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Computer Networking

Circuit switching vs Packet switching - pre vs on-demand link resource allocation
- aka statistical multiplexing
Channel partitioning protocol categories: FDM vs TDM vs CDM
Delays: processing, queuing, transmission, propagation, packetization (VoIP)
Packet types: message, segment, datagram, frame
Application Architecture: client-server or P2P
Socket - interface between the app layer and the transport layer; aka API
Multimedia apps are delay and jitter sensitive but loss-tolerant
Elastic apps are delay-tolerant but loss-sensitive
Protocol Characteristics:
- connection-oriented vs connectionless service (TCP vs UDP)
- stateful vs stateless (BGP, FTP, RTSP vs HTTP)
- persistent vs non-persistent connections
- in-band vs out-of band control connection (HTTP vs FTP, RTSP, SIP)
- pull vs push (HTTP vs SMTP)

ARQ (Automatic Repeat reQuest) protocols capabilities:
- error detection - timeout
- receiver feedback - ACK
- retransmission
TCP
- Flow Control - speed-matching service to ensure sender doesn’t overflow receiver’s buffer by using the receive window (rwnd)
- Congestion Control - throttling the sender due to congestion within the network by using the congestion window (cwnd)
  - AIMD (Additive Increase Multiplicative Decrease) - saw tooth behavior

Network layer can provide:
- connection service using virtual-circuits (VCs)
  - maintain connection state using signaling messages
  - 3 phases: VC setup, data transfer, VC teardown
- connectionless service aka datagram networks (IP)
Router components: input ports, switching fabric, output ports, routing processor
Router functions: route propagation and forwarding path computation
Packet scheduler:
- at the output port, chooses one packet among those queued for transmission
- plays a crucial role in providing QoS
Routing algorithm classification:
- Adaptive vs Oblivious (routing decisions based on network state (load, congestion))
- Global vs Decentralized; aka link-state vs distance-vector
- Static vs Dynamic
- Intra-AS vs Inter-AS
Network link types:
- Point-to-Point: PPP, HDLC
- Broadcast: Ethernet

Wireless network types:
- infrastructure-based single-hop (WiFi) or multi-hop (Mesh)
- infrastructure-less single-hop (bluetooth) or multi-hop (MANET)
Handoff - mobile client moving from beyond the range of one AP into the range of another AP
Mobility management principles:
- home network, home agent, permanent address
- foreign network, foreign agent, COA (Care-of Address)

Multimedia application classes:
- streaming stored audio/video
- streaming live audio/video
- real-time interactive audio/video
PCM (Pulse Code Modulation) - speech encoding technique with a sampling rate of 8k samples per second and 8 bits per sample, giving a rate of 64 kbps
Multimedia protocols:
- RTSP - network control protocol used for establishing and controlling media sessions between endpoints
- RTP - used for carrying audio and video media streams
- RTCP - provides out-of-band statistics and control info for RTP
- SIP - used for session establishment/management; works with RTP or UDP
- H.323 - similar to SIP but more complex

Scheduling mechanisms: FIFO, priority queueing, WFQ
Policing mechanisms: criteria: average rate, peak rate, burst size
DiffServ - service differentiation based on traffic classes; elements:
- Edge functions: packet classification and traffic conditioning
  - traffic profile uses a meter to classify, mark and shape/drop packets
- Core function: forwarding
  - PHB - different performance based on packet markings
    - EF - guaranteed to receive enough bandwidth to meet configured rate
    - AF - divides traffic into 4 classes, each with 3 drop preferences
IntServ - provides QoS guarantees to individual application sessions
- uses RSVP to install soft-state in routers using call setup signaling
- not widely used

Properties of secure communication:
- Confidentiality, Endpoint Authentication, Message Integrity
Encryption - provides confidentiality by keeping data private
- Symmetric Encryption
  - has fundamental problem of key distribution
  - Cipher classes: stream ciphers and block ciphers (AES)
- Public Key Cryptography - asymmetric encryption
  - Diffie-Helman - one of the first algorithms
  - RSA - popular public key cryptography algorithm
Hash Function takes an input and computes a fixed-length string
- it is computationally infeasible to find the input from the output
- MD5 and SHA hash algorithms are widely used
MAC performs message integrity using hash functions with a shared key
- does not require an encryption algorithm
- HMAC is a popular standard and works with MD5 or SHA
Digital Signatures - provide peer authentication, message integrity and non-repudiation
- provides similar services as MAC but requires PKI
- sender encrypts message’s hash using his private key (aka signs it)
PKI
- Public key certification - verifying that a public key belongs to a specific entity
- CA - binds a public key to a particular entity, validates identities and issues certs
- Digital Certificate contains owner’s public key and unique info
  - is signed by the CA
SSL/TLS secures TCP by providing: confidentiality, data integrity, client/server authentication
- provides TCP’s services to applications enhanced with security services
IPSec protocol suite provides security at the network layer
- AH protocol provides authentication and data integrity (51)
- ESP protocol provides authentication, data integrity and confidentiality (50)
- Transport mode or Tunnel mode (more popular)
- SA - network layer unidirectional logical connection
- IKE - automated mechanism for creating SAs
Firewall categories: packet filters, stateful filters, application gateways
DoS attack categories: vulnerability attack, bandwidth flooding, connection flooding

Network management areas: performance, fault, configuration, security, accounting
Network management architecture components: manager (NMS), managed devices, agent (SNMP software)
SNMP - network management protocol used for conveying information and commands between the manager and an agent executing on behalf of that entity within a managed network device
- request-response mode to query or modify MIB object values or unsolicited trap messages from the agents to the manager