Update

# Conflicts:
#	Network_Plus/Network+_OSI.md

.gitignore

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+.obsidian/*

Network_Plus/Network+_OSI.md

@@ -1,58 +1,57 @@
 # __Network +__ 
 
-## __OSI Model__
+# __OSI Model__
 ## __Layer 1__ Bites 
   * Physical Layer 
-    * It is the connents like Cat 6 RJ45 and fiber.
+    * It is the connects like Cat 6 RJ45 and fiber.
     * Its the on and off on the cables.
 ---
 
-## __Layer 2__ Frames
+## __Layer 2__ - Frames
 * ### Data Link Layer.
     * Packagers data int frames and transmits those frames on the network.
-    * Layer 2 devices view nteworks __logically__.
+    * Layer 2 devices view networks __logically__.
 * ### MAC Address 
     * Media Access Control
-    * Physical addressing system of a device which operates on the logial topology.
+    * Physical addressing system of a device which operates on the logical topology.
     * Uses a 48-bit address assigned to a network interface card. 
     * __EX:__ `D2:51:F1:3A:34:65` 
-    * `D2:51:F1` is the vedor code 
+    * `D2:51:F1` is the vendor code 
 * ### Logical Link Control
-    * Provides connection services and allows acknowledgemnt of receipt of message.
+    * Provides connection services and allows acknowledgment of receipt of message.
     * Is the basic form of flow control.
-    * Provides basic error control functios.
+    * Provides basic error control functions.
     * Uses a check sum. 
 * ### How communication synchronized.
     * Isochronous
-        * Netwok devices use a common reference a common refernce clock source and create time slots for transmission.
+        * Network devices use a common reference a common reference clock source and create time slots for transmission.
     * Synchronous 
         * Network devices agree on clocking method to indicate beginning and end of frames and can use control characters. 
-    * Asynchonous
+    * Asynchronous
-        * Network devices reference thier own internal clocks and use start and stop bits 
+        * Network devices reference their own internal clocks and use start and stop bits 
 * ### What Devices are layer 2
     * network cards
-    * Briges
+    * Bridges
     * Switch
     * MAC Address
 ---
 ## __Layer 3__ Packets
-
 * ### Network Layer
     * Forwards traffic (routing) with logical address. 
     * __IP address__ IPv4 IPv6
     * Logical addressing 
         * Ip Addressing  IPv4 and IPv6
     * Switching (Routing)
-    * Route discovery and selction
+    * Route discovery and selection
     * Connection Services 
-    * Banwidth usage
+    * Bandwidth usage
     * Multiplexing
 * ### How should data be __forward__ or __routed__ 
     * Packet Switching (Most common)
         * Data is divided into packets and then forwarded to is IP address.
     * Circuit Switching
-        * Dedicated communication link is establed between two devices.
+        * Dedicated communication link is established between two devices.
-        * It uses one path when the connect establed and the whole time the connect is there. 
+        * It uses one path when the connect established and the whole time the connect is there. 
     * Message Switching
         * Data is divided into messages which may be stored and then forwarded. 
 * ### Route Discovery and Selection
@@ -75,17 +74,36 @@
 
 ---
 
-## __Layer 4__ Segments
+## __Layer 4__ - Segments
 * ### Transport Layer
     * TCP Transmission Control Protocol
         * Connection-oriented protocol that is a reliable way to transport segments across the network 
-        * Will ask for an acknowledgement  
+        * Will ask for an acknowledgement. 
         * ![TCP](../pics/tcp.png) 
         * This is a Three-way handshake.
 
-
     * UDP User Datagram Protocol
         * Connectionless protocol that is an unreliable way to transport segments across the network 
+	    * If it dropped, Sender is unaware
 
+    * TCP vs UDP
+    * ![TCP vs UDP](../pics/tcp_vs_udp.png)
     * Windowing
+        * Allows the clients to adjust the amount opf data in eash segment.
+        * Allows you to send more or fewer for eash segment.
     * Buffering
+        * Occurs When devices allocate memory to store segments if bandwidth isn't readily avaiable
+
+---
+## __Layer 5__ - Session
+* Session Layer
+    * Keeps conversations separate to prevent intermingling of data
+    * Setup
+        * Checking of user credentaials and assigning numbers to sessions to help identify them.
+        * Some random number that would be assigned. 
+    * Maintain
+        * Transfer Data (back and forth)
+        * Reestablish connedtion
+        * Acknowlegde receipt
+    * Tear down 
+        * Ending of a session after the transfer is done or when the other party disconnects. 

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