the site links are created by KCC
KCC and Topology Generation
The KCC is a built-in process that runs on all domain controllers. It is a dynamic-link library that modifies data in the local directory in response to systemwide changes, which are made known to the KCC by changes to the data within Active Directory. The KCC generates and maintains the replication topology for replication within sites and between sites.
The KCC has two major functions:
Configures replication connections (connection objects) between domain controllers. Each connection object defines incoming replication from a replication partner. Within a site, each KCC generates its own connections. For replication between sites, a single KCC per site generates all connections between sites.
Converts the connection objects that represent inbound replication to the local domain controller into the replication agreements that are actually used by the replication engine.
By default, the KCC reviews and makes modifications to the Active Directory replication topology every 15 minutes to ensure propagation of data, either directly or transitively, by creating and deleting connection objects as needed. The KCC recognizes changes that occur in the environment and ensures that domain controllers are not orphaned in the replication topology.
Connection objects
connection objects between multiple domain controllers Lesson 3 page 63 in your book Mr. ITT Student. :)
Three is the number of maximum hops between domain controllers
Outbound replication is when a domain controller transmits replication information to other domain controllers on a network andInbound replication is when a domain controller receives updates to the Active Directory database from other domain controllers on the network.
The Knowledge Consistency Checker (KCC) is a built-in process that runs on all domain controllers and creates the replication topology for the forest. By default, the KCC runs at 15-minute intervals and designates the replication routes between domain controllers on the basis of the most favorable connections that are available at the time. The KCC creates replication connections between domain controllers in the same site automatically. When there is more than one site, configure links between the sites; the KCC can then create the connections automatically between the sites as well. from: http://technet.microsoft.com/en-us/library/dd277429.aspx
Active Directory in general uses a multimaster scheme for updating the directory databases between domain controllers, there are specific functions that can only be performed on specific domain controllers. These specific functions are assigned to one of the five FSMO roles, (pronounced "fiz-moe roles") which can be assigned to one or more Domain Controllers.
Domains can be very complicated. If you create diffrent names for the domains it can couse issues in connectivity. The primary Domain controller should have the Base line name of the entire forest(All of the computers in a network) When creating second domains they can have subnames. Example: Primary domain controller is called Contoso.com, When adding other domain controllers they should look like this: Contoso.xyz.com If you create a domain with a completely diffrent name it will not be able to join the primary domain. If you create all the domain controllers with the exact same name then they will not know what to connect to or witch one is primary
Replication
Multiple registration of Domains is when you create multiple Domain names for your website such as '.com' and '.co.uk'. By Daniel
Service Intergration protocol (SIP)
Replication The data is available with all domain controller(DC) in case any DC fails other has same files with it.
The KCC is a built-in process that runs on all domain controllers and generates replication topology for the Active Directory forest. The KCC creates separate replication topologies depending on whether replication is occurring within a site (intrasite) or between sites (intersite). The KCC also dynamically adjusts the topology to accommodate new domain controllers, domain controllers moved to and from sites, changing costs and schedules, and domain controllers that are temporarily unavailable.