New and Legacy communication issues

Challenges with maintaining Legacy systems

It can make perfect sense to continue to run existing reliable and proven systems, especially if operational requirements have not changed. Alas, the developing nature of technology means that from time-to-time, issues arise. 

Changes to email encyption protocols 

Modern computer communication services support the Transport Layer Security (TLS) encryption protocol. This aims to protect the information sent and received over a standard Simple Mail Transfer Protocol (SMTP) connection between two computers while ensuring that they both agree and understand the method of data transfer.   

However, the earlier versions of TLS 1.0 and 1.1 have been deemed by the industry to be not secure enough and have been superseded by versions 1.2 and 1.3. You and/or your service provider may have already transitioned to the latest protocols. However, if you have old hardware running legacy software, as support from service providers is withdrawn, you may find your email stops working.

How you can tell if it’s an issue

If you’re using an Apple Mac then the Safari Browser has supported TLS 1.2 for web traffic protection since version 7 in 2013. However, if you’re still running ‘El Capitan’ OSX 10.11 with Apple Mail 9.3, it won’t support TLS 1.2 for email. Other computer hardware and software combinations may also run into problems.

Most browsers including Safari ended support for TLS 1.0 and 1.1 in March 2020, and various service providers have either already dropped or soon will withdraw operation of the older TLS protocols.

For instance, will stop support of TLS 1.0 and 1.1 on 17th August 2021. Other service providers may have different end of life dates. If you’re using the service then there’s an easy way to check:

send an email to:

This will provide an automated reply telling you what protocol you’re using (works with iPhones and iPads too), like this:

            “started”: true,
            “protocol”: “TLSv1.2”,
            “cipher”: “ECDHE-RSA-AES256-GCM-SHA384”,
            “keysize”: 256

Other service providers may have similar methods of verifying the protocols, so it’s worth checking with them. Failing that, you may be able to examine the headers of your emails, to look for something like this:

version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128

Solutions if you’re affected

To ensuring your email continues to function, the options include: 

  1. Updating your operating system. In the case of Apple Mail on Mac computers, this means moving to ‘Sierra’ OSX 10.12 as Mail cannot be separately upgraded.
  2. Using a different email client with TLS 1.2 support, e.g. Mozilla Thunderbird.
  3. Using a browser based solution for your email
  4. Changing your settings to send and receive email without encryption (not recommended) 

Balancing New Requirements and Legacy Support

If you want to stick with your current hardware and software choices, this does present a problem, particularly if you’re otherwise happy with your setup and are unable to upgrade.

Alas if you want full compatibility (and security) with the latest industry supported functionality, whilst retaining operation of other  legacy applications, consideration has to be made to invest in new hardware to run in parallel with older systems, which continue to be maintained to perform dedicated compatibility functions.

YellowsBest: Keeping Customers Operational

If you have similar or other new requirements and legacy maintenance needs, please get in touch to discuss how we may be of assistance to keep you operational.

Mobile Evolution and the Extinction Event

When Giants ruled … mobile communications

A long time ago, great “Dinosaur beasts” of Mobile Communications were supreme.  The beginnings were in the 1970’s with the launch of a Motorola handset weighing 2kg. This was followed by other barely portable products with huge batteries such as the Nokia Talkman. Only for the ‘new adopters’ who had to be in touch all the time.

Then came the ‘Bricks’ 

From these humble beginnings, soon a range of solid, reliable but ‘bricklike’ big and heavy phones appeared, like the Nokia 2110 and the Motorola Dynatac 8000X, as featured in the 1987 movie “Wall Street”. Designed for upwardly mobile business people.

Diverse expansion 

Then came a period of rapid expansion with a diverse range of more affordable products to suit wide consumer tastes. Various forms, colours and accessories became more and more important, with slide phones like the Nokia 8110 as featured in the 1999 film “The Matrix” and flip phones like the Motorola Razr, providing a ‘Star Trek’ appeal.

Feature explosion

An expansion of more and more features to make mobiles do more fuelled the explosion of product ranges. Cameras and music players were added to increase the functionality of these increasingly sophisticated and compact pocket-sized devices, such as the Nokia 6230.

Nokia 6230

A glance at the 2004 Carphone Warehouse catalogue shows how varied mobiles had become, with the top 10 dominated by Nokia, Sony-Ericsson, Siemens and Motorola as the biggest manufacturers of the time.

2004 Carphone Warehouse “Top 10”

‘Tyrannosaurus’ functionality heavyweights 

For a while, the king of the land was the bulky, terrifyingly expensive but impressive (for its time) Nokia Communicator, offering phone, text, email and even fax. Opening up to reveal a full QWERTY keyboard, the range started with the 9000 which appeared in the 1997 film “The Saint” and had evolved by 2007 into the even more powerful E90.  

Nokia E90 Communicator

Extinction Event: The Death of the incumbents

But then came biggest shock to the world of mobile communications: the launch of the first Apple iPhone on 9th January 2007.

Like a meteorite striking the earth, this shock spelt the end for many mobile types which couldn’t compete with the sudden demand for ‘touch-screen’ devices using apps.

