HP OpenVMS Systems Documentation
Compaq PATHWORKS for OpenVMS (Advanced
In addition to the network card and the network card driver, a network computer must have a protocol driver, also called a transport protocol or a protocol. The protocol driver works between the upper-level network software---such as the workstation and server---and the network adapter card. The protocol packages the data that are sent over the network in a way that the computer on the receiving end will understand.
The process of associating a protocol driver with the network adapter card with which it will work and establishing a communication channel between the two is called binding.
For two computers to communicate on a network, they must use identical protocols. In the case where computers are configured to use multiple protocols, they need to have only one protocol in common to communicate. For example, a server that uses both NetBEUI and TCP/IP can communicate both with workstations that use only NetBEUI and with workstations that use only TCP/IP.
The Advanced Server allows connections from the transports and protocols shown in Table A-1, Supported Transports and Protocols.
|Protocol||Client Transport||Server Transport Component|
|NetBEUI (with NETBIOS)||LAN Manager||LAN Manager|
The remainder of this section provides an overview of each of these
protocols with basic information about each protocol and its advantages
A.3.1 TCP/IP Protocol
TCP/IP was developed in the late 1970s as a result of a research project on network interconnection by the Department of Defense Advanced Research Projects Agency (known as ARPANet, the precursor to the Internet). TCP/IP is actually a suite of protocols that defines various interactions between computers sharing the protocol.
Since the PC began its rise in popularity, TCP/IP has become a standard protocol for support in the PC networking environment.
TCP/IP has a reputation as a difficult protocol to configure and manage. However, current implementations are making it easier. For example, in TCP/IP, the Dynamic Host Configuration Protocol (DHCP) provides server support and is one of the most important advances in PC networking. Without DHCP, system administrators had to manually assign the four-byte IP addresses to each computer. With DHCP enabled, a DHCP server can manage a range of IP addresses and assign one to each computer as it logs on to the network.
The principal advantage of TCP/IP is that it provides communication across interconnected networks with different operating systems and hardware architectures.
TCP/IP provides compatibility with the Internet, a collection of networks and gateways linking universities, corporations, government offices, and military installations worldwide.
Table A-2, TCP/IP Protocol, summarizes the advantages and disadvantages of using the TCP/IP protocol.
|Provides connectivity across different operating systems and hardware platforms.||Slower than NetBEUI on small LANs.|
|Provides Internet connectivity.||Can be difficult to administer.|
|Provides routing support.||More overhead than NetBEUI.|
The NetBIOS Extended User Interface (NetBEUI) was first introduced by IBM in 1985. NetBIOS, an integral part of the NetBEUI protocol driver, is a programming interface that implements many session layer functions. NetBEUI is a small, efficient, and fast protocol with low overhead.
"Overhead" in this context refers to the additional network control information, such as routing and error checking, that the protocol adds to data that the application layer needs to send across the network.
One reason for NetBEUI's lower overhead is that NetBEUI does not require an explicit acknowledgment (ACK) of each frame before it sends the next. Instead, the computer packages up several ACKs and sends them all at once. Requiring an ACK for every packet wastes network resources. NetBEUI dynamically determines the number of frames the sender can transmit before receiving an ACK, based on the network's current conditions.
NetBEUI was developed for LANs segmented into workgroups of 20 to 200 computers, with gateways connecting LAN segments to one another or to mainframes. NetBEUI is optimized for very high performance when used in departmental LANs or LAN segments. For traffic within a LAN segment, NetBEUI typically is the fastest protocol.
While NetBEUI is fast on small LANs, it is not so effective on large networks because it has a poor addressing scheme. NetBEUI does not allow duplicate computer names on the same network. This prevents a network from having two computers with the same name---something difficult to eliminate on a large network.
Table A-3, NetBEUI Protocol, summarizes the advantages and disadvantages of the NetBEUI protocol.
|Tuned for small LAN communication, and therefore is very fast on LANs.||Not routable.|
|Good error protection.||Performance across WANs is poor.|
|Small memory usage.||Requires each network computer to have a unique name.|
DECnet-Plus is a proprietary protocol; it is a collection of many layered protocols offered together as a major data communications network. Developed as a distributed network, it supports a wide range of applications and programs.
One of the DECnet protocol's major advantages is flexibility in network configuration and applications functionality. DECnet-Plus includes the Local Area Transport (LAT) protocol that terminal servers use to communicate with hosts.
Table A-4, DECnet-Plus Protocol, lists the advantages and disadvantages of the DECnet-Plus protocol.
|Major flexibility in network configuration.||Complex network architecture.|
|Maintains a high level of availability, even in the event of node or link failure.|
|Supports a wide range of communications facilities, such as Ethernet and X.25.|