# Group Class of Service - Overview

Group Class of Service (GCOS) provides a way to manage communication between mailboxes for a particular set of users. For example, if two departments need to communicate with a supervisor but not with each other, the GCOS of the supervisor needs only to contain the group numbers of the two departments. Each department's GCOS will contain only the group number of the supervisor.

GCOS usage is essential to the operation of the system, and especially for large systems with many mailbox owners, or owners who have multiple mailboxes.

NuPoint Unified Messaging supplies a default GCOS (GCOS1) that includes all groups and so allows communications between all mailboxes. You can create your own custom GCOS as required to a maximum of 32,000.

There are two types of GCOS: bitmapped and affinity.

## Bitmapped GCOS

This GCOS must be defined as containing a number (up to 128) of groups. Two users can exchange messages if their GCOS has any group number in common. Bitmapped GCOS can have several groups defined, or none, allowing for a range of complexity in message exchange. Although bitmapped GCOS are more complex than Affinity, they are also much more flexible.

Bitmapped GCOS are numbered from 1-64.

## Affinity GCOS

This GCOS is not defined - all mailboxes with the same Affinity GCOS can communicate with each other (but not with anyone else). Affinity GCOS works well when mailboxes require communication within particular groups but not across groups. Easier to use than bitmapped GCOS, they are also less flexible.

Affinity GCOS are numbered 65 - 32,267

## Which Type of GCOS Should I Use?

When choosing GCOS, consider the following factors:

- To allow all mailboxes to exchange messages, assign the Default GCOS 1, which contains all 128 groups.

- Mailboxes with bitmapped GCOS and those with affinity group GCOS cannot interact.

- If you assign GCOS 1 to one mailbox and GCOS 65 to another, these mailboxes cannot exchange messages. If you mix the two types, one mailbox cannot communicate with another.

- Every mailbox that shares the same group in a bitmapped GCOS or shares the same affinity GCOS can exchange messages (even if the shared group is in a different GCOS).

- Bitmapped GCOS are useful when you need to develop complex relationships.

- Although mailbox owners may be in the same Dial-by-Name database, they can only reach others in the database who share the same GCOS group (in a bitmapped GCOS) or affinity group.

Parent topic: Group Class of Service