Indeed companies like Nokia, once the biggest of them all, couldn’t adapt and died a death, as well documented in the BBC documentary “The Rise and Fall of Nokia

Survival of the fittest

The ‘smartphones’ from Apple and later Android-based from the likes of Samsung became an increasing hit, wiping out much diversity and seeing a seismic shift away from many form factors to the now standard “slate” style of device.

Apple iPhone 4
Apple iPhone 4

Some ‘featurephones’ as they came to be known have lingered on, and in recent years companies like HMD global, who under licence have taken some iconic Nokia designs such as the 3310 and made a successful relaunch. Diversity is now finally creeping back with new variants such as the ‘folding’ Samsung Galaxy Z Fold2.

Your Paradigm shifts

Any memories or stories to tell? @YellowsBestLtd would be keen to hear your thoughts and experiences of sudden technology ‘paradigm shifts’. Let us know if we can be of any assistance with your future solution or services requirements. 

Legacy Transmission & Line Codes

Before Fibre, there was copper!       

It’s almost difficult to believe that not so very long ago (ok, going back maybe more than 50 years) there were no optical fibre or digital transmission paths of any flavour of technology providing our communications infrastructure.

Analogue FDM

From early to mid 20th Century, an extensive core copper cable network was rolled out, based on analogue FDM (frequency Division Multiplexing) over coaxial pairs, with the valve-based technologies occupying a lot of space and consuming much power. 

Digital PCM

The late 1960s saw the introduction of digital PCM (Pulse Code Modulation) sampling at 8kHz. The ITU-T (International Telecommunication Union – then known as CCITT) standardised 30-channels at 64kbit/s in a 2.048Mbit/s multiplexing system, using 8-bit A-law algorithm (the USA adopted 24-channel 1.544Mbit/s with μ-law algorithm).

Problems with high bit-rates

The higher bit rates gave rise to crosstalk interference problems on many existing cables. Also, data signals transmitted as voltage levels in unipolar NRZ (Non-Return to Zero) format are not self clocking and have a significant DC component, wasting power. Bipolar RZ (Return-to-Zero) type AMI (Alternate Mark Inversion) coding prevents the build up of the DC-component for longer distance and addresses the issue of data containing multiple ones. However, long sequences of zeros still present problems with a lack of transitions causing difficulties maintaining synchronisation.

Introduction of Line Codes

Line Coding of the format mB-nB was introduced to overcome these issues. Initially 4B3T (four Binary, three Ternary) was used. This encodes each 4-bit input group into a 3 symbol output using the three states of positive, negative and no pulses.

e.g. ‘0000’ is coded as ‘+0-‘

This improved efficiency in terms of bit per symbol over AMI, which itself is an example of a 1B1T code. Improvements in transverse screened cables were also made. However, transmission problems with high-speed digital data were still encountered due to unsuitable copper cabling which needed to be addressed.

PDH Higher Order Multiplexing

By the late 1970s, the UK had adopted the ITU-T recommended PDH (Plesiochronous Digital Hierarchy) of E-carrier higher-order multiplexing at 8Mbit/s, 34Mbit/s (in the US, T-carrier at 6Mbit/s, 45Mbit/s) and 140Mbit/s. 

The lower rates of the E-carrier system adopted HDB3 coding, which replaces 4 ‘0’s with ‘000V’ or ‘B00V’ (or in the US for T1, B8ZS coding which replaces 8 ‘0’s with ‘000VB0VB’).

CMI (Coded Mark Inversion) was included in the ITU-T standards for higher-order PDH at 140Mbit/s PCM (as well as SDH at 155Mbit/s electrical STM-1). This is a 1B2B type of NRZ coding where a ‘0’ is represented by ’01’ and a ‘1’ as an alternatively ’00’ and ’11’, with +V and -V representing the coding levels.  

The advantage of the coding is it makes clock recovery by the receiver simple and for maintaining synchronisation alignment with a long sequence of ‘0’s or ‘1’s.     

Line Coding examples

Optical fibre systems

From the beginning of the 1980s, early optical-fibre multi-mode systems operating at 850nm were deployed, and later single mode at 1300nm, using the PDH multiplexing capacities. 

Typical of long-haul PDH optical-fibre systems, the 2 Mbit/s, 8 Mbit/s and 34 Mbit/s ‘Dynanet’ products from Nokia have ITU-T G.703 compliant digital interfaces using the HDB3 code, but using an optical transmission Line Code of 5B6B. This is another type of mB-nB code, where in this case 5 bit data words are coded using 6-digit code words

e.g. ‘00000’ being represented as ‘100111’. 

As well as its use on electrical systems, CMI Line Coding has also been popular for use on short-haul optical-fibre transmission such as ’tactical’ fibre optical systems operating at 2 Mbit/s.

SDH / SONET – A different approach

For optical SDH systems, STM-1 and above, scrambling is employed instead of line codes to ensure the incoming bit stream contains sufficient transitions for maintaining synchronisation. This works by combining the data signal with a pseudo-random bit sequence generated by a scrambler polynomial generator.

i.e. with a sequence of length of 127, the generating polynomial is 1+x6+x, leading to input data ‘00000000001111111111’ being scrambled as ‘11111110000001000001’.

