diff --git a/content/notes/21-data-link-layer-LAN.md b/content/notes/21-data-link-layer.md
similarity index 99%
rename from content/notes/21-data-link-layer-LAN.md
rename to content/notes/21-data-link-layer.md
index c79ea0563..0534ec8fe 100644
--- a/content/notes/21-data-link-layer-LAN.md
+++ b/content/notes/21-data-link-layer.md
@@ -1,5 +1,5 @@
 ---
-title: "21-data-link-layer-LAN"
+title: "21-data-link-layer"
 aliases: 
 tags: 
 - cosc203
diff --git a/content/notes/22-LAN-physical-layer.md b/content/notes/22-LAN-physical-layer.md
index c5b11ec71..800896c22 100644
--- a/content/notes/22-LAN-physical-layer.md
+++ b/content/notes/22-LAN-physical-layer.md
@@ -47,8 +47,21 @@ Address resolution protocol
 arp table: each IP node on lan has table
 - IP/MAC mappings for some LAN nodes
 - mapping is forgotten after TTL is exceeded (usually 20min)
-- 
+
+![arp example](https://i.imgur.com/dnj9Fvi.png)
 
 # Switch vs Router
+switch:
+- link layer deivce
+- takes an active role
+- store and foward ethernet frames
+- examine incoming frame's MAC addr, selectively forward frame to one-or-more outgoing links when frame is to be fowarded on segment, uses CSMA/CD
+- transparent
+	- hosts unaware of presence of switches
+- plug and play, self-learning
+	- switches do not need to be configured
+
+multiple simultaneous transmissions
+- hosts have direct connection to sw
 
 # All layers together
\ No newline at end of file