Show All
Top 5Join Our Community
Tag Archives: Low-latency
…waiting for the WARP drive
While recent blog posts on low-latency networks were focused on speeds and feeds of data transport between two given locations the underlying physics were always considered as a constant that cannot be changed. It is widely accepted that fiber optic transport is the fastest and most efficient way to transfer information in networks and the speed of light seems to be the natural barrier here. To break this natural barrier, things like WARP drives or usage of wormholes could be the next alternative but unfortunately research has not reached a status yet that would make such things seem realistic (see NASA – Status of “Warp Drive”). But before we start thinking about speeds faster than speed of light we could actually still improve the speed we are using today for fiber optic transmission.
Let’s take a Bit Time to talk about low latency
Talking to customers who are interested in lowest latency solutions, the term “Bit Time” comes up over and over again. But it is not clear what it actually means in terms of low latency and whether a lower “Bit Time” is always better than a higher one. So let’s try to explore the background and the implications here.
In general “Bit Time” stands for the time it takes to transmit a bit for a given network data rate. At Gigabit Ethernet (=1Gbps data rate) the “Bit Time” is 1/(1Gbps) = 1/109 = 1 nanosecond. In other words it takes 1 nanosecond to transmit a bit at 1Gbps. For higher data rates like 10GE the “Bit Time” is even shorter with just 0.1 nanoseconds = 100 picoseconds. But make no mistake – this does not say anything about the actual speed of the signal – it only indicates how many bits can be transmitted during a given second. The speed at which those bits travel over a fiber link is still subject to the maximum speed of light in a fiber, which is approximately 200,000 km/s.
Mobile backhaul evolution – bringing broadband to all
With HSPA and EVDO maturing, WiMAX being deployed and LTE getting ready to buzz around, it is soon changing the way mobile phones will access the networks. The bandwidth-hungry new services, applications and the non-stop touch clicks on your smart handhelds are eventually going to obsolete the mature 3G networks.
Whereas, the 4G radio access networks are definitely envisioned to control this ever-increasing wireless broadband traffic, what about the evolution of the backhaul network? Is it ready? Or is it going to be a major bottleneck analogous to the traffic jams seen if only one lane was operating out of a four lane expressway.
Low latency for dummies
Besides cloud computing and virtualization, low latency seems to be another buzz word of the year. But reading through all the publications can get a little confusing. While the business benefits of having a lower latency (=faster) network than your competitor are obvious and understandable the technology behind it becomes a little blurry. Let me try to explore some of the myths that exist around low latency technology.
The higher the bandwidth the lower the latency
People often confuse transport speed with transport capacity and often tend to think bigger (capacity) is better. Let’s look at an analogy from the real world: No one would honestly claim that a bus that can carry 100 passengers can reach its destination faster than a sports car that only transports 2 passengers. The bus has a higher capacity but this does not mean that it has a faster speed. If you only want to get from A to B as fast as possible you generally take the sports car. In addition, getting on and off the bus will add to the travel time where the sport car passengers can take their seats very quickly. In networking terms this means that larger capacity is not necessarily faster speed – in a lot of cases larger capacity actually means slower performance. A larger capacity transmission typically requires additional processing and error correction in order to successfully send the signal on a fiber optic link – this can add a lot of latency.
Some equipment can transport data faster over fiber than others
Although it would be nice: the maximum achievable speed of any information transmission cannot be faster than the speed of light in vacuum. Since fiber optic cables have a refractive index that is around 1.47 the actual speed of light in fiber optic cables is slower by exactly that factor. This results in a transport latency that is around 5 microseconds per km. As long as your transport is happening over the same standard fiber (there are some “faster” fiber cables deployed on a small scale) and since warp drive has not been developed yet all transport is subject to the same delay.
Optoelectrical processing in each intermediate node has no effect on latency and offers additional value in regards to service granularity and virtualization
Each time a signal goes through an optoelectrical process there is additional latency that is added to the transport. Hence, in most cases, latency can be reduced by staying optical as long as possible. Today’s optical components even allow signal amplification, switching and re-routing in optical domain.
Electrical signal processing can improve the signal latency
In most cases the electrical processing of signals (including multiplexing and the introduction of forward error correction (FEC)) generates additional delay. The problem can even get worse if the algorithms are not latency optimized. The safest approach seems to be touching the signal as little as possible.
So after discussing some of the myths, the question still stands what is the optimum solution for lowest latency transmission? Generally one should try to stay in the optical domain as long as possible. Perhaps more importantly, the transport solution should seamlessly adapt to the transport protocol and data rate being used by the end device. If a server works best with a 1GE signal than this should be the signal transported. This implies that the search for the lowest latency network doesn’t start with the transport network but with the optimum choice for the interconnection protocol within the server. Last but not least, generally the low hanging fruit for squeezing time out of your system is changing your optical transport network. Optical equipment changes combined with shorter fiber routes can provide significant savings – remember that for each km saved the earnings are 5 microseconds.
To read more about low-latency optical transport, please click here.
Connecting data centers over distance – how to speed up your data…
In recent years networking in enterprise data centers has undergone dramatic changes and following today’s discussions about FCoE and data center convergence it is obvious the speed of change will even increase. But it seems to me not even the recent advancements in technology have made it to the minds of all users.
Traditionally everything that had to be transported over distance had to be converted in order to fit into a carriers Sonet/SDH transport infrastructure. But new technologies like WDM, MPLS or even Ethernet have emerged replacing Sonet/SDH and still it seems some people out there love the “old” technology so much – they want to convert everything into it.
