Chapter 28 Services; Overview; What You Can Do In This Chapter; What You Need To Know - ZyXEL Communications NXC5200 User Manual

C
H A P T E R

28.1 Overview

Use service objects to define TCP applications, UDP applications, and ICMP
messages. You can also create service groups to refer to multiple service objects
in other features.

28.1.1 What You Can Do in this Chapter

• The Service screens
NXC's list of services and their definitions.
• The Service Group screens
the NXC's list of service groups.

28.1.2 What You Need to Know

The following terms and concepts may help as you read this chapter.
IP Protocols
IP protocols are based on the eight-bit protocol field in the IP header. This field
represents the next-level protocol that is sent in this packet. This section
discusses three of the most common IP protocols.
Computers use Transmission Control Protocol (TCP, IP protocol 6) and User
Datagram Protocol (UDP, IP protocol 17) to exchange data with each other. TCP
guarantees reliable delivery but is slower and more complex. Some uses are FTP,
HTTP, SMTP, and TELNET. UDP is simpler and faster but is less reliable. Some uses
are DHCP, DNS, RIP, and SNMP.
TCP creates connections between computers to exchange data. Once the
connection is established, the computers exchange data. If data arrives out of
sequence or is missing, TCP puts it in sequence or waits for the data to be re-
transmitted. Then, the connection is terminated.
In contrast, computers use UDP to send short messages to each other. There is no
guarantee that the messages arrive in sequence or that the messages arrive at all.
NXC5200 User's Guide
(Section 28.2 on page 415) display and configure the
(Section 28.2 on page
28
Services
415) display and configure
413