As set out in an earlier blog post, the original UMUX SDH product range was launched in 1991 by Ascom which subsequently became Keymile. The portfolio expanded to include UMUX, LINERUNNER and MILEGATE multiservice communication platforms, along with UNEM network management, and were extensively deployed worldwide. In 2010, Keymile acquired the XMP1 product line from Aastra.
Based on this experience, Keymile in 2016 then launched its ‘next generation’ XMC20 hybrid multi-service Ethernet / MPLS-TP, traditional access and transmission all-in-one network platform, including end-to-end encryption.
The mission-critical business of the Keymile Group, that focussed particularly on Rail, Oil and Gas markets, was sold to ABB in 2017, while the residual Keymile company telco business was purchased in 2019 by DASAN Zhone Solutions Inc (a merger company formed in 2016 from DASAN Network Solutions and Zhone Technologies), renamed to DZS in 2020. Licensing arrangements enabled ABB-Branded XMC20 products to be supplied to ABB’s business market shares, along with ABBs long-standing FOX 515 and 615 PDH/SDH/Hybrid platforms.
Subsequently the UMUX, LINE RUNNER, MILEGATE, XMP1 and FOX515 product lines were discontinued, in favour of the XMC20 and FOX 615 portfolio.
In 2020 the joint venture Hitachi ABB Power Grids was established, with Hitachi acquiring 81.1% ownership. Hitachi completed the purchase of the remaining 19.9% stake in 2022, rebranding as Hitachi Energy in 2021 to reflect the new ownership.
DZS filed for Chapter 7 bankruptcy in 2025. Canada’s MNSi (Managed Network Services Inc.) acquired the assets and formed a new US-based company, Zhone Technologies Inc.
Continuing to provide critical infrastructure services
The XMC20 Hybrid Multi-Service Platform for Ethernet / MPLS-TP and traditional services provides an all-in-one network element. The XMC25, XMC23 and XMC22 subracks, providing 4, 8 or 21 slots for core units, line cards and gateways offer multi-service features in compact and scalable housings designed for harsh environments.
It offers a modular architecture providing a wide range of interfaces, services and technologies and high reliability required by mission critical networks.
Keeping Customers Operational
@YellowsBestLtd with our aim of Keeping Customers Operational assist with seeking out new products and legacy equipment spares to maintain new and well-established systems, as well as built-to-order cables and connectors to suit exact requirements, so please contact us if there is anything you require.
Given the investment that has been made over many years, coupled with the fact may operational requirements have not changed, it makes sense to keep systems in place. And it can be the case that suggested replacements cannot provide equivalent operational lifetimes which therefore become obsolete faster than existing deployments. By suppling spares, offering repair services and technical assistance, we are able to support these aims of continued operational service.
Refurbished and Surplus Spares in Demand
Since these product families continue to prove their excellent availability and reliability to customers, we continue to provide stock of many of these items, either in new, surplus or refurbished condition. Current stocks include:
Chassis: MXMC25, MileGate (can be converted to XMC20 via software load)
Certain product elements are from time-to-time sought after in order to maintain operations of deployed systems or keep stocks of spares at levels to ensure that SLAs for maintenance and support are achieved.
We are currently interested in locating these products:
XMC20 ETO12 – Ethernet unit providing 12 Ethernet interfaces for optical or electrical SFP modules.
MileGate SUE12 – High density Ethernet line card for business services and advanced IP applications
MileGate SUE16 – High density active Ethernet Fibre-to-the-Home (FTTH) line card for residential subscribers
We would be keen to hear from you should you be able to supply these parts, or alternatively whether we can be of any assistance with your solution requirements for legacy systems and new technologies, so please let us know !
For decades, various communication protocols have been utilised to connect telecommunications and computer hardware devices over short and long distances. To avoid incompatibility problems, standards were formulated and agreed, but meanwhile, a continuous drive to provide improved performance has meant an evolution of various alternatives.
Today with the dominance of USB, there are connector types and associated data protocols that have become almost universal for the wired serial connection of new devices over short-distances (when the use of wireless alternatives like WiFi and Bluetooth are not possible or appropriate). Whilst Ethernet has become the preference for local IT networks, for long-distance telecommunications, fibre-optic transmission is providing the benefits of reliable high bandwidth services.
