• For Specialists

    A blog for service providers focused on QoS, QoE, and network performance. Join us for in-depth analysis of industry news, technology, and solutions driving performance in mobile networks, cable MSO business services, cloud and data center connectivity, enterprise WANs, and financial networks.

  • Join us Live

    We host webinars each month covering topics from solution design to performance assurance technology and demos of our latest innovations. Join us engineers online for tailored insight and Q&A with our network engineers.
    Upcoming Webinars:

    Click Here
  • Learn on YouTube

    Accedian is the Performance Assurance Specialist for mobile networks, enterprise to data center connectivity, and service provider SDN. With dozens of videos covering network performance and QoE, our YouTube channel is a unique training resource.

    Watch Now

Thursday, September 30, 2010

New Hibernia-Atlantic cable will save 5 ms on New York to London route

Hibernia Atlantic’s new trans-Atlantic submarine cable will shave 5 milliseconds or more off the return-path latency between New York and London. The lowest-latency trans-Atlantic cable currently active, Global Crossing’s AC-1, can deliver latency of 60.8 milliseconds to the western point of England from New York. Connecting AC-1 onward to London costs a few additional milliseconds. By contrast, Hibernia’s new Project Express cable promises to allow sub-60 ms latency from New York all the way to greater London.

“Financial institutions engaged in high-velocity trading are speed demons,” noted TeleGeography VP of Research Tim Stronge. “They claim that shaving off just a few milliseconds of connectivity between two trading locations can earn them tens of millions of dollars a year, so they’re willing to pay extra for the fastest path.”
Bandwidth prices across the Atlantic remain among the lowest in the world. According to TeleGeography’s Bandwidth Pricing Database, the median price of a 10 Gbps wavelength between New York and London is approximately $10,500 per month, compared with $230,000 for the same amount of capacity between Miami and Brazil. By building along a unique, low-latency path, Hibernia aims to break out of the trans-Atlantic commodity pricing prison.

Tuesday, August 24, 2010

Sources of latency in optical systems used by financial customers

Every optical-transport function that is intended to contribute to the successful beaming of traffic across fiber connections can inject small amounts of latency into the process. Today’s financial network manager must be cognizant of all of them.


Color conversion (“Transponding” and “muxponding” ) are two common sources of delay. When traffic is readied for transport across a Wavelength Division Multiplexing (WDM) optical network, it’s converted to a color of light to be carried across the glass fiber. This is transponding.
Additionally, in many cases, lower-speed traffic, such as a 1 Gbps information feed, is aggregated into a higher-speed signal such as a 10 Gbps transport link. When multiple feeds are muxponded, significant latency can occur
Optical amplification also can produce latency in a financial network. The “Erbium-Doped Fiber Amplifier” (EDFA) can introduce microseconds of latency, so financial network managers should instead demand amplifier designs that have been specifically engineered for the contemporary low-latency challenge.
Dispersion compensation is another potential source of latency. At higher speeds, such as 10 Gbps, optical data signals sometimes smear into a rainbow of colors within a fiber cable. It’s an effect called “chromatic dispersion” and its effects can include an increasing degradation of the data signal over distance.
There are fiber Bragg gratings (FBGs) that have been designed to offset dispersion while introducing only negligible delay. In some cases the alternative is to rely on hundreds of kilometers of dispersion-compensating fiber (DCF) that is ill-suited for low-latency applications.
Electrical signal regeneration likewise introduces additional latency. Conventional regeneration techniques may yield hundreds of microseconds of delay. State-of-the-art low-latency techniques will introduce latency of only nanoseconds.

Sunday, May 9, 2010

Why LTE requires low latency

There are two obvious reasons why LTE networks will require both lower latency and higher bandwidth backhaul: LTE simply is the lowest latency air interface and features bandwidth that cannot be supported by legacy backhaul protocols.

Edge and EVDO networks can handle average peak data rates using two or three T1 links, but need more than that to handle peak rates. But HSPA networks cannot do so, either efficiently or conveniently. To support peak rates on an HSPA network, about 45 Mbps is required.
An LTE network using a 10-MHz channel requires nearly a DS-3 (45 Mbps) just to handle average load, and needs an Ethernet connection to handle peak loads.
Also, where older GPRS or EDGE data networks featured round-trip latencies in the 600 millisecond to 700 msec. range, LTE networks feature round-trip latencies in the 50 msec. range.
That means Ethernet speed backhaul and lower-latency performance is required.

