You ask – We Answer: Top SFP-10G-SR Questions Customers Are Asking
SFP-10G-SR nowadays in 2017 is industry leading mainstream optical module in terms of quantity used. Definitely, 40G and 100G optical transceivers are becoming increasingly popular, but because of stable technology (first SFP+ modules arrived in market already by 2006) and it’s reduced pricing SFP-10G-SR is dominant choice for short range optical connections. Indeed, we even saw some market reports stating that SFP-10G-SR optics occupy about 25% of 10GbE ports shipped worldwide. Because of such wide adoption of SFP+ short-range modules by thousands of enterprises, Telco’s and data centers it is typical, that many uncertain concepts and myths arise. We will try to clarify some of them based on most popular doubts or questions our customers have expressed.
You ask – We Answer: Top SFP-10G-SR Questions Customers Are Asking
SFP-10G-SR is optical transceiver based on widely used SFP+ (Small Form-Factor Pluggable) MSA Standard. Every optical transceiver we can characterize by three groups of its properties – optical, electrical and environmental.

SFP-10G-SR is optical transceiver based on widely used SFP+ (Small Form-Factor Pluggable) MSA Standard. Every optical transceiver we can characterize by three groups of its properties – optical, electrical and environmental.  Optical properties define such key factors as transceivers operational center wavelength and its bandwidth, compatible optical cable type. Transmission power and receiver sensitivity define optical budget and as a result maximum distance. Laser or photonic components are most expensive items on every optical transceiver BOM and price of these components are key price drivers of whole transceiver. SFP-10G-SR Transceivers use VCSEL (Vertical-Cavity Surface-Emitting Laser) laser diode as light emitter. Briefly – VCSEL lasers main advantage is low cost and simple production process, but VCSEL can emit only relatively wide beam of light, therefore it is adaptable only with multi-mode fiber. VCSEL’s on SFP-10G-SR transceivers use 850nm as center wavelength and occupy 20nm (840-860nm) spectrum. As receiver or light detector SFP-10G-SR modules use PIN photodiode, which is relatively cheap but with rather low sensitivity, if compared with another type of photodetectors used in long-range transceivers – APD (avalanche photodiode). Application of VCSEL Laser diode and PIN photodetector deliver minimum guaranteed optical budget of 4.6 dB, the distance which we can achieve with this optical budget will depend on Cable Category Type we will use. Please check below table for more information:

Electrical properties to most end users are interesting from four following aspects – which link protocols transceiver support, power consumption, digital diagnostics function and in which devices transceiver is compatible. Most SFP+ SFP-10G-SR Transceivers can support baud rates from 0.6 up to 10.52 Gbps and whole range of such applications as:

SFP+ SFP-10G-SR Transceivers support listed protocols in theory, but in many occasions some of them are software limited by settings in transceiver firmware, as in some choosy equipment platforms it can cause incompatibility. Power consumption for all 10G SFP modules varies depending on their reach – for shorter-range modules it is about 1W but for greater distances like 40km to 80km, it is around 1.5W. Power supply for all SFP’s is 3.3V as defined by MSA.

Digital Diagnostics Function (also called DOM/DDM) – its functionality defined by MSA SFF-8074 that first released on 2001 and later SFF-8472. This function rely on built in allocated memory called A2h and define access protocol and procedures, with allows host device, which operates optical transceiver or its network management system, to access main Key Performance Indicators of Transceiver in real time. The transceiver generates these diagnostic data by digitalization of internal analog data. It allows accessing such data as transceiver temperature, internally measured supply voltage, TX bias current, TX output power and received optical power. This digital diagnostics memory also accommodates warning threshold levels for KPI’s, which can trigger alarms on host system, in case of misconfiguration. Nowadays almost all optical transceivers are equipped with digital diagnostic interface by default. 5 or 10 Years ago, digital diagnostic function were considered as additional feature, so it is still a chance that in case of using some old transceivers You may encounter items without this small but useful function.