Optical PDH still serving

In most cases higher-order optical PDH has been decommissioned, but optical transmission at 2Mbit/s is still in operation for many low-data rate applications, where costly replacement with SDH, WDM or carrier Ethernet would bring no advantage. An example product is the Nokia DF2-8 which continues to offer reliable access services, particularly in the Utilities and Transportation industries.

DF2-8 – TA 21518

Copper systems still in operation 

Though core copper electrical transmission systems have now been discontinued, much of ‘last mile’ telephony and related broadband connections are still copper access. For extended data transmission applications, copper systems are still deployed and maintained. Such products include the Nokia DSL2i copper line equipment (including power feeding repeaters) using SHDSL (Single-pair High-speed Digital Subscriber Line). This uses TC-PAM (Trellis-Coded Pulse-Amplitude Modulation) which is a 4B1H Line Coding, since translates 4 binary digits into 1 Hexadecimal (16) levels. It improves range, especially when used with regenerative repeaters, and improved ADSL (Asymmetric Digital Subscriber Line) compatibility. 

ACL2i PF GEN – T65580

Feedback and assistance

This has been a necessarily very brief run-through of legacy transmission and some of the Line Codes employed. @YellowsBestLtd would be keen to hear your experiences and knowledge of transmission systems and performance of Line Codes. If we can be of any assistance with your solution requirements, including both new and legacy technologies, then please get in touch

Maintenance of Legacy networks – Spares, Connectors and Cables

Continued use of Legacy Telecoms  – Nokia PDH ‘Dynanet’

Public Operator and Private Network Customers across the Telecoms, Utilities, Transport and Public Safety markets maintain ‘legacy’ infrastructure for mission critical applications, which continue to deliver good operational service with high availability. 

Typical products utilised are those from the ‘Dynanet’ family of PDH Transmission telecoms products, which were first introduced by Nokia over 20 years ago, and were continued in recent years by DNWP. Production of the majority of the product range was ceased in 2019. 

In order to maintain these systems and networks, it’s still possible to supply spares from surplus stocks and refurbished items to keep networks operational. 

Don’t forget the Connectors and Cables!

One challenge for the continued use of existing infrastructure, particularly when installing replacement parts, is sourcing the appropriate specialised and often propriety connectors for cabling of interfaces and management connections.  

Regarding ‘Dynanet’, fortunately some products can still be produced, notably the Euro / SMB connectors, along with the DCN Adapter C4.0, related management software products and other items such as the TPS64 and NDUE. Listed here are a few of those currently available new:

Part NumberDescription
SMB Connector for RD179 cable
Euro Connector 3×32
Euro Connector 3×7
Euro Connector 3×7 – 21470
Part NumberDescription
24201TPS Control Unit
24202TPS Channel Unit
T37882.02NDM DC Unit, enhanced (NDUE)
T31094.01DCN Adapter C4.0
DCN Adapter C4.0 – T31094.01

We are able additionally produce a wide range of cable products to suit most connection requirements, utilising our UK-based manufacturing partner.  Bespoke cable assemblies, control boxes, harnesses, wiring looms, panels, fibre optic products are some of the network solutions available. 

@YellowsBestLtd satisfies world-wide customer product sourcing requirements for current and ‘legacy’ equipment technologies from a wide range of Original Equipment Manufacturers (O.E.M.s), surplus stocks and refurbished items.

Hence, please check and if you do have any requirements, please let us know. We look forward to hearing from you.

Remaining stocks of Nokia ‘Dynanet’ spares – Update

Surplus and Refurbished Items for continued operational service

Many Customers have ‘legacy’ telecommunications networks which are continuing to provide good operational service. Particularly where functional requirements have not changed, it makes sense to avoid or delay costly and time-consuming change-out replacement projects, by obtaining spare parts.

@YellowsBestLtd satisfies world-wide customer product sourcing requirements for current and ‘legacy’ equipment technologies from a wide range of Original Equipment Manufacturers (O.E.M.s).

Stocklist of Nokia ‘Dynanet’ Spare Parts – Available for immediate supply

For the ‘Dynanet’ family of PDH Transmission telecoms products, which has provided 20+ years of service, we still have a few spare units are in stock and available for immediate supply. These items have been mostly retrieved from operational service during Customers’ decommissioning projects, and have been refurbished, tested and are warranted for working operation.

Given that production of the majority of the product range was ceased in 2019 or before, it is recommended to consider purchasing spare parts whilst there is still availability.

Here is a list of the main items currently in stock, though there may be a few additional parts that can be supplied.  Hence, please check and if you do have any requirements, please let us know. We look forward to hearing from you.

