Learn Windows XP Professional: The TCP/IP Protocol (Page 3) Page 3

As mentioned previously, the TCP/IP suite of protocols maps to a four-layer conceptual model based on the seven layer Open System Interconnection (OSI) protocol model. The TCP/IP four-layer conceptual model maps out as follows:

Network Interface Layer - This layer effectively puts the frames on the wire from the sending node and pulls frames off the wire at the receiving node. As such, it basically correlates to the Physical Layer of the OSI model.

Internet Layer - The Internet Layer protocol of the TCP/IP suite encapsulate packets into Internet datagrams. There are four Internet protocols that operate at this layer. The Internet Layer basically (but not entirely) correlates to the Network Layer of the OSI model.


The Internet Protocol provides connectionless packet delivery for all other protocols and does not guarantee packet arrival or correct packet sequence, nor does it acknowledge packet delivery. IP has the main responsibility of addressing and routing packets between nodes, and it does not try to recover from network errors.


The Address Resolution Protocol maps IP addresses to physical machine addresses (MAC addresses) that are located on the LAN. IP broadcasts a special ARP inquiry packet containing the IP address of the destination system. The system that owns the IP address replies by sending its physical address to the requester. The MAC sublayer communicates directly with the network adapter card and is responsible for delivering error-free data between network.


The Internet Control Message Protocol is a message control and error-reporting protocol used between network nodes. Higher-level protocols use the information in these datagrams to recover from any transmission or other errors.

IGMP The Internet Group Management Protocol provides a way for nodes to report their multicast group membership to nearby multicast routers. Multicasting allows nodes to send content to multiple other nodes within that multicast group by sending IP multicast traffic to a single MAC address (but by allowing it to be processed by multiple nodes). IGMP is part of the Network layer of the OSI model. Windows XP Professional supports multicast for things such as Windows 2000 Server NetShow Services.

Transport Layer - The two Transport layer protocols provide communication sessions between computers, and these sessions can be connection-oriented or connectionless, as outlined below. The Transport Layer basically (but not entirely) correlates to the Transport Layer of the OSI model.


The Transmission Control Protocol is a connection-oriented protocol that provides reliable communication by assigning a sequence number to each segment of data that is transmitted so that the receiving host can send an acknowledgment (ACK) to verify that the data was received. If an ACK is not received, the data is retransmitted. TCP guarantees the delivery of packets, ensures proper sequencing of the data, and provides a checksum feature that validates both the packet header and its data for accuracy.


User Datagram Protocol is a connectionless protocol that does not guarantee the delivery or the correct sequencing of packets. Applications that use UDP typically transfer small amounts of data at once and the data sent is usually not considered critical. TFTP (Trivial File Transfer Protocol) uses UDP.

Application Layer - The Application Layer is where applications that are specifically written to operate over networks gain their access. There are two TCP/IP services, Winsock and the NetBIOS over TCP/IP (NetBT) interface, that network applications most commonly use on Windows XP Professional networks. The Application Layer basically (but not entirely) correlates to the Application Layer of the OSI model.


Winsock is the standard interface used for socket-based applications and TCP/IP protocols. Winsock allows the network application to bind to a specific port and IP address on a node, initiate and accept a connection, send and receive data, and then close the connection.


NetBIOS over TCP/IP is the standard interface for NetBIOS services, including name, datagram, and session services. It also provides a standard interface between NetBIOS-based applications and TCP/IP protocols ,and it is the network component that performs computer name to IP address mapping name resolution. There are currently four NetBIOS over TCP/IP name resolution methods: b-node, p-node, m-node and h-node.

That's a wrap for this week. Be sure to check back in next week for the next article in this series which will cover TCP/IP Addressing in Windows XP Professional.

In the meantime, best of luck in your studies and please feel free to contact me with any questions on my column. And remember,

"A hacker's worst nightmare is that Server Administrators will wake up and do their job"

This article was originally published on Jul 29, 2002
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