KR20000034487A - Method for transmitting upstream packet of a cable modem - Google Patents

Abstract

PURPOSE: A method for transmitting upstream packet of a cable modem is provided so that the efficiency of use of the channel band become increased by preventing the variable delay occurring when transmitting the upstream packet since if the upstream packet exists, the upstream packet stored to the memory of MPU is read in advance and stored to a memory buffer. CONSTITUTION: A method for transmitting upstream packet of a cable modem includes several steps. If an upstream packet exists, a step is to require the allocation of band of transmission of the upstream packet to CMTS(Cable Modem Termination System) (S303). Before receiving a MAP message from the CMTS, the upstream packet stored in a memory is read previously and stored to the separate local memory buffer (S304). A step is that when a MAP message is received from the CMTS, the timing of transmission of the upstream packet is founded from the MAP message, and the upstream packet stored to the local memory buffer is transmitted by correctly making the timing match to the corresponding time.

Description

A method for transmitting an upstream packet in a cable modem

The present invention relates to an uplink packet transmission method of a cable modem, and more particularly, to an uplink packet transmission method of a cable modem in which an uplink packet is stored in a local memory buffer and transmitted at precisely timed timing (opportunity).

In general, the cable modem network is a network system that is attracting attention together with ISDN, multi-digital subscriber line (xDSL), etc. in the field of remote access, and is connected to the Internet and intranet to subscribers at a high speed of Mbps. It provides various services such as telecommuting, video conferencing, and web search.

The concept of cable modem networks, which have a wide user base in the United States, is to bring cable TV (CATV) networks into the data communication field. In terms of using coaxial cables, they are similar to each other. A cable modem network connects a coaxial cable to a personal computer (PC) via a cable modem, while connecting the TV to the set-top box after connecting the box. At this time, there may be one PC or multiple PCs connected to the cable modem.

Cable modems are divided into workgroup, multiuser, and personal. Workgroup cable modems are designed for small groups with 4 or 8 ports for connecting PCs, enabling them to build small LANs, and multi-user cable modems for libraries and schools. It is used in relatively large places such as factories and factories.

1 is a schematic configuration diagram of a general cable modem network, in which a plurality of cable modems 11 to 14 (CM: Cable Modem) are connected to a cable network 20, and each cable modem 11 to 14 is connected to a subscriber. A personal computer (PC), which is a customer premises equipment (CPE), is connected, and a cable modem terminal system (CMTS) 30 is connected between the cable network 20 and the backbone network 40. . Here, the subscriber receives a service such as the Internet from the backbone network 40.

The cable modems 11 to 14 (CM) buffer and memory packets of an upstream channel input from a PC and a downstream channel packets input from a cable modem terminal system 30 (CMTS). In the state stored in the (not shown in the figure) is properly processed so that the subscriber can receive various services from the backbone network 40 connected to the cable modem terminal system (30, CMTS).

The cable modem terminal system 30 (CMTS) is located at the head end to provide an uplink channel and a downlink channel. The cable modem terminal system 30 transmits broadband data at a rate of 500 Kbps to 30 Mbps through a downlink channel, and each cable modem 11 to 14 CM transmits 96 Kbps to 10 Mbps over an uplink channel. Receive narrowband query data transmitted by dot method.

The cable modems 11 to 14 (CM) connected to one cable line in the cable network 20 are connected to an uplink channel in a time division multiple access (TDMA) manner, wherein each cable modem The cable modem terminal system 30 (CMTS) is solely responsible for controlling and managing the uplink channel connection between the 11 to 14 CM. That is, the cable modem terminal system 30 (CMTS) designates a time period for transmitting an uplink packet to each cable modem (11-14, CM) so that the cable modems (11-14, CM) simultaneously send packets. Do not transmit.

On the other hand, the cable modem (11 ~ 14, CM) and the cable modem terminal system (30, CMTS) using the medium (MA) frame that is the basic transmission unit in the upstream (upstream) and downstream (downstream) and It is equipped with a MAC chip (not shown in the figure) that processes the MAC frame by sending and receiving data.

The MAC chip uses an MPU (Direct Memory Access) through a direct memory access (DMA) at a time point designated by the cable modem terminal system 30 (CMTS) when there is a data packet (uplink packet) to be transmitted to the cable modem terminal system 30 (CMTS). The uplink packet stored in the memory of the MicroProcessor Unit (not shown) is transmitted.

