1、 International Telecommunication Union ITU-T G.999.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2009) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Access networks Interface between the link layer and the physical layer for di
2、gital subscriber line (DSL) transceivers Recommendation ITU-T G.999.1 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.
3、200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE
4、TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at h
5、ierarchical bit rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission system
6、s for customer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERIS
7、TICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.999.1 (10/2009) i Recommendation ITU-T G.999.1 Interface between the link la
8、yer and the physical layer for digital subscriber line (DSL) transceivers Summary Recommendation ITU-T G.999.1 defines a point-to-point interface between the LINK layer device such as a network processor and a PHY device supporting multiple DSL lines, such as VDSL2, ADSL2, and SHDSL. Source Recommen
9、dation ITU-T G.999.1 was approved on 9 October 2009 by ITU-T Study Group 15 (2009-2012) under Recommendation ITU-T A.8 procedures. ii Rec. ITU-T G.999.1 (10/2009) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, inf
10、ormation and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a w
11、orldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down i
12、n WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication adm
13、inistration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory prov
14、isions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention
15、to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outs
16、ide of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest
17、 information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.999.1 (10/2009) iii CONTEN
18、TS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations 1 5 Reference model . 2 6 Encapsulation 3 6.1 Fragmentation . 3 6.2 Identification . 5 6.3 Data flow control (DFC) 5 6.4 Ethernet adaptation . 6 6.5 Error detection 7 6.6 Resulting encapsulation format and bit-ordering . 8 7 Configura
19、tion parameters . 9 Annex A Stream identification with multi-line DSL PHY devices 10 Annex B LINK/PHY physical interface . 11 Bibliography. 14 Rec. ITU-T G.999.1 (10/2009) 1 Recommendation ITU-T G.999.1 Interface between the link layer and the physical layer for digital subscriber line (DSL) transce
20、ivers 1 Scope This Recommendation defines an interface between a LINK device and a PHY device. The interface is a single point-to-point interconnection from the LINK layer device to a PHY device, and it is intended for use with all current and developing xDSL Recommendations (e.g., ADSL2, VDSL2, SHD
21、SL, etc.). 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject
22、 to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document wit
23、hin this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.992.3 Recommendation ITU-T G.992.3 (2009), Asymmetric digital subscriber line transceivers 2 (ADSL2). ITU-T G.992.5 Recommendation ITU-T G.992.5 (2009), Asymmetric digital subscriber line (AD
24、SL) transceivers Extended bandwidth ADSL2 (ADSL2plus). IEE 802.3 IEE 802.3-2005, CSMA/CD Access Method and Physical Layer Specifications. (http:/standards.ieee.org/) IEEE 802.3ap IEEE 802.3ap-2007, Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Spec
25、ifications Amendment 4: Ethernet Operation over Electrical Backplanes. (http:/standards.ieee.org/) 3 Definitions No definitions are provided for this Recommendation. 4 Abbreviations This Recommendation uses the following abbreviations: DEST MAC ADD Destination MAC Address DFC Data Flow Control EoF E
26、nd of Frame ETH Ethernet encapsulation function FCS Frame Check Sequence GMII Gigabit Medium Independent Interface IFG Inter-Frame Gap MAC Media Access Control 2 Rec. ITU-T G.999.1 (10/2009) MDI Media Dependent Interface MII Media Independent Interface PCP Priority Code Point PRE Preamble RXC_MFS Ma
27、ximum Fragment data Size supported by near-end receiver SFD Start Frame Delimiter SID Stream Identification SoF Start of Frame SOURCE MAC ADD Source MAC Address TCI Tag Control Identifier TPID Tag Protocol Identifier TX_MFS Maximum Fragment data Size to be used by near-end transmitter TXC_MFS Maximu
28、m Fragment data Size supported by near-end transmitter VLAN Virtual Local Area Network XOFF Transmit Off XON Transmit On 5 Reference model The LINK/PHY interface reference model is shown in Figure 5-1. This reference model shows the following primitives defined in Annex K of ITU-T G.992.3 and Annex
29、K of ITU-T G.992.5. Primitives are labelled n, where n corresponds to an individual stream, with n = 0N1 for a LINK/PHY interface transporting N streams. Stream(n).request: This primitive is used by the transmit PHY port to request one or more data units from the transmit LINK layer function to be t
30、ransported. By the interworking of the request and confirm, the data flow is matched to the PHY port configuration (and underlying functions). Stream(n).confirm: The transmit LINK layer function passes one or more data units to the PHY port to be transported with this primitive. Stream(n).indicate:
31、The transmit PHY port passes one or more data units to the receive LINK layer function that have been transported with this primitive. The data unit is a block of data consisting of an integer number of octets for transport between a PHY port and a link port. The contents of a data unit is vendor di