Compatibility of transceivers is determined by marketing policy choice of host systems vendors. Majority of vendors have simply decided to follow MSA (Multi-Source Agreement) guidelines and has not implemented any restricting functions in software of their host devices. It means that these systems support transceivers of any producer, if their production and encoding comply MSA. Some decided to take advantage of market conditions and permit using only their OEM Products. Here You can read more about implications using 3rd party products on these systems. These protection algorithms are different vendor by vendor – but they all work on top of MSA guidelines. Some vendors use very basic identification by serial and part number, others have implemented quite advanced mathematical functions, like F=MD5 (Vendor Name + Serial + PN + Production Date). Anyhow – mathematics are mathematics and optical transceiver industry has found out how to provide desired results for host system mathematical functions, what allows using 3rd party transceivers with protected host systems and achieve huge investment savings.

Side effect of this protectionism policy is that industry is not using common terminology when speaking about optical transceivers, but many different part numbers and slang terms, which is only generating confusion and alphabet soup. For example – SFP-10G-SR, according to IEEE 802.3ae standard 10G optical Ethernet operating over MMF with 850nm wavelength name is 10GBASE-SR. So – why all equipment manufacturers don’t have 10GBASE-SR-SFP, but such variations for same thing as:

All listed part numbers describes technically the same SFP-10G-SR with exact same functionality and this is just a beginning of list – we guess that if complete, this table could contain several hundred rows.

Because of biased perspective on optical transceivers from majority of equipment vendors, there is lack of good and structured education on this topic. Many network engineers need to gather knowledge on this important part of network by trial – error approach. In order to contribute our industry we will try to shed some light on most common questions we hear from our customers:

SFP-10G-SR and SFP-10G-LR: What is the Difference?
Well, both are SFP+ modules produced by guidelines of MSA, both supporting same network protocols or applications and same from electrical interface properties. SFP-10G-SR are using 850nm photodiodes in order to be used with Multi-mode fiber, with allows it to reach Short Distance – up to 300m. SFP-10G-LR use DFB laser with 1310nm wavelength suitable for single-mode optical cable, with minimum guaranteed budget about 6dB. 6dB budget allows SFP-10G-LR to reach about 10km or as IEEE considers – Long Reach;

Is Cisco original SFP-10G-SR and FET-10G the same?
Both, SFP-10G-SR and FET-10G transceivers from hardware perspective is exactly the same, just different coding. FET-10G has special coding features to be recognizable and usable only between Nexus 2000, Nexus 5000 and Nexus 7000 series.

Is Cisco SFP-10G-SR transceiver supported in other manufacturers switches?
Well, it depends on switch manufacturer. Most of host system vendors has no protectionism policy and accepts any MSA compatible transceiver in their systems. All of the protection algorithms comes on top of MSA guidelines, so Cisco SFP-10G-SR will work on all MSA compatible systems. However – if it will be used with system using different own proprietary algorithm, it will not be supported.

What is difference SFP-10G-SR= vs SFP-10G-SR-S= ?
Many, who reading official vendor papers, will answer this question that Cisco S-class optics are more budgetary class of transceivers designed especially for enterprise and data center connections. As both SFP-10G-SR= and SFP-10G-SR-S= have almost identical specifications, economy is achieved by dropping unnecessary features / link protocols – such as OTN/SONET. We however would say that both these transceivers are the same – just different firmware configuration in order to switch-off some protocols and of course opportunity of marketing and revenue protection.

Why SFP-10G-SR can’t establish connection over 200m of Multi-mode cable?
As first, we would recommend to test these transceivers using short distance patch cable. If still no luck in establishing link, there may be some actual problem with transceiver hardware, but if You are able successfully establish link then problem is link budget. Check carefully type of Your multi-mode cable, because in case of older OM1 cable specification maximum distance is only about 33m in case of 62.5 micron core and 82m in case of 50 micron core. In order to reach 300m You need as minimum OM3 specification multi-mode cable.

What is best option for short-range 10G connections – DAC, Optical or Cat5/6?
We would say that there is not always universal answer fitting all scenarios. It can happen that You need use 10GBase-T because of existing circumstances – have already copper cables in wall or equipment You need to connect has already 10G Copper ports. If so – 10G Base-T is only option. If You have totally free choice – optical connection is best choice from cost and latency aspects. You can read more about this in our article -”10G Copper SFP+ – Necessary & Useful Option”. If we talking very short distances – then Direct Attach Cables would be best option.

Does SFP-10G-SR modules support GE?
Yes – SFP-10G-SR modules can support GE speeds, but this depend also on host system port properties. In case of Cisco Catalyst switches it will not mostly work, but in some systems You can configure 10G port to run in GE mode and it will be supported by transceiver module.
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