Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
2000-03-30
2004-06-15
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S395400, C370S471000, C370S474000, C370S535000, C398S043000
Reexamination Certificate
active
06751214
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to improved methods and apparatus for transmitting information via a communication link. More importantly, the present invention relates to improved protocols, methods, and devices for transmitting both ATM and packet data over a transport-layer protocol such as SONET in a manner that facilitates more efficient dynamic allocation of bandwidth and traffic management.
The use of the SONET (Synchronous Optical Network) as a transport mechanism at the transport-layer for both (Asynchronous Transfer Mode) ATM and packet data is well known. As the term is employed herein, data includes any type of information that may be represented digitally, and includes such time-sensitive data such as streaming video or voice, and/or non time-sensitive data such as computer files. Packet technology includes TCP/IP, token ring, etc. One example of packet technology is IP (Internet Protocol) packets transmitted over OSI layer
2
. Another example of packet technology is Ethernet. ATM and SONET technologies are well known and well defined and will not be elaborated further here. Similarly, the various layers of the OSI 7-layer model are also well known and well defined.
Typically speaking, ATM traffic or packet traffic do not mix in the same unchannelized optical fiber, or in the same TDM channel if the optical fiber is channelized. In the former case, one may think of the entire fiber as a single channel, which is employed to transport either ATM traffic or packet traffic. To facilitate discussion,
FIG. 1
is a prior art logical depiction of ATM cells transported within SONET frames in an arrangement commonly known as ATM-over-SONET in an unchannelized optical fiber. As can be seen in
FIG. 1
, a plurality of ATM cells (53 bytes each) may be packed into a single SONET frames (such as in between SONET overhead blocks
102
and
104
). Although only four full ATM cells
106
,
108
,
110
, and
114
are shown, one skilled in the art will appreciate that a typical SONET payload may have the capacity to carry many cells. If there is no room left in a SONET frame to put an entire cell therein, the SONET circuitry may break up a cell and transport a partial cell in that SONET frame (as shown with partial cell
112
a
). The remaining portion of the cell that was broken up is then transported in the next SONET frame (as shown with partial cell
112
b
). Furthermore, if there are no ATM cells to transport in a SONET frame, idle cells are typically inserted to fill the frame. Note that since SONET operates at a lower level, as far as the ATM layer is concerned, the fact that an ATM cell was broken up and reassembled by the SONET layer is completely transparent.
FIG. 2
is a prior art logical depiction of packets transported within SONET frames in an arrangement commonly known as packet-over-SONET in an unchannelized optical fiber. Similar to the situation of
FIG. 1
, a plurality of packets (which may be variable in length) may be packed into a single SONET frame (such as in between SONET overhead blocks
202
and
204
. However, since the packets may have variable lengths, flags are employed between packets to help delineate where the packets are in the data stream. With reference to
FIG. 2
, these flags are shown as flags
206
,
208
,
210
,
212
, and
214
. Flag
214
is a flag inserted to fill in the frame if there is no packet data to fill. Again, if the frame is full, a packet may be broken up to be transported in different frames. This is shown with packet
216
, which is shown broken up into partial packets
216
a
and
216
b
and transported in two different frames. Again, since SONET operates at a lower level, as far as the packet layer is concerned, the fact that a packet was broken up and reassembled by the SONET layer is completely transparent.
In either case, the entire unchannelized optical fiber is used to transport only ATM traffic (
FIG. 1
) or packet traffic (FIG.
2
). To allow ATM traffic and packet traffic to share a single optical fiber, the optical fiber may be channelized into different time division multiplex (TDM) channels. Within each channel, the traffic is again either entirely ATM or entirely packet. This situation is logically depicted in FIG.
3
.
In
FIG. 3
, an STS-3 SONET transport arrangement is shown, wherein the full bandwidth of the optical fiber is channelized into three different STS-1 channels or time slots: slots
1
,
2
, and
3
. ATM cells are shown packed into slot
1
, while packets are shown packed into slot
3
to illustrate that ATM and packet traffic may occupy different channels to share the optical fiber. Again, both ATM cells and packets may be broken up for transport in parts if the bandwidth available in a slot is already full.
Prior art
FIG. 4
shows, in a high level depiction, how ATM and packet data from various sources may be multiplexed into different separate channels in the same optical fiber. With reference to
FIG. 4
, ATM data is destined for slot
1
, while packet data is destined for slots
2
and
3
. A multiplexer
402
takes data from the ATM stream
404
, the packet stream
406
, and the packet stream
408
, and multiplexes them using a time-division multiplexing scheme onto time slots
1
,
2
and
3
respectively. At the other end, a demultiplexer
410
demultiplexes the data into ATM stream
412
, packet stream
414
, and packet stream
416
respectively.
While the TDM multiplexing scheme of
FIGS. 3 and 4
allow ATM traffic and packet traffic to share different separate channels in the same optical fiber, there are disadvantages. By way of example, within each STS-1 channel (which is 51.84 Mbps), the traffic within each channel must be either all ATM cells or all packets. Because of this limitation, the channels must be pre-allocated in advance for each type of traffic. If given type of high-priority traffic (e.g., streaming video over ATM) is assigned to a given channel or time slot, and the bandwidth requirement associated that traffic type increases beyond the capacity of the channel, transmission delay can occur. Even though the network operator can assign one or more additional channels to handle the increase in this ATM traffic, there is a nontrivial time delay associated with the detecting the congestion condition (and possibly concurrently coordinate to unallocate channels previously allocated to other non-priority traffic if there are no free channels left), coordinating with the receiving end to allocate the additional channels, and changing network parameters to allocate the additional channels to handle the increased bandwidth requirement of the high-priority traffic. As can be appreciated from the foregoing, the complex coordination, unallocation of channels and reallocation of them to the priority traffic involves a nontrivial amount of operational complexity and/or time delay. For some types of data (e.g., time-critical data), this delay is unacceptable. For this reason, many network operators tend to reserve an unduly large amount of bandwidth overcapacity to handle potential traffic increases when dealing with time-critical data, which leads to inefficient use of network bandwidth as the reserved bandwidth tends to stay unused most of the time. Furthermore, each traffic type can employ bandwidth only in a discrete, channel-size chunk. If additional bandwidth is allocated to a given traffic type, an entire slot (51.84 Mbits in case of STS-1) is added even if the increase in traffic only requires a portion of the capacity offered by an entire slot.
In view of the foregoing, there are desired improved techniques for allowing ATM traffic and packet traffic to share the bandwidth of a channel in a manner that facilitates dynamic allocation of bandwidth between traffic types and more efficient traffic management.
SUMMARY OF THE INVENTION
The invention relates to techniques for transmitting both ATM cells and packets over a single channel in an optical fiber. The technique includes providing a transport-layer device which is configured to transmit packet data
Nguyen Joseph A.
Parruck Bidyut
Ramakrishnan Chulanur
Azanda Network Devices, Inc.
Hsu Alpus H.
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