asap: an as-aware peer-relay protocol for high quality voip
DESCRIPTION
ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP. Shansi Ren, Lei Guo, and Xiaodong Zhang Ohio State University. VoIP Packets Traveling in Internet. Long router queuing delay!. Alice, I am Bob~~. Bob, What did you say?!!. Internet. Alice. Bob. Bob -> Alice voice pkts. - PowerPoint PPT PresentationTRANSCRIPT
ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP
Shansi Ren, Lei Guo, and Xiaodong Zhang
Ohio State University
Internet
Bob Alice
VoIP Packets Traveling in Internet
Alice, I am Bob~~
Bob, What did you say?!!
Long router queuing delay!
Bob -> Alice voice pkts.
Alice -> Bob voice pkts.Internet routing is Critica
l for VoIP Quality!
VoIP Quality Requirements
Mean Opinion Score (MOS) metric MOS > 3.5 is acceptable.
Network factors E2E one-way latency < 150 ms E2E loss rate < 0.5%
Some Facts of VoIP in Internet
Two end hosts communicate through their direct IP routing path by default.
Direct routing path may not always meet the VoIP quality requirements.
Overlay routing sometimes may have better routing performance.
Internet
host B
host A
host C
host Dhost E
direct IP routing path
1-hop overlay routing path
2-hop overlay routing path
host A communicates with host C
direct, 1-hop, and 2-hop overlay routing
Internet Routing• Internet consists of Autonomous Systems (ASes), and hosts are a
dministered in the unit of AS.
• ASes are connected by core routers, and routing between ASes relies on the Border Gateway Protocol (BGP).
• Connected ASes has customer-provider and peer-peer relationship.
• An customer AS connecting to multiple upstream ASes is called a multihoming AS. (or multiple providers)
• Valley-free: a direct Internet routing path has the form (customer-provider)*(peer-peer)?(provider-customer)*.
Targeted Research Questions
How insufficient is Internet direct routing for VoIP?
Under what condition, can overlay routing (relay) improve VoIP quality?
What kind of quality does Skype provide, and what are the limits in its routing?
How to design efficient routing methods for high quality VoIP with low overhead?
Outline of Talk
VoIP application introductionVoIP application introduction
Internet e2e latency measurementsInternet e2e latency measurements
Skype measurement and observations
ASAP protocol design and evaluation
Conclusion
Limewire software
modification
Gnutella IP crawler
BGP tables and updates
Gnutella IP probing
IP prefix and origin
AS extraction
online Gnutella IP addresses
IP prefix table
AS-level cluster Identification and delegate IP selection
King tool based prober
development
cluster delegate IP addresses
King prober
pairwise IP DNS server
latency measurement
pairwise delegate IP late
ncy
E2E Latency Measurement Procedures
Sessions and their RTTs
A session consists a pair of end host.
We randomly generate 105 sessions among cluster delegates.
We measure session direct RTTs using king facility.
For delegates a, b, c, relay path a-b-c RTTa-b-c = RTTa-b + RTTb-c + relay delay.
Internet e2e RTT Measurement
host a
host b
host c
DNS server of host b DNS server of host c
Internet
IP of host c?
IP of host c?
IP of host c
IP of host c
host a measures RTTb-c via recursive DNS queries
Direct vs 1-Hop RTT
50% sessions have optimal 1-hop RTT < direct IP RTT
25% sessions whose opt. 1-hop relay can reduce direct IP RTT by
more than 50%
Overlay Routing Reduces RTT
Sessions whose direct IP RTTs > 300 ms
Sessions opt. 1-hop RTTs are always < 300 ms
Relay Improves VoIP Quality
There are 2% and 10% of sessions with direct RTTs above 300 ms and 250 ms, respectively.
We can always find one-hop relay paths whose RTTs are below the threshold for these sessions.
Peer relay plays an important and critical role in improving the quality for VoIP applications.
AS A
AS D
AS G AS H
AS E AS F
AS B AS C
direct path between AS A and AS Bdirect path between AS B and AS C
direct path between AS A and AS C
provider-to-customer edge
peer-to-peer edge
AS H is
congested
1-hop relay path between AS A and AS C via AS B
Direct Path Is Congested
AS AAS B AS C
AS D AS E
AS F AS G
AS H AS I
direct path between AS A and AS C
direct path between AS A and AS Bdirect path between AS B and AS C
provider-to-customer edge
peer-to-peer edge
Multi-homed AS B As 1-hop Relay
1-hop relay path between AS A and AS C via AS BAS B is multi-homed, connects to AS A and AS C
Outline of Talk
VoIP application introductionVoIP application introduction
Internet e2e latency measurementsInternet e2e latency measurements
Skype measurement and observationsSkype measurement and observations
ASAP protocol design and evaluation
Dalian, China
Shanghai, China
Beijing, China
Jingzhou, China
Vancouver, Canada
Bozeman, MT
Austin, TX
Jersey City, NJ
Reston, VAWilliamsburg, VA
Baltimore, MD
Skype Experimental Sites and Sessions
We have chosen 14 representative Skype sessions
Skype Relay Selection Limits
Limit 1: Long latency due to improper relay node selections.
Session 4
Session 10300 ms
300 ms
Limit 2: Probing multiple latent nodes in the same AS.
