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Synchronous High Speed Serial Interface Clocking

IP.com Disclosure Number: IPCOM000115232D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 126K

Publishing Venue

IBM

Related People

Abdelnour, G: AUTHOR [+5]

Abstract

The High Speed Serial Interface (HSSI) standard was developed to allow users to attach to high speed communication lines (up to 52 Mbps) without the need to develop the analog circuits required to conform to the CCITT standards for high speed data transmission. This standard was first developed for data transmission only. Non-synchronous data transmission occurs without problems because of the pseudo-random arrival rate of the data within the network.

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Synchronous High Speed Serial Interface Clocking

      The High Speed Serial Interface (HSSI) standard was developed
to allow users to attach to high speed communication lines (up to 52
Mbps) without the need to develop the analog circuits required to
conform to the CCITT standards for high speed data transmission.
This standard was first developed for data transmission only.
Non-synchronous data transmission occurs without problems because of
the pseudo-random arrival rate of the data within the network.

      New voice and video applications require the servicing of
information in a continuous bit stream.  When continuous bit stream
transmission is required, non-synchronous transmission methods are
not sufficient to guarantee certain grades of service to the
customer.  In continuous bit stream transmission, the number of bits
into the network must be equal to the number of bits out of the
network or a frame slip occurs causing a loss of one frame's worth of
information (192 bits).  With stratum 3 frequency tolerances of 20
parts per million at both the transmit and receiving ends of a
network, this amounts to four frame slips every second which is
unacceptable.  This technical disclosure describes a method for
synchronizing the HSSI interface clock to the highly-accurate system
clock provided by a system clock card for a bandwidth manager and
guarantees that there will be no clock slippage for a minimum of 2
days.  Back-up methods in case of system clock failure are also
described.

      A bandwidth manager receives user input on the port side,
performs routing and bandwidth allocation, and then transmits the
information to the network through multiple trunks.  The data is then
routed through the network to the trunk of an end-user bandwidth
manager where it is sent to the end user.  In network operation data
received from a user is transmitted to another destination.  Data
traffic by nature is pseudo-random and bursty in nature.  Therefore,
the current design methods incorporate buffers to account for this
bursty nature and thereby ensure uninterrupted data delivery.  The
bit-by-bit clocking rate accuracy is not important since variations
in clock frequencies are minor in comparison to the bursty data
traffic.

      However, when attaching bandwidth managing type equipment,
transmission of data, voice and video are transmitted simultaneously
and therefore, must be managed more closely.  Specifically, the
information into the bandwidth manager must be delivered to the end
user without the loss or addition of information (Fig. 1).  With the
current tolerance of networks, frame slips and loss of data occur too
frequently to provide an acceptable grade of service to the customer.
To avoid this problem the bandwidth manager extracts a highly
accurate clock from the network and synchronizes all its clocks to
it.  Since the receiving bandwidth manager and the transmitting
bandwidth manager synchronize clocks to th...