通信设备的负荷和输送信息质量的研究 [8]
论文作者:英语论文论文属性:作业 Assignment登出时间:2016-03-23编辑:cari2点击率:19895
论文字数:8632论文编号:org201603181350499330语种:英语 English地区:澳大利亚价格:免费论文
关键词:通信设备有线宽带输送信息
摘要:本文主要介绍了WiMAX技术,它能提供更好的服务质量,创造高性能的架构,在得到全球监管机构的认可下,会成为下一个大事件。
links are unidirectional, so bi-directional link uses two CIDs. Three CIDs, When a subscriber station joins the network, are given to it each with different QoS necessities used by different management levels: Basic, Primary Management and Secondary Management links[24].
Basic link transmits brief, time-critical MAC and radio link control (RLC) messages. Primary Management link transports longer, more latency liberal messages like registration requests and privacy and key management messages- messages that are used for authentication and connection setup[24]. Secondary Management link will permit a particular protocol being run at a higher layer to transport standards-based management messages, for instance (DHCP), (TFTP), and Simple Network Management Protocol (SNMP). Additional connections are served by MAC for other reasons such as to transmit the UL and DL transmission schedules. A connection identifier might carry traffic for several different upper-layer sessions[24].
2.9.1.2 MAC message format
Base station MAC and subscriber station MAC swap messages known as Protocol Data Units. The messages comprise of three parts: the fixed length MAC header, the changeable-length Payload and the Cyclic Redundancy Code. There are two types of MAC header. The first is the Generic MAC header (GMH) used to transport about all the standard MAC Management messages. The second is the Bandwidth Request Header (BRH), it is sent alone, with no payload. Excepting Bandwidth Request PDUs (with no payload) MAC PDUs might hold either MAC management messages or convergence sub-layer data- MAC Service Data Unit (MSDU). Payload is optional also. CRC is optional too and is used only when SS request for it in its QoS parameters[24]. MSDUs are fragmented and packed within MPDUs which are then transmitted on air.
2.9.1.3 Generic MAC header format
Figure 2.8 shows the format of the GMH. HT stands for Header Type, this is used to specify whether the header is generic or bandwidth request. For generic header HT bit is set to zero. Encryption control (EC) bit specifies whether the payload is encrypted or not. If set to zero specifies that payload is not encrypted and set to one means payload is encrypted. For generic header it is set to one. The information regarding which management message is saved in the payload is contained in Type field. CRC indicator (CI) shows the existence of optional CRC at the ending of MPDU. CI=0 indicates no CRC is appended, CI=1 indicates CRC is appended to the PDU. Encryption key sequence field ensures that BS and SS are synchronized while making use of traffic encryption keys and Initializing Vectors (IV). This field is only significant when EC bit is set to1. 11 bit LEN field is used to specify the length in bytes of MAC PDU comprising header and CRC. Connection identifier (CID) 16 bit field is used to specify which connection the MPDU is servicing. Header check sequence (HCS) is an 8 bit field used to identify errors in the header field.
2.9.1.4 Bandwidth request PDU
A 6-Byte bandwidth request header is transmitted to ask for the changes for granted characteristics of a connection. Format of BRH is shown in figure 2.9. The HT bit is set to 1 to show that the header is a bandwidth request. The EC bit is set to 0. The 6-bit type field can acquire value 0 to show an incremental bandwidth request or a value of 1 to show a collective request. The bandwidth re
本论文由英语论文网提供整理,提供论文代写,英语论文代写,代写论文,代写英语论文,代写留学生论文,代写英文论文,留学生论文代写相关核心关键词搜索。