In the establishment of cell packing connection, you must configure the MNCP size and MCPT timeout value. This information will be recorded into the cell input and output hardware packaging field programmable gate array (FPGA).
Know something about the cell packing technology knowledge is still very useful, so I did a little research on Cisco router on the cell pack, take out here and share with you, I hope useful for everyone. Cell packs (also known as cell series) is a multiple cell relay asynchronous transfer mode (ATM) cell encapsulation mechanism with a IP/MPLS packet. It allows carriers to overcome the problems of bandwidth inefficiency inherent in cell relay transmission.
Cell relay bandwidth efficiency
Cell relay can lead to packet switching network (PSN) bandwidth efficiency is low, mainly due to the following reasons. Cell relay needs to exchange all cell relay packet, which will reduce the packet forwarding rate (PPS). For example, if you need to transfer six ATM cells, network core devices to exchange six packet forwarding, cost six groupings of resources (such as bandwidth). However, if the use of cell packing technique, six ATM cell packaging technology to the same packet, network core devices only need to exchange a packet, and only requires forwarding a packet resource. Therefore, packet forwarding telecom operators can use cell packing technique saves the network core resources.
Cell relay will cause the lower bandwidth utilization. For example, suppose a telecom operators hope to contain packet-over-SONET (POS) interface multiprotocol label switching (MPLS) core transmission of a cell relay ATM cell stream. In the network operators on the edge, ATM cells (52 bytes of header checksum [HEC] does not include a byte) with 4 byte control word, 4 bytes, 4 bytes of virtual circuit label tunnel label and 4 bytes of Cisco high-level data link control (HDLC) layer second header. The total overhead of ATM cells for each 52 bytes to 16 bytes. Therefore, POS fiber on the final packet size of 68 bytes (ATM cell 16 bytes 52 bytes of overhead). In this case, cell relay bandwidth waste rate is about 23.52% (16/68).
In this case, if the cell packing technique, and assume that you will be the six cell package to the same MPLS packet, then the total cost still is 16 bytes, but the payload is 312 bytes, so the bandwidth efficiency is increased to about 95.12%. Therefore, telecom operators can use credit package technology will bandwidth utilization rate increased by 18.65% (from 76.47% to 95.12%). Cisco 12000, 7500 and 7200 series routers support cell packaging technology, but this paper introduced it in 4 port IP service engine (ISE) implementation on the ATM-over-SONET OC-12/STM-4 and 4 ISE ATM-over-SONET OC-3/STM-1 port line.
The bandwidth savings
Cell packaging technology mainly contains two parameters: the minimum cell pack a number (MNCP) size (also known as cell packing size) and maximum cell packing timer (MCPT) timeout value. In the establishment of cell packing connection, you must configure the MNCP size and MCPT timeout value. This information will be recorded into the cell input and output hardware packaging field programmable gate array (FPGA). These parameters are as follows:
◆ size between MNCP ranged from 2 to 28 ATM cells
◆ MCPT timeout value between 2 to 4095 microseconds (US) between (can be configured by IOS range)
◆ MCPT hardware programming is in the range of 50uS to 25ms (MCPT timeout stepping accuracy of 50uS)
The maximum MNCP value of 28 ATM cells, because MTU of Ethernet is 1500 bytes. If a MPLS packet ATM cell number exceeds 28, then it will be discarded in the Ethernet interface. Although the Cisco IOS command line interface (CLI) allows you to set the MCPT value to a value between 2-4095us, hardware programmable range is 50uS to 25ms, step unit is 50us.
During the label propagation and binding, PE1 and PE2 by setting the LDP interface parameter field, the exchange value of MNCP. When the PE1 receives a PE2 MNCP, it will be stored in the PE1 predefined VC/VP/ port database, and vice versa. Any changes to any one vendor on the edge of MNCP will lead to the label was withdrawn and virtual circuit to set up at both ends, and the old value will be replaced by the new value.
If the PE1 does not support cell packing (MNCP = 1), PE2 should be a cell only transmitted in each MPLS packet, but can receive the package cell -- if PE2 started the cell package technology. MCPT has an important role in the local scope, it usually depends on the ATM connection speeds of OC-3 or OC-12. If the MCPT timer timeout, packed cell will immediately by a MPLS packet sent -- even pack has not been completed; the number of cells in a group did not reach MNCP. A cell packing technology of packet in the MPLS network life cycle.
In the input provider edge, the ATM cell to ATM port, reconstructed by the segmentation and (SAR) chip for processing. SAR chip will each ATM cell is divided into AAL0, AAL5 or OAM cells. For the AAL0 cell effectively, the SAR chip will remove a byte from the ATM cell header in the HEC, will send the remaining 52 bytes of ATM cell to FPGA cell pack. Cell package FPGA is based on MNCP and MCPT configuration parameters of packaging cell. Enter the ATM cell in the MCPT before the time-out period, queuing constitute a cell pack, until it reaches a predetermined cell package size. At this time, the FPGA generates the control word, the T code is 0, indicating the AAL0 ATM cell types, packet generates a sequence number for each cell. The remaining fields are set to 0.
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