Active Directory Component

Logical Structure Physical Structure: 

Domains sites
Trees Domain Controllers
Forest
Organizational Unit

A.D. Components: 

1 Logical structure is useful for organizing the network.
2 Logical components cannot be seen
3 Physical structure is useful for representing our organization for developing the organizational structure.
4 It reflects the organization (mirrors)
5 Physical structure can be seen. Ex. Site – India, US, UK etc.

TREE:

A tree is a group of domains which share contiguous name space.
If more than one domain exits we can combine the multiple domains into hierarchical tree structures.
The first domain created is the root domain of the first tree.
Additional domains in the same domain tree are child domains.
A domain immediately above another domain in the same domain tree is its parent.

FOREST:

Multiple domain trees within a single forest do not form a contiguous namespace. i.e. they have non-contiguous DNS domain names. Although trees in a forest do not share a name space, a forest does have a single root domain, called the forest root domain
The forest root domain is, by definition, the first domain created in the forest.
The two forest wide predefined groups – Enterprise.
Administrators and schema administrators reside in this domain.

Physical structure 
SITES:

Site is a combination of TCP/IP, subnets, connected with high-speed links.
Sites provide replication

There are 2 types of replications
1. Intrasite replication
2. Intersite replication

Intrasite Replication:

It is a replication with in the same site. It offers full time replication between DC & ADC when they are within the same site.

Intersite Replication:

It is a replication between two different sites.
Intersite replication is implemented when the sites are away from each other.

-It requires a site link
-Site link is a logical connection between sites, which can be created & scheduled.
-Site link offers communication only at scheduled intervals.