Ethernet and 802.11 wireless LAN—and WAN technologies—such as Frame Relay and
Asynchronous Transfer Mode (ATM). By being independent of any specific network technology,
TCP/IP can be adapted to new technologies.
The Network Interface layer of the DARPA model encompasses the Data Link and Physical layers
of the OSI model. The Internet layer of the DARPA model does not take advantage of sequencing
and acknowledgment services that might be present in the Data Link layer of the OSI model. The
Internet layer assumes an unreliable Network Interface layer and that reliable communications
through session establishment and the sequencing and acknowledgment of packets is the
responsibility of either the Transport layer or the Application layer.
Internet Layer
The Internet layer responsibilities include addressing, packaging, and routing functions. The
Internet layer is analogous to the Network layer of the OSI model.
The core protocols for the IPv4 Internet layer consist of the following:
The Address Resolution Protocol (ARP) resolves the Internet layer address to a Network
Interface layer address such as a hardware address.
The Internet Protocol (IP) is a routable protocol that addresses, routes, fragments, and
reassembles packets.
The Internet Control Message Protocol (ICMP) reports errors and other information to
help you diagnose unsuccessful packet delivery.
The Internet Group Management Protocol (IGMP) manages IP multicast groups.
For more information about the core protocols for the IPv4 Internet layer, see "IPv4 Internet
Layer" later in this chapter.
The core protocols for the IPv6 Internet layer consist of the following:
IPv6 is a routable protocol that addresses and routes packets.
The Internet Control Message Protocol for IPv6 (ICMPv6) reports errors and other
information to help you diagnose unsuccessful packet delivery.
The Neighbor Discovery (ND) protocol manages the interactions between neighboring
IPv6 nodes.
The Multicast Listener Discovery (MLD) protocol manages IPv6 multicast groups.
For more information about the core protocols for the IPv6 Internet layer, see "IPv6 Internet
Layer" later in this chapter.
Transport Layer
The Transport layer (also known as the Host-to-Host Transport layer) provides the Application
layer with session and datagram communication services. The Transport layer encompasses the
responsibilities of the OSI Transport layer. The core protocols of the Transport layer are TCP and
UDP.
TCP provides a one-to-one, connection-oriented, reliable communications service. TCP establishes
connections, sequences and acknowledges packets sent, and recovers packets lost during
transmission.
In contrast to TCP, UDP provides a one-to-one or one-to-many, connectionless, unreliable
communications service. UDP is used when the amount of data to be transferred is small (such as
the data that would fit into a single packet), when an application developer does not want the
overhead associated with TCP connections, or when the applications or upper-layer protocols
provide reliable delivery.
TCP and UDP operate over both IPv4 and IPv6 Internet layers.
Note The Internet Protocol (TCP/IP) component of Windows contains separate versions of the
TCP and UDP protocols than the Microsoft TCP/IP Version 6 component does. The versions in the
Microsoft TCP/IP Version 6 component are functionally equivalent to those provided with the
Microsoft Windows NT® 4.0 operating systems and contain all the most recent security updates.
The existence of separate protocol components with their own versions of TCP and UDP is known