Table of Contents
1. Open Systems Interconnection Model
- OSI Model
- Defined in ISO/IEC 7498 and ITU-T X.200
1.1. 7. Application Layer
1.1.1. Hypertext Transfer Protocol
1.1.2. Secure Shell Protocol
- SSH
1.1.3. Lightweght Directory Access Protocol
- LDAP
- It is a subset of X.500
- Deals with any kind of directory structures
- Lightweight Directory Access Protocol - Wikipedia
1.1.4. Domain Name System
- See
1.2. 6. Presentation Layer
- Establish data formatting
1.2.1. ASN.1
- Abstract Syntax Notation One
- Notation for abstract types and values as specified in ITU-T X.680 to X.683.
1.2.2. Transport Layer Security
- TLS
- Secure Socket Layer (SSL) is deprecated legacy version of TLS.
- TLS 1.3 (since 2018) and TLS 1.2 (since 2008) are currently in use.
1.2.2.1. Handshake
- Handshake Begin: Client provide the server available ciphers.
- Server picks a cipher and notifies the client.
- Server provides:
- a digital certificate which contains server name and the trusted certificate authority (CA) to prove the authenticity
- public encryption key of the server
- Client confirms the validity of the certificate.
- Client encrypt a random number (PreMasterSecret) with the public key and send to the server.
- Both parties perform (or Elliptic Curve Diffie-Hellman) on that random number and generate a session key.
1.3. 5. Session Layer
1.3.1. Network Socket
- Enable across a network, as the endpoint.
- Identified by a socket address which is a triad of transport protocol, IP address, port number.
1.3.1.1. Datagram Socket
- Connectionless. UDP.
1.3.1.2. Stream Socket
- Connection-Oriented. TCP, SCTP, DCCP.
1.3.1.3. Raw Socket
- Direct without transport layer.
1.3.2. Remote Procedure Call
1.3.3. Domain Name System
- DNS
1.4. 4. Transport Layer
1.4.1. Transmission Control Protocol
- TCP
- Establish a connection
1.4.2. User Datagram Protocol
- UDP
1.5. 3. Network Layer
1.5.1. Internet Protocol
- IP
- Connectionless
0.0.0.0/0refers to any IP address.xxx.xxx.xxx.0/8,xxx.xxx.0.0/16represents the networkxxx.xxx.xxx.255/8,xxx.xxx.255.255/16is used for broadcasting, that is, everything within the network.- It is routed as broadcast.
1.5.1.1. Subnet Mask
- It represents which IP address range the subnetwork is using.
- It is specified as a single number:
192.168.219.0/8, or with a full subnet mask:255.255.255.0- The number specifies the number of bit from the end.
1.5.1.2. Gateway
- The IP address that are not within the same subnetwork is redirected to the gateway.
1.5.2. Border Gateway Protocol
- BGP
- Layer 4 protocol that finds the shortest route over the IP network.
1.5.3. Internet Control Message Protocol
- IMCP
- Auxillary protocol for IPv4.
- The packet is contained in IP, but it is treated as a special case.
pingandtracerouteutilize this.- RFC1122
requires hosts to return ICMP errors whenever possible, instead of
dropping packets.
- Type 3, Code 3:
DESTINATION PORT UNREACHABLEis used when manually rejecting an access to a port.
- Type 3, Code 3:
1.5.3.1. Control Messages
- Type 0:
ECHO REPLY - Type 3, Code *:
DESTINATION UNREACHABLE - Type 11:
TIME EXCEEDED.
1.6. 2. Data Link Layer
1.6.1. Medium Access Control
- MAC
1.6.2. Logical Link Control
- LLC
- MAC and LLC are the sublayers defined by IEEE 802
- Others includes 802.3 Ethernet, 802.11 Wi-Fi, 802.15.4 Zigbee
1.6.3. Network Switch
- Switching Hub, Bridging Hub, Ethernet Switch, MAC Bridge
- It is a multiport network bridge.
- Forwards data based on their destination MAC addresses.
- Some switches use IP addresses as well, and they are specially called a multilayer switches.
1.7. 1. Physical Layer
- voltage levels, the timing of voltage changes, physical data rates, maximum transmission distances, modulation scheme, channel access
2. Network Coding
The packets can be added in the hub between the sender and recipent. And when enough packets are transferred the original packets can be restored.
It is useful because it allows multiple packets to use the same wire at the same time, just using mathematics.
3. Space-Time Coding
The MIMO(Multi-Input Multi-Output) is used to counteract the effect of interferece in the radio signals.
3.1. Alamouti Scheme
Signals are sent from two different location, and it is sent twice with alternating sign difference. (AB | -BA) The signal can be reconstructed regardless of the signal fading due to interference.