Maintenance of legacy standards for connecting and communicating
Despite this, many older infrastructure systems and devices continue to utilise historic protocols and connections, and so it is still of benefit to recognise and be able to maintain ways to interoperate. There follows a non-exhaustive overview and comparison of the most popular standards and types of serial data communication methods.
RS-232 (V.24 / V.28)
Introduced way back in 1960 by the Electronic Industries Alliance (EIA), this is probably the longest surviving communications standard, but over time due to various revisions and lack of uniformity of connector types and connections, incompatibilities can arise. This resulted in the need for conversion cables, gender changers, etc.
It is a serial, full-duplex, unbalanced, single ended communications standard which has limitations in terms of transmission distance, noise immunity and operating speed, and can only be used for point-to-point connections.
Given its age, it pre-dates most of modern computing, and was established for the relatively new purpose of communicating between a teleprinter, designated as the Data Terminal Equipment (DTE) and a modem, the Data Communication Equipment (DCE). The standard defines a range of ‘circuits’ (pin assignments) which include data – TxD (transmit) and RxD (receive) – along with various control signals such as DTR (data terminal ready), RTS (request to send) and CTS (clear to send).
When directly connecting two DTEs, such as two computers without using modems, a ‘null modem’ or cross-over cable is needed to swap the connections between the transmit / receive data and control lines.
Over the years, this extended to the uses of connecting computers to various peripheral devices like printers, as well as to other computers. Most PCs then came to be equipped with a “D-Type” port, initially for 25-pin connectors but eventually 9-pin became much more common.
Voltage levels are defined for the signals, in the range of -3V to -15V i.e. negative voltage representing a logic ‘1’ (mark) and between +3V to +15V i.e. positive voltage as logic ‘0’ (space). The range between -3V and +3V as invalid, and typically voltages are expected between +/5V to +/-12V whilst peak voltages can up to +/- 25V.
RS-232 TTL
This variant to the RS-232 standard is designed for more convenient interoperation with low voltage circuits over shorter transmission ranges. This specifies a positive voltage of +5V representing logic ‘1’, and 0V for logic ‘0’, which unfortunately can cause operational difficulties through confusion regarding the deployed types. Naturally, this requires correct interfacing and use of converters to provide the required voltage level shifting and inversion between variants.
RS-423 (V.10 / X.26)
Originally designed and launched in 1975 as a replacement for RS-232, offering longer distance and faster speed communication, it failed to become widely adopted. It did however feature on the BBC Micro in the 1980s, utilising an unusual 5-pin DIN connector.
Sharing similarities with RS-232 as a serial, full-duplex, unbalanced, single ended communications standard, it notably adds multi-drop capability, making it possible for one transmitter to send data to up to 10 receivers. It’s voltage range is restricted to +/- 6V, with the driver output between +3.6V to +6V representing logic ‘0’ and -3.6V to -6V for a logic ‘1’.
RS-422 (V.11 / X.21)
This standard, also launched in 1975, provides serial, simplex, balanced, differential communications. Like RS-423 it provides multi-drop capability for one transmitter and 10 receivers.
It was more successful as an upgrade to RS-232 as it provided better noise immunity through the use of twisted pairs of conductors carrying two differential data lines. Full-duplex communication is provided by using 4 wires and two transmitters and two receivers to send the data in both directions.
The differential voltage between the pair of transmit lines and pair of receive lines determine the logic states, rather than the nominal 0V to 5V signals compared to ground, with the maximum common-mode voltage in the range +/-7V.
Typically, line A (or Y) is labeled TxD- / RxD- and is the non-inverted signal and line B (or Z) is TxD+ / RxD+, which is the inverted or complement of the same signal. Then B greater than A usually represents logic ‘1’, following the RS232 convention that this state is represented by a negative voltage, in this case line A of at least less than -0.2V with respect to B. Conversely, A higher than B by at least more than +0.2V, therefore represents logic ‘0’.
It is important to assign these lines correctly; for instance, on a Nokia DM2 multiplexer, the UR / UT specifications for the MI service interface assign logic ‘1’ to a negative voltage, but this doesn’t make it clear whether this is referring to B >A or A > B. In practice, this can be addressed simply by reversing the two input and/or the two output A & B connections should the opposite assignment apply.
