V7122 Gateway User Guide 275No-Op PacketsThe gateway's No-Op packet support can be used to verify Real-Time Transport Protocol(RTP) and T.38 connectivity, and to keep NAT bindings and Firewall pinholes open. No-Oppackets are available for sending in RTP and T.38 formats.Users can control the activation of No-Op packets by using the ini file parameterNoOperationSendingMode. If No-Op packet transmission is activated, users can control thetime interval in which No-Op packets are sent in the case of silence (that is, no RTP or T.38traffic). This is performed using the NoOpInterval ini parameter.Receipt of No-Op is always supported. RTP No-Op:The RTP No-Op support complies with IETF’s draft-wing-avt-rtp-noop-03.txt (titled ‘A No-Op Payload Format for RTP’). This IETF document defines a No-Op payload format forRTP.The draft defines the RTP payload type as dynamic. Users can control the payload typewith which the No-Op packets are sent. This is performed using theRTPNoOpPayloadType ini parameter. 3Com’s default payload type is 120. T.38 No-Op:T.38 No-Op packets are sent only while a T.38 session is activated. Sent packets are aduplication of the previously sent frame (including duplication of the sequence number).Point-to-Point Protocol over Ethernet (PPPoE)PPPoE is a method of sending the Point-to-Point Protocol over Ethernet network.Point-to-Point Protocol (PPP) OverviewPoint-to-Point Protocol (PPP) provides a method of transmitting data over serial point-to-point links. The protocol defines establishing, configuring and testing the data link connectionand the network protocol.The PPP standard describes a state machine used to establish a valid connection betweentwo hosts over a serial connection. There are three major stages described, helping toestablish a network layer (such as an IP) connection over the point-to-point link: LCP (LinkConfiguration Protocol) Authentication and NCP (Network Control Protocol). Once thenetwork protocol is configured, the two hosts can communicate, sending network layerprotocol (such as IP) over the PPP connection (a small PPP header is added at thebeginning of each packet).At the initial phase, the hosts use LCP (link configuration protocol) to negotiate for linkcharacteristic and parameters. Packets sent in this phase have two octets of ‘PPP header’followed by LCP message with variable length. Various parameters and options are
