4 SDH

Synchronous Digital Hierarchy (SDH) provides mapping, muxing (byte interleaved TDM), and framing to mainly carry PDH and Ethernet traffic. Overhead bytes ensure the management of payload and pointers allow dynamic allocation of payload in STM frame with which justification can be done under specified limit.

The SDH is supported in accordance with ITU-T G.841.

4.1 EoS

Ethernet over SDH (EoS) provides a simple, flexible and cost-effective solution to customers offering Ethernet based services. An EoS transport solution fundamentally addresses the following key issues:

• LCAS

• VCAT

• GFP-F

• AN

• LI

• Flow control

• Differential delay

4.1.1 LCAS

Link Capacity Adjustment Scheme (LCAS) is specified by ITU-T G.7042 and is a protocol for a standard based hitless scheme to increase or decrease the capacity of a VCAT link between the sources (Transmitter) and sink (Receiver). The LCAS uses a control packet within the H4 byte for High Order and within the Z7/K4 byte for low order links.

4.1.2 VCAT

Virtual Concatenation (VCAT) is specified by ITU-T G.7043 and enables end-to-end connections that precisely match the client requirements without wasting bandwidth. High-order VCAT provides a 155Mb/s (AU-4) resolution. The VCG members need not be in adjacent channels and can take different paths through the network, so ingress and egress elements must be able to tolerate up to 64ms of differential delay between VCG members.

4.1.3 GFP-F

Generic Frame Procedure - Framed (GFP-F) is specified by ITU-T G.7041. It encapsulates bursty client traffic such as Ethernet and also RPR. The received client signal frame is mapped in its entirety into one GFP frame. GFP-F works relative to client frame boundaries (For example, 1 SONET frame per GFP-F frame).

4.1.4 AN

Auto Negotiation (AN) is to negotiate and select a common speed and mode of communication between two link partners.

4.1.5 LI

Link Integrity (LI) or point to point communication, a live feature checks end-to-end (client to client) integrity of the link and if there is a breach of integrity anywhere in the link, then forcefully the health client sides are made down.

4.1.6 Flow control

Rate shaping mechanism to avoid packet drops.

4.1.7 Differential delay

Differential delay measures the difference in time among the channels of a multi-channel with respect to the maximum differential delay allowed for a signal to arrive at its destination. In practice, the maximum amount of differential delay that can be compensated is implementation specific. VCAT allows that channel to be temporarily removed from the data carrying channels.

NOTE: The TJ1600 product family supports a differential delay of 64ms.