| Summary: | 碩士 === 國立臺灣大學 === 資訊工程研究所 === 84 === IEEE 802.12 是一種高速區域網路的標準.這種區域網路一方面繼承了
ISO/IEC 8802-3(以太網路)及 ISO/IEC 8802-5.2(權杖環網路)的資料封
包格式,一方面又沒有封包碰撞的困擾和權杖環繞的付擔.也就是說,它不
但和目前世界上最流行的兩種區域網路相容,還比它們更好.然而,該標準
至目前為止,仍未能加入頻寬預約功能.而頻寬預約功能卻是即時服務中重
要的關鍵.除此之外,IEEE 802.12 網路的型狀,其實頗適合同時傳輸多份
資料.而目前的標準中也未考慮.因此,我們將在這篇論文中,提出兩種架
構,以達到頻寬預約的目的.其中一種甚至能夠達成同時傳輸功能.我們的
目的,是希望能夠藉此在 IEEE 802.12 網路上面,提供即時服務,甚而增進
系統產能.在我們所提出的第一種架構中,我們將依循另一種叫作 FDDI 的
高速區域網路的概念,來發展即時排程.FDDI 網路中,有一種特殊的設計,
叫作 SBA (Synchronous Bandwidth Allocation,同步頻寬配置).SBA 可
以用來規範每個結點所能使用的系統資源,而所付出的代價則是複雜的權
杖環繞協定.在我們的方法中,則可利用 IEEE 802.12 網路 polling 的概
念,來完成類似 SBA 的規範,卻又不須要付出權杖環繞的代價.雖然第一種
架構可以用簡單的方法達成頻寬預約功能,但卻有兩個缺點.首先, SBA 中
有一個參數,叫作 TTRT (Target Token Rotation Time,目標權杖環繞時
間),這個參數既用來當作資料量的刻度標準,又當作延遲的上限.因此造成
這兩個量值彼此相關,而破壞了它們原本互無關係的事實.另一方面,第一
種架構用了 IEEE 802.12 網路原有的 polling 概念,因此無法達成同時
傳輸功能.因此,在第二種架構中,我們改採 store-and- forward 的概念,
並在每一個中間結點採用 deadline-first 期限排程法,來達到最好的即
時排程,以及同時傳輸的目的.
IEEE 802.12 is the draft standard of a high-speed local area
network. It inherits the frame formats of ISO/IEC 8802-3
(Ethernet) and ISO/IEC 8802-5.2 (Token Ring), while both the
packet collision and the complicated token rotation overhead
are eliminated. This means it is not only backward compatible
with two of the most popular local area network standards in
the world, but also outperforms them. Nevertheless, in the
standardization so far, bandwidth reservation is still not
covered, which is vital in real-time services. Moreover, the
topology of IEEE 802.12 networks makes it possible to transmit
data between different end nodes concurrently, which is not yet
considered in the standard either. Therefore we propose two
mechanisms in this thesis to perform bandwidth reservation, and
one of which can even achieve concurrency, which is called
Concurrent Demand Priority, such that real-time services can be
supported in an 802.12 network, and the throughput can be
significantly improved. In the first approach, we follow the
concept of FDDI high-speed local area networks, to develope
real-time scheduling in the IEEE 802.12 network. FDDI uses an
algorithm, which is named SBA (Synchronous Bandwidth
Allocation), to manage the system resource used by all the end
nodes. Its overhead is the token rotation time. However, in our
approach, the polling concept of 802.12 networks can be used to
eliminated the token rotation overhead, while achieving the
real-time scheduling. Although it works, the first approach
leaves two problems. First, SBA introduces corelation between
delay bound and traffic scale. Second, concurrency is not
achieved. Therefore we use the concept of store-and-forward in
the second approach, with deadline-first scheduling.
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