1、 Rec. ITU-R M.1636 1 RECOMMENDATION ITU-R M.1636 Basic reference models and performance parameters of Internet Protocol packet network transmission in the mobile-satellite service (Questions ITU-R 85/8, ITU-R 87/8, ITU-R 112/8 and ITU-R 233/8) (2003) Summary This Recommendation provides basic refere
2、nce models and definitions of performance parameters of Internet Protocol packet network transmission in the mobile-satellite service (MSS). The defined reference models and performance parameters are intended as a technical basis on which the performance objectives and availability are developed, i
3、n combination with the technical and operational characteristics for packet network transmission in the MSS. The ITU Radiocommunication Assembly, considering a) that Internet Protocol (IP) packet transmission has become one of major services in modern communication networks including mobile-satellit
4、e systems; b) that hypothetical reference circuits, technical characteristics, performance objectives and availability requirements have been stipulated for conventional MSS in a number of existing Recommendations; c) that technical characteristics and performance should be defined on the basis of I
5、P packet layers, in addition to basic digital transmission performance of MSS bearer links; d) that definitions are needed for reference models, technical characteristics and performance parameters as a technical basis for the development of IP packet transmission in MSS; e) that studies are continu
6、ing for performance and availability of IP packet transmission in other forums of ITU-T and ITU-R; f) that properties inherent to MSS should be taken into consideration when performance objectives and availability requirements are discussed for IP packet network transmission; g) that studies conduct
7、ed using a basic reference model of IP packet data transmission are meaningful, however, advanced reference models are needed to conduct study for more advanced IP packet data transmission in MSS, recommends 1 that the basic reference models in Annex 1 should be applied as a minimum set of IP packet
8、 transmission in MSS; 2 that the technical characteristics in Annex 2 should be used for studies and definition of performance parameters and availability for IP packet applications in MSS defined in Annex 1; 2 Rec. ITU-R M.1636 3 that the performance parameters and definitions in Annex 3 should be
9、employed for IP packet transmission in MSS defined in Annex 1. Annex 1 Basic reference models of IP packet transmission in MSS 1 Introduction MSS systems provide mobile application with worldwide coverage. Recently IP packet transmission has been introduced in some MSS systems. However, IP packet tr
10、ansmission networks are not formally structured. A hypothetical reference connection has not been well defined for IP packet transmission networks. It is therefore important to define the use of MSS links in IP packet transmission services and to establish a reference model on which characteristics
11、and performance can be discussed for MSS. 2 Basic reference model for IP packet transmission in MSS MSS links will not be used as high-speed backbone links of IP core networks. They are intended as part of the access portion to an edge router, in the global IP network. Two applications for MSS links
12、 are considered. The first is a user-terminal to router (R) access connection as shown in Fig. 1. The second considers a larger capacity connection between a mobile local area network (LAN) and an edge router as illustrated in Fig. 2. 1636-01RRRRFIGURE 1User-terminal to router connectionSatelliteFee
13、der link(FSS)CorenetworkGatewayearth stationUserterminalSatellite link Terrestrial sectionLANService link(MSS)Rec. ITU-R M.1636 3 1636-02RRRRRFIGURE 2LAN to router connectionSatelliteFeeder link(FSS)CorenetworkGatewayearth stationSatellite link Terrestrial sectionLANService link(MSS)MobileterminalLA
14、N2.1 Reference models The classification of MSS topologies is shown in Table 1 and the corresponding routing is shown in Fig. 3. This Recommendation covers reference models denoted by a “Yes” in Table 1. Both GSO and non-GSO satellite systems are included. Non-GSO systems cover low Earth orbit (LEO)
15、 and medium Earth orbit (MEO) satellites but not high Earth orbit (HEO) satellites. Bent-pipe systems are assumed because on-board processing adds extra processing time and inter-satellite links (ISLs) require additional propagation delay. TABLE 1 Classification of MSS system configurations Characte
16、ristics Route GSO HEO MEO LEO Single hop A-B-C-D Yes No Yes Yes Double hop no ISL A-B-C-B-A or A-B-C-C-B-A No No No No Double hop via ISL A-B-B-A No No No No 4 Rec. ITU-R M.1636 1636-03RRRRRRAABCCDBSatelliteFeeder link(FSS)CorenetworkGatewayearth stationUserterminalSatellite link Terrestrial section
17、LANService link(MSS)ISL connection notconsidered in this RecommendationDouble hop connection notconsidered in this RecommendationConnection considered in thisRecommendationFIGURE 3Packet routing considered in this RecommendationSatelliteThese models provide definitions of the MSS section and interfa