RS-485
This standard came out in 1983, and brings further enhancements over RS-232 whilst retaining a degree of backwards compatibility with RS-422. It provides serial, semi-duplex, balanced, differential communications. Like RS-422 it uses twisted pairs of differential data lines to provide improvements to transmission distance, noise immunity and operating speed. But through use of bidirectional transceivers, it only requires 2 wires to provide both directions of data transfer (though not at the same time, i.e. semi-duplex).
This can be upgraded to 4 wire full-duplex operation by adding an additional pair of transceivers, but in practice this is not necessary unless for interworking with existing RS-422 components. It extends transmission capability to true multi-point communication, with the possibility for use of up to 32 transmitters and 32 receivers, by means of a tristate mode so that drivers are switched off when not transmitting.
Usually, line A is named D- as the non-inverting signal and line B is its complement, the inverted signal named D+, such that when the voltage of D+ is high, D- is low. With B greater than A by +0.2V then this represents logic ‘1’. The opposite polarity, resulting in a voltage difference of B lower than A by -0.2V, is therefore logic ‘0’.
Its improved maximum common-mode voltage range of -7V to +12V aids its ability to operate in multi-point configurations, allowing for wider differences in ground potential between the drivers and receivers.
Conversion between RS-422 and RS-232
This naturally loses the RS422 advantages of differential data for noise suppression and transmission distance.
For RS232 a negative voltage is logic ‘1’; when the device transmits this to the RS422 RxD- or A input the differential voltage with respect the RxD+ or B input held at GND is B > A i.e. logic ‘1’. Whereas with a positive voltage from the RS232 device the RS422 input differential voltage is A > B, equating to logic ‘0’.
However, when the RS422 TxD- or A output is low it could be the case that this not as negative a voltage as the -3V the RS232 device is expecting, and so technically is invalid according to the specification. However, in practice for many devices their operating threshold is beyond -1.5V and since B > A it is interpreted anyway as logic ‘1’. When the RS422 TxD- or A output is high, A > B which results in logic ‘0’ at the RS232 receiver.
Interconnection of RS-485 and RS-422
Since RS-485 transceivers are generally ‘backwards compatible’, they can be applied to interface with existing RS422 devices. For full-duplex communication, 2 transceivers are used in the 4-wire configuration of RS422, and the semi-duplex capabilities of RS485 are ignored. Plus the RS422 restrictions of only one driver and up to 10 receivers per transmission direction apply.
The RS422 driver TxD+ and TxD- lines are respectively connected to the D+ and D- pins of a RS-485 device acting as a receiver. Similarly, the D+ and D- pins of a RS485 device acting as transmitter are connected to the RxD+ and RxD- lines of the RS422 receiver(s).
Comparison with USB
Whilst USB has become the De Facto standard for modern short distance wired connections, it is useful to compare this against the legacy protocols in order to understand the similarities and differences, and why it may be important to maintain or even extend existing interconnections.
USB 1.0 / 2.0 provide serial, semi-duplex, balanced, differential communications, analogous to RS-485 whilst offering much faster communication packaged in a smaller and more convenient 4-pin form-factor.
USB 3.0 uses two additional pairs of conductors in a compact 9-pin connector to operate full-duplex like RS-422, whilst maintaining backwards compatibility with older USB connections, and provides various further improvements including even faster ‘SuperSpeed’ transmission.
However, USB only provides for point-to-point connections, with lower power and limited to TTL voltage levels, and as a result shorter transmission distances.
In conclusion, the choice of use depends on the various differing applications such as the interconnection of computer peripherals, industrial control, remote monitoring and multi-device connections.
Consequently, for legacy interworking and improved performance over longer transmission distances with wider voltage ranges, dedicated USB to RS-232 / RS-423 / RS-422 / RS-485 converters are available.
Keeping Customers Operational
@YellowsBestLtd with our aim of Keeping Customers Operational assist with seeking out new products and legacy equipment spares to maintain new and well-established systems, as well as built-to-order cables and connectors to suit exact requirements.
We would be keen to hear your experiences of using communications protocols and whether we can be of any assistance with your solution requirements for legacy systems and new technologies, so please get in touch!
