Introduction to Networking for NonStop S-Series Servers

TCP/IP Network Connections

Introduction to Networking for HP NonStop S-Series Servers—520670-005

10-2

A Brief Look at TCP/IP

Transmission Control Protocol/Internet Protocol (TCP/IP) is a set of layered

communications protocols for connecting workstations and larger systems. The

interface was defined by users at several universities under the auspices of the U.S.

Department of Defense Advanced Research Projects Agency (ARPA). While it is not

currently part of the Open Systems Interconnection (OSI) standards, TCP/IP has been

implemented by most major computer vendors and is therefore a de facto standard for

multivendor connectivity.

TCP implements functions corresponding to layer 4 of the OSI Reference Model: the

Transport Layer. It is connection-oriented and provides for the reliable exchange of

data between a sending and a receiving system, no matter how many intermediate

nodes the data traverses. TCP regards the data as a stream of bytes; it is not record-

oriented. It guarantees that all data sent will be received by the destination system and

will arrive in the order in which it was sent.

An alternative to TCP is the User Datagram Protocol (UDP). It is connectionless and

record-oriented: it guarantees only that a packet received at the destination node is

exactly what the sender sent. UDP does not guarantee that every packet will be

delivered nor that packets will arrive in the order in which they were sent. Overhead for

UDP is substantially less than for TCP.

IP implements functions corresponding to layer 3 of the OSI Reference Model: the

Network Layer. Specifically, it handles the routing of data through a network, which

typically consists of many different (heterogeneous) subnetworks. IP is connectionless;

it routes data from a source address to a destination address; each message, or

datagram, contains the information required to locate the destination node. Routers

along the way contain the information required to locate the next stop (or gateway) on

the path to the destination.

Associated with TCP/IP are several higher-level services that implement functions at

layers 5 through 7 of the OSI Reference Model. The applications HP implements as

products are described in HP NonStop TCP/IP, Parallel Library TCP/IP, and NonStop

TCP/IPv6 on page 10-3.