Comparison between Skype and SIP-based Peer-to-Peer Voice-Over-IP

Overlay Network

Comparison between Skype and SIP-based Peer-to-Peer Voice-Over-IP

Overlay Network

Johnson Lee

EECE 565 Data Communications

2

Outline

• P2P versus Client-Server

• P2P-SIP design goal

• Overlay Network of Skype and P2P-SIP

• Login Sequences

• Advance Service Comparison

• Security

• Performance

3

Peer-to-Peer / Client-Servier

• Client-Server vs P2P– Scalability– Infrastructure cost

• Structured vs Unstructured– Search time– Data distribution

4

P2P-SIP Design Goals

Goal Description Zero Configuration The system should be able to automatically configure itself. (e.g. by

detecting NAT and firewall settings, discovering neighbouring peers and performing initial registration.)

Heterogeneous

nodes

It should be able to adapt to available resources and distinguish between peers with different capacity and availability constraints. This favors the distinction between nodes and super-nodes as in KaZaA.

Efficient Lookup Blind search based on flooding is inefficient. The system should use an underlying DHT to optimize lookup.

Advanced Services It should support advanced telephony services such as offline voice messaging, multi-party conferencing, call transfer and call forwarding as well as advanced Internet services such as presence and instant messaging.

Interoperability It should easily integrate with existing protocols and IP telephony infrastructure. We choose SIP as the signaling protocol for interoperability.

Goal Description Zero Configuration The system should be able to automatically configure itself. (e.g. by

detecting NAT and firewall settings, discovering neighbouring peers and performing initial registration.)

Heterogeneous

nodes

It should be able to adapt to available resources and distinguish between peers with different capacity and availability constraints. This favors the distinction between nodes and super-nodes as in KaZaA.

Efficient Lookup Blind search based on flooding is inefficient. The system should use an underlying DHT to optimize lookup.

Advanced Services It should support advanced telephony services such as offline voice messaging, multi-party conferencing, call transfer and call forwarding as well as advanced Internet services such as presence and instant messaging.

Interoperability It should easily integrate with existing protocols and IP telephony infrastructure. We choose SIP as the signaling protocol for interoperability.

5

Skype Overlay Network

• Unstructured• KaZaA predecssor based

– Super node– Ordinary node– Login server

• STUN and TURN protocols for firewall and NAT traversal– Simple Traversal of UDP over NAT– Traversal Using Relay NAT

6

P2P-SIP Overlay Network

• Based on Chord Distributed Hash Table (DHT)

• Structured• O(log N) lookup time• Finger table

• STUN and TURN firewall and NAT traversal as well

7

Login Sequence 1 - Skype

Start

Send UDP packet(s) to HC IP

address and port

Responsewithin 5 s

TCP connectionattempt with HC IPaddress and port

Connected

TCP connectionattempt with HC IP

address and port 80(HTTP port)

Connected

TCP connectionattempt with HC IPaddress and port 443 (HTTPS port)

Connected

ConnectionAttempt == 5

Failure

Wait for 6 seconds

Success

Yes

Yes

No

No Yes

No

Yes

No

Yes

No

8

Login Sequence 2 – P2P-SIP

• Multicast TTL = 1

• Service Location Protocol (SLP) [LAN peers]

• Bootstrap

• Cached

9

Advanced Services Comparison

• Offline Messaging Issue – Where to store?– Skype stores at it message originator– P2P-SIP proposes storing it at DHT

• Replication strategy for reliability

• Call transfer and call forwarding are SIP features that would be available in non-P2P SIP.– Super node instead of centralized database– Required feature for SIP (not as crucial for Skype)

Offline

Messaging Multi-Party Conference

Call Transfer

Call Forwarding

Presence Instant

Messaging Skype ◦ ◦ ◦ ◦

P2P-SIP ◦ ◦ ◦ ◦ ◦ ◦

Offline

Messaging Multi-Party Conference

Call Transfer

Call Forwarding

Presence Instant

Messaging Skype ◦ ◦ ◦ ◦

P2P-SIP ◦ ◦ ◦ ◦ ◦ ◦

10

Security

• P2P-SIP– Malicious Node

Hop-by-hop TLS(Tunneling)

– FreeridingIncentives

– Problem:No centralized

login server to certify.

Trust via reputation?

• Skype– Encryption

AES 256bits– Key Exchange

RSA 2048– Public Key

Certified by Login Server

11

Performance

• P2P-SIP Scalable?– Yes, suppose nodes support 10 request/sec, minimum refresh

rate of one minute, call rate of one call per minute per node

• Latency?– P2P-SIP:

10,000 node system avg 6 hopes, SIP call setup ~200ms; therefore, 1-2 s delay

– SkypeAverage 3-8 second for user location based on a 2004 study

rc

C

N 2max90102x = C = 10, c = 1/60, and r = 1/60

3002 =

12

References1. Skype Networks. http://www.skype.com2. KaZaA. http://www.kazaa.com3. K. Singh and H. Schulzrinne. Peer-to-peer Internet telephony using SIP.

Technical Report CUCS-044-04, Department of Computer Science, Columbia University, New York, NY, Oct. 2004.

4. J. Rosenber, Henning Schulzrinne, G. Camarillo, A. R. Johnston, J. Peterson, R. Parks, M. Handley, and E. Schooler, "SIP: session initialiozation, protocol,” RFC 3261, Internet Engineering Task Force, June 2002

5. P2P-SIP. http://www.p2psip.org/6. Singh, K. and Schulzrinne, H. 2005. Peer-to-peer internet telephony

using SIP. In Proceedings of the international Workshop on Network and Operating Systems Support For Digital Audio and Video (Stevenson, Washington, USA, June 13 - 14, 2005). NOSSDAV '05. ACM Press, New York, NY, 63-68. DOI= http://doi.acm.org/10.1145/1065983.1065999

Questions/Comments?Questions/Comments?

Thank You For Listening

14

Login Sequence - Incoming

15

Service Location Protocol

• RFC 2608

• Allows computers and other devices to find services in a local area network without prior configuration.

• “service:printer:lpr://myprinter/myqueue”

16

Advanced Encryption Standard• Aka Rijndael• Block Cipher• Replaces DES (and the modified 3DES)• 128, 192, 256 bits keys

1. AddRoundKey — each byte of the state is combined with the round key; each round key is derived from the cipher key using a key schedule.

2. SubBytes — a non-linear substitution step where each byte is replaced with another according to a lookup table.

3. ShiftRows — a transposition step where each row of the state is shifted cyclically a certain number of steps.

4. MixColumns — a mixing operation which operates on the columns of the state, combining the four bytes in each column using a linear transformation.