Next-generation framer/mappers

Next-generation framer/mapper devices are driving network transport efficiencies, says Deepak Sharma, Marketing Manager at Cypress Semiconductor.

Every day, we asked to do more with less by our bosses, our companies and our customers.

This requirement is particularly evident in the task of moving data across a transport infrastructure in an optimal, cost-efficient manner.

The original transport network was based on a simple "configure and forget" rule.

It relied on Sonet/SDH TDM (time division multiplexing) capabilities.

But the shift to packet-based transport requirements has forced the industry to develop new standards and architectures.

This, in turn, has resulted in the evolution of framer/mapper chips at the physical-layer level to provide a way to use the existing transport network more efficiently for data services.

Today, the transport network must work efficiently with both voice and data.

But the unpredictable or "bursty" nature of data traffic is not ideally suited for transport over an existing TDM channel.

If a designer creates a TDM channel that can handle the maximum data rate coming in, the link is underused most of the time.

On the other hand, if they create a TDM channel based on average rate, then packets might be dropped when a critical burst comes through.

Another wrinkle is the proliferation of data transport protocols, such as Ethernet, Fibre Channel (FC), Escon, DVB and Ficon along with the need to move them transparently across the WAN.

For example, if a corporation with headquarters in Los Angeles wants to back up its data in Texas and transport it across the network via FC, from a deployment perspective, it needs: a flexible-bandwidth mechanism to adapt the Sonet/SDH channels to the data being transported over them; a mechanism to flexibly and, ideally, dynamically change the bandwidth of the Sonet/SDH channels configured across the network; and an efficient means of mapping multiprotocol data onto Sonet/SDH channels.

Although there are some new and exciting technologies such as 10GbE over fibre with the potential to meet these requirements, most vendors remain focused on increasing the efficiency and flexibility of the existing infrastructure.

(There is more than $200 billion of Sonet/SDH equipment deployed to date).

We will look at three key standards that achieve this goal.

Virtual concatenation [1][2] is an inverse multiplexing technique that enables an arbitrary number of Sonet/SDH channels to be combined into a single, byte-synchronous stream.

In other words, it allows an arbitrary number of either low-order (VC-12 or VC-3 in SDH, or VT1.5 in Sonet) or high-order (VC-4 in SDH or STS1/STS3c/STS12c in Sonet) channels to be "logically" combined into a single channel.

This channel can be routed independently through the network.

This implies that only the source and the destination nodes need to be VC-capable, the protocol itself is transparent to intermediate nodes.

A single OC48/STM-16 frame can be used to transport one GbE, one FC, one DVB and one Fast Ethernet packet, al