However, in the conventional DMA process of the MAC chip, since a variable latency occurs depending on whether the MPU bus is used, each cable modem frequently fails to transmit an uplink packet at an accurate timing. If the cable modem terminal system does not transmit the packet exactly at the specified time, the cable modem terminal system may collide with the packets transmitted from the other cable modem and retransmit the packet later. there was.

The present invention has been made to solve the above problems, and when there is a packet (uplink packet) to be transmitted through an uplink channel, the uplink packet stored in the memory of the MPU is moved to a local memory buffer and then the cable modem terminal system. It is an object of the present invention to provide a cable modem uplink packet transmission method in which a variable delay that may occur due to a DMA process is prevented in advance by transmitting the signal at precisely timed timing (opportunity).

In order to achieve the above object, an uplink packet transmission method of a cable modem according to the present invention is a method of transmitting an uplink packet to a cable modem terminal system by a cable modem, and if an uplink packet exists, upstream to the cable modem terminal system. Requesting transmission band allocation, reading uplink packets stored in memory and storing them in a separate local memory buffer before receiving a MAP message from the cable modem terminal system, and receiving a MAP message from the cable modem terminal system. The method may further include determining an accurate transmission timing of the uplink packet from the MAP message and transmitting the uplink packet stored in the local memory buffer at a precise timing at the corresponding time.

1 is a schematic diagram of a typical cable modem network;

2 is a schematic diagram of a cable modem to which the present invention is applied;

3 is a flowchart illustrating an uplink packet transmission procedure of the MAC chip illustrated in FIG. 2.

<Description of the symbols for the main parts of the drawings>

140: MAC chip (Medium Access Control chip) 141: local memory buffer

160: Microprocessor Unit (MPU) 170: Dynamic RAM (DRAM)

200: MPU bus

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The cable modem to which the present invention is applied uses the Internet Protocol (IP) and has a hierarchical structure as shown in Table 1 below for transparent transmission of IP messages.

Hierarchy Tier Network layer - Data link layer Logical Link Control (LLC) Sublayer Link Security Sublayer Medium access control (MAC) sublayer Physical layer Transmission Convergence (TC) Sublayer Physical Media Dependent (PMD) Sublayer

That is, the cable modem has a vertical hierarchical structure of a network layer, a data link layer, and a physical layer. The data link layer is divided into a logical link control (LLC) sublayer, a link-security sublayer, and a medium access control (MAC) sublayer, and the physical layer is transmitted. It is divided into a convergence sublayer and a physical medium dependent (PMD) sublayer. The network layer (IP layer) transmits IP traffic.

The media access control (MAC) sublayer of the data link layer supports a protocol data unit (PDU) of variable length. In the MAC protocol, bandwidth allocation is controlled by a cable modem terminal system (CMTS), the upstream is divided into mini slots at predetermined time intervals, and a variable length packet is supported to increase bandwidth utilization efficiency.

The transport convergence (TC) layer of the physical layer is present only in the downstream to provide additional services such as digital video, and the physical media dependent (PMD) sublayer is a modulation scheme of 64QAM and 256QAM in the downstream. It supports functions such as error correction codes of Solomon and Trellis, and supports upstream QPSK and 16QAM modulation schemes, TDMA, fixed length frames and variable length PDUs.

On the other hand, the MAC frame exchanged between the cable modem and the cable modem terminal system (CMTS) is composed of a MAC header defining the contents of the MAC frame, and a data PDU whose length and presence is determined according to the MAC header. The MAC frame is transmitted with a physical medium dependent (PMD) sublayer over header in front of the MAC header in the upstream and an MPEG transport header in the downstream.

Among the MAC headers, the MAC management header is used to transmit a management message of the MAC frame. The MAC management message transmitted by the cable modem terminal system (CMTS) to the cable modem through the downlink channel is called an 'assigned MAP'. That is, the cable modem terminal system (CMTS) defines a band of an uplink channel for the cable modem to transmit an uplink packet by transmitting an allocated MAP to the cable modem.

The MAP message includes a fixed length header and a variable length IE (Information Elements). The IE is classified into a 14-bit SID (Service IDentifier), a 4-bit Interval Usage Code (IUC), and a starting offset of 14 bits.

