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/