Part NumberDescription
CC 24002DB2 2×2 Mb/s Branching Unit (B2), 75ohm
CC 24011DB2 2 Mb/s Switching Unit (X2), 75ohm
CC 24101DN2 2×2 Mb/s Interface Unit (IU2), 75ohm
CC 24111DN2 Control Unit (CU), 75 ohm
CF 24186DN2 19in Subrack
CF 24186.09DN2 19in Subrack, grey-L91 EMC
CG 24170DN2 Bus Power Unit (BPU)
CG 24171DN2 Extended Bus Power Unit (EBPU)
CU 24013Data Interface Unit (DIU) 2M, nx64k: G.703/704, 75ohm
D-21470Euro Connector, 3×7
D-24204Optical Teleprotection Interface Unit, C37.94
T30506.0917-slot DYNANET Subrack
T30851.02Subrack Power Adapter (SPA)
T31094.01DCN Adapter C4.0
DCN Adapter C4.0 – T31094.01
Part NumberDescription
T37870.01NDM 19in 17-slot Subrack
T37871.01NDM DN2 19in 17-Slot Subrack
T37882.01NDM DC Unit (NDU)
T37882.02NDM DC Unit (NDUe)
T37885.01NDM Ring Generator
Ring Generator – T37885.01
Part NumberDescription
T37885.02NDM Ring Generator + DC/DC converter
Ring Generator – T37885.02
Part NumberDescription
T37889.01NDM Backup Unit (NBU)
NDM Backup Unit – T37889.01
Part NumberDescription
T65520.01ACL2 RM DC Power Gen
T65580.01ACL2i PF GEN Line Terminal Card
ACL2i PF GEN – T65580
Part NumberDescription
TA 21513Optical Line Terminal Repeater (DF2-8), 1300 nm LED MM/SM
TA 21516Optical Line Terminal Repeater (DF2-8), 1300 nm LASER SM
TA 21518Optical Line Terminal Repeater (DF2-8), 1300 nm LASER LP
DF2-8 – TA 21518
Part NumberDescription
TC 21101DM2 Multiplexing Unit, 75ohm
TC 21301DM8 Multiplex Equipment, 75ohm
TC 21705Supervisory Substation
TC 21710.01TMS Adapter
TG 21261Ring Generator 25HZ 15W
TU 21122.5Data Interface Unit (DIU) 48..64k, V.11, 10ch
TU 21124Data Interface Unit (DIU) nx64k, V.11/V.35/X.21, 2ch
TU 21124.05Data Interface Unit (DIU) nx64k, V.11/V.35/X.21, sync
TU 21125Data Interface Unit (DIU) 48..64k with sync, X.21
DIU X.21 – TU 21125
Part NumberDescription
TU 21205Channel Unit SUB/SUB
TU 21206Channel Unit SUB/SUB
Channel Unit Subscriber / Subscriber – TU 21206
Part NumberDescription
TU 21215Channel Unit SUB/EXCH
TU 21216Channel Unit SUB/EXCH
Channel Unit Subscriber / Exchange – TU 21216
Part NumberDescription
TU 21234.20Channel Unit E&M/VF-P, 10 ch, 20 E&M ch
TU 21236.10Channel Unit 8ch E&M/uP: 2xe&m/vf
TU 21255.01Channel Switch, 4 port
TV 21640.08Power Interface Adapter DC

Legacy Telecoms Spares – Nokia ‘Dynanet’ Update

Nokia DCN Adapter – Management & Other products

The ‘Dynanet’ family of PDH Transmission telecoms products were first introduced by Nokia over 20 years ago, and were continued in recent years by DNWP. These have well served Public Operator and Private Network Customers across the Telecoms, Utilities, Transport and Public Safety markets with high availability mission critical infrastructure, and indeed some networks are continuing to provide good operational service. 

Production of the majority of the product range was ceased in 2019. However, some products remain available to order, notably the DCN Adapter C4.0, related management software products and other items such as the TPS64, NDUE and Euro / SMB connectors.

Nokia DCN Adapter

Continued Supply of Spare Parts – Surplus and Refurbished Items

@YellowsBestLtd satisfies world-wide customer product sourcing requirements for current and ‘legacy’ equipment technologies from a wide range of Original Equipment Manufacturers (O.E.M.s).

For the ‘Dynanet’ range, we should be able to continue to supply refurbished and surplus equipment for as long as required, but the effect of the discontinuation of production is squeezing the availability of remaining stocks, with a consequential impact on pricing.

Hence, for those customers continuing to maintain their networks, it is recommended to consider purchasing spare parts whilst there is still availability.  Please get in touch to advise what you need!

Legacy mobile phones – Nokia 6230 & 2610

When phones got small (before they went big again)

In technology terms it seems a lifetime ago, now that large and ever-increasingly powerful ‘smartphones’ are commonplace, but it wasn’t so long since the trend was for mobiles to get smaller and smaller …

The evolutionary beginnings are clear, mobile phones started off as ‘bricks’: heavy, not very portable and limited in use. So the target became to make them ever smaller whilst cramming in as much functionality as possible.

The pinnacle of this development was just about reached with the Nokia 6230, a ‘feature phone’ which boasted a clock, calendar, calculator, music player, radio, photo and video cameras and a few basic games, even a limited internet browser, as well as texts and phone calls of course! A colour screen too, admittedly small (2.5cm square) and low-resolution by today’s standards, but with a battery that would last days not hours providing long talk and standby time. All squeezed into 10x4x2cm package; quite remarkable back in 2003.

Nokia 6230

This was about as small as phones got, and the small-size-format was so successful that it carried on like this for a few years, as illustrated by low-cost ‘entry’ devices such as the 2610 from 2006. Almost exactly the same size and weight, benefiting from improved screen and build but missing a camera – then still considered a ‘premium feature’, now so common place it’s hard to imagine any phone without one. Almost all of today’s phones are much wider, taller but thinner – how times have changed!