Organisations that deploy, own and maintain infrastructure systems and networks make considerable investments in time and money, and it makes complete business sense to maximise the return on these investments. Even if it were desirable to make wholesale replacements, such projects take time to undertake. Ideally, if the equipment is performing satisfactorily and operational requirements have not changed, then is better to keep the existing equipment maintained for as long as possible.
Critical infrastructure systems are typically built to last, with high availability and reliable system components, and interchangeable spare parts. But sooner or later, repairs to elements are needed. During initial deployment and warranty periods, this is not normally an issue, but over time, these services become more specialised and difficult to obtain, as vendors advance their portfolios and discontinue older products.
@YellowsBestLtd specialises in ‘Keeping Customers Operational‘ by sourcing equipment spare parts and hardware repairs to modern and legacy systems. Should you have any requirements, please get in touch; we would be very pleased to hear from you, and look forward to being of assistance.
Take a look at some of the elements for which we provide hardware repairs services: Recent repairs requests
Although the installation of fibre broadband services have been rolling out across the UK for some time now, there still seems much confusion relating to the various services on offer.
@YellowsBestLtd has been receiving ‘Fibre To The Premises’ (FTTP – sometimes referred to as ‘Fibre To The Home’ FTTH) from @Gigaclear since our formation in 2015. We are therefore able to provide this brief summary of our experiences and comparison of the types possible and their capabilities:
Full Fibre (FTTP) – fibre runs directly to the office or house, giving the fastest and most reliable speeds. This is what we had installed by Gigaclear; a dedicated fibre line into a fibre modem which can be directly connected to using ethernet cable or via a wifi router.
Part Fibre or ‘Fibre to the Cabinet’ (FTTC) – fibre runs to the neighbourhood cabinet, and then data runs over copper lines into the building. The transmission speed and bandwidth is therefore reduced in comparison to Full Fibre. This is the type of on offer to many consumers where the local telephony provider is not able to rollout fibre replacement for the ‘last mile’ of copper connection.
Copper or non-fibre – the traditional, existing telephone lines are used to provide the broadband service. This naturally provides the slowest speed and least data bandwidth. Many communities still rely on this as the only means of internet connection, since no fibre broadband deployment has been made.
The net result is that with Full Fibre, it is possible to receive previously unheard of speeds. Indeed the maximum service on offer is so fast, it outstrips the requirements of most homes and businesses. It is therefore typical that a reduced service is selected purely for cost-saving purposes.
Our own experiences have found that the Ultrafast 300 service from Gigaclear to be more than adequate for our needs. This is a screen shot of an actual speed test of the service we are being provided with:
In many cases the ‘full fibre’ service we have chosen, approximately a third the speed of the maximum possible, is still at least 10x faster than part or no fibre services. Not only is it faster, it provides a very stable connection less prone to interference and service outages. Thought due to network backhauling connections, is not unknown for interruptions to be possible; fortunately these are relatively rare.
The main difficulty for most businesses and homes remains the lack of universal provision. Whereas we have no reservations in recommending Gigaclear’s full-fibre service, we recognise this is not available everywhere. It is just fortunate for us that rural communities like ours was prioritised in their initial service rollout.
@YellowsBestLtd our mission is in “Keeping Customers Operational”. We’re always keen to enhance our range of #business services, increase the #enterprise infrastructure we support and expand our mix of #sustainable solutions we offer for supply and maintenance of new and legacy #technologies and products for our customers.
Please get in touch to help us understand your management services or solutions requirements, whether you’re implementing new systems or maintaining existing infrastructure networks to serve your operational business needs.
It’s been a challenging time for businesses generally, and particularly in the United Kingdom, with Brexit in many cases adding cost and time to trading, and Covid-19 restricting travel and networking.
So it seemed an appropriate time to launch a new varient of the Yellows Best Limited website, now additionally utilising “.co.uk” as a signifier of commitment to our home market location.
Keeping Customers Operational
The new YellowsBest.co.uk promotes the same blend of Services and Solutions for “Keeping Customers Operational”, but presented in a different and modern single-page layout, making it particularly mobile device-friendly where ‘vertical scrolling’ is more appealing than using the traditional ‘horizontal tabbed’ layout.
