Understand the technologies behind Ethernet over NG-PDH and NG-SONET/SDH.

Next Generation SONET/SDH and PDH (NG-SONET/SDH and NG-PDH) are two solutions developed to support efficient transfer of packet data across the existing telecommunications network.

A number of packet over SONET/SDH solutions exist, which are capable of mapping packet data to SONET/SDH. This includes Packet over SONET (see http://en.wikipedia.org/wiki/Packet_over_SONET) and LAPS (ITU-T X.85/X.86). However, these technologies were inefficient in matching packet data to available SONET/SDH capacity.

The introduction of three new technologies provided a more efficient solution. These were:

• Generic Framing Procedure (ITU-T G.7041 GFP)
• Virtual Concatenation (ITU-T G.707 VCAT for SONET/SDH)
• Link Capacity Adjustment Scheme (ITU-T G.7042 LCAS)

GFP is an encapsulation method for transporting packet data over circuit-switched networks. There are two versions:

• GFP-F - A Frame version for transport of already framed data, such as IP, MPLS, Ethernet etc.
• GFP-T - A transparent block code version for transport of non-framed data, typically used for storage protocols such as ESCON, FICON, Fiber Channel etc.

VCAT enables virtual concatenation of SONET/SDH containers to efficiently match the packet data rate. Standard container sizes are defined as part of the SONET/SDH standards, but these were designed for voice services and their associated multiplexing services. To support services larger than these containers, concatenation of standard containers can be performed.

Contiguous Concatenation (CCAT) is already available and allows adjacent containers to be concatenated and sent over the same path, but VCAT allows non-adjacent containers to be used and be sent over different paths offering a greater level of flexbility. Groupings of virtual containers are called Virtual Concatenation Groups (VCG).

LCAS allows VCGs and members of VCGs to be added or removed without affecting ongoing transmission. This effectively means that the available bandwidth for packet data transmission can be adjusted on-the-fly to match the bandwidth requirements of the packet data to be transmitted.

For NG-PDH, the same technologies are used for transport of packet data over bundles of PDH connections. The relevant standard extensions are:

• GFP for Ethernet over NG-PDH (ITU-T G.8040)
• VCAT for Ethenet over NG-PDH (ITU-T G.7043)
• LCAS for Ethernet over NG-PDH (ITU-T G.7042)

For more details on these technologies see:

Ethernet over SONET/SDH Tutorial

http://en.wikipedia.org/wiki/Generic_Framing_Procedure

http://en.wikipedia.org/wiki/Virtual_concatenation

http://en.wikipedia.org/wiki/LCAS