroments. Base Stations, from companies such as GPT, are delivering mobility to the PBX as the cellular radio services did for the PSTN. As with the dedicated mobile networks, CLAN technology will bring mobility to the fixed cabled LAN enviroment CLAN APPEAL ~~~~~~~~~~~ CLAN Technology represents the convergence of two of telecommunications fastest growing markets; LANs and mobile communications. But on the face of it, it seems unlikely that cordless/cableless/wireless data comms should appeal users. Hitherto, data commms manafacturers have designed products to promote peace of mind for the user. Suppliers have offered safety, security reliability and robustness. Some Industry observers argue that CLAN technology seems to offer additional problems in transmitting data - interference, security and a health risk. So does CLAN technology applied to local area networking deliver a benifit to the user, or is it just another example of a technology driving the market? Fixed Cable LANs are undoubtedly a success. The speed of the technology race is fast. As the LAN Market generally is progressing so quickly, there are many other technologies apart from CLANs vying for the Network Managers attention. There are Fibre Optic Devices and the FDDI (Fibre Distributed Data Interface) ISO Network Standard, Bridging Routers, very small aperture terminals (VSATs) and Satellite links, and data broadcasting for example. It is considered that CLANs will address a niche in the market. However, it doesnt take much to see that the technology is not going to upsurp fixed cable LANs. But cable is expensive, inflexible and at times undependable. It is considered that up to 90 per cent of failures in fixed LANs are caused by cabling difficulties. The cost of changing cabling structure or installing additional nodes restricts the users mobility. To avoid such inconvenience and cost of moving nodes, the LAN has to be planned carefully before it is installed. In a large installation, this could require a dedicated computer system to manage the miles of cable and the changes to the morphology. All of this could be overcome by using CLAN Technology. Despite differences in propagation techniques and portions of the radio spectrum used by CLANs, the Hardware components are remarkably similar. Each Network is no more than a network interface card installed in the networked terminals/PCs and an external omnidirectional antenna. At a minimum, the software component of the CLAN would include network drivers, diagnostic software and installation tools, and optional monitoring and diagnostic packages. Other extras include encryption facilities, boot ROM sockets and longer antenna extension cables. DATA PROPOGATION ~~~~~~~~~~~~~~~~ Once the components are installed, the CLAN behaves like a Token Ring, Ethernet or Arcnet without the inconvenience of cabling. There are three different propogation technologies being used in the transmission of data over CLANs: Spread Spectrum Technology (SST), Infra Red and Microwave. SST ~~~ The most popular to date has been SST, which is a technique that was developed in the Second World War. In Essence, SST spreads the signal over a broadband at a much lower density than a conventional radio signal. The early SST CLANs in North America operated between 902 to 928Mhz which clashed with the UK Cellular operators Cellnet and Vodafone, who already used this frequency band. This led to a wait for CLAN supppliers while the DTI allocated an alternative range, in collaboration with the frequency management committee of CEPT. In May, The DTI allocated the 2.445 to 2.475Ghz band which provides commonality with Holland and Germany. The Industry's MPT (Model Product Type) specification for UK CLANs is being finalised, as are the UK licensing requirements. Manafacturers and products in this sector are : TeleSystems of Canada ARLAN (Advanced Radio LAN) [Marketed by ChaseCom of London Sold by resellers such as : HS dataline, Frontline, Hawke Systems] Califrnia Microwave of US Radio Link [Marketed by IT Security International of Welwyn Garden City " " Telecom Systems of Crawley Sold by Resellers such as: Rock Technology Systems, Maxim Networks] NCR WaveLAN [Developed at Utrecht in Europe] Figure 3 shows the structure of the radio link system and Figure 4 shows possible Network Topologies. Figure 3 ~~~~~~~~ Radio Link Structure +---------+ | Modem | Data | and | Data | Control | +-<----->| Unit |<----->-+ Tx/Rx 1 | +---------+ | | Data | ^ ^ | | Rx 2 Interfaces | | | | | | +----------+ | | +----------+ | | <==========>| Interface| | | | Radio |<---+ | <==========>| Unit | | | | Unit |<------+ +----------+ | | +----------+ ^ | | ^ Control Port | | | | +---<------+ +---->-----+ Control Control Figure 4 ~~~~~~~~ Radio Link Topologies * * | | ===> +---+ +---+ <=== >---| | /\/\/\/\/\ | | ---< ===> | | | | <=== +---+ +---+ Point to Point * +-+ * | | | \/\/\/\/\/\ +-+ +---+ \/\/\/\/\/\ * ====| | \/\/\/\/\/\ +-+ | | \/\/\/\/\/\ | | +---+ +-+ * +-+ | | +-+ * Multi Drop +-+ | | +-+ * * | | +---+ +---+ | | \/\/\/\/\/\/\/\/\/\/ | | +---+ / +---+ / \ / / \ \ / \ / \ / / * / \ * | / \ \ | +---+ +---+ | | \/\/\/\/\/\/\/\/\/\/ | | +---+ +---+ Network NCR, whose product operates in the US across frequencies from 902 to 926 Mhz, regards the DTI allocation as fine for the current product offerings but a little light for future product development. NCR believs it will need a greater bandwidth if it is to meet future user requirements and is looking for commonality across the whole of Europe. Radio Link uses the frequency hopping SST technique as opposed to the direct sequence spectrum spreading technique, which is based on amplitude modulation. Low power levels are used and the frequency hopping sequence is pseudo random, making it virtually impossible to detect and intercept any signals. Figure 5 shows the principle of frequency hopping. Figure 5 ~~~~~~~~ +---->------+ | | | +-----|<---+ +<-+ | | | | | | |+-<-+| +--|>--+| | | || || | | || +-->|--|----+ +--||-->||-+| |+-->---+| | |+<-+| | || || || || || || | || || +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ |1| |5| |4| |2| |6| |3| |7| |0| |9| |8| +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ---------------->------------------ FREQUENCIES Signal Hops frequency using pseudo random pattern It should be stressed that SST products can be a substitution for cable but are not a replacement for cable. They cannot compare with Token Ring or Ethernet Performance, for example. INFRA-RED ~~~~~~~~~ Infra red propagation is not a means of radio transmission. In fact, of the three CLAN technologies, it has the most limitations. But it does have the advantage that its bandwidth is easily re-used. There are major limitations in that it has proven difficult to modulate infra-red propogation for data transmissions, it needs line of sight transmission paths and it cannot penetrate walls. Consequently, Infra Red is only applicable in an open office enviroment. It was also until recently possible to transmit at 1M bit/s because of the difficulties of modulating the infra red carrier. BICC Data Networks has now launched Infra LAN which is said to operate at a data rate of 4M bit/s. This is compatible with the IEEE 802.5 standard and provides IBM Token Ring connectivity without any hardware or software modifications to existing equipment. The company chose Infra-Red Technology because it 'frees end users from concerns about licensing approvals, network security, standards incompatibility or any other issues facing spread spectrum or microwave based cableless systems'. Certainly, DTI licensing is not neccesary for user's sites or individual departments. The Infra Red signals are also immune from radio frequency interference and are secure from outside signal interception. BICC has also announced its intention to launch a sister product which would be compatible with IEEE 802.3 Ethernet products. MICROWAVE ~~~~~~~~~ Microwave is the third principle technology suitable for CLANs. A much publicised product her is Motorola's WIN (Wiring Inbuilding Network) system which has gained FCC approval in the US. It transmits at a frequency of 18Ghz and is capable of running at 15M bit/s although it is marketed at 10M bit/s (So making it perceived as an Ethernet or Token Ring equivalent). Microwave techniques are less sensitive to physical obstructions and will penetrate through walls although the transmission distance is limited to 100 feet. To make the WIN system viable several technical hurdles have to be overcome associated with equipment size, expense and the complexity of 18Ghz systems. For the UK, Motorola is having to rework the product to enable it to meet DTI specifications and this probably will have happened by the time you read this article. Microwave has two advantages over both SST and Infra-Red: There is a lot of spectrum available at at these frequencies and the propogation characteristics of 18Ghz enable the WIN system to re-use the same frequencies at a range of some 120 feet via a series of deployed microcells in the office enviroment. However, against this system is the perceived health risk. While there is no empirical connection between high frequency radiation and health risks, there could well be a serious psychological barrier which would prove insurmountable. PRACTICALITIES ~~~~~~~~~~~~~~ For all the difficulties experienced by fixed LANs, CLANs is not always or neccesarily the perfect answer. CLANs have their own range of operating difficulties : office construction materials disrupt over-the-air transmission between CLAN components to varying extents depending on the propogation method selected; each office hs its own