These mobile phones show off the relatively recent past of technology development, built to survive the harsh environment of the home of the Finnish manufacturer. So now, 15 or so years later – these ‘legacy’ models are still in working order, having out-lasted the company that made them! 

Much has since changed in the world of mobiles, such that they’re not even used much as just ‘phones’, and Nokia’s phone business itself came and went, though now being revived by HMD Global. Despite promoting smart phones such as the ‘flagaship’ Nokia 9, it’s also interesting to see the ‘re-introduction’ of some ‘classic’ small-size-format phones, such as the 3310, harking back to those early beginnings.       

@YellowsBestLtd we’re here to help #business customers maintain and keep operational “legacy” products and #enterprise equipment, as well as newer #systems, so let us know if we can assist by sourcing and supplying spares, repair and support services to ensure #technologies continue to serve and perform. Please get in touch to discuss your Management Services and Solutions requirements; we look forward to hearing from you.

Legacy Computing – Windows through time

DOS Beginnings – the early days of ‘personal computing’

The ‘Personal Computer’ (PC) launched by IBM in 1981 was a breakthrough that revolutionised the workplace, though the early ones were quite limited especially in terms of how to use them and what they displayed. Not only did they have no ‘touch screens’ for ‘swiping’ and ‘apps’ as we know them now, but there was no ‘graphical user interface’ either. Rather than a ‘desktop’ with icons and a mouse pointer, there was just a black screen with text and a flashing cursor.


This was Microsoft DOS (Disk Operating System), which seemed to be the ‘proper’ way to use computers for at least a decade.

GEM - Atari ST
GEM – Atari ST

Indeed, some PC users were initially ‘suspicious’ of icons and windows which had appeared on the Apple Mac as well as other alternatives in use like GEM on the Atari ST.

People had become so used to typing commands, and knew all the ‘switches’ and other modifiers e.g. DIR /W to display a list of the files across the screen rather than in a column. And ‘WP’ was all you needed to get ‘Word Perfect’ to launch – the then favoured Word Processor, which gave rise to some still familiar short-cuts like ‘Control-C’ to copy.

Desktop computing takes-off and ‘Windows’ takes-over

Windows 3.1
Windows 3.1

Windows 3.1 showed PC users something different from around 1992, when 386 and 486 PCs powerful enough to run it well became available.

mouse tutorial
mouse tutorial

It even came with a tutorial to show users how to use a mouse!

Windows 3.1 floppy disks
Windows 3.1 floppy disks

No-one enjoyed having to install it using 7 floppy disks though.

And at first it seemed somewhat unnecessary to run existing applications.

Windows 95 – DOS prompt

Indeed, there was a bit of an ‘outcry’  that Windows 95 and later variants didn’t first boot into DOS!

But then it was realised there were some key benefits. Now you could delete a whole directory in one go without having to clear out each ‘level’ – not always the safest feature! Email really became more useable when you didn’t have to log in specifically to check to see if you had messages; now it could be running all the time in its own window.

The rise of the Internet – and security issues

Windows 98 ‘desktop’

With each variant of ‘Windows’ came more sophistication, and suddenly a whole world of connected information could be accessed with Netscape and then Internet Explorer, which then meant Windows really became a ‘must have’.

Internet Explorer - WinXP
Internet Explorer – Windows XP

Certain difficulties were experienced getting old and new applications to behave themselves in the Windows environment; stability and also backwards compatibility started to become issues. Users now had to deal with ‘blue screen’ crashes of Windows, and then a variety of increasing security threats and viruses requiring ever-more enhanced anti-malware protection applications and mandatory backups.

The continuing need for ‘Legacy’ support

Although the majority of modern offices, educational establishments and homes now use the latest PC hardware as well as phone and tablet computing devices running the newest generation of operating software and applications, some industrial workplaces have professional implementations of systems that still make use of early computing platforms (ranging from desktop PCs to OSS servers), where the basic requirements are unchanged, and particularly in stand-alone use where security threats aren’t an issue. And some people still have old PC games to play!

Drive Setup
Drive Setup

It can however be quite a task to restore the operation of legacy systems, particularly if backups are missing or incomplete.

FDISK for partitioning
FDISK for partitioning

Associated issues include obtaining the appropriate hardware replacement parts such as disks (modern versions can be too high capacity to work well with old systems) requiring the right settings of cylinders, heads and sectors, and preparation using FDISK and FORMAT commands.

Floppy Disk
Floppy Disk

Software ‘patching’ of configurations may be needed, hunting out correct versions of driver files and specifying the right parameters. Creating a floppy disk with ‘boot’ files can also be a helpful tool!

Emulation and Virtualisation

There’s still a way today to run legacy software even without the old PC hardware, and that’s via the ‘joy’ of emulation and virtualisation. Even using an Apple Mac or Linux computer, it’s possible to run various flavours of Windows legacy software.

Particularly useful applications to enable this include:


DOSBox – a handy emulator tool which enables the running of old DOS based applications in an application window. Relatively straight-forward to setup, with the ability to ‘mount’ folders so that files can be imported.


VirtualBox – a fully featured virtualisation tool that allows the creation of ‘virtual machines’ into which can be installed a full operating system, such as Windows 3.1, Windows 95 or Windows XP. The tool also emulates CD and Floppy drives for  loading disk images and running legacy applications.