Limit 3: Taking a long time to find major relays.
relay node DNS zone name relay path RTT
85.64.x.x barak-online.net 360 ms
85.65.x.x barak-online.net 359 ms
two probed relay nodes in session 8
Limit 4: Generating non-negligible overhead.
before
stabilization
after
stabilization
10
10
Skype Measurement Summary
Although we do not know the routing algorithm of Skype: Non-optimal replay nodes are used often. Seems to only reply on probes to find a relay
node in a ad-hoc way: many probes. The relay nodes are frequently changed even
after the sessions are established. It is an AS-unaware routing.
ASAP: AS-Aware Peer-Relay Selection Method
ASAP Design Rationale
In general, peer nodes with the same IP prefix are relatively close to each other.
With publicly available BGP tables and updates, an up-to-date annotated AS graph can be built.
Paths with longer AS hops are likely to have longer latencies.
An Internet AS-level direct IP routing path usually has the valley-free property.
bootstrap1
bootstrap2
surrogate SA
end host h1
surrogate SB
end host h2
Internet AS graph
IP prefix to clusterSurrogate IP table
IP prefix to ASN tablecluster’s close
cluster set
Internet AS graph
cluster’s top node table
end host h3
cluster Acluster B
cluster C
Three Types of ASAP Nodesbootstrap’s data
structure
cluster surrogate’s data structure
Type 3: end hosts
Type 2: surrogatesType 1: bootstraps
AS 1
AS 2
AS 3
AS 4
AS 5
AS 6
h1
s1
s2
s4s5
s6
s3
h4
h3
h6
provider-to-customer edge
peer-to-peer edge
s1 close cluster
ping
pong
good, 75 ms
s2 – 75 ms
bad, 350 ms
good, 180 ms
s5 – 180 ms
good, 220 ms
s6, h6 – 220 ms
good: RTT < 300 ms && loss rate < 5%
bad: RTT > 300 ms || loss rate > 5%
good, 52 ms
s3, h3 – 52 ms
Close Clusters Construction Process
AS 1
AS 2
AS 3
AS 4
AS 5
AS 6
h1
s1
s2
s4s5
s6
s3
h4
h3
h6
provider-to-customer edge
peer-to-peer edge
h1-h4 Close Relays Selection Process
s1 close cluster
s2 – 75 mss5 – 180 mss6, h6 – 220 mss3, h3 – 52 ms
s4 close cluster
s2 – 50 mss5 – 170 ms
RTTh1-s2 + RTTh4-s2 = 125 ms < 300 mss2 is good relay for h
1-h4 VoIP session
bootstrap1
bootstrap2
surrogate SA
end host h1
surrogate SB
end host h2
Internet AS graph
IP prefix to clusterSurrogate IP table
IP prefix to ASN table
cluster’s close cluster set
Internet AS graph
cluster’s top node table
end host h3
cluster Acluster B
cluster C
control pkt.
voice pkt.
surrogate? surrogate IP
surrogate IP
surrogate?
close set? close set
close set?close set
h2’s close set
h2’s close set?
voice pktsvoice pkts
voice pkts
voice pkts
ASAP Call Session Processbootstrap’s data
structure
cluster surrogate’s data structure
Evaluation Metrics
Number of quality paths: number of relay paths satisfying the RTT and loss rate requirements
Shortest RTT and highest MOS of these quality paths
Overhead: measured by the number of generated messages to find quality path relay nodes
Different Routing Methods
DEDI: uses dedicated relay nodes. (SOSP’01)
RAND: randomly selects relay nodes. (OSDI’04)
MIX: is a combination of RAND and DEDI.
ASAP: selects relay nodes using our AS-aware method.
OPT: always chooses relay nodes that give the shortest overlay routing latency. (Offline method)
Number of Quality Paths
For 90% sessions, ASAP can find more than 5,000 quality paths
DEDI, RAND, and MIX can find no more than 500
quality paths for all sessions
Shortest Path RTT 115 ms
In ASAP and OPT, all sessions have shores
t RTT < 115 ms
1 s
In DEDI, RAND, and MIX, more than 5%
sessions have shortest RTT > 1s
Highest Path MOS 3.85
In ASAP and OPT, all sessions have highes
t MOSs > 3.85
2.9
In DEDI, RAND, and MIX, about 3% sessions have
highest MOSs < 2.9
ASAP Is Highly Scalable
23,366 end hosts 103,625 end hosts
The number of quality paths found by ASAP remains stable under different end host population.
ASAP Has Moderate Overhead
DEDI, RAND, and MIX all probe fixed number of nodes, i.e., 160, 160,
and 200 nodes
In ASAP, 85% sessions generate less than 300
messages
Conclusion
In a global overlay systems, 10% sessions of direct path cannot meet VoIP quality requirements.
For these sessions, there always exist multiple relay paths that can meet the requirements.
Existing relay selection methods, including Skype, do not always select proper relay nodes.
Optimal replay nodes can be found by AS-aware routing. We show ASAP is scalable, light-weight, and outperforms
all existing solutions.
ASAP source code and results can be found at
http://www.cse.ohio-state.edu/~sren/VoIP-Peer-Relay/