EarthLink SIPshare implementation notes

Building the network
Distributed content search
Content transfer

Building the network

EarthLink SIPshare peers builds its network by sending to each peer in its peers file a stateful SIP Subscribe message.

Here, the Peer A at 209.179.2.62 is "subscribing" to the peer list of Peer B at 209.179.2.61: 

         SUBSCRIBE sip:peer-list@209.179.2.61;transport=udp SIP/2.0
         Call-ID: 5560a044871b02ba7074e4816857f27d@209.179.2.62
         CSeq: 1 SUBSCRIBE
         From: "fluxMark" <sip:msp@209.179.2.62>;tag=1308
         To: "Peer List" <sip:peer-list@209.179.2.61>
         Via: SIP/2.0/UDP 209.179.2.62:5060;branch=z9hG4bKed6ffbb76ca2ed9b3aa7d938cb05ee19
         Max-Forwards: 70
         Contact: "fluxMark" <sip:msp@209.179.2.62:5060;transport=udp>
         Event:  x-earthlink-sip-fpx
         Accept: application/x-earthlink-peerlist-fpx
         Content-Length: 0
to which Peer B responds 
         SIP/2.0 200 OK
         Call-ID: 5560a044871b02ba7074e4816857f27d@209.179.2.62
         CSeq: 1 SUBSCRIBE
         From: "fluxMark" <sip:msp@209.179.2.62>;tag=1308
         To: "Peer List" <sip:peer-list@209.179.2.61>;tag=9791
         Via: SIP/2.0/UDP 209.179.2.62:5060;branch=z9hG4bKed6ffbb76ca2ed9b3aa7d938cb05ee19
         Max-Forwards: 70
         Contact: "fargesiaMark" <sip:102@209.179.2.61:5060;transport=udp>
         Expires: 86400
         Content-Length: 0
thus creating a dialog for subsequent Notify messages.

When Peer B learns of peers not already part of its network, it sends an in-dialog Notify to each Peer A that has subscribed to its peer list 

         NOTIFY sip:msp@209.179.2.62:5060;transport=udp SIP/2.0
         Call-ID: 5560a044871b02ba7074e4816857f27d@209.179.2.62
         CSeq: 1 NOTIFY
         To: "fluxMark" <sip:msp@209.179.2.62>;tag=1308
         From: "Peer List" <sip:peer-list@209.179.2.61>;tag=9791
         Max-Forwards: 70
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=z9hG4bKe20d35dcc81aef8501106f28a47d9036
         Contact: "fargesiaMark" <sip:102@209.179.2.61:5060;transport=udp>
         Event:  x-earthlink-sip-fpx
         Subscription-State: active;expires=86400
         Content-Type: application/x-earthlink-peerlist-fpx
         Content-Length: 96
         
         <?xml version="1.0" encoding="UTF-8"?>
         <peerlist>
           <peer>209.179.2.62</peer>
         </peerlist>
followed by 200 OK from Peer A 
         SIP/2.0 200 OK
         Call-ID: 5560a044871b02ba7074e4816857f27d@209.179.2.62
         CSeq: 1 NOTIFY
         To: "fluxMark" <sip:msp@209.179.2.62>;tag=1308
         From: "Peer List" <sip:peer-list@209.179.2.61>;tag=9791
         Max-Forwards: 70
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=z9hG4bKe20d35dcc81aef8501106f28a47d9036
         Contact: "fluxMark" <sip:msp@209.179.2.62:5060;transport=udp>
         Content-Length: 0
In this case, Peer B is informing Peer A that B now knows about A. This is not particularly useful to Peer A, but when B's network grows, A will learn from B the addresses of other hosts not A.

Distributed content search

When Peer U wishes to locate content on the network, it sends a search message to all the Peers V to whom it has subscribed for peer lists. This choice of to which peers to send a content search message is somewhat arbitrary.

We could have chosen to send to all Peers W of which we are simply aware, whether we are subscribed to their respective peer lists or not, and which is a superset of all Peers V. We chose the set V for simplicity.

