4600 Series IP Telephone LAN Administrator’s Guide
NAT
A Network Address Translator is an application that can be administered between your network and the Internet. The NAT translates network layer IP addresses so your local intranet IP addresses can duplicate global, Internet addresses. A detailed discussion of NAT is beyond the scope of this document, but it should be noted that use of NAT can lead to problems affecting the consistency of addressing throughout your network. In Release 1.6 and earlier Releases of the 4600 Series IP Telephones, NAT is not recommended for networks handling IP-based telephony traffic. As of Release 1.7, all 4600 Series IP Telephones support NAT interworking; hence, there are no problems with NAT and Release 1.7 of the 4600 Series IP Telephones. Note, however, that support for NAT does not imply support for Network Address Port Translation (NAPT). Specifically, the 4600 Series IP Telephones do not support communication to the PBX through any NAPT device.
QoS
Quality of Service (QoS) is a term covering several initiatives to maximize the quality of the voice heard at both ends of a call that originates, terminates, or both, on an IP-based telephone. These initiatives include various prioritization schemes to offer voice packets a larger or prioritized share of network resources. These schemes include standards such as IEEE’s 802.1D and 802.1Q, the Internet Engineering Task Force’s (IETF’s) “Differentiated Services”, RTP Control Protocol (RTCP) and Resource ReSerVation Protocol (RSVP), and port-based priority schemes such as UDP port selection. Documentation for your LAN equipment will elaborate on the extent your network can support any or all of these initiatives. See Chapter 4, Server Administration for some implications of QoS for the 4600 Series IP Telephones.
As of Release 1.7, both the 4620 and 4630 IP Telephones provide information to the end user about network audio quality that may be of use to the LAN Administrator. For specific information, see QoS with 4620 and 4630 IP Telephones on page 4-22.
SNMP
Simple Network Management Protocol (SNMP) is a family of standards-based protocols and procedures to allow vendor-independent management of data networks. Using a simple set of protocol commands, an SNMP-compliant device will store information in standard format in one or more Management Information Bases (MIBs). In general, devices will support the standards- specific MIB termed MIB-II. In addition, devices may define one or more "custom MIBs" that contain information about the specifics of the device.
Release 1.1 of the 4600 Series IP Telephones is fully compatible with SNMPv2c (a later version of SNMP) and with Structure of Management Information Version 2 (SMIv2), although the telephones will respond correctly to queries from entities that comply with earlier versions of SNMP, such as SNMPv1. "Fully compatible" means that the telephones will respond to queries directed either at the MIB-II or the Custom MIB. The 4600 Series IP Telephone Custom MIB is read-only (values therein cannot be changed externally via network management tools). Similarly, although the 4600 Series IP Telephone’s MIB-II has read/write permissions in accordance with the standard, to improve security any writes to MIB-II are saved but otherwise ignored.
SNMP
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