We hope this provides Customers old and new with a welcome alternative, though the original YellowsBest.com will continue to be maintained, along with it’s associated blog for ‘informal’ views and news updates.
Assisting with your requirements
It would be interesting to receive feedback as to how useful you may find this additional site, and whether there is anything else you’d like to see featured.
Of course, @YellowsBestLtd online content ultimately serves the purpose of highlighting the types of services and solutions we can provide. Customers may therefore be prompted to get in touch to discuss their specific requirements, which we can usually assist with.
From time-to-time, hardware elements within infrastructure systems fail, and repair services are required for a diverse range of parts procured over a considerable period of time, from a multitude of Original Equipment Manufacturers (O.E.M.s), some of which no longer exist.
YellowsBest is able to provide a comprehensive repairs management service for both new and old equipment items, all to a standard equivalent to the original working condition and with warranted operation.
Component Level Repairs Example: SES Displayboards
An example of the type of equipment that we are often asked to assist with is the MS1 Matrix LED ‘displayboards’ produced by SES and used for professional signage applications.
LED ‘displayboards’
Typical issues to deal with are Faulty LEDs, damaged capacitors and broken sockets, which have occurred in operational use over time. Adding to this are problems stemming from heat gun damage and resoldering caused by previous ‘user fixes’. But these issues are addressable and the boards restored to full working condition.
Other types of equipment for repair services include Telecommunications products, power supplies and CCTV cameras.
Typical Items for Repair Services
Reduce – Reuse – Recycle
@YellowsBestLtd helps Customers with their operational needs, and one aspect is to #Reduce the demand for avoidable whole-scale replacements through a combination of #Reuse of refurbished spares and repair of system elements. When removal and disposal of no-longer serviceable infrastructure parts is necessary, we can also assist with the resale and #Recycle for ‘value recovery’ of valuable materials.
Most customers have implemented their private network infrastructure systems over a number of years, and for many their operational requirements have not changed. Consequently, it makes more sense both financially and environmentally to maintain these systems rather than embark on complete change-outs. We can assist by supplying critical and hard-to-find spare parts and hardware repair services, even when the systems have been declared ‘obsolete’ (i.e. no longer in production) by the O.E.M. We look forward to hearing from you.
Phased Discontinuation of Production – 31st May 2019 – 31st January 2020
The production of the ‘Dynanet’ family of PDH Transmission telecoms products, first introduced by Nokia over 20 years ago, and continued in recent years by DNWP, is finally being ended.
This product range has 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.
Essentially almost all the old equipment items, with a very few exceptions such as the TPS64, are being completely discontinued in a phased way according to these milestones, which have already commended:
31st May 2019 – DM8 Multiplexers, DF2-8 Optical Terminals, RPSA
31st October 2019 – DM2 Multiplexers, Subs/Exch & VF Cards, DN2 IU2, Service Terminals, V.28/V.11 DIU
31stJanuary 2020 – DB2, DN2 CU & BPU, G.703 & V.110, DIU, Ethernet I/F, Ring Gen, NDM 19” Subrack, NDA
@YellowsBestLtd satisfies customer product sourcing requirements for current and ‘legacy’ equipment technologies.
Should you wish to read the full ‘ramp-down’ notice and know more about obtaining equipment before it is no longer available, then please get in touch.
The UMUX platform provides carrier-grade reliable multi-service multiplexing and aggregation functions over copper and fibre networks. A variety of voice (POTS, FSX, FSO, ISDN) and data (e.g. G.703, V.11, V,24, V,35) interfaces, SHDSL and Ethernet (including PoE+ and EoS) services are available.
UMUX module range
The modular and flexible housing provided by the UMUX 1500 (8U, 21-slot) and UMUX 1200 (4U, 8-slot) 19” subracks provide the perfect solution for all applications and locations, offering redundant controller and power supplies.
‘Legacy’ telecoms history
The UMUX SDH product portfolio was originally launched 1991 by Ascom, which subsequently became Keymile.
In 2003, by when 70,000 units had been deployed worldwide, the ‘enhanced’ UMUX multiservice access platform was introduced, offering the delivery of ATM, TDM and IP based services from the same platform, with support for IP/Ethernet, ADSL, VoDSL and G.SHDL.
