The Transmission Control Protocol/Internet Protocol is a network communication protocol. It can be used as a communications protocol on private networks and it is the default protocol in use on the Internet. When you set up any system to have direct access to the Internet, whether it is via dial-up or one of the high speed technologies in use today, your system will need to utilize the TCP/IP protocol whether it is a Windows based system or not.
Also, if the given system needs to communicate to other TCP/IP systems on the local LAN or WAN it will need to utilize the TCP/IP protocol as well.
[NOTES FROM THE FIELD] – Indirectly connected computers, such as those on a LAN that hit the Internet via certain default gateways, certain types of routers, Proxy Servers, ISA Servers or other indirect means, do not necessarily need to use the TCP/IP protocol. The need only use the network protocol in use for their LAN, where that LAN protocol would communicate with the directly connecting mechanism, (default gateway, router, Proxy Server or other direct device). That directly connected device would need to use the Internet default protocol of TCP/IP.
TCP/IP is technically made up of two protocols. The upper layer, Transmission Control Protocol, on the sending system is responsible for breaking down the data into smaller packets to be transmitted over the network, (local and Internet), while the TCP layer on the receiving node reassembles the packets it receives back into the original data structure.
The lower layer, Internet Protocol, addresses each individual packet so that it gets delivered to the correct node. Each routing device on the network, be it a hardware router or a server system that is performing routing functions, will check the destination address to see where to forward the message.
[NOTES FROM THE FIELD] – This is just a basic overview of TCP/IP and I didn’t want to get too involved with it here within this article. There is bountiful information on TCP/IP all over the Internet and before poring through the RFCs I would first suggest you try TCP/IP Frequently Asked Questions or TCP/IP Protocol Suite – Questions & Answers.
The TCP/IP Model
The TCP/IP suite of protocols maps to a four-layer conceptual model which is based on the seven layer Open System Interconnection (OSI) protocol model.
The detailed function of each layer of the Open System Interconnection (OSI) protocol model is beyond the scope of this topic, however, the 60 second overview is as follows:
Physical Layer – Defines the interface between the medium and the device. This layer also transmits bits (ones and zeros) and defines how the data is transmitted over the physical medium. Some examples of Network Components found at this layer are Multiplexers, Passive Hubs, Active Hubs, Repeaters and other types of signal Amplifiers
Data Link Layer – This layer is actually divided into to sublayers, Logical Link Control, which mainly handles error correction and flow control and Media Access Control, which mainly handles the communication with the network adapter card. Some examples of Network Components found at the Data Link layer are Bridges, Switches and certain Advanced Cable Testers.
Network Layer – This OSI layer is responsible for translating logical network address and names such as computernames to their MAC addresses and for addressing and routing data packets over the network. If routers at this layer can’t forward the data frames as large as the source node has sent, this OSI layer will break down the data into smaller units that the devices can handle. Some examples of Protocols found at the Network Layer are IP, ARP, RARP, ICMP, RIP, OSFP, IGMP, IPX, NWLink and NetBEUI. Some examples of Network Components found at this layer are Brouters, Routers, some types of ATM Switches and Frame Relay hardware.
Transport Layer – The Transport Layer adds an additional connection below the Session layer and helps manage data flow control between nodes on the
network. This layer divides the data into packets on the sending node and the transport layer of the receiving node reassembles the message from packets. The Transport Layer provides error-checking to guarantee error-free data delivery by requesting retransmission if some packets don’t arrive error-free. It also sends acknowledgment of successful transmissions back to the sending node. Some examples of Protocols found at this layer are TCP, ARP, RARP, SPX and NWLink. Some examples of Network Components found at the Transport Layer are Gateways and certain types of Brouters.
Session Layer – This OSI layer, as the name implies, establishes, maintains and ends sessions between transmitting nodes across the network and manages which node can transmit data at a certain time and for how long. Some examples of Protocols found at this layer are Names Pipes, NetBIOS Names, RPC and Mail Slots. Some examples of Network Components found at the Session Layer are Gateways and certain types of Proxy Servers.
Presentation Layer – The Presentation Layer technically performs the translation of the data from the way applications understand it to the way networks understand it on the transmission end and then back on the receiving node. It is responsible for protocol conversions, data encryption / decryption, and data compression / decompression where the network is considered. Some examples of Network Components found at the Presentation Layer are Gateways and certain types of Redirectors. There are no Protocols that normally operate in this layer.Application – The Application Layer of the OSI model allows access to network services for applications specifically written to run over the network, such as email and file transfer programs such as FTP. There are many Protocols found at the Application Layer, some of which include FTP, TFTP, BOOTP, SNMP, SMTP, TELNET, NCP, and SMB.
The TCP/IP suite four-layer conceptual model is 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 and basically correlates to the Physical Layer of the OSI model. Internet Layer – 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.
IP 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. ARP Address Resolution Protocol maps IP addresses to a 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. ICMP 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.
TCP 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. UDPUser 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 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 close then close the connection. NetBT 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 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.
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Jason Zandri has worked as a consultant, systems engineer and technical trainer for a variety of corporate clients in Connecticut over the past five years and currently holds the position of Technical Account Manager for Microsoft Corporation.
He has also written a number of COMPTIA and MICROSOFT prep tests for Boson Software and holds a number of certifications from both companies. Currently, he writes part time for a number of freelance projects, including numerous “HOW TO” and best practices articles for 2000Trainers.com and MCMCSE.com.
