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