Keymile was sold to ABB in 2017 when the UMUX range was discontinued, and then was acquired in 2019 by DZS.
Continuing to provide operational service
The UMUX, together with the UNEM network management system and ‘sister’ LINERUNNER and MILEGATE products, continues to provide operational service with various global Operator, Utilities and Transport companies.
@YellowsBestLtd supports requirements to maintain these networks by supplying various spare part items from refurbished and surplus stocks in perfect working order.
There follows a list of the main elements that are typically provided, though other items can be provided. Please let us know of any specific requirements you may have. We look forward to being of assistance.
The Nokia ‘Dynanet’ family of PDH Transmission telecoms products has served customers well for the last 20+ years, and indeed some networks continue providing good operational service.
Dynanet Subtrack
@YellowsBestLtd has supported requirements to maintain these networks by supplying various spare part items from refurbished and surplus stocks in perfectly working order.
However, demand has recently reduced and warehouse space is needed, so now the time has come to recycle / dispose of a large proportion of the remaining equipment. Consequently, there remains a short-term opportunity to obtain any items still required to maintain existing deployed infrastructure, before the products are gone.
Here is a stock list of the main items currently available, 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 – before it’s too late! We look forward to hearing from you.
Part Number
Description
24204
TPSO H/W Module
CC 24002
DB2 Branching Unit, B2 2×2 Mb/s 75 ohm
CC 24011
DB2 2 Mb/s Switching Unit, X2 75 ohm
CC 24101
DN2 Interface Unit (IU2) 2×2 Mb/s 75 ohm
CC 24111
DN2 Control Unit (CU) 75 ohm
CF 24186
DN2 19″ Subrack
CF 24186.09
DN2 Subrack 19″, grey-L91 EMC
CG 24170
DN2 Bus Power Unit (BPU)
CG 24171
Extended DN2 Bus Power Unit (EBPU)
CU 24013
Data Interface Unit (DIU) 2M, nx64k: G.703/704, 75 ohm
T30506.09
17-slot DYNANET Subrack
T30851.02
Subrack Power Adapter (SPA)
T37870.01
NDM ACM2 19in 17-slot subrack
T37871.01
NDM DN2 19″ 17-Slot Subrack
T37882.01
NDM DC Unit (NDUe)
T37882.02
NDM DC Unit (NDUe)
T37885.01
NDM Ring Generator
T37889.01
NDM Backup Unit (NBU)
T65520.01
ACL2 RM DC Power Gen
T65580.01
ACL2i PF GEN Line Terminal Card
TA 21513
Optical Line Terminal Repeater 2-8 M, 1300 nm LED MM/SM
TA 21516
Optical Line Terminal Repeater 2-8 M, 1300 nm LASER SM
TC 21101
DM34 Mux Card
TC 21301
DM8 Multiplex Equipment, 75 ohm
TC 21705
Supervisory Substation
TC 21710.01
TMS Adapter
TG 21261
Ring Generator 25HZ 15W
TU 21122.5
Data Interface Unit (DIU) 48..64k V.11 10ch
TU 21124
Data Interface Unit (DIU) NX64k V.11/V.35/X.21 2CH
@YellowsBestLtd has now reached the significant milestone of completing three years of trading; something often useful to be able to state when qualifying for opportunities and registering with business customers.
Our aim continues to be “Keeping Customers Operational”; understanding requirements and fulfilling them by providing a range of management services and solutions, including:
consultancy, such as business development planning
technical support, e.g. day-rate engineering, NMS assistance
systems supply, including legacy IT servers / workstations
spares for infrastructure, in particular telecoms and CCTV cameras
repairs at module and component level, e.g. LED displayboards
value recovery through reverse logistics, resale and recycling
As we move forward in year four, we’d very much like to discover what else to provide to our existing Customers, as well as what would be of interest to potential clients. We’re always keen to enhance our range of #business services, increase the #enterprise infrastructure we support and expand our mix of #sustainable solutions we offer for supply and maintenance of new and legacy #technologies and products.
Please get in touch to discuss your challenges; whether you’re implementing new systems or maintaining existing infrastructure to serve your operational business needs. We look forward to hearing from you.
