1、 International Telecommunication Union ITU-T G.998.2TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 2(12/2007) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Access networks Ethernet-based multi-pair bonding Amendment 2 Recom
2、mendation ITU-T G.998.2 (2005) Amendment 2 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.200G.299 INDIVIDUAL CHARACT
3、ERISTICS 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 TELEPHONY G.450G.499 TRANSM
4、ISSION 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 hierarchical bit rates based
5、 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 systems for customer access to IS
6、DN 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.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT
7、 GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.998.2 (2005)/Amd.2 (12/2007) i Recommendation ITU-T G.998.2 Ethernet-based multi-pair bonding Amendment 2 Summary
8、Amendment 2 to Recommendation ITU-T G.998.2 includes new functionality for discovery/aggregation and pair management at the bonding layer. Source Amendment 2 to Recommendation ITU-T G.998.2 (2005) was approved on 7 December 2007 by ITU-T Study Group 15 (2005-2008) under Recommendation ITU-T A.8 proc
9、edure. ii Rec. ITU-T G.998.2 (2005)/Amd.2 (12/2007) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a p
10、ermanent 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 worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, esta
11、blishes 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 in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary st
12、andards 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 administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the R
13、ecommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents
14、 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 to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed
15、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 outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had recei
16、ved 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 information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr
17、/. ITU 2008 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.998.2 (2005)/Amd.2 (12/2007) iii CONTENTS Page Annex C Frame-based protocol for discovery/aggregation and link management. 2 C.1 Bonding
18、control architecture 3 C.2 Operational overview of bonding aggregation control protocol 4 C.3 Protocol operation 7 C.4 Bonding aggregation control protocol frame formats 15 Rec. ITU-T G.998.2 (2005)/Amd.2 (12/2007) 1 Recommendation ITU-T G.998.2 Ethernet-based multi-pair bonding Amendment 2 This ame
19、ndment includes new functionality for discovery/aggregation and pair management at the bonding layer. New Annex C describes a frame-based protocol (the bonding aggregation control protocol (BACP) that exchanges information allowing two systems to seamlessly control mapping of physical media entities
20、 to physical medium attachment aggregation functions. In clause 2, add the following reference to IEEE 802.3-2005, the standard that replaced IEEE 802.3 (2002) and IEEE 802.3ah (2004). Original references to IEEE 802.3 (2002) and IEEE 802.3ah (2004) have been retained and, when explicity identifying
21、 the 2005 version, this amendment refers to IEEE 802.3-2005: 11 IEEE 802.3 (2005), Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications. NOTE Original references to IEEE 802.3 (2002) and IEEE 802.3ah (2004) have been retained and, when expl
22、icitly identifying the 2005 version, this Recommendation refers to IEEE 802.3-2005. Amend the definition of physical media entity: 3.10 physical media entity (PME): In IEEE 802.3-2005, a reference to an individual transceiver contained within an aggregate group where a transceiver carries only one p
23、acket stream. This Recommendation also supports operation over transceivers carrying multiple (at gamma interface logically separated) packet streams. In this Recommendation, a PME is a reference to one logical channel out of a set of one or more channels on the same individual transceiver. Each suc
24、h PME carries a single packet stream and is contained within one aggregate group. NOTE 1 In case pre-emption is used on a bearer channel, two PMEs each reference one of the two logical channels on the same bearer channel. In case pre-emption is not used on a bearer channel, a PME defaults to a refer
25、ence to the one bearer channel. NOTE 2 Although such a PME cannot be physically isolated within a transceiver carrying multiple packet streams, the naming PME is maintained for consistency with IEEE 802.3-2005 and for consistency in case the transceiver carries only one packet stream. Add the follow
26、ing text to the end of clause 6.2.2: The network side uses the PME_ID of each link in the bonding group to retrieve management data through Ethernet OAM (clause 30/57 of IEEE 802.3). Each G.994.1 CLR message shall include the 48-bit remote discovery register and the 32-bit PME aggregate register. Th
27、e network side may derive the PME_IDs of each of the links in the bonding group by adding the links one-by-one to the bonding group during PME aggregation, and observing the change in the PME aggregate register with each addition. However, to allow parallel initialization of the links in the bonding
28、 group and, hence, to allow shortening of the bonding group initialization time, the remote side should also include the 5-bit PME_ID in each CLR message. Corresponding G.994.1 codepoints are defined for the PME_ID as a supplement to IEEE 802.3 clause 61. Replace clause 8 with the following: 8 Hands
29、hake Clause 61.4 of IEEE 802.3-2005 defines the handshake operation for the IEEE standards 2BASE-TL and 10PASS-TS. That clause defines handshake procedures for discovering which pairs 2 Rec. ITU-T G.998.2 (2005)/Amd.2 (12/2007) are provisioned in which aggregate groups using the PME aggregation and
30、PME aggregation discovery codepoints of the IEEE handshake tree. The procedures of that clause are followed in this Ethernet bonding Recommendation with the following exceptions. There is no “PAF enable“ parameter as described in clause 61.4 of IEEE 802.3-2005 11. That parameter is used to define wh
