doc.: ieee 802.11-11/1183r0 submission september 2011 masataka ohta, tokyo institute of...
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 1
doc.: IEEE 802.11-11/1183r0
Submission
IP over Congested WLANDate: 2011-09-19
Name Affiliations Address Phone email Masataka Ohta Tokyo Instutute
of Technology 2-12-1-W8-54, Ookayama, Meguro, Tokyo 152-8552, JAPAN
+81-3-5734-3299
Authors:
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 2
doc.: IEEE 802.11-11/1183r0
Submission
Abstract
IP layer delays caused by unreliable broadcast/multicast over congested WLAN is discussed
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 3
doc.: IEEE 802.11-11/1183r0
Submission
802.3 and 802.11 are Different
• Unicast over 802.3 and 802.11 are reliable– thanks to retransmissions with CSMA/CD and CSMA/CA
• Broadcast/Multicast over 802.3 is reliable– thanks to retransmissions with CSMA/CD
• Broadcast/Multicast over 802.11 is not reliable– no retransmission with CSMA/CA
• ACK can not be sent because there may be no or more than one recipients
– packets may be lost with considerable probability by simultaneous transmissions in a slot or by hidden terminals
– packet losses over congested WLAN are not negligible
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 4
doc.: IEEE 802.11-11/1183r0
Submission
Fast Initial Link Setup?
• May not be meaningful, if upper layer setup consumes time by broadcast/multicast packet losses
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 5
doc.: IEEE 802.11-11/1183r0
Submission
IPv4 over Congested WLAN
• ARP (Address Resolution Protocol) [RFC826] may be delayed due to packet losses– ARP request is broadcast
– ARP reply is unicast and safe
• DHCP (Dynamic Host Configuration Protocol) [RFC2131] may also be delayed– DHCP discover and DHCP request are broadcast
• not a problem if a DHCP server is AP or within wired LAN
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 6
doc.: IEEE 802.11-11/1183r0
Submission
For Fast Initial and Subsequent IPv4 Setup
• 802.11ai needs address allocation mechanisms other than DHCP– may be as a integrated part of the initial link setup
• ARP delay can be prevented if proxy ARP is replied from an AP, if the AP has all the ARP information or AP communicate with an address allocation server
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 7
doc.: IEEE 802.11-11/1183r0
Submission
IPv6 over Congested WLAN
• ND (Neighbor Discovery) [RFC2461] may be delayed due to packet losses– RS (router solicitation), RA (router advertisement), NS (neighbor
solicitation) are multicast
– NA (neighbor advertisement) is usually unicast
– Address allocation with ND• optional RS to request RA
• RA tells a node to use SAA (stateless address autoconfiguration) [RFC2462] or DHCPv6 [RFC3315]
– SAA needs DAD (duplicate address detection), which use NS and NA
– DHCPv6 is like DHCP
– Address resolution is with NS and unicast NA
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 8
doc.: IEEE 802.11-11/1183r0
Submission
IPv6 is Multicast Intensive with Minimum Intervals Counted in Seconds (1)
• RA and optional RS use multicast– minimum interval (MI) of RA and RS are 3 and 4 seconds
• RS needs 0~1 second initial delay
– mobility supporting router SHOULD use RA MI of 0.03 second [RFC3775]• no RS is necessary and delay caused by waiting lossy RA is solved
• frequent RA should better be carried over 802.11 beacon, though
– RA MI of 3 seconds is still applicable to non-mobile routers• too bad even if packets are not lost
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 9
doc.: IEEE 802.11-11/1183r0
Submission
IPv6 is Multicast Intensive with Minimum Intervals Counted in Seconds (2)
• SAA use multicast NS, which requires joining solicited-node multicast address corresponding to the target address, using MLD (multicast listener discovery) [RFC2710], which use multicast– if MLD packet is lost, default retransmission interval is 0~10
seconds, against which RFC3775 specifies no exception
• DHCPv6 solicit message have 0~1 second initial delay
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 10
doc.: IEEE 802.11-11/1183r0
Submission
What are These?RFC4068: Fast Handovers for Mobile IPv6 (FMIPv6)
RFC4260: Mobile IPv6 Fast Handovers for 802.11 Networks
• Do reduce RS delay and, *IF* lucky, other delays
• DAD remains, unless, e.g., “the NAR can have a list of all nodes on its subnet, perhaps for access control”– have overhead of access control based on (random) SAC address!?
– should better have a rational address allocation mechanism
• Complex inter-router protocol to reduce AAA latency– routers should better share AAA cache
• Experimental (4068) and informational (4260) RFCs modifying basic ND only for mobile IPv6 only– should better have a rational address allocation mechanism
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 11
doc.: IEEE 802.11-11/1183r0
Submission
For Fast Initial and Subsequent IPv6 Setup
• 802.11ai needs address allocation mechanisms other than the current ND, SAA or DHCPv6– may be as a integrated part of the initial link setup
– a problem is that IPv6 people loves ND and SAA• modifications on retransmission timeout and initial delay could be a
compromise
• Address resolution delay by lost NS may be prevented *IF* proxy NA from an AP could be tolerated
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September 2011
Masataka Ohta, Tokyo Institute of Technology
Slide 12
doc.: IEEE 802.11-11/1183r0
Submission
References
• [RFCs]: available from www.ietf.org/rfc.html by RFC numbers