CPU fix for Win95
CPU fix for Win95

Takes a bit of work to set up, preparing a virtual ‘hard disk’, and then installing the operating system. There’s a ‘work-around’ needed to take account of modern processors being ‘too fast’ for the old operating software! Also, to set the display to the necessary resolution and get sound working, special video and audio drivers may need to be installed.



Or you could try the Windows 95 ‘computer as an’ App created by Felix Rieseberg, which can be downloaded and installed on macOS, Windows and Linux!


@YellowsBestLtd we can assist with support services for both legacy and new software and hardware solutions, so please get in touch if you have any requirements you’d like to discuss;  we look forward to hearing from you.

Legacy mobile phones

The original ‘smartphone’ – Nokia Communicator

Remember way back in the late 90’s and early 2000s, when Nokia ruled the mobile phone market, they launched the Communicator series. Essentially it was the coming together of a mobile phone and a PDA, joined with a hinge that ‘opened up’ to reveal a full QWERTY keyboard and display screen. Always somewhat big and bulky, it initially was way ahead of anything else, offering phone, text, email and even fax communication.

Nokia E90 Communicator

The E90 was the last and most feature-packed variant, produced in 2008. More compact and powerful, it featured colour screens inside and out, video and photo cameras with flash, 3G telephony, Bluetooth and WiFi connectivity, together with internet browsing, GPS maps, photos, video and music players, radio, clock, calendar, contacts and a file manager, plus games and the ability to install apps like quick office for document creation and spreadsheeting. In short, it had everything we’ve come to expect in a ‘smartphone’, lacking one key ingredient – a ‘touch’ screen.

Nokia E90
Nokia E90 (closed)

10 years on, it’s a testament to Nokia’s impressive build quality that it looks almost as good as new and still works as well as it did, though of course without the ability to pinch, zoom and swipe, and no ‘app store’. The photo and video quality now looks very basic, as do the limited number of games and apps; but it is possible to load it up with an up-to-date Opera web-browser and Google maps. The music player still works well, using a headset or in speaker mode, as does email and texts – and naturally it can still make telephone calls!

Nokia E90 Communicator
The original ‘smartphone’ – Nokia Communicator

The Nokia phone business itself didn’t fair so well, being eclipsed by the competition and then sold off, as recently well documented in “The rise and Fall of Nokia” (shown previously on BBC4, now on youtube) by Arto Koskinen. However, more recently Nokia phones have made a bit of a comeback, relaunched by HMD Global. Though probably no hope of a new Communicator model?!

Mobile phones for all – Nokia 5110 ‘featurephone’

If you can remember the 20th Century and the dawn of the mobile phone, then the Nokia 5110 maybe familiar. Introduced in 1998, during the period of Nokia’s seemingly unstoppable rise, and helped them become the world’s number one mobile phone producer, which they remained for the next 14 years.

Nokia 5110
‘Featurephone’ for all – Nokia 5110

This was the breakthrough when phones ceased to be ‘bricks’ (though still including an external antenna) and became mass-market devices that everyone could consider carrying, even just as an ‘emergency’ phone. Text messaging was included, though many people at the time couldn’t see what the point of that was: “its easier to just ring someone, isn’t it?” How times have changed! Plus it had a clock, calculator, and a choice of ring tones including the now famous ‘Nokia tune’. And Nokia introduced the world to ‘snake’, heralding in the era of mobile gaming. No app store yet, and ‘touch screens’ and even colour displays were still to come. But you could now choose the colour of the product; they didn’t have to be just black anymore!

'snake' game
Nokia 5110 – ‘snake’ game

The phones themselves were of the solid long-lasting construction that characterised the products of that time from the Finnish manufacturer, perhaps due to the harsh winter environment of home they were built to survive, which is why 20 years later, it still works! Looking back, the surprising thing is that despite its rugged nature, a case was often used, and given the (now, seemingly) impressive talk and standby time, it was quite usual to have a spare battery too. Perhaps that was because they were still seen as an expensive luxury, and given that ‘normal’ desk phones didn’t run out of power, ‘early adopters’ wanted to make sure they could always make use of their investment.

Legacy 'Featurephone'
Nokia 5110 with accessories

Much has since changed in the world of mobiles, such that they’re not even used much as just ‘phones’, and Nokia’s phone business itself came and went, though now being revived by HMD Global. On the cusp of the launch of a new ‘flagship’ model, the Nokia 6.1 plus, it’s also interesting to see the ‘re-introduction’ of some ‘classic’ phones, the 8110 and 3310, harking back to those early beginnings.

@YellowsBestLtd we’re always keen to hear from #business customers looking to maintain and keep operational “legacy” products and #enterprise equipment, as well as newer #systems, helping to source and supply spares, repair and support services so that assets and #technologies continue to serve and perform. Please get in touch to discuss your Management Services and Solutions requirements; we look forward to hearing from you.

Nokia, Marconi and Ericsson SDH – ‘Synfonet’, ‘SMA’ and ‘OMS’

‘Legacy’ Networks; long history, but still important and operational!

Back in the day, when PDH (Plesiochronous Digital Hierarchy) was all there was for telecommunications optical and copper transmission, a familiar site was the ‘Multiplexer Mountain’.

