To support the massive Internet expansion of recent years, carriers significantly increased the capacity of backbone and core networks. Overview This otherid2ic describes the background and functions of LCAS, and the advantages of LCAS to networks. Basic Concepts Learning the basic . mechanism of LCAS in SDH/SONET network and point out that even though LCAS really brings us much more advantages in SDH transmission network, it also.

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Status messages are continuously exchanged and consequent actions taken. This is a bit used to acknowledge the detection of renumbering of the sequence or a change in the number of VCG members.

The network management system orders the source to add a new member e.

OptiX OSN 7500, 3500, and 1500 Feature Description (SDH Transport Domain)(V200R011C00_04)

In this example, the deleted member has the highest sequence number. This member is not provisioned to participate in the VCG. Each word is associated with a specific member i. The operation of LCAS is unidirectional. Although SONET and SDH were originally designed to transport voice traffic, advent of these new mechanisms has made it perfectly suitable for carrying more dynamic and bursty data traffic.

The status of all the members is returned to the transmitter in the control packets of each member. These messages capture the status of all the VCG members at the receiver.

This acknowledgment is used to synchronize the transmitter and the receiver. The LCAS mechanism can also automatically decrease the capacity if a member in a VCG experiences a failure in the network, and increase the capacity when the fault is repaired.


Although autonomous addition after a failure is repaired is hitless, removal of a member due to path layer failures is not hitless. Or, the receiver has received and acknowledged a request for addition of this member. LCAS is resident in the H4 byte of the path overhead, the same byte as virtual concatenation.

The following control words are sent from the receiver to the transmitter. See All Related Store Items. Multiple members can be added simultaneously for fast resizing. The transmitter can, for example, read the information from member No.

Link Capacity Adjustment Scheme

This means that in order to bidirectionally add or remove members to or from a VCGthe LCAS procedure has to be repeated twice, once in each direction. The destination notices the F IDLE command and immediately drops the channel from the reassembly process.

The protocols behind LCAS are relatively simple. The source sees the R OKassigns the member a sequence number that is one higher than the number currently in use.

If this is not the case, then the other members with sequence numbers between the newly deleted member and the highest sequence number are renumbered. This member is provisioned to participate in the VCG and has a good path to the receiver.

Link Capacity Adjustment Scheme | SONET and SDH: Advanced Topics | InformIT

The incoming signal for this member experiences no failure condition. Related Resources Store Articles Blogs.

This member is in the process of being added to the VCG. This capability is particularly useful in environments where dynamic lcax of capacity is important. This member is in the process of being deleted from the VCG. The following is a typical sequence for adding a member to the group.

Link Capacity Adjustment Scheme – Wikipedia

The state machine at the transmitter can sdj in one of the following five states:. As long as no return bandwidth is available, the transmitter uses the last received valid status. The incoming signal for this member experiences some failure condition, or an incoming request for removal of a member has been received and acknowledged.


The transmitter and the receiver communicate using control packets to ensure smooth transition from one state to another.

At a frame boundary, the source includes the VC in the byte interleaving and sets the control command to F EOSindicating that this VC is in use and it is the last in the sequence. In lcaas descriptions below, we use the term member to denote a VC. LCAS uses 7 others for its purposes, leaving 5 reserved for future development.

This member is provisioned to participate in the VCG and has a failed path to the receiver. Virtual concatenation uses 4 of the 16 bytes for its MFI and sequence numbers. The following control words are sent from source to the receiver in order to carry out dynamic provisioning functions.

The source node starts sending F ADD control commands in the selected member. Indicate that this VC is currently not a member of the group. Indicate that this member is normal part of the group and does not have the highest sequence number. These actions are independent of each other, and they are not required to be synchronized.