Sunday, March 28, 2010

Another national LTE network coming?

There’s quite a lot of fourth-generation mobile network construction happening, and about to happen, in the U.S. market, but the wild card now is that an entirely-new Long Term Evolution network might be built using spectrum originally allocated for satellite networks.


Harbinger Capital, which recently merged with SkyTerra, proposes to build a fully integrated satellite-terrestrial network to serve North American mobile users, featuring national LTE facilities that would operate on a wholesale-only basis.
The Federal Communications Commission apparently has required that, as part of the Harbinger purchase of SkyTerra, the firm operate as a wholsaler, and also that AT&T and Verizon traffic cannot account for more than 25 percent of total traffic carried on the Harbinger network.
The planned network would launch before the third quarter of 2011 and cover nine million people, with trials set initially for Denver and Phoenix. The next milestone is that 100 million people have to be covered by the end of 2012, 145 million by the end of 2013 and at least 260 million people in the United States by the end of 2015. Harbinger told the FCC that all major markets will be installed by the end of the second quarter of 2013.
Before any of that could happen, though, Harbinger would have to find additional investors willing to provide $5 billion worth of investment capital.
Analyst Chris King at Stifel Nicolaus estimates that Verizon’s LTE network will cost about $5 billion to deploy. Clearwire has also spent billions on its network, with analyst estimates ranging from $3 billion to about $6 billion. There is no particular reason to think the ubiquitous terrestrial network Harbinger expects to build would cost less.

Thursday, March 18, 2010

LTE: Cleaning up the cell site

I’ve winced every time I’ve heard the time “convergence” over the past several years. Convergence has always been a marketing word for “mess”, where multiple technologies co-exist and intermingle in ways that increase Tylenol consumption and slow down true telecom innovation.

Today’s wireless networks, including the current 3G deployments, still rely on this dirty word with “converged” cell site connections – duplicating provisioning of both TDM private lines for voice, timing and signaling and Ethernet for data.
There are many good reasons why. Until recently, Ethernet hasn’t proven as reliable as required to carry conversations, and T1s are already in place at cell sites where sync is required to keep radios locked on a common frequency and phase for roaming hand-offs. Necessary for now, but inefficient (and despised?) all the same.
LTE offers a chance to do some spring cleaning at the cell site, simplifying backhaul connectivity with a single, performance-assured Carrier Ethernet link. Simplicity looks like it’s making its way back into telecom, right?
Unfortunately, we may be gaining capacity and working with less equipment, but the clutter has simply moved from physical equipment to the way it’s configured. No one ever had their Mom tell them “clean up your virtual room”, but this is where the mess goes in LTE backhaul networks – into the provisioning, monitoring and performance assurance required to compensate for having all your data running through a single pipe.
Making a clean break to a fully packet-based architecture, voice calls will be VoIP, carried over the same all-IP infrastructure carrying the latest generation of multicast and on-demand web-based video, Internet, messaging and email traffic. With each vying for available bandwidth, maintaining per-application Quality of Service (QoS) is critical – the best-effort, limited-bandwidth backhaul connections serving legacy data services will not suffice.
4G services require ultra-low latency, jitter, and packet loss with assured throughput and availability. Latency can spell the end of conversations if signaling delays interrupt session continuity when roaming between cells. Jitter and packet loss can make audio inaudible and video unwatchable. Insufficient backhaul bandwidth leads to congestion, increasing latency, packet loss and packet retransmission resulting in degraded QoS. Availability is the most basic of all – if the network goes down, so do your customers – outages and lack of bandwidth are the primary drivers for customer churn.
So while Ethernet to the cell site is certainly the future (and looks clean from the perspective of slick, stylized network diagrams), it doesn’t come without its own baggage. Best to be prepared for the surprises that are popping up in field trials – keep an eye on QoS, monitor it proactively or you may just discover the monsters in the closet.
CTIA next week will be a good place to explore these trends – check out the backhaul pavilion, get trained and attend the talks going on to learn all about what we’re facing.