Q4. When designing a board with a Maxim telecommunication device, is there any restriction on
PCB trace length from the device to the transformer?
A4. Application note 3410, "Guidelines for Laying Out T3 and E3 Network Interfaces," explains how to layout the network
interfaces for Maxim T1/E1 and T3/E3 products. This application note provides layout considerations, trace-widths
calculations, and different scenarios for ease of design. It also describes how to maintain the proper impedances when
laying out a circuit board with a T1/E1 or T3/E3 networking interface.
8. TDM-over-Packet (TDMoP) Questions
Q1. What is the difference between VoIP and TDMoIP?
A1. Both voice-over-IP (VoIP) and TDM-over-IP (TDMoIP) protocols offer a way to transport real-time voice data over IP
networks. However, VoIP and TDMoIP are quite different from each other. VoIP was designed to transport voice data as
packets over IP networks instead of using the traditional public switch telephone network (PSTN), while TDMoIP was
designed to emulate the PSTN over an IP network. Both solutions accomplish the same task, the transmission of voice
data, but are implemented in different ways.
Because the two protocols are implemented differently, each has different strengths and weaknesses. For example, VoIP
uses data compression when transmitting voice data. This includes voice compression as well as silence compression.
TDMoIP does not compress voice data at all. So, if you are bandwidth limited, VoIP is the superior choice for this
application.
Unfortunately, VoIP is a complex protocol that is difficult to integrate with legacy services or connect to legacy PSTN
equipment. Upgrading legacy services to a VoIP solution is possible, but it is often costly and time consuming. This is not
the case with TDMoIP, for which integration with legacy equipment is straightforward. Unlike VoIP, TDMoIP is compatible
with legacy TDM services, protocols, and signaling.
Q2. What is the difference between MII and RMII, and how do they relate to products like the
DS34T108?
A2. Media-independent interface (MII) and reduced media-independent interface (RMII) are the specifications that are
used to communicate between an Ethernet PHY and a media access control (MAC) device. IEEE® 802.3 defines MII as a
complete interface with 16 pins that has both data and control signals. RMII reduces the pin count from 16 to 8. However,
the tradeoffs of using RMII are that the Tx and Rx clock lines are tied together, and the transmission clocks range from
25MHz to 50MHz.
Figure 1 shows the connections between the DS34T108 and a generic Ethernet PHY in MII mode. Note that all 16 pins
are required when operating in MII mode. The transmit and receive paths are in separate clock domains.
Figure 1. The DS34T108 is connected to an Ethernet PHY in MII mode.
(167 paginas)
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