How protocols work.

Packets 1

Protocol Stacks 2

Connectionless versus Connection-Oriented Protocols 2

Standard Protocol Stacks 2

Microsoft Network Protocols 3

To understand the basics of Windows networking, you MUST understand today's lesson completely.  It is vitally important that you understand how protocols work, and where they are placed inside the OSI model. A protocol is a set of basic instructions that both computers must follow in the right order in order to communicate.  The basic steps involved for one system to communicate must be followed in order, including; 

The computer that receives the data must then perform the following steps;

If the computers do not perform all the steps in the proper order, the message will not reassemble properly and will be unusable.  Therefore, if a standard set of rules , or protocol, is not followed, the information will not be transferred.  Although there are many more steps involved in the transfer of data, the basic premise remains the same.

Packets

Computers generally send and receive small chunks of data called packets.  Protocols work in various levels of the OSI model to modify, disassemble, and reassemble packets as they move down the OSI model on the sending computer and up the OSI model on the receiving computer.  Protocols define how this movement of data takes place.

All packets contain specific information, regardless of the protocol used to send them.  The contents include;

There are three sections this data is separated into.

Each level of the OSI model on the sending computer adds some information to the packet, and each level removes the comparable information on the receiving computer.  The only exception to this rule is the physical layer, which does not add or remove any information from the packet, as it is only designed to transfer and receive the data from and to the NIC.


Protocol Stacks

Although the term protocol is generally referred to as working through the entire OSI model, it is actually a series of complementary protocols working together at different layers of the model that allow this system to function.  Protocols that work together within an OSI model are called a Protocol Stack, or suite.  Each layer handles a different part of the communications process and has its own rules and requirements.  It is also standard that higher-level protocols are more complex.

As many different protocols may work on a single computer, and many different adaptor cards could be within a single computer, a process had to be devised that bound a single network card to a single protocol and vice versa.  This is appropriately called the binding process.  It allows several several protocols to be bound to a single NIC (i.e. TCP/IP and IPX/SPX), and allows multiple NICs to be bound to a single protocol.  Multiple network cards can be required if a server is to connect to both an Ethernet LAN and a Fiber Optic backbone.

The binding process also allows protocol stacks to be bound to others.  For example, the device driver can be bound to the NIC, and TCP/IP can be bound to the device driver, and the NetBIOS session layer can be bound to TCP/IP.

Connectionless versus Connection-Oriented Protocols

There are two different methods that communications can be arranged; Connectionless and Connection-Oriented.

Connectionless systems optimistically assume that all data will arrive at a given location, so no systems are included with the protocol to guarantee data delivery or assure that data is received in the right sequence.  This allows the protocols to have a lower processing overhead, and makes them faster.  UDP/IP (User Datagram Protocol) is an example of a connectionless protocol.

Connection-oriented systems assume the opposite.  They assume that some information will be lost or damaged, and therefore there must be a system to track that information.  Connection-Oriented protocols contain information that guarantees delivery and sequencing to the destination computer.  They do this by negotiating for retransmission of data, and after the higher level layers of the protocol reassemble the data, corrupt and missing data is resent.  This means that no matter how long the data transfer takes, reliable data delivery is guaranteed.  Transmission Control Protocol (TCP/IP) is an example of a Connection-Oriented protocol.

Connectionless systems can be extremely fast in small networks, but break down on larger networks were information must travel through more routers, hubs, bridges, and systems.  The longer the packet stays in transport, the more chance there is for corruption.  Therefore use of connectionless protocols is not suggested for larger networks.

Standard Protocol Stacks

There are several standard protocols used by networking systems today;

Protocols within the stacks exist at all levels of the seven-layer OSI model, but they may be divided into three types;



Microsoft Network Protocols

There are three protocols provided by Microsoft with it's operating systems; NetBEUI, NWLink, and TCP/IP.  Each protocol had different requirements and different applications.  NetBEUI is meant for small networks with a single server.  NWLink is for medium sized networks.  TCP/IP is meant for large enterprise networks.

NetBEUI : NetBIOS Extended User Interface - NetBEUI implements the NetBIOS Frame transport protocol.  It was developed by IBM to support small LANs under OS/2 and LAN Manager.  It was not meant to handle workgroups of over 200 systems, and therefore is not routable. NetBEUI 3.0, the latest version of NetBEUI, has several advantages over other protocols when used on small networks;

Although it is fast on small networks, NetBEUI has several disadvantages;

NWLink : Netware Link - This is Microsoft's version of Novell's IPX/SPX protocol stack.  XNS, developed by Xerox as one of the first network protocols, is the grandfather of IPX.  NetLink is meant to interlink existing Netware servers, as a precursor to converting to Microsoft-authored services and protocols.

Netware by itself does not allow File and Printing services to and from NetWare services.  These services are performed by the Client Services For Netware (CSNW) redirector that also comes with Windows NT.  NWLink will allow Windows NT to act as either the client or the server in Novell IPX?NetBIOS client-server applications.  

There are several advantages to NWLink, including;

The disadvantages of NWLink are as follows;

Without a standard numbering system, it is very difficult to create interconnections with NWLink between existing enterprise organizations.  This limits the world-wide appeal of TCP/IP even though it is much slower then NWLink.

TCP/IP : Transmission Control Protocol

This is the primary Internet Protocol.  It is the related directly to the suite of protocols developed by the Department Of Defense's Advanced Projects Research Agency. (ARPA)  TCP/IP is the most widely used protocol in networking, having originally been used to link together military organizations in the late 1960's.  (This network was originally referred to as ARPANet, and was the start of the internet we know today.)  Eventually educational institutions eventually caught on to the TCP/IP network, seeing collaboration between institutes as a huge advantage.  When e-mail caught on in the early 1990's, the internet as we know it was born.

TCP/IP was originally designed for Unix-based computers.  When Hyper-Text Transfer Protocol (HTTP) was developed to share Hyper-Text Markup Language between servers, the World Wide Web was formed.  This eclipsed IPX as the world's largest network language when the commercial form of the internet was born.  

In order to make TCP/IP compatible with Netware servers, Microsoft has included NetBT (NetBIOS over TCP/IP) in accordance with Internet Protocol Requests for Comments (RFD) 1001 and 1002

TCP/IP's advantages are as follows;

TCP/IP had the following disadvantages

TCP/IP is the hardest protocol to administer and troubleshoot, although new protocols such as WINS and DHCP are simplifying this problem