new file mode 100644
--- /dev/null
+++ b/src/event/quic/ngx_event_quic_connection.h
@@ -0,0 +1,179 @@
+/*
+ * Copyright (C) Nginx, Inc.
+ */
+
+
+#ifndef _NGX_EVENT_QUIC_CONNECTION_H_INCLUDED_
+#define _NGX_EVENT_QUIC_CONNECTION_H_INCLUDED_
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_event.h>
+#include <ngx_event_quic_transport.h>
+#include <ngx_event_quic_protection.h>
+
+
+#define NGX_QUIC_SEND_CTX_LAST  (NGX_QUIC_ENCRYPTION_LAST - 1)
+
+
+typedef struct ngx_quic_connection_s  ngx_quic_connection_t;
+
+
+typedef struct {
+    ngx_queue_t                       queue;
+    uint64_t                          seqnum;
+    size_t                            len;
+    u_char                            id[NGX_QUIC_CID_LEN_MAX];
+    u_char                            sr_token[NGX_QUIC_SR_TOKEN_LEN];
+} ngx_quic_client_id_t;
+
+
+typedef struct {
+    ngx_udp_connection_t              udp;
+    ngx_quic_connection_t            *quic;
+    ngx_queue_t                       queue;
+    uint64_t                          seqnum;
+    size_t                            len;
+    u_char                            id[NGX_QUIC_CID_LEN_MAX];
+} ngx_quic_server_id_t;
+
+
+typedef struct {
+    ngx_rbtree_t                      tree;
+    ngx_rbtree_node_t                 sentinel;
+
+    uint64_t                          received;
+    uint64_t                          sent;
+    uint64_t                          recv_max_data;
+    uint64_t                          send_max_data;
+
+    uint64_t                          server_max_streams_uni;
+    uint64_t                          server_max_streams_bidi;
+    uint64_t                          server_streams_uni;
+    uint64_t                          server_streams_bidi;
+
+    uint64_t                          client_max_streams_uni;
+    uint64_t                          client_max_streams_bidi;
+    uint64_t                          client_streams_uni;
+    uint64_t                          client_streams_bidi;
+} ngx_quic_streams_t;
+
+
+typedef struct {
+    size_t                            in_flight;
+    size_t                            window;
+    size_t                            ssthresh;
+    ngx_msec_t                        recovery_start;
+} ngx_quic_congestion_t;
+
+
+/*
+ * 12.3.  Packet Numbers
+ *
+ *  Conceptually, a packet number space is the context in which a packet
+ *  can be processed and acknowledged.  Initial packets can only be sent
+ *  with Initial packet protection keys and acknowledged in packets which
+ *  are also Initial packets.
+*/
+typedef struct {
+    enum ssl_encryption_level_t       level;
+
+    uint64_t                          pnum;        /* to be sent */
+    uint64_t                          largest_ack; /* received from peer */
+    uint64_t                          largest_pn;  /* received from peer */
+
+    ngx_queue_t                       frames;
+    ngx_queue_t                       sent;
+
+    uint64_t                          pending_ack; /* non sent ack-eliciting */
+    uint64_t                          largest_range;
+    uint64_t                          first_range;
+    ngx_msec_t                        largest_received;
+    ngx_msec_t                        ack_delay_start;
+    ngx_uint_t                        nranges;
+    ngx_quic_ack_range_t              ranges[NGX_QUIC_MAX_RANGES];
+    ngx_uint_t                        send_ack;
+} ngx_quic_send_ctx_t;
+
+
+struct ngx_quic_connection_s {
+    uint32_t                          version;
+
+    ngx_str_t                         scid;  /* initial client ID */
+    ngx_str_t                         dcid;  /* server (our own) ID */
+    ngx_str_t                         odcid; /* original server ID */
+
+    struct sockaddr                  *sockaddr;
+    socklen_t                         socklen;
+
+    ngx_queue_t                       client_ids;
+    ngx_queue_t                       server_ids;
+    ngx_queue_t                       free_client_ids;
+    ngx_queue_t                       free_server_ids;
+    ngx_uint_t                        nclient_ids;
+    ngx_uint_t                        nserver_ids;
+    uint64_t                          max_retired_seqnum;
+    uint64_t                          client_seqnum;
+    uint64_t                          server_seqnum;
+
+    ngx_uint_t                        client_tp_done;
+    ngx_quic_tp_t                     tp;
+    ngx_quic_tp_t                     ctp;
+
+    ngx_quic_send_ctx_t               send_ctx[NGX_QUIC_SEND_CTX_LAST];
+
+    ngx_quic_frames_stream_t          crypto[NGX_QUIC_ENCRYPTION_LAST];
+
+    ngx_quic_keys_t                  *keys;
+
+    ngx_quic_conf_t                  *conf;
+
+    ngx_event_t                       push;
+    ngx_event_t                       pto;
+    ngx_event_t                       close;
+    ngx_msec_t                        last_cc;
+
+    ngx_msec_t                        latest_rtt;
+    ngx_msec_t                        avg_rtt;
+    ngx_msec_t                        min_rtt;
+    ngx_msec_t                        rttvar;
+
+    ngx_uint_t                        pto_count;
+
+    ngx_queue_t                       free_frames;
+    ngx_chain_t                      *free_bufs;
+    ngx_buf_t                        *free_shadow_bufs;
+
+#ifdef NGX_QUIC_DEBUG_ALLOC
+    ngx_uint_t                        nframes;
+    ngx_uint_t                        nbufs;
+#endif
+
+    ngx_quic_streams_t                streams;
+    ngx_quic_congestion_t             congestion;
+    off_t                             received;
+
+    ngx_uint_t                        error;
+    enum ssl_encryption_level_t       error_level;
+    ngx_uint_t                        error_ftype;
+    const char                       *error_reason;
+
+    ngx_uint_t                        shutdown_code;
+    const char                       *shutdown_reason;
+
+    unsigned                          error_app:1;
+    unsigned                          send_timer_set:1;
+    unsigned                          closing:1;
+    unsigned                          shutdown:1;
+    unsigned                          draining:1;
+    unsigned                          key_phase:1;
+    unsigned                          validated:1;
+};
+
+
+ngx_quic_frame_t *ngx_quic_alloc_frame(ngx_connection_t *c);
+void ngx_quic_queue_frame(ngx_quic_connection_t *qc, ngx_quic_frame_t *frame);
+void ngx_quic_close_connection(ngx_connection_t *c, ngx_int_t rc);
+
+#endif