That said, Peer U sends a stateless Subscribe to Peer V, to whom it happens to be subscribed for peer lists: 

         SUBSCRIBE sip:search@209.179.2.62;transport=udp SIP/2.0
         Call-ID: d33a2b31a59ea843a33a37e20c56aade@209.179.2.61
         CSeq: 1 SUBSCRIBE
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=5256
         To: "Search" <sip:search@209.179.2.62>
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=30392e3137392e322e36313a3530363
         Max-Forwards: 70
         Contact: "fargesiaMark" <sip:102@209.179.2.61:5060;transport=udp>
         Event:  x-earthlink-sip-fpx
         Accept: application/x-earthlink-cachehits-fpx
         Content-Type: application/x-earthlink-searchfilter-fpx
         Content-Length: 88

         <?xml version="1.0" encoding="UTF-8"?>
         <search>
           <regex>mount<regex>
         <search>
Note that the Subscribe body contains a filter document specifying in what content Peer U is interested. Peer V responds: 
         SIP/2.0 200 OK
         Call-ID: d33a2b31a59ea843a33a37e20c56aade@209.179.2.61
         CSeq: 1 SUBSCRIBE
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=5256
         To: "Search" <sip:search@209.179.2.62>;tag=6132
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=30392e3137392e322e36313a3530363
         Max-Forwards: 70
         Contact: "fluxMark" <sip:msp@209.179.2.62:5060;transport=udp>
         Expires: 0
         Content-Length: 0
         

         NOTIFY sip:102@209.179.2.61:5060;transport=udp SIP/2.0
         Call-ID: 03fc7456478dfef5548c5c47af4b2cae@209.179.2.62
         CSeq: 1 NOTIFY
         From: "fluxMark" <sip:msp@209.179.2.62>;tag=6243
         To: <sip:102@209.179.2.61:5060;transport=udp>
         Via: SIP/2.0/UDP 209.179.2.62:5060;branch=30392e3137392e322e36323a3530363
         Max-Forwards: 70
         Contact: "fluxMark" <sip:msp@209.179.2.62:5060;transport=udp>
         Event:  x-earthlink-sip-fpx
         Subscription-State: terminated
         Content-Type: application/x-earthlink-cachehits-fpx
         Content-Length: 216
         
         <?xml version="1.0" encoding="UTF-8"?>
         <sharing>
           <file>
             <name>mountains.jpg</name>
             <size>3342000</size>
             <digest>287af1e2a0180a4df0edd01ee9b38130</digest>
           <file>
         <sharing>
where Peer V sends a stateless Notify containing content hit information to Peer U's Contact header field. Note that with the Notify message sent, the "subscription" for this content has expired and is terminated. If Peer U wants to be notified of new content on Peer W that matches this same regex, Peer V must perform another search to pick up information on this new content. Peer W will not, in other words, notify Peer U if matching content develops on W after the initial search by U.

Peer U sends its 200 OK in response to Peer V's Notify: 

         SIP/2.0 200 OK
         Call-ID: 03fc7456478dfef5548c5c47af4b2cae@209.179.2.62
         CSeq: 1 NOTIFY
         From: "fluxMark" <sip:msp@209.179.2.62>;tag=6243
         To: <sip:102@209.179.2.61:5060;transport=udp>;tag=789
         Via: SIP/2.0/UDP 209.179.2.62:5060;branch=30392e3137392e322e36323a3530363
         Max-Forwards: 70
         Contact: "fargesiaMark" <sip:102@209.179.2.61:5060;transport=udp>
         Content-Length: 0
The content search becomes fully distributed on behalf of Peer U, when all Peers V send a similar message (not shown) to all Peers W known to it, preserving the Contact header field value from the original message from Peer U. Each receiving Peer W examines its content store and issues a Notify to Peer U similar to Peer V's Notify above, but matching W's content store, not V's.