18、ce points in the entire IP packet network. It should be noted that the satellite section consists of a service link in the MSS and a feeder link categorized as FSS. All discussion in this Recommendation will be based on these models for consideration of technical characteristics and performance of I
19、P packet services in the MSS. 2.2 Usage of a physical connection for logical connections Due to the nature of multiple access of MSS by a number of users, there may be many cases for the use of a satellite bearer circuit by user IP connections. The simplest case is a dedicated use of a satellite bea
20、rer circuit for a single IP connection by one user (Fig. 4a). In this case, the satellite bearer circuit is considered to have fixed transmission capacity. There is another case where multiple users share capacity of a satellite bearer circuit. In the latter case, a portion of fixed capacity within
21、the satellite bearer circuit is assigned to each of the multiple users (Fig. 4b). From the viewpoint of each user, it is theoretically possible in the case of Fig. 4c to change the assigned capacity dynamically during the use by multiple users based on the concept of “best effort service”. Dynamic c
22、apacity allocation is taken into consideration in this Recommendation. In this context, a “user” refers to a user mobile terminal to the satellite link. A LAN output that is connected to the satellite link is therefore a user even though the LAN accommodates multiple IP service users. Rec. ITU-R M.1
23、636 5 1636-04aRUserterminalGatewayearth stationService linkN kbit/sFeeder linkN kbit/sSatelliteFIGURE 4aSatellite link for single user connection1636-04bRSatellite4N kbit/s2N kbit/sN kbit/sN kbit/sUserterminal AUserterminal BUserterminal CTotal capacity4N kbit/sN kbit/sN kbit/s2N kbit/sTo user termi
24、nal ATo user terminal BTo user terminal CGatewayearth stationFIGURE 4bSatellite link shared by multiple user connections with fixed capacity allocation6 Rec. ITU-R M.1636 1636-04cRSatellite4N kbit/sUserterminal AUserterminal BUserterminal CTotal capacity4N kbit/sFrom user terminal AFrom user termina
25、l BFrom user terminal CGatewayearth stationFIGURE 4cSatellite link shared by multiple user connections with dynamic capacity allocationDynamic capacityallocationDynamic capacity allocationAnnex 2 Technical characteristics to support lower layers of IP packet transmission in the MSS 1 Technical chara
26、cteristics and transmission parameters Since IP packet transmission application is provided over an MSS digital link, it is natural to describe technical characteristics focusing on transmission parameters. The following parameters are basic information to characterize such MSS digital link in which
27、 IP packet transmission application is provided. Conventional definitions are assumed for these parameters. a) Bearer transmission characteristics Type of modulation Transmission rate (bit/s) Scheme of forward error correction (FEC) Threshold BER Percentage of time better than the threshold BER. Rec
28、. ITU-R M.1636 7 b) Packet transmission characteristics for Layer 2 General description of Layer 2 protocol Frame structure for MSS satellite link and packet to frame adaptation Packet length Packet header structure Error control and retransmission capability of Layer 2 Packet collision control sche
29、me, if necessary Protocol stack conversion for MSS satellite link. c) Delay characteristics Propagation delay (ms) In the case of GSO satellite systems, the propagation delay is dependent upon the location of the mobile relative to the satellite orbital location, and is regarded to be constant for e
30、ach stationary mobile if a slight fluctuation is disregarded. On the other hand, in the case of intermediate circular orbit satellite systems of MEO, the smallest propagation delay at the sub-satellite point is 69 ms and the largest propagation delay at the edge of satellite coverage is 103 ms. The
31、propagation delay will be less for the case of LEO satellite systems. Delay jump on satellite handover (ms) A sudden change of propagation delay may occur as the result of handover from one satellite to another in the non-GSO or GSO satellite constellation. The probability of handover between satell
32、ites is different for non-GSO and GSO satellite systems. For GSO systems, it might only occur for non-stationary mobile terminals, due to mobile relocation or blockage due to infrastructure. In the case of intermediate circular orbit satellite systems of MEO, the largest value of delay jump will be
33、resulted by satellite handover from one satellite located at the low elevation with the largest propagation delay (103 ms) to another with the smallest propagation delay (69 ms). The largest delay jump will be 34 ms for this case. Annex 3 Performance parameters and definitions for IP packet transmis