topology and each CLAN will have to be set up accordingly - which could mean anything from adjusting an antenna position to moving the server location. Differences between wavelength availability in different countries decreases the opportunity for volume production and keeps prices high. This is known to concern NCR who are looking for commonality across the whole of Europe - They do not want a different product for each country they market in. (-=[AH]=- Have omitted a load of guff on marketing strategies and pricing here to keep the article precise and technically orientated) The speed at which data can be transmitted is lower than that for a fixed cable due to the limited availability of unused radio spectrum - a point which is obviously seized on by BICC. The faster of the SST CLANs runs at 2M bit/s compared with the 10M bit/s of Ethernet, and the 4/16M bit/s of Token Ring. For many, 2M bit/s may not be fast enough. Limited spectrum availability means that CLANs have to be regulated, which could have an effect on the market's growth. The area of licensing sites to operate a CLAN is a particular area of deep discussion, with one anticipated outcome being a 'plug in and go' solution without the added complexity of licensing. Security on CLANs is seen by users as being weaker than it is for a fixed LAN. Using radio suggests the possibility of Networks being broken into. In fact, the use of radio in no way compromises the security of the network. SST is the most secure form of CLAN because it is so difficult to decode. Despite the fact that telecommunications has suffered from being driven by the technology available rather than by user needs, there are situations where CLAN technology could solve real problems. This could be either by extending the usefulness of fixed LANs or in new market opportunities, not neccesarily as a substitute product. APPLICATIONS ~~~~~~~~~~~~ The most succesful CLAN application to date has been in the retail industry where the Point of Sale (PoS) Terminals in large stores have become intelligent terminals that resemble a PC rather than an old fashioned till. Todays PoS terminal requires access to shared applications over a store wide LAN. But department stores change their layouts to encourage customers to look at different merchandise. So the store management can lose track of the cabling or damage cabling when it is being moved, The work has to be carried out at night or on a Sunday, etc. CLAN technology overcomes all these problems. NCRs WaveLAN product was first piloted in JC Penny's Department store in Chicago. Figure 6 illustrates a trial system used to demonstrate CLANs to the Marks and Spencer chain of stores; as a result, an order for 500 systems has been placed. Figure 6 ~~~~~~~~ Demonstration radio link system for Marks and Spencer. | * | First Floor | | (500ft from Host) +-+ +---------+ | | |---- | CONSOLE | | +-+ +---------+ | Radio | Link PoS x 3 | | | --------------------------------------------------+ ^ | * | | Ground Floor | | | (200ft from Host) +-+ +---------+ | | | |---- | CONSOLE | Concrete | +-+ +---------+ Floors | Radio | | Link PoS x 4 | | | | v | --------------------------------------------------+ | * | | | +-+ +--------+ | Basement | |----| ICL | | +-+ | System | | Radio | 25 | | Link +--------+ | --------------------------------------------------+ Configuration for trial system shown. Marks and Spencer is now taking 500 units. Operating in the 2.4 to 2.5 Ghz frequency band, each unit makes four frequency hops per second and never goes back to the same frequency in less than 1.3 seconds. Other Applications include : Networking within listed buildings where internal rewiring is not allowed. Buildings where the ducts are already full to capacity. Buildings where the structure is such that it makes it un-economical to cable. Companies with short leases on their premises, making the installation of a fixed LAN un-economical. Mobile teams that stay on various sites temporarily, eg: teams of auditors or management consultants. Hospitals can take advantage of a flexible data link between nursing stations and patients to keep a constant monitor of the situation. Manafacturing companies could install flexible computer aided manafacturing and process control, eg: in hostile enviroments such as steel mills, hazardous work areas,etc.. As part of an organisations contingency plan to back up conventional cabling in the event of a disaster. A LAN could be set up centrally for a company's satellite sites which would save on time and travel costs and a LAN could be installed without the expertise leaving its central location. Inter Building or Network Bridges for Multiple Networks. Also, a CLAN can be connected into a wired backbone offering an even broader flexibility to the user. -=[SD]=- -=[SD]=- -=[SD]=- -=[SD]=- -=[SD]=- -=[SD]=-