To prevent searches from circulating indefinitely on the network, each Peer W maintains a list of Call-IDs seen up to some maximum number, and refuses to forward search messages bearing Call-IDs seen in the past.

Content transfer

When Peer U locates interesting content on Peer W, it can request a content transfer using a SIP Invite message. The Invite is made to the hash of the content file, learned from the associated Notify above: 
         INVITE sip:287af1e2a0180a4df0edd01ee9b38130@209.179.2.62;transport=udp SIP/2.0
         Call-ID: a8d78ccab367086072f280ef0b818bca@209.179.2.61
         CSeq: 1 INVITE
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=6591
         To: "Download" <sip:287af1e2a0180a4df0edd01ee9b38130@209.179.2.62>
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=z9hG4bK9e89e38564ca687a0a0ad1a9ec5f23c1
         Max-Forwards: 70
         Contact: "fargesiaMark" <sip:102@209.179.2.61:5060;transport=udp>
         Allow: INVITE,BYE,SUBSCRIBE,NOTIFY
         Content-Type: application/sdp
         Content-Length: 91
         
         v=0
         o=- 0 0 IN IP4 209.179.2.62
         s=EarthLinkPFX
         c=IN IP4 209.179.2.62
         t=0 0
         m=data 1960 udp
The Invite SDP body contains offer information on where to connect to the Peer W's FSP file server process, in this case 209.179.2.62 UDP port 1960.

Peer W responds with a 200 OK, but changes the SDP service port to match where its FSP server is running and awaiting file transfer block requests: 

         SIP/2.0 200 OK
         Call-ID: a8d78ccab367086072f280ef0b818bca@209.179.2.61
         CSeq: 1 INVITE
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=6591
         To: "Download" <sip:287af1e2a0180a4df0edd01ee9b38130@209.179.2.62>;tag=8923
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=z9hG4bK9e89e38564ca687a0a0ad1a9ec5f23c1
         Max-Forwards: 70
         Content-Type: application/sdp
         Contact: "fluxMark" <sip:msp@209.179.2.62:5060;transport=udp>
         Content-Length: 97
         
         v=0
         o=- 0 0 IN IP4 209.179.2.62
         s=EarthLinkPFX
         c=IN IP4 209.179.2.62
         t=0 0
         m=data 2121 udp

which is followed by Peer U's ACK 

         ACK sip:msp@209.179.2.62:5060;transport=udp SIP/2.0
         Call-ID: a8d78ccab367086072f280ef0b818bca@209.179.2.61
         CSeq: 1 ACK
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=6591
         To: "Download" <sip:287af1e2a0180a4df0edd01ee9b38130@209.179.2.62>;tag=8923
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=30392e3137392e322e36313a3530363
         Max-Forwards: 70
         Content-Length: 0
Peer U now issues FSP-like requests (not shown) out of the SIP signalling band for the content on Peer W. When Peer U finishes the transfer, it sends a SIP Bye message: 
         BYE sip:msp@209.179.2.62:5060;transport=udp SIP/2.0
         Call-ID: a8d78ccab367086072f280ef0b818bca@209.179.2.61
         CSeq: 2 BYE
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=6591
         To: "Download" <sip:287af1e2a0180a4df0edd01ee9b38130@209.179.2.62>;tag=8923
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=z9hG4bKa596629d94b7acc25178d9fd9cdc93d6
         Max-Forwards: 70
         Content-Length: 0
followed by Peer W's 200 OK response: 
         SIP/2.0 200 OK
         Call-ID: a8d78ccab367086072f280ef0b818bca@209.179.2.61
         CSeq: 2 BYE
         From: "fargesiaMark" <sip:102@209.179.2.61>;tag=6591
         To: "Download" <sip:287af1e2a0180a4df0edd01ee9b38130@209.179.2.62>;tag=8923
         Via: SIP/2.0/UDP 209.179.2.61:5060;branch=z9hG4bKa596629d94b7acc25178d9fd9cdc93d6
         Max-Forwards: 70
         Content-Length: 0
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