User's Manual Part 2

Tech-X Flex User Guide - Firmware v06.50 Tech-X Flex
®
(NG2)
7-36
Intro
Overview
Wi-Fi
Ethernet
System
IP/Video
MoCA
RF
Specs
MoCA data link layer
MoCA defines a MAC (media access control) protocol that determines how nodes may access the
shared media to transmit/receive Ethernet frames. It specifies two general types of MAC layer frames:
• Control frames - Frames that contain MoCA network management messaging
• Data frames - Frames that contain the end-user application data (internet, IPTV, etc.)
The two primary types of control frames are bandwidth requests and media access plans (MAPs).
Because the meshed nature of the logical network allows only one node to transmit at any given time, the
network coordinator (NC) must coordinate all transmission by all nodes. When a node wants to transmit,
it sends a bandwidth request to the NC. In turn, the NC regularly broadcasts MAPs which are effectively
precise schedules about which node can transmit and when. Not only does a MAP tell a node when it
should transmit, it also allows the target node to know when to expect the transmission.
Another type of media access control is the admission request and associated negotiations. When a new
device is connected to the network, it must request admission to the network from the NC and then
complete a set of qualifying steps. It finds the appropriate channel and the NC location by a mechanism
known as beacons, which the NC also regularly broadcasts. Because admission control is only initiated
by a new device, no admission control frames would be expected on a stable network.
7.7.5 Common coaxial cable problems that affect MoCA
The following cable-related issues can affect MoCA performance:
• A fault in the cable, such as a short circuit or other condition which may affect the electrical continuity.
Because a MoCA network is physically interconnected, a critical short-circuit can prevent the
transport of all MoCA signaling to all devices, including the WAN and the LAN (see Example physical
MoCA network on page 7-32).
• A bad connection, perhaps caused by corrosion, a loose connector, or poor connector crimping.
• Attenuation due to the excessive use of cable splitters or the general splitter configuration. In
particular, the presence of “splitter jumps,” where two nodes communicate through the outputs of one
or more splitters, can have an impact on channel characteristics. For example:
Figure 7-23 Splitter jump, through a single splitter
Splitter jump
In
Out
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