34、sion in the MSS Introduction Performance parameters on an IP packet basis are essential in IP packet transmission service over the MSS. The definitions provided in ITU-T Recommendations Y.1540 and Y.1541 should be the basis for this analysis. At the same time, aspects inherent to the MSS should be t
35、aken into account. It is inappropriate in MSS applications to pay too much attention to detailed parameters. The special properties of GSO and non-GSO MSS systems should be properly reflected in the definition of general parameters. It is also important to select parameters which are suitable for al
36、locating performance objectives to sections of IP connection including an MSS satellite link. 8 Rec. ITU-R M.1636 2 Definitions of performance parameters 2.1 IP packet related parameters The following parameters are considered essential. Definitions and interpretation in the context of the MSS are g
37、iven for each parameter. These parameters will be sufficient to characterize IP packet transfer over an MSS link. Other parameters such as spurious IP packet rate are considered to be too detailed for application to MSS links. 2.1.1 IP packet transfer delay (IPTD) IPTD is the total transmission dela
38、y for an end-to-end IP connection. IPTD can also be defined for a section of the end-to-end connection. IPTD for the end-to-end connection shall be properly allocated to all the sections that form the end-to-end connection. Since transmission delay is considered by some standard engineers to be larg
39、e over a satellite link, it is essential to identify an allowable amount for IPTD for the mobile satellite link section including both feeder and service links. IP packet transmission systems are classified to delay sensitive systems and error sensitive systems. A system requirement decides which sy
40、stem to be employed, based on the priority of importance for less delay or less error. IPTD for an MSS link, IPTDsat, can be determined separately for each system. It should be noted that IPTDsatis considered after establishment of a satellite link, and that delay associated with random access trans
41、mission for dynamic capacity allocation might be included in signal processing delay for framing and adaptation for the MSS link, denoted by Tprocessingbelow. a) IPTD for delay sensitive systems For delay sensitive systems, which have no retransmission capability at Layer 2, IPTDsatis defined as: IP
42、TDsat= Tpropagation+ Tprocessing+ Tbufferwhere: Tpropagation: propagation delay of an MSS link Tprocessing: signal processing delay for framing and adaptation for the MSS link Tbuffer: buffering delay at a router or at an interface to connect the MSS link to a terrestrial section. b) IPTD for error
43、sensitive systems For error sensitive systems, which have a retransmission capability at Layer 2, IPTDsatvaries with the number of retransmission times. If a definition of IPTDsatfor error sensitive systems is required, it may be described as follows: IPTDsat= +=+11, ,Nnbufferprocessingnnpropagation
44、TTT where: N : times for retransmission Tn, propagation: Tpropagationfor the n-th time transmission Tn, processing: Tprocessingfor the n-th time transmission. Rec. ITU-R M.1636 9 It is to be noted that the large value of IPTDsat, after several retransmission trials at Layer 2, in a satellite link mi
45、ght not be meaningful, because the retransmission scheme at Layer 4 or higher might discard the delayed IP packet for its timeout. In addition, it may need a probabilistic term to be considered within the expression to support a retransmission mechanism. These are issues for further study to determi
46、ne a more appropriate definition of IPTDsatfor error sensitive systems. 2.1.2 IP packet delay variation (IPDV) IPTD varies, it depends on various factors that include congestion in the part of the network considered by this Recommendation as well as framing and retransmission control in Layer 2. IPD
47、V can be defined in many ways as discussed in the ATM Recommendations but for the purpose of this Recommendation it will be assumed to be the difference between the largest IPTD and the smallest IPTD as follows: For delay sensitive systems, which have no retransmission capability at Layer 2: IPDV =
48、IPTDmax IPTDminwhere: IPTDmax: largest IPTD IPTDmin: smallest IPTD. For error sensitive systems, which have retransmission capability at Layer 2, the statistical method in Appendix 2 of ITU-T Recommendation Y.1541 is applied, where: IPTDmax: largest IPTD during a measurement interval IPTDmin: smalle
49、st IPTD during a measurement interval. Several values of IPDV are measured over a large time interval, comprising several short measurement intervals. The X% of these IPDV must meet the defined objective. The value of X is to be determined. Note that the fluctuation of propagation delay also affects IPDV. In the case of non-GSO satellite systems, variation of propagation delay due to satellite movement should be included. In addition, a sudden change of propagation delay may occur as the result of handover from one satellite to another in a satelli
