【技術(shù)精品課件】多媒體技術(shù)-展示頁
2025-02-15 20:15本頁面
【正文】 ? 無論哪個源端都是用同一個組播樹傳輸數(shù)據(jù) ? 路由器只需要維護 (*,G) 狀態(tài)（ (*,G) state at intermediate routers） ? Eg: CBT, PIMSM 源基樹（ Sourcebased Trees） Router Source Receiver S R R R R R S S 共享樹（ Shared Tree） RP Router Source Receiver S S S R R R R R Shared vs. SourceBased Trees ? Sourcebased trees ? Shortest path trees – low delay, better load distribution ? More state at routers (persource state) ? 在密集模式的網(wǎng)絡(luò)環(huán)境下比較有效（ Efficient in densearea multicast） ? Shared trees ? Higher delay (bounded by factor of 2), traffic concentration ? Choice of core affects efficiency ? Pergroup state at routers ? 比較適合稀疏模式的網(wǎng)絡(luò)環(huán)境（ Efficient for sparsearea multicast） Corebased Routing Protocols ? Specify “meeting place” aka “core” or “rendezvous point (RP)” ? Sources send initial packets to core ? Receivers join group at core ? Requires mapping between multicast group address and “meeting place” ? Examples: CBT, PIMSM 協(xié)議獨立組播路由協(xié)議：Protocol Independent Multicast (PIM) ? Support for both shared and persource trees ? Dense mode (persource tree) ? Similar to DVMRP ? Sparse mode (shared tree) ? Core = rendezvous point (RP) ? Independent of unicast routing protocol ? Just uses unicast forwarding table PIM Protocol Overview ? Basic protocol steps ? Routers with local members Join toward Rendezvous Point (RP) to join shared tree ? Routers with local sources encapsulate data in Register messages to RP ? Routers with local members may initiate datadriven switch to sourcespecific shortest path trees ? PIM Specification (RFC2362) Source 1 Receiver 1 Receiver 2 PIM Example: Build Shared Tree (*,G) Receiver 3 (*,G) (*,G) (*,G) (*,G) (*,G) Join message toward RP Shared tree after R1,R2 join RP Source 1 Receiver 1 Receiver 2 Data Encapsulated in Register (*,G) Receiver 3 (*,G) (
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