Introduction of New Verse Protocol Jiří Hnídek Technical University of Liberec Czech Republic

Transcription

1 Introduction of New Verse Protocol Jiří Hnídek Technical University of Liberec Czech Republic

2 Introduction & History Network protocol Real-time sharing of 2D/3D data Eskil Stenbeerg author of original Verse Uni-Verse consortium Ph.D. studies Implementation of Verse protocol to Blender New Verse specification and implementation

3 Demonstration

4 Original Verse weak parts Only one UDP socket (client, server) Security Not described in specification, handshake, etc. Not aware of Man-in-the-middle attack XOR encryption, own RSA, no MAC Resend mechanism API and data model Inefficient data transmission No PMTU discovery (packet fragmentation)

5 Network protocol Data model Verse API Implementation

6 Network Protocol

7 Requirements Real-time Low latencies Sharing Reliability (semi-reliability) Robustness Security Application layer

8 Transport Protocol UDP Datagrame, unreliable, widely supported TCP Stream, realiable, widely supported SCTP Message based, reliable/semi-reliable, modern, not widely supported DCCP Datagrame, unreliable, congestion control, handshake, teardown, not widely support

9 Design of New Network Protocol Specification Verification Promela, Spin Implementation Testing & Conformance Testing

10 Main Features of New Verse Protocol TCP and TLS (OpenSSL) used for: User authentication Negotiation of UDP connection, cookie, etc. UDP used for real-time sharing Handshake, PMTU discovery, Teardown New resend mechanism DTLS (OpenSSL - experimental) Commands with variable length, compression Congestion control, scheduling (WIP)

11 Resend Mechanism Basic principle Resend only fresh data (drop obsolete) Positive and negative acknowledgment Piggy-packing of acknowledgment Acknowledgment of acknowledgment Compression of ACK- NAK vector

12 client server o o pay_id= >+ ack_id=17 ack=31 +< pay_id=52 ack_id=17 ack=31 +< ack_id=26 ank_id=31 ack= >+ pay_id=32 ack_id=26 ank_id=31 ack= >X pay_id=33 ack_id=26 ank_id=31 ack= >+ ack_id=18 ank_id=52 nak=32 ack=33 +< pay_id=53 ack_id=18 ank_id=52 nak=32 ack=33 +<

13 Packet Structure P A A S F 0 Version RES A C N Y I RES Window Size Y K K N N Payload ID ACK_NAK ID ANK ID (last acknowledged payload packet) ACK & NAK Commands System Commands Node Commands

14 Packet Structure of Old Verse Payload ID Commands

15 Compression Command compression Every command has length (except ACK/NAK) More commands with same type is transferred as one command with many parameter One command type has several modification More or less items could be repeated DTLS, Zlib DEFLATE

16 Example of g_vertex_set_real32

17 Data Model

18 Nodes One type of node Access permissions, Locks Subscribers Priorities of nodes (WIP) Links between nodes (tree structure) Tag groups Tags (char, short, int, float, string, etc.) Arrays

19 Access Permissions User can read content of node (r) User can change content of node (w) Owner of node can read and change content of node (u) Special access for some other user (ACL) Permissions for other users (o)

20 Special Nodes Root Node (ID=0) Owner: server, Permissions: other:r (same: ID=1*,2) Parent of Avatar Nodes (ID=1) Server creates and destroys avatar nodes Server is owner of Avatar nodes, perm: user:w Parent of User Nodes (ID=2) Server create user nodes during start Parent of Scene Nodes ID=3 (owner: server, perm: other:rw)

21 Example of Node Tree

22 Implementation

23 Verse Server Main listen thread Listening TCP socket Create new TCP connection thread and socekt Each connection has 2 threads TCP thread: negotiation of new UDP connection UDP thread: own UDP socket, data exchange One data thread Synchronization with UDP thread with 'queue'

24 Threads of Verse Server

25 Verse Client Each connection has 2 communication threads (TCP, UDP) Each connection has own TCP and UDP socket Communication between main thread and UDP thread with 'queue'

26 Queue

27 Technology: Server & Client Pure C language, sockets Libraries pthread, OpenSSL, (LDAP) Doxygen documentation libverse.a 75 kb libssl.a + libcrypto.a = 2MB

28 New Verse API

29 #include <verse.h> Registration of callback functions: Each callback function has own function for registration (less confusing for developers) Examples: void register_receive_user_authenticate(void (*func) (const uint32 session_id,const char *username, const uint8 auth_methods_count, const uint8 *methods))

30 Connect to the server Connect: int verse_send_connect_request(const char *hostname, const char *service, const uint16 flags, uint32 *session_id) hostname: name of server service: port number, /etc/services flags: DGRAM_SEC_NONE/DGRAM_SEC_DTLS session_id: unique identifies of session with server At least basic callback function has to be registered before calling verse_send_connect_request()

31 Call callback functions int verse_callback_update(const int session_id) When received commands are in incoming queues, then appropriate callback function is called Call it from main application thread. How often should it be called? Once per frame!

32 verse_send_* functions These functions add appropriate commands to the outgoing queues Commands are removed from queue by connection thread and sent to the server Call them as often as you want Example: int verse_send_node_create(const uint32 session_id)

33 Acknowledgment This work was supported by the research project TUL/7822/115 financed by MŠMT of the Czech Republic.

34 Thanks for your attention!