32、scretionary and outside the scope of this Recommendation. For example, a data unit may contain an Ethernet frame, an Ethernet bonding fragment, one or more ATM cells or an ATM AAL5 PDU. The LINK/PHY interface reference model adds the following blocks: frag: Fragmentation of each data unit, with a ta
33、g control identification (TCI) field added to each fragment, and with each fragment not to exceed the configured maximum fragment length; tag: Identification of fragments through insertion of a data stream or pause identification tag into the TCI field; ETH: Ethernet adaptation by adding fields for
34、compliance with the IEEE 802.3 frame format; the ETH block is configurable to be used or not; Rec. ITU-T G.999.1 (10/2009) 3 FCS: Error detection through addition of frame-check-sequence; PAUSE: Data flow control through a single PAUSE unit containing the data flow control states of all N streams; d
35、ec: Decapsulation to recover data units (confirm and indicate primitives) and data flow control states (request primitives), comprising the reverse operation of the frag, tag, and ETH blocks. Data unit encapsulation is defined as the cascade of the frag, tag, ETH and FCS blocks. Pause init encapsula
36、tion is defined as the cascade of the PAUSE, ETH and FCS blocks. Encapsulation overhead depends on whether or not the ETH block is used. G.999.1(09)_F5-1LINK/PHYreferencepointLINKPORT(n)PHY PORT(n)Stream(n).confirmTag muxFrag(n)Tag(n)n = 0N1ETHOptionalFCSn = 0N1dec(n)Stream(n).confirmTag demuxPAUS E
37、RxPAUS ETxFCS ETHOptionalN1n = 0N1n = 0Stream(n).indicateStream(n).indicateTag(n)dec(n)Frag(n)Stream(n).requestStream(n).requestTag muxTag demuxLINK side PHY sideEach pause unit transmitsstream(n).request for n = 0.N 1Figure 5-1 Reference model for the LINK/PHY interface The LINK device and PHY devi
38、ce shall use a physical point-to-point interconnection. The LINK/PHY interface shall support a data rate of at least 1 Gbit/s for the encapsulated data units. The minimum required bit rate at the LINK/PHY reference point may be higher (e.g., 1.25 Gbit/s if 8B/10B encoding is used). 6 Encapsulation 6
39、.1 Fragmentation The fragmentation block (see Figure 5-1) shall fragment each data unit as shown in Figure 6-1. The fragment format is shown in Figure 6-2. 4 Rec. ITU-T G.999.1 (10/2009) G.999.1(09)_F6-1Fragment dataFragment dataFragment dataFragment dataHeaderHeaderHeaderHeader(SoF=1 and EoF=0)(SoF
40、=0 and EoF=0)(SoF=0 and EoF=0)(SoF=0 and EoF=1)Fragment 1Fragment 2Fragment n-1Fragment nData unitFigure 6-1 Data unit fragmentation LSB MSB 2 Octets TCIN octets FragmentData 000 001 EoF SoF 0 0000000LENGTH2 Octets Figure 6-2 Non-tagged fragment format The fragment header shall consist of the tag co
41、ntrol identifier (TCI) field and the LENGTH field. The capability to insert the LENGTH field is mandatory. When Ethernet encapsulation is enabled, the LENGTH field shall be inserted. When Ethernet encapsulation is disabled, the LENGTH field is configurable to be used or not (see Table 7-1). When the
42、 LENGTH MODE is set to 1, the LENGTH field shall be appended; otherwise, the LENGTH field shall not be appended. In the TCI field, the SoF and EoF bits shall be defined as shown in Table 6-1. The remaining TCI bits shall be as define in Figure 6-2 and partly further defined by the tag function. The
43、LENGTH field shall contain the number of data unit octets in the fragment data field. Table 6-1 Definition of the data unit delimiters SoF EoF Description 0 0 Next fragment of data unit 1 0 First fragment of data unit 0 1 Last fragment of data unit 1 1 Single fragment data unit For each fragment, th
44、e value of the length field shall not exceed the maximum fragment data size (TX_MFS). If the length of a data unit is less than or equal to the TX_MFS value, then that data unit shall be transmitted as a single fragment. If the length of a data unit is higher than the TX_MFS value, then that data un
45、it shall be transmitted in multiple fragments, where fragments may have the same or a different length. The value of TX_MFS shall be configurable and shall not exceed the near-end maximum transmit fragment data size (TXC_MFS), and it shall not exceed the far-end maximum receive fragment data Rec. IT
46、U-T G.999.1 (10/2009) 5 size (RXC_MFS). If TX_MFS is configured as ZERO, then each data unit shall be transmitted as a single fragment. The valid values of TX_MFS, TXC_MFS, and RXC_MFS are all integers in the range from 0 to 2047 (included). NOTE There are no mandatory values defined for the TXC_MFS
47、 and RXC_MFS. 6.2 Identification The tag block (see Figure 5-1) shall tag each data fragments TCI field with the stream identification (SID) value, resulting in the tagged fragment format shown in Figure 6-3. LSB MSB 2 Octets TCIN octets FragmentData SoF EoF1000sid1sid0sid2 sid3 sid4 sid5 sid6 sid7
48、sid8 sid9 LENGTH2 Octets Figure 6-3 Tagged fragment format The valid SID value is any 10-bit unsigned integer. Up to 1024 data streams can be identified. The allocation of a SID value to each data stream is technology dependent, and is defined in Annex A for DSL transceivers. 6.3 Data flow control D
49、ata flow control (DFC) is a mechanism that prevents congestion by ensuring that transmitting devices do not overwhelm receiving devices with data. This is achieved by the receiving device informing in advance the transmitting device when no further data can be received (e.g., when the RX-Buffer-Filling becomes critical), after which the transmitter stops transmission (= Transmission-Off = XOFF = Active-Backpressure) until the receiver indicates