IE designation IUC SID offset Request One any starting offset of REQ region REQ / Data 2 multicast starting offset of IMMEDIATE Data region Initial Maintenance 3 broadcast / multicast starting offset of MAINT region (used in initial Ranging) Station maintenance 4 unicast starting offset of MAINT region (used in Periodic Ranging) Short maintenance 5 unicast starting offset of Data Grant assignment; if inferred length = 0, then it is a Data Grant Pending Long datagrant 6 unicast starting offset of Data Grant assignment; if inferred length = 0, then it is a Data Grant Pending Null IE 7 zero ending offset of the previous grant. Used to bound the length of the last actual interval allocation Data ack 8 unicast CMTS sets to 0 Reserved 9-14 any reserved Expension 15 expanded IUC # of additional 32bit words in this IE

In Table 2, Request IE provides an upstream interval when requesting a band for upstream data transmission, and Request / Data IE provides an upstream interval when requesting a band or short data packet to be transmitted. The Initial Maintenance IE provides an interval when new stations connect to the network, and the Station Maintenance IE provides an interval when the stations need to maintain a fixed network. Data Grant IE provides an opportunity for cable modems to transmit one or more upstream PDUs. Short Data Grant IE is used when the bandwidth is less than or equal to the maximum burst size specified in the Upstream Channel Descriptor (UCD). Long Data Grant IE is used for more than the maximum minislot of short data defined in UCD. The null IE terminates the actual allocation in the IE list, and the Data Acknowledge IE recognizes that the data PDU has been sent.

2 is a schematic diagram of a cable modem to which the present invention is applied. The cable modem includes a tuner 110, a modulator 120, a demodulator 130, a MAC chip 140, and a local memory buffer ( 141, encryption / decryptor 150, MPU 160, DRAM (Dynamic RAM, 170), flash memory (180), Ethernet MAC layer processing unit 190, Ethernet physical layer processing unit 191 and a transformer 192 are provided. The MAC chip 140, the MPU 160, the DRAM 170, the flash memory 180, and the Ethernet MAC layer processor 190 are connected to the MPU bus 200, respectively.

The tuner 110 receives an RF signal (downlink packet) through an F-connector and outputs the demodulated signal to the demodulator 130. The demodulator 130 demodulates the received RF signal (16QAM modulated signal) to the MAC chip ( The MAC chip 140 filters the received downlink packet (MAC frame) and stores the received downlink packet (MAC frame) in the DRAM 170 through the MPU bus 200.

The packet stored in the DRAM 170 is read by the MPU 160 to perform processing such as packet filtering, address verification, bridging, and the like, and then stored in the DRAM 170 and then MAC. The chip 140 reads the packet stored in the DRAM 170 to determine whether to send the packet. At this time, if the packet is a packet to be transmitted to a subscriber facility (not shown), the MPU 160 sends the packet. The header is attached to the DRAM 170 to be stored in the DRAM 170, and then the Ethernet MAC layer processor 190 reads the packet stored in the DRAM 170 through the MPU bus 200. Here, the downlink packet read by the MAC layer processing unit 190 is then transmitted to the subscriber equipment through the Ethernet physical layer processing unit 191, transformer 192, RJ-45 connector.

If there is a data packet (uplink packet) to be transmitted to the cable modem terminal system (CMTS), the MPU 160 filters the packet and stores the packet in the DRAM 170 through the MPU bus 200 and then the MAC chip 140. Signal to the presence of an uplink packet. When the MAC chip 140 is notified of the existence of an uplink packet from the MPU 160, the MAC chip 140 reads an uplink packet stored in the DRAM 170 in advance and stores it in the local memory buffer 141. Then, the cable modem terminal system (CMTS) The timing is precisely set at this specified time (opportunity), and the uplink packet stored in the local memory buffer 141 is read, attached to a header, and transmitted to the modulator 120.

The modulator 120 outputs the 16QAM modulated uplink packet received from the MAC chip 140 to the tuner 110, and the tuner 110 outputs the 16QAM modulated uplink packet through the F-connector. CMTS).

The cipher / decoder 150 encrypts the content of data carried in the uplink packet transmitted so that the other cable modem cannot know.