31、ether bonding is performed. As this Recommendation references bonded operation only, that parameter is not required. The “PME identification“ Spar(2) bit indicates that PME identification is included in the CLR message. The corresponding Npar(3) field contains the five-bit value (0 to 31) of the PME
32、 ID. The “BACP support“ NPar(2) bit indicates support for the BACP protocol specified in Annex C. If this bit is set to ZERO in the CLR or CL message, then the bit shall also be set to ZERO in the MS message. If this bit is set to ONE in both the CLR and CL message, then this bit shall also be set t
33、o ONE in the MS message. Table 2 describes the meaning of the “BACP support“ bit in the MS message. Table 2 Interpretation of MS message bits for BACP BACP support Meaning 0 Use the G.994.1-based discovery/aggregation. Do not use BACP discovery/aggregation/management 1 Use BACP for discovery/aggrega
34、tion/management. Do not use G.994.1-based discovery/aggregation Unlike the handshake operations of IEEE 802.3-2005 11, this Recommendation defines the bonding layer to operate independently of the TPS-TC. Each line may select its TPS-TC independently of the others, as long as the maximum differentia
35、l latency of the pairs is maintained as specified in this Recommendation. NOTE This Ethernet bonding Recommendation uses the PME aggregation and PME aggregation discovery codepoints in ITU-T Rec. G.994.1. The definition of these variables is in clause 45.2.3.20 (PME aggregation) and 45.2.6.8 (PME ag
36、gregation discovery) of IEEE 802.3-2005. The transactions used to exchange these codepoints (e.g., “Get“, “Set if Clear“, “Clear if Same“) are defined in clause 61.4 of IEEE 802.3-2005. Note that an example of the aggregation discovery procedure is contained in clause 61A of IEEE 802.3-2005. Add the
37、 following new Annex C: Annex C Frame-based protocol for discovery/aggregation and link management This annex describes a frame-based protocol, referred to as the bonding aggregation control protocol (BACP), that exchanges information allowing two systems to control which PMEs are mapped to which PA
38、Fs in a simple and seamless manner. In this annex, a “system“ is defined as a piece of equipment, such as a DSLAM or a CPE device, associated with a set of PAFs and PMEs. This protocol is used in lieu of the G.994.1 discovery/aggregation process defined in clause 8. Rec. ITU-T G.998.2 (2005)/Amd.2 (
39、12/2007) 3 This protocol is backward compatible with existing Ethernet bonding implementations and standards. C.1 Bonding control architecture The bonding control architecture is shown in Figure C.1. A bonding control engine (BCE) sends and receives BACP data units (BACPDUs). The BACPDUs are Etherne
40、t frames that are transmitted and received through a standard PAF function. A mux function between the MAC and MII interface (see Note) is required to insert and remove BACPDUs into the data path. BACPDUs are identified by the headers of the Ethernet frame as discussed in clause C.4. NOTE Architectu
41、rally the BCE is in a bonding control sublayer (BCS) similar to the Ethernet OAM sublayer shown in Figure 57-3 of IEEE 802.3-2005. Figure C.1 Bonding control architecture The bonding control engine uses BACPDUs to exchange information with a BCE on a remote system. The information in these frames is
42、 then used by the BCE to control the flexible cross-connect shown in Figure C.1, mapping specific PMEs to specific PAFs. All PMEs on which BACP is enabled are PAF enabled, meaning that the PAF function is always in use, and the PME carries fragments rather than full Ethernet frames. This ensures tha
43、t the BCE simply controls the flexible cross-connect, and does not have to change encapsulations on the PMEs. Because the BCE essentially moves PMEs from one PAF to another, systems that implement BACP should be careful in that moving PMEs from PAFs that are carrying user (higher layer) data, such a
44、s an Internet service, since they would have a clear effect on that service. Implementations should take care in protecting higher layer services as the protocol operates and PME aggregation or removal occurs. In order to achieve seamless insertion and removal of PMEs into a bonded group, the cross-
45、connect and PAF must support the ability to separately control the receive and transmit connectivity 4 Rec. ITU-T G.998.2 (2005)/Amd.2 (12/2007) between a PME and a PAF. For example, it must (temporarily) be possible for a PME to be mapped to a PAF receive (reassembly) process, but not to the PAF tr
46、ansmit (segmentation) process. It is also assumed that the BCE has knowledge of when PMEs are activated and deactivated. Once a PME is activated (i.e., able to transmit and receive fragments), BACP can be used to control to which PAF the PME is connected, and provide smooth transitions of a PME into
47、 or out of a PAF. Because BACP uses standard Ethernet frames transmitted through the PAF, the BCE does not control over which PME(s) the BACPDUs are sent. Thus BACP cannot be used for per-PME link monitoring. C.2 Operational overview of bonding aggregation control protocol This clause provides an ov
48、erview of the operational behaviour of the BCE and BACP protocol. Additional details are supplied in later clauses. C.2.1 Group identification and bonding eligibility In order to determine which PMEs are eligible to be aggregated with other PMEs, a system assigns a group ID (GID) to each PME. The GI
49、D parameter is specified in clause C.3.1.1. Two PMEs are eligible to be aggregated if they have the same GID on both systems to which they are attached. Specifically, if the GIDs associated with PME1 on the local system and remote systems are G1local and G1remote, respectively, and if the GIDs associated with PME2 are G2local and G2remote, then PME1 and PME2 are eligible to be aggregated if G1local = G2local and G1remote = G2remote. In the typical environment, a CPE device would assign the same GID to all of the PMEs attached
