diff --git a/model/model.go b/model/model.go
index e5f5143..162f279 100644
--- a/model/model.go
+++ b/model/model.go
@@ -2,6 +2,7 @@
 package model
 
 import (
+	"sort"
 	"strings"
 	"time"
 )
@@ -287,6 +288,42 @@ type Stat struct {
 	Conns    int64 `json:"conns"`
 	BytesIn  int64 `json:"bytesIn"`  // client -> target
 	BytesOut int64 `json:"bytesOut"` // target -> client
+	// Sources are the busiest client addresses behind these numbers (at most MaxSources),
+	// busiest first. Addresses beyond that are only counted in the totals above.
+	Sources []SourceStat `json:"sources,omitempty"`
+}
+
+// MaxSources is how many client addresses an edge names per port in one report.
+const MaxSources = 10
+
+// SourceStat is one client address's traffic on a port since the last report.
+type SourceStat struct {
+	IP       string `json:"ip"`
+	Conns    int64  `json:"conns"`
+	BytesIn  int64  `json:"bytesIn"`
+	BytesOut int64  `json:"bytesOut"`
+}
+
+// TopSources keeps the n busiest of a port's client addresses (by bytes, then connections), busiest first.
+func TopSources(all map[string]*SourceStat, n int) []SourceStat {
+	out := make([]SourceStat, 0, len(all))
+	for _, s := range all {
+		out = append(out, *s)
+	}
+	sort.Slice(out, func(i, j int) bool {
+		a, b := out[i], out[j]
+		if ta, tb := a.BytesIn+a.BytesOut, b.BytesIn+b.BytesOut; ta != tb {
+			return ta > tb
+		}
+		if a.Conns != b.Conns {
+			return a.Conns > b.Conns
+		}
+		return a.IP < b.IP
+	})
+	if len(out) > n {
+		out = out[:n]
+	}
+	return out
 }
 
 // LogEntry is one access-log line.
@@ -325,16 +362,19 @@ type ContainerPort struct {
 
 // EdgeReport is what blacktip posts back.
 type EdgeReport struct {
-	IPs        []string                 `json:"ips"`
-	PublicKey  string                   `json:"publicKey"` // the edge's WireGuard public key
-	Status     map[string]MappingStatus `json:"status"`
-	Stats      map[string]Stat          `json:"stats"` // deltas since last report
-	Containers []Container              `json:"containers"`
-	MailChecks map[string]MailCheck     `json:"mailChecks"` // by mail-egress ID
-	Version    string                   `json:"version,omitempty"`
-	AutoUpdate bool                     `json:"autoUpdate,omitempty"`
-	UpdateMsg  string                   `json:"updateMsg,omitempty"` // outcome of the update asked for by UpdateID
-	UpdateID   string                   `json:"updateId,omitempty"`
+	IPs       []string                 `json:"ips"`
+	PublicKey string                   `json:"publicKey"` // the edge's WireGuard public key
+	Status    map[string]MappingStatus `json:"status"`
+	Stats     map[string]Stat          `json:"stats"` // deltas since last report
+	// StatsSeconds is how long Stats covers (the time since the previous report that carried them),
+	// so a rate can be worked out however irregular the reports are.
+	StatsSeconds float64              `json:"statsSeconds,omitempty"`
+	Containers   []Container          `json:"containers"`
+	MailChecks   map[string]MailCheck `json:"mailChecks"` // by mail-egress ID
+	Version      string               `json:"version,omitempty"`
+	AutoUpdate   bool                 `json:"autoUpdate,omitempty"`
+	UpdateMsg    string               `json:"updateMsg,omitempty"` // outcome of the update asked for by UpdateID
+	UpdateID     string               `json:"updateId,omitempty"`
 	// progress of that update, for the dashboard's progress bar and log
 	UpdateStage string   `json:"updateStage,omitempty"`
 	UpdatePct   int      `json:"updatePct,omitempty"`
diff --git a/model/model_test.go b/model/model_test.go
index bdb18fc..742e2b4 100644
--- a/model/model_test.go
+++ b/model/model_test.go
@@ -23,3 +23,19 @@ func TestRedirectLocation(t *testing.T) {
 		t.Error("IsRedirect is wrong")
 	}
 }
+
+func TestTopSources(t *testing.T) {
+	all := map[string]*SourceStat{
+		"a": {IP: "a", Conns: 1, BytesIn: 10, BytesOut: 5},
+		"b": {IP: "b", Conns: 9, BytesIn: 1},
+		"c": {IP: "c", Conns: 2, BytesIn: 100},
+		"d": {IP: "d", Conns: 3, BytesIn: 1},
+	}
+	got := TopSources(all, 3)
+	if len(got) != 3 || got[0].IP != "c" || got[1].IP != "a" || got[2].IP != "b" {
+		t.Fatalf("order: %+v", got) // c most bytes, a next, then b beats d on connections
+	}
+	if got := TopSources(all, 10); len(got) != 4 {
+		t.Fatalf("all: %+v", got)
+	}
+}