The cable modem configured as described above will be described in detail with reference to the flowchart shown in FIG. 3 for transmitting an uplink packet according to an embodiment of the present invention.

3 is a flowchart illustrating an uplink packet transmission procedure of the MAC chip illustrated in FIG. 2.

First, when the MAC chip 140 is notified of the existence of an uplink packet from the MPU 160 (S301), it determines whether the corresponding packet is a guaranteed packet (S302).

As a result of the determination in step S302, if the current packet to be transmitted through the uplink channel is a packet that requires guarantee, the MAC chip 140 requests upstream transmission band allocation to the cable modem terminal system (CMTS) (S303).

After the step S303, the MAC chip 140 reads an uplink packet stored in the DRAM 170 and stores it in the local memory buffer 141 before receiving the MAP message from the cable modem terminal system (CMTS) (S304). .

After the step S304, when the MAC chip 140 receives the MAP message from the cable modem terminal system (CMTS) (S305), the MAC chip 140 finds the exact transmission timing of the uplink packet from the received MAP message and accurately localizes the timing at the reserved time. After reading the uplink packet stored in the memory buffer 141 and attaching the header, the packet is transmitted to the cable modem terminal system (CMTS) through the modulator 120, the tuner 110, and the F-connector (S306). In this case, if the uplink packet is stored in the local memory buffer 141 in advance, a variable delay caused when the uplink packet is transmitted due to the conventional DMA process can be prevented, so that the time designated by the cable modem terminal system (CMTS), that is, the reserved time The uplink packet can be transmitted at precisely timing.

After the step S306, the MAC chip 140 determines whether an ACK message is received from the cable modem terminal system (CMTS) within a predetermined time (S307). Here, it is determined whether the ACK message is received because the uplink packet is a packet requiring guarantee.

If the ACK message is received within a predetermined time as a result of the determination in step S307, the MAC chip 140 recognizes that the uplink packet transmitted in step S306 is correctly transmitted to the cable modem terminal system (CMTS), and then moves up from the local memory buffer 141. If the packet is deleted (S308) and no ACK message is received within a predetermined time, the process branches to step S303 to retransmit the uplink packet stored in the local memory buffer 141 to the cable modem terminal system (CMTS).

Meanwhile, as a result of the determination in step S302, when the packet (uplink packet) to be transmitted through the uplink channel is not a packet that requires guarantee, the MAC chip 140 reads the uplink packet stored in the DRAM 170 and then stores the local memory. The buffer 141 is stored in advance (S309).

After the step S309, the MAC chip 140 reads an uplink packet stored in the local memory buffer 141 at a contention time interval not allocated to a specific cable modem in the upstream transmission band and attaches a header to the modulator 120. And transmits to the cable modem terminal system (CMTS) through the tuner 110 (S310). In this case, if the uplink packet is stored in the local memory buffer 141 in advance, the uplink packet can be transmitted at a more accurate timing even in the contention time.

After step S310, the MAC chip 140 branches to step S308 to delete the uplink packet from the local memory buffer 141. Since the cable modem terminal system (CMTS) does not transmit a separate ACK message to the cable modem side for the uplink packet transmitted in the contention time of the upstream transmission band, the MAC chip 140 immediately transmits the uplink packet to the local memory buffer ( In step 141, the uplink packet is deleted.

As described above, when the uplink packet exists, the uplink packet stored in the memory of the MPU is read in advance and stored in the local memory buffer of the MAC chip, thereby preventing a variable delay occurring during uplink packet transmission due to the conventional DMA process. That is, the cable modem terminal system can transmit an uplink packet precisely at a specified time (opportunity), thereby reducing the number of collisions with packets transmitted by other cable modems, thereby reducing the bandwidth of the uplink channel. There is an effect that can increase the use efficiency.

Claims (1)

In the method for the cable modem to transmit an uplink packet to the cable modem terminal system, Requesting upstream transmission band allocation to the cable modem terminal system if an uplink packet exists; Reading upstream packets stored in a memory and storing them in a separate local memory buffer before receiving a MAP message from the cable modem terminal system; Receiving the MAP message from the cable modem terminal system, determining the exact transmission timing of the uplink packet from the MAP message, and transmitting the uplink packet stored in the local memory buffer at a precise timing at the corresponding time. Uplink packet transmission method of cable modem.