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Transport of Media Independent Handover Messages Over IP I-D: draft-rahman-mipshop-mih-transport-01.txt 67th IETF Annual Meeting MIPSHOP Working Group Key Concepts • Re-use existing well proven Internet protocols for – – – – Discovery of MIH nodes Transport of MIH messages Security Etc. • Use functionalities already provided by MIH (IEEE 802.21) & focus on transport mechanism • Define new functionality at MIH application layer where needed Network Model An MIH application enabled node that supports and/or manages MNs for seamless HO Mobility Manager #1 Mobility Manager #N Internet Signaling over IP Signaling over IP Cellular Network WiMAX Network WiMAX BS Cellular BS WLAN Network WLAN AP MIH Proxy L2 Signaling MN contains MIH application & multiple access technologies Mobile Node Mobility Contains MIH Proxy Function Summary of Proposal • Hard coding or DHCP to discover Mobility Manager (MM) – Mobile Node (MN) discovers MM at initialization – Depends on number of MMs – DHCP as per draft-daniel-dhc-mihis-opt-02.txt (Park, et al.) • UDP as MIH transport mechanism between MM and MN – Easy to implement, simple & fast, used by many other control protocols e.g. SIP • IPSec for security mechanism • Existing MIH functionalities in order to – Setup and keep track of MIH node identifiers, session and transaction identifiers – Discover capabilities of MIH peers – Provide reliability with optional ACK bit fields • Retransmission timers at MIH application layer to complement UDP for reliability – And associated congestion control mechanism An MIH Enabled Mobile Node • The MIH application shall have a newly defined port number (from IANA) New Port Number MIH App. Other App. UDP IP WLAN WLAN Interface Cellular Cellular Interface Transport Mechanism for Reliable MIH Message Delivery • Sender of MIH message may request an acknowledgement – Done by setting ACK Request bit in MIH message • Sender sets retransmission timer based on type of MIH message (i.e. Information, Event, Command) – If ACK does not arrive within timeout period then retransmit – If ACK arrives within timeout then assume message delivered correctly • If ACK Request bit was set, the receiver shall send an ACK message – Done by setting ACK Respond bit in MIH message – ACK can be piggy backed with data MIH Application Retransmission Timers • Three retransmission timers defined for Information Service (IS), Event Service (ES), and Command Service (ES) Message Content IS Associated Retransmission Timer Information Timer (T1) ES Event Timer (T2) CS Command Timer (T3) Example Value Notes 1000 ms T1 > T2 Least time Sensitive 500 ms T3 < T2 < T1 100 ms T3 < T2 Most time sensitive MIH Signaling Example 1: Directly Over UDP/IP Mobile Node Cellular WLAN Mobility Manager Power up: connect to WLAN 1 Obtain Neighbor List 2 Send a request for IS (e.g. NL) and set application timer T1 ACK not received timeout after T1 3 4 5 Retransmit request for IS and re-set application timer T1 Send IS response (with piggy backed ACK) and set application timer T1 Send ACK MN then decides to move to cellular (based on radio conditions) 6 7 Send ‘Link Up’ ES to inform about HO completion (no ACK required) Session continues over cellular MIH Signaling Example 1: Via WLAN MIH Proxy Mobile Node 1 Cellular WLAN (Proxy) Mobility Manager Power up: connect to WLAN Obtain Neighbor List 2 Send a request for IS (e.g. NL) Inter-work L2 message to UDP/IP message 3 Forward IS request ACK not received timeout after T1 4 5 6 7 Retransmit IS request Send ACK Send IS response Send ACK Inter-work UDP/IP message to L2 message 8 Forward IS response NAT Traversal, Fragmentation, & Security • MNs can be behind NATs – If MNs behind NATs initiate sessions with MM then there will be no NAT traversal problems • Trend in IEEE 802.21 is to use small MIH messages – ES and CS: small and will not require fragmentation – IS can be large: use IP fragmentation when needed together with retransmission timers for reliability • Use relevant IPSec features i.e. Encapsulated Security Payload and/or Authentication Header for secure messaging Conclusions • Re-use existing protocols as much as possible and define new functionalities only where needed • Use UDP: existing, fast, & simple to use transport protocol – Used by other protocols e.g. SIP commonly uses UDP, CAPWAP also uses UDP, & the IETF NETLMM Working Group also considers UDP for transport • Use existing MIH (IEEE 802.21) functionalities: – Provides options for ACKs, sessions & transactions management • Use MIH Application Retransmission timers for reliability