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author | Bernd Wachter <bwachter-tmw@lart.info> | 2010-08-13 19:14:33 +0300 |
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committer | Bernd Wachter <bwachter-tmw@lart.info> | 2010-08-15 00:34:20 +0300 |
commit | 7950455d2370bfcdd1ed5472c9e5401b0fd8dbe8 (patch) | |
tree | 9867118f14595a22bf648b089337b6df7f1192bd /libs/enet/design.txt | |
parent | 07d6c28b6cbd83a73b0613bffe67be90a86d58ca (diff) | |
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Add enet files
Diffstat (limited to 'libs/enet/design.txt')
-rw-r--r-- | libs/enet/design.txt | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/libs/enet/design.txt b/libs/enet/design.txt new file mode 100644 index 00000000..9a88dba9 --- /dev/null +++ b/libs/enet/design.txt @@ -0,0 +1,117 @@ +* Why ENet? + + ENet evolved specifically as a UDP networking layer for the multiplayer +first person shooter Cube. Cube necessitated low latency communcation with +data sent out very frequently, so TCP was an unsuitable choice due to its +high latency and stream orientation. UDP, however, lacks many sometimes +necessary features from TCP such as reliability, sequencing, unrestricted +packet sizes, and connection management. So UDP by itself was not suitable +as a network protocol either. No suitable freely available networking +libraries existed at the time of ENet's creation to fill this niche. + + UDP and TCP could have been used together in Cube to benefit somewhat +from both of their features, however, the resulting combinations of protocols +still leaves much to be desired. TCP lacks multiple streams of communication +without resorting to opening many sockets and complicates delineation of +packets due to its buffering behavior. UDP lacks sequencing, connection +management, management of bandwidth resources, and imposes limitations on +the size of packets. A significant investment is required to integrate these +two protocols, and the end result is worse off in features and performance +than the uniform protocol presented by ENet. + + ENet thus attempts to address these issues and provide a single, uniform +protocol layered over UDP to the developer with the best features of UDP and +TCP as well as some useful features neither provide, with a much cleaner +integration than any resulting from a mixture of UDP and TCP. + +* Connection management + + ENet provides a simple connection interface over which to communicate +with a foreign host. The liveness of the connection is actively monitored +by pinging the foreign host at frequent intervals, and also monitors the +network conditions from the local host to the foreign host such as the +mean round trip time and packet loss in this fashion. + +* Sequencing + + Rather than a single byte stream that complicates the delineation +of packets, ENet presents connections as multiple, properly sequenced packet +streams that simplify the transfer of various types of data. + + ENet provides sequencing for all packets by assigning to each sent +packet a sequence number that is incremented as packets are sent. ENet +guarentees that no packet with a higher sequence number will be delivered +before a packet with a lower sequence number, thus ensuring packets are +delivered exactly in the order they are sent. + + For unreliable packets, ENet will simply discard the lower sequence +number packet if a packet with a higher sequence number has already been +delivered. This allows the packets to be dispatched immediately as they +arrive, and reduce latency of unreliable packets to an absolute minimum. +For reliable packets, if a higher sequence number packet arrives, but the +preceding packets in the sequence have not yet arrived, ENet will stall +delivery of the higher sequence number packets until its predecessors +have arrived. + +* Channels + + Since ENet will stall delivery of reliable packets to ensure proper +sequencing, and consequently any packets of higher sequence number whether +reliable or unreliable, in the event the reliable packet's predecessors +have not yet arrived, this can introduce latency into the delivery of other +packets which may not need to be as strictly ordered with respect to the +packet that stalled their delivery. + + To combat this latency and reduce the ordering restrictions on packets, +ENet provides multiple channels of communication over a given connection. +Each channel is independently sequenced, and so the delivery status of +a packet in one channel will not stall the delivery of other packets +in another channel. + +* Reliability + + ENet provides optional reliability of packet delivery by ensuring the +foreign host acknowledges receipt of all reliable packets. ENet will attempt +to resend the packet up to a reasonable amount of times, if no acknowledgement +of the packet's receipt happens within a specified timeout. Retry timeouts +are progressive and become more lenient with every failed attempt to allow +for temporary turbulence in network conditions. + +* Fragmentation and reassembly + + ENet will send and deliver packets regardless of size. Large packets are +fragmented into many smaller packets of suitable size, and reassembled on +the foreign host to recover the original packet for delivery. The process +is entirely transparent to the developer. + +* Aggregation + + ENet aggregates all protocol commands, including acknowledgements and +packet transfer, into larger protocol packets to ensure the proper utilization +of the connection and to limit the opportunities for packet loss that might +otherwise result in further delivery latency. + +* Adaptability + + ENet provides an in-flight data window for reliable packets to ensure +connections are not overwhelmed by volumes of packets. It also provides a +static bandwidth allocation mechanism to ensure the total volume of packets +sent and received to a host don't exceed the host's capabilities. Further, +ENet also provides a dynamic throttle that responds to deviations from normal +network connections to rectify various types of network congestion by further +limiting the volume of packets sent. + +* Portability + + ENet works on Windows and any other Unix or Unix-like platform providing +a BSD sockets interface. The library has a small and stable code base that +can easily be extended to support other platforms and integrates easily. + +* Freedom + + ENet demands no royalties and doesn't carry a viral license that would +restrict you in how you might use it in your programs. ENet is licensed under +a short-and-sweet MIT-style license, which gives you the freedom to do anything +you want with it (well, almost anything). + + |