vault backup: 2022-10-18 15:09:16

content/notes/22-LAN-physical-layer.md

@@ -62,6 +62,46 @@ switch:
 	- switches do not need to be configured
 
 multiple simultaneous transmissions
-- hosts have direct connection to sw
+- hosts have dedicated direct connection to switch
+- switches can buffer packets
+- ethernet protocol used on each incoming link so:
+	- no collisions: full duplex
+		- A to A'  and B to B' can transmit simultaneously, without collisions
+	- each link is its own collision domain
+		- A to A' and C to A' cannot happen simultaneously
+	- each swtich has a switch table, each entry:
+		- mac of host, inferface, time stamp
+		- looks like a routing table
 
-# All layers together
+self-learning
+- learns which hosts can be reached through which interface
+	- when frame is recieved, switch records the sender/location pair in table
+- filtering/forwarding
+	- if frame dest is unknown: flood
+	- if known send just one link
+
+
+## vs routers
+- both store-and-foward
+	- R: network layer
+	- S: link layer
+- both have forwarding table
+	- R: routing using IP and routing algorithms
+	- S: learn forwarding table using flooding, learning, MAC
+
+# physical layer
+- transmit and recieve bit streams over a physical transmission medium
+- conversion betwen digital bits to analogue
+- define characteristics linke, voltage, data rate etc
+
+# All layers together
+- connect to internet:
+	- need to get IP addr of:
+		-  itself
+		-  first hop router
+		-  DNS server
+- uses DHCP: dynamic host configuration protocol
+- DHCP is inside UDP inside IP inside Ethernet frame
+- frame is broadcast on LAN with dest FFFFFFFFFFF, recieved at router running DHCP server
+- DHCP creates a DHCP ACK with the info and sends it back to the client
+	- can allocate temporaty IP address