标题: | 利用MPLS技术支援GPRS传输网路的QoS MPLS and QoS enhancement for GPRS Transport Networks |
作者: | 王健欣 Chien-Hsin Wang 曾建超 Chien-Chao Tseng 资讯科学与工程研究所 |
关键字: | 多协定标签交换;服务品质;通用封包无线电服务;顺畅换手;MPLS;QoS;GPRS;smooth handoff |
公开日期: | 2002 |
摘要: | 目前General Radio Packet Service (GPRS) 的核心网路是属于利用IP绕送的私有网路 (private network)。GPRS网路使用IP协定来传输信息封包与资料封包,但其IP定址及绕径机制却独立于外部的网际网路 (Internet)。GPRS网路对于行动台而言,如同一个连接外部网际网路的one-hop default router。行动台的资料封包必须先经由GPRS Tunneling Protocol (GTP) 封装,然后再经由GPRS核心网路内的IP-tunnels绕送。而IP-GTP-IP tunneling的机制产生了三项重大的缺点:(1)较长的封包标头,(2)较长的封包绕送延迟,(3)外部网际网路与GPRS核心网路之间的即时连线服务品质 (Quality of Service, QoS) 协调的困难度较高。 为了解决GPRS网路因IP-GTP-IP tunneling机制所产生的缺点,我们提出一个架构,将Multi-Protocol Label Switching (MPLS) 协定加入GPRS的的protocol stack,称为MiGPRS。MiGPRS使用标签交换 (label switching) 的机制替代IP routing,于GPRS核心网路内传输资料封包。由于GPRS核心网路通常为一私有管理的网路,所以我们可以在每对GGSN-SGSN 之间预先建立label switched path (LSP),使用更有效率的label switching来替代IP routing。利用label switching方式,MiGPRS可以加速封包的传输速度以及缩短封包标头长度,因而增加系统的capacity。此外;我们使用label stacking机制,将GPRS transmission plane中的GPRS Tunneling Protocol (GTP) 层移除。利用具有较短长度的MPLS label来代替GTP header,MiGPRS可以更进一步地缩减封包标头的长度。 为了在MiGPRS网路中提供QoS服务,前述在每对GGSN-SGSN之间的pre-configured LSPs为constraint-based routed LSPs (CR-LSPs)。由于CR-LSPs本身具有的connection-oriented特性,我们可以使用CR-LSPs来提供Differentiated Service (Diff-Serv)以支援GPRS网路与Internet之间的点对点服务品质控制 (End-to-End QoS Control) 传输。此外;MiGPRS也在每对SGSN-SGSN之间预建handoff CR-LSPs来支援inter-SGSN顺畅换手 (smooth handoff) 。当行动台在进行inter-SGSN handoff时,这些handoff CR-LSPs可以被使用来让旧的SGSN转传 (forward) in-flight packets到新的SGSN。然而当行动台进行换手时,我们必须保留足够的频宽给handoff CR-LSPs,以维持行动台即时连线的服务品质。因此;我们提出一个分析模型来计算行动台的inter-SGSN换手率,并根据分析的inter-SGSN换手率,提出一个handoff CR-LSPs的频宽估计模型,以计算handoff CR-LSPs所需的频宽。最后,我们进行模拟来分析handoff model的精准性以及显示MiGPRS的效能。模拟的结果验证MiGPRS在平均封包延迟、封包丢失率和连线成功率等都有优越的表现。 The core network of General Packet Radio Service (GPRS) is an IP-based private network. It adopts IP protocol in transporting both signal and data packets but its IP addressing and routing is independent of that in the external Internet. The GPRS core network appears to the GPRS mobile stations (MSs) as a one-hop default router to the external Internet. All IP data packets of GPRS MSs are first encapsulated in GPRS Tunneling Protocol (GTP) and then routed through the IP-tunnels in the GPRS core network. This IP-GTP-IP tunneling mechanism results in three significant drawbacks: (1) larger data packet header, (2) longer IP routing delay, and (3) more difficult to provide QoS guaranteed services and support identical QoS agreements across the GPRS core network and Internet. In order to overcome above three deficiencies of the GPRS core networks, we propose a protocol stack that embeds Multi-Protocol Label Switching (MPLS) into the protocol stack of GPRS, henceforth referred as MiGPRS. MiGPRS adopts label switching, instead of IP routing, mechanism to transfer data packets in the GPRS core network. Because the GPRS core network is normally constructed as a privately controlled administration domain, we can pre-configure a label switched path (LSP) between each GGSN-SGSN pair to replace IP routing with a more efficient label switching. With label switching, MiGPRS can speed up packet transmission and shorten packet header length, and thus increase system capacity. Furthermore, we also adopt label stacking mechanism to eliminate the GPRS Tunneling Protocol (GTP) layer from the GPRS transmission plane. By replacing the GTP header with a shorter MPLS label, MiGPRS can further reduce header lengths of data packets. In order to support QoS guaranteed services in MiGPRS, the pre-configured LSPs between each GGSN-SGSN pair are constraint-based routed LSPs (CR-LSPs). Because of the connection-oriented characteristic of CR-LSPs, we could use CR-LSPs to provide Differentiated Services (Diff-Serv) for end-to-end QoS control across the GPRS core network and Internet. Besides, MiGPRS also pre-configure handoff CR-LSPs between each SGSN-SGSN pair to support inter-SGSN smooth handoff. These handoff CR-LSPs could be used by the old SGSN to forward in-flight packets to the new SGSN when an MS performing an inter-SGSN handoff. However, we need to reserve sufficient bandwidth for the handoff CR-LSPs so that we can retain the QoS requirement of MSs’ real-time streams, when MSs are performing inter-SGSN handoffs. Therefore we first present an analytic model to calculate the inter-SGSN handoff rate of MSs and then propose a bandwidth estimation model for handoff CR-LSPs according to the inter-SGSN handoff rate obtained from the analytic model. Finally, we conduct simulation to analyze the accuracy of the handoff model and show the effectiveness of MiGPRS. Simulation results show that MiGPRS is very effective in terms of mean packet delays and packet dropping ratios. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#NT910392011 http://hdl.handle.net/11536/70082 |
显示于类别: | Thesis |