PDH Multiplexer Mountain

Then came the new transport technologies: SDH (Synchoronous Digital Hierarchy) for high-speed digital communication (via optical fibre and radio links); and (D)WDM ((Dense) Wave Division Multiplexing) as an optical solution for raising the capacity of existing fibre networks (particularly when the fibre-count was limited).

Nokia launched the ‘Synfonet’ range as the big brother to their successful ‘Dynanet’ PDH portfolio, with SDH capacity of initially STM-1 (155MBit/s) and STM-4. Later came STM-16 and WDM.

Synfonet – STM-1/4

  • All in one subrack (REG, TM, ADM, DXC)
  • Wide range of tributaries
  • 64kbit/s cross-connection server
  • Upgradable from STM-1 to STM-4 while in service
  • Compact, flexible and easy to expand

Nokia Synfonet

Synfonet – STM-16

  • 2.5 Gbit/s, four times the throughput rate of STM-1/4

Nokia Synfonet

Synfonet – WDM

  • 4–channel multiplexing / demultiplexing
  • 8-channel multiplexing / demultiplexing
  • Up to 20 Gbit/s per fibre

Nokia Synfonet

But in 1999, Marconi Communications acquired (for over $100M) Nokia’s Synfonet brand, SDH and DWDM transport equipment products and about 120 staff from its Cambridge research and development business under the deal.

Inevitably over time Marconi rationalised their portfolio and the Synfonet range was discontinued, in favour of the SMA and MSH SDH equipment.

Business however took a downward path and in 2005 Ericsson acquired the key assets of Marconi (for SEK 16.8 billion). “Marconi” then became the registered trade-mark branding for Ericsson to promote these products, until phasing them out.

Marconi® Series 1 SMA1 Multiplexer

  • Flexible SDH Multiplexer
  • Terminal, Add/drop (ADM) or Digital Cross-Connect (DXC)


Marconi® Series 3 & 4 SMA Multiplexers

  • Full range of options, including size and power variants
  • SMA1, SMA4, SMA16c and SMA16c+ Series 3 models
  • Tributary interfaces from 2MBit/s to STM-4
  • SMA1/4, SMA1/4c, SMA1/4E and SMA1/4UC Series 4 models
  • Supports ATM and IP with enhanced data functionality
  • Metro access and metro core deployment, and customer premises


Marconi® SMA 16-64 Multiplexers

  • Advanced ADM, DXC and low-order aggregator
  • Delivers 2.5GBit/s and 10GBit/s data transport capabilities
  • Full VC-12 granularity allowing single-layer access without VC-4 layer
  • Metro core deployment


Marconi® MSH Series

  • Family of STM Multiplexers, Regenerators and Cross Connects
  • MSH11C, MSH41C, MSH51C, MSH63, MSH64, MSH64C and MSH86 Models.


Marconi® MSH2K

  • Foundation of Marconi’s switching portfolio
  • DXC functionality, capacity of 320GBit/s
  • Support for STM-1 to STM-64 electrical interfaces
  • Embedded DWDM and support of SDH protection / restoration
  • Seamless transition from Ring to Mesh network architectures
  • Capable of upgrade to Multi-Layer Switch (MLS)
  • Metro core deployment


Marconi® MSH64C

  • Based on same platform as MSH2K
  • Core ADM/XC, 80GBit/s switch, capacity of 32 x STM-64 interfaces
  • Consolidating and grooming traffic.
  • Gigabit Ethernet interfaces for data transport
  • Embedded DWDM interfaces


From 2007, Ericsson launched the (still) Marconi® branded OMS (Optical Multi Service) portfolio of advanced SDH multiplexers, including OMS 1200, OMS 1400 and OMS 1600 providing multi-service products for Metro-Edge and Metro networks. The “Marconi” brand was later dropped by Ericsson for this OMS range.

OMS 1200 range

  • Range of SDH ADM
  • Optimised for ring and terminal applications

OMS1200 series

OMS 1400 range

  • Compact energy efficient multiservice and packet optical transport.
  • Optimized for use in Metro Access networks
  • Carrier class Ethernet and TDM services interworking with metro and core Networks based on SDH, Ethernet or IP/MPLS
  • Applications ranging from high capacity customer sites, fixed or mobile backhaul/Radio Access Network (RAN) aggregation and transport


OMS 1600 range

  • Compact, multiservice transport and switching platform
  • Terminal, Add/Drop and Cross-connect multiplexers
  • Line, ring, star and meshed networks
  • Modular configurability, comprehensive switching options
  • High port density reducing space and power consumption
  • Range of data and TDM services, fulfilling ITU- T G.782 requirements

OMS1600 Series

The OMS range provided packet evolution capabilities to Ericsson’s optical networking portfolio and strengthened its Full Service Broadband offering, meeting the demand from operators to evolve their network to support a mix of services and traffic types, with dexterous backhaul connectivity, TDM or Ethernet-based, with telecom quality, flexibility and scalability.

Perhaps this ‘potted history’ helps explain the ’journey’ these products took, and clarifies why they can be referred to as both Nokia and Marconi, or indeed Ericsson. Although now discontinued by these manufacturers, the products are extensively deployed and still in use by Telecoms Operators, Utilities and Transport companies.

