Data Sheet
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T1/E1 line diagnostic loopbacks (local line, local payload, and network payload)
Feature Details
Protocol-Independent Data Transport
These SPAs provide completely bit-transparent, bidirectional, point-to-point data transport. Every
bit presented to an ingress port is transported unchanged to the corresponding egress port by
encapsulating the data bits into an IP packet for transport across an IP network. The data ports do
not care about the structure or content of the data stream. Consequently, these SPAs are ideally
suited to transport data streams that are not suited to be carried using other platform interfaces.
Such data streams might include:
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Leased-line emulation services
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Encrypted data
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Data protocols that cannot easily be migrated to native IP, ATM, Frame Relay, HDLC, and
so on
Data Integrity
Because these SPAs do not consider the content of any circuit emulation data stream, it is
important to engineer the transport network in such a way as to minimize the risk of losing any
data packets. To help ensure that a data stream is delivered, without gaps, to the destination CPE,
data packets are held in a dejitter buffer at the destination port to eliminate any delay variation
(that is, jitter) experienced by successive packets traveling through the network. The dejitter buffer
is user configurable up to 320 milliseconds (±160 milliseconds).
Flexibility in Delay vs. Overhead
These SPAs support a wide variety of payload sizes from 1 byte (for very low-speed data streams)
to 1312 bytes. This provides the user the ability to control the overall efficiency as well as the end-
to-end delay of the system by controlling the packetizing delay.
Clocking Flexibility
For circuit emulation services, In order to achieve bit-transparent circuit emulation without bit
errors, it is imperative that both endpoints of the circuit use the same bit clock frequency. The
network should be synchronized end to end for proper operation. Three options are available for
achieving proper clocking and synchronization of network when deploying circuit emulation
services over packet network. They are:
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Synchronous mode: In this option, a GPS or BITS clock source is available to be fed into
the edge router to clock the packets for transmission. The clock is received from a line
interface and is used by the router to transmit the TDM frames, received from the packet
network to the final destination.
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Differential clocking mode: Often a GPS or a BITS clock source may not be available for
service providers at every possible site, such as a remote cell site. However, they may have
a common clock source that is fed into all the elements of the network. In this scenario, the
system will use the common clock source as well as observe the timestamps received from
the CEoP PWE packets received from the packet network and calculate the differential to
recover an accurate clock. This recovered clock reference is then used to transmit the TDM
frames.
(20 pages)
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