Supporting ‘Legacy’ Networks and Keeping Customers Operational

From time-to-time Customers benefit from services from @YellowsBestLtd

  • Locating Nokia, Marconi, Ericsson (and other vendors) hard-to-find replacement items
  • Hardware repair services to existing parts
  • Supplying additional spares for newer systems to increase capacity or provide alternative interfaces

This way these ‘legacy’ but still important networks can continue to be maintained and kept operational.

To illustrate the possible requirements for spares and repairs, some key parts from the above networking technologies are listed, as follows:

Nokia - Synfonet


Part Code Family Description
STM-4 (T30023.01 – 71.02) Synfonet STM-4 card
STM-16 (T30172.02 – .06) Synfonet 2 x STM-1/4 WDM Mux
WDM MUX (T30172.41) Synfonet 2 x STM-1/4 WDM Mux
STM-1 E/140M (T3033.01) Synfonet 140Mbit/s STM-1 electrical IU
34M/45M (T30046.02) Synfonet 34/45Mbit/s electrical IU
2M TA (T30041.01 – 43.01) Synfonet 2Mbit/s interface units
CU (T30073.01) Synfonet Node control and timing unit
SSW (T30053.01) Synfonet System Switch Unit
SU-A (T30084.01) Synfonet Service unit / EOW
SPIU (T30093) Synfonet PSU Card
TSW0 (T30110.01) Synfonet 64 kbit/s cross-connect unit
TSW1 (T30063.01) Synfonet Cross-connect unit for STM-4

Marconi - SMA / MSH


Part Code Family Description
02HAM00002AAJ SMA-1/4 21 X 2M LTU Balanced
02HAM00003AAL SMA-1/4 63 X 2M LTU Unbalanced
03HAT00010AAS SMA-1/4 10/100MB Ethernet Module
1HAM61217AAK SMA-1/4 Power Unit
1HAT 60796 AKU SMA-16 STM-16 OPT.TCM AHK S16.1 (SC)
1HAK 60596 AAE SMA-16 STM-16 RX OPT S16.1
1HAK 60701 ABM SMA-16 STM-16 TX OIC 1310nm (FC/PC)
1HAT 60730 ADL SMA-16 STM-16 LINE UNIT 1550nm (FC/PC)
1HAT 60730 AJX SMA-16 STM-16 LINE UNIT 1310nm (FC/PC)
1HAT 60730 AMA SMA-16 STM-16 L-16.1 SC
1HAT 60730 ANS SMA-16 STM-16 L-16.2/3 SC
SN99AD SMA-16 Power Supply Unit
Part Code Family Description
133-1467/01 MSH86 Matrix Shelf
131-9475/21 MSH64 STM-64 S64.2 SC/PC
131-9475/22 MSH64 STM-64 L/V/U64.2 SC/PC
131-8685/01 MSH11C 3 X 34MBit/s Tributary Unit G.703
133-1260/01 MSH84 MSH86 Shelf Type 5
130-3118/01 MSH84 Trib Matrix Board
130-3132/01 MSH84 Control Matrix Sub Unit
130-3142/01 MSH84 Main Control Sub Unit
1MBD60697AAT MSH2K Shelf
02MBB00001ABG MSH2K S-16.1 Module, LC
02MBB00001ACY MSH2K L-16.1 Module, LC
02MBB00001ADR MSH2K L-16.2 Module, LC

Ericsson – OMS


Part Code Family Description
03HAG00001AAX OMS1200 A/D Mux System Chassis
03HAM0019AAQ OMS1200 HI Power DC Supply
03HAN00007AAH OMS1200 AC Power & Battery Backup
03HAN00009AAM OMS1200 Fan Unit
03HAT00041AAQ OMS1200 Common Control ADM Unit-A
03HAT00041ABH OMS1200 Common Control ADM Unit-B
03HAT00045ABR OMS1200 Ethernet Prnt Card
1HAT61107ABC OMS1200 64 x 2M Core Trib Card
1HBA60828AAX OMS1200 32x 2M Unbalanced LTU
1HBA60832AAA OMS1200 32x 2M Balanced LTU
1HAT61106BAE OMS1200 Comm/Aux/ANC Unit
1HAM61217ABC OMS1200 Power LTU Mod
Part Code Family Description
03HA500032AAC OMS1664 STM-1 Switch Card
03HAM00006AAT OMS1664 STM-1 Line Terminating Card
03HAM00015AAG OMS1664 10/100 Electrical LTU-Type 2 (SK57BC)
03HAT00015AAD OMS1664 STM-4 Line Card
03HAT00016AAF OMS1664 STM-4/16 Core Card
03HAT00021AAK OMS1664 STM-16 Line Card
03HAT00020AAH OMS1664 STM-64 Line Card
03HAT00029ACM OMS1664 16xE1
03HAT00053AAK OMS1664 140M Transmux Card
03HAT00057ABL OMS1664 Ethernet L2 Data Switch Prnt Card
03HAT00054AAM OMS1664 Ethernet Layer 2 (8+16 Ports) (SK58AB)
1HAG60619AAK OMS1664 Standard Shelf
1HAG60620AAF OMS1664 Compact Shelf

Please get in touch and let us know what you need to keep your network in good shape!