Protocols

Overview Client-Server and peer-to-peer describe who talks to whom on a network: one funnels every request through a central server, the other lets nodes exchange data directly as equal peers. The choice shapes scalability, fault tolerance, and who ultimately controls the data. Comparison Diagram Client-ServerPeer-to-PeerServerCCCAll requests routed through serverPPPPPPeers connect directly to each other Comparison Table Aspect Client-Server Peer-to-Peer Node roles Clients and servers have fixed, asymmetric roles Every node acts as both client and server (servent) Connection establishment Clients connect to a known server address (DNS/IP) Nodes discover peers via bootstrap lists, DHTs, or trackers Request handling Server processes and responds to each client request Any peer can serve or request data from any other peer Resource provisioning Server owns the compute, storage, and bandwidth Resources are contributed and shared across participating peers Scalability pattern Scaling requires adding server capacity or replicas Scaling often improves as more peers join and share load Fault tolerance Server outage disrupts all clients (single point of failure) Network tolerates individual peer failures; no single point of failure Security & trust Trust is centralized; server enforces auth and access control Trust is distributed; peers must verify each other independently Typical examples Web apps, REST APIs, email, banking systems BitTorrent, blockchain networks, LAN gaming Key Differences Client-Server relies on a central server as the single source of truth; peer-to-peer distributes data with no authoritative hub. Adding capacity in client-server means scaling the server tier; in peer-to-peer, each new node can add capacity to the network. A server outage is a single point of failure for client-server, while peer-to-peer degrades gracefully as peers leave. Client-server centralizes access control, while peer-to-peer pushes trust and verification onto each peer. When to Use Each Client-Server ...

Overview Circuit switching and packet switching are the two fundamental ways a network can move data between endpoints. Circuit switching reserves a dedicated path for the full duration of a session, like a traditional phone call, while packet switching breaks data into independent packets that share network links and find their own way to the destination. The choice affects everything from latency predictability to how efficiently bandwidth gets used. Comparison Diagram Circuit Switching Packet Switching A B Dedicated path reserved for the entire call A B 1 2 Packets routed independently, paths may differ, may arrive out of order Comparison Table Aspect Circuit Switching Packet Switching Connection setup Requires an explicit call-setup phase (signaling) before any data flows No setup phase; data is sent as soon as packets are ready Path allocation A fixed end-to-end path is established and used for the whole session No fixed path; each packet is routed hop-by-hop and may take a different route Resource reservation Bandwidth is exclusively reserved, so idle time on the circuit is wasted Bandwidth is statistically multiplexed and shared among many flows Data transfer format Continuous stream of data sent in the order it was generated Data split into discrete packets, each carrying its own header for routing Latency and jitter Predictable, constant latency once the circuit is established Variable latency and jitter caused by queuing and differing routes Ordering and reliability Data always arrives in the order sent, since the path never changes Packets can arrive out of order or be lost, requiring reassembly/retransmission Failure handling A link failure breaks the whole call, forcing re-establishment Traffic can be dynamically rerouted around a failed link Session teardown An explicit signal releases the reserved circuit when the call ends No teardown needed; the flow simply stops when packets stop being sent Key Differences Circuit switching reserves a dedicated path for the whole session; packet switching has no fixed path at all Circuit switching wastes idle capacity through exclusive reservation, while packet switching relies on statistical multiplexing to share bandwidth Packets can be independently rerouted around failures, while a circuit failure kills the entire call Circuit switching guarantees ordered, steady-latency delivery; packet switching risks out-of-order arrival and jitter A circuit needs an explicit call setup phase before data flows, while packet switching starts transmitting immediately When to Use Each Circuit Switching ...

Overview Full duplex and half duplex describe how a communication link handles data flowing in both directions. A full duplex link sends and receives at the same time over independent paths, while a half duplex link shares a single channel and must alternate between sending and receiving. The distinction determines whether devices collide, how much of the link’s bandwidth is usable, and how much delay is added when a device switches from listening to talking. ...

Overview The OSI Model is a conceptual seven-layer framework that ISO designed to standardize how network communication should be described, while the TCP/IP Model is the four-layer protocol suite that actually powers the internet. Real devices implement TCP/IP directly, but engineers still borrow OSI’s vocabulary to reason about and troubleshoot problems layer by layer. Comparison Diagram OSI ModelTCP/IP Model7. Application6. Presentation5. Session4. Transport3. Network2. Data Link1. PhysicalApplicationTransportInternetNetwork Access Comparison Table Aspect OSI Model TCP/IP Model Purpose Theoretical reference model for describing how network communication should work Practical protocol suite that actually runs the internet Layer count 7 layers 4 layers (sometimes taught as 5) Layer structure Application, Presentation, Session, Transport, Network, Data Link, Physical Application, Transport, Internet, Network Access Development origin Designed by ISO in the late 1970s/80s before matching protocols existed Grew out of DARPA’s ARPANET; protocols came first, the model was described afterward Protocol coupling Layers defined independently of any specific protocol Layers map directly onto real protocols like IP, TCP, and HTTP Encapsulation granularity Splits presentation and session concerns into their own distinct layers Folds presentation and session functions into the single Application layer Real-world adoption Rarely implemented exactly as specified; used mainly as a teaching and reference framework Implemented in essentially every networked device and across the internet Troubleshooting use Provides layer-by-layer vocabulary for isolating where a problem occurs Maps directly to the tools and protocols engineers actually configure and debug Key Differences OSI has seven layers while TCP/IP condenses the same concerns into four layers OSI is a theoretical reference model; TCP/IP is the actual protocol suite running the internet OSI separates Session and Presentation into distinct layers; TCP/IP merges them into one Application layer TCP/IP’s protocols were built first and the model described them afterward, while OSI’s layers were designed before implementation When to Use Each OSI Model ...

Overview DHCP and DNS are both foundational network services, but they solve different problems in a device’s journey onto the network. DHCP automatically assigns a device its IP address and network configuration when it joins a subnet, while DNS translates human-readable domain names into the IP addresses needed to actually reach other hosts. Comparison Diagram DHCP DNS Client (no IP) DHCP Server DHCPDISCOVER leased IP + gateway local subnet, broadcast Client (has IP) DNS Resolver example.com? 93.184.216.34 global, hierarchical gives device an address gives a name an address Comparison Table Aspect DHCP DNS Primary purpose Assigns an IP address and network configuration to a device Translates a domain name into an IP address Triggered by A device connecting or booting onto the network An application needing to resolve a hostname Transport protocol UDP, ports 67 (server) and 68 (client) UDP or TCP, port 53 Discovery mechanism Client broadcasts DHCPDISCOVER on the local subnet Client sends a unicast query to a configured resolver address Data returned IP address, subnet mask, default gateway, DNS server list IP address (A/AAAA record) or other record types like MX, CNAME, TXT State and validity Lease with an expiration time that must be renewed Record with a TTL, cached locally then re-queried after expiry Scope Local network segment or subnet Global, hierarchical, distributed across the internet Key Differences DHCP assigns IP addresses to devices; DNS resolves domain names to those addresses. DHCP requests use broadcast discovery on the local subnet; DNS clients send unicast queries to a configured resolver. DHCP assignments are leases that expire and renew; DNS answers are cached per record TTL. DHCP typically hands out the DNS server addresses a client should use, linking the two protocols at boot time. When to Use Each DHCP ...

Overview IPv4 and IPv6 are the two versions of the Internet Protocol responsible for addressing and routing packets across networks. IPv4 relies on 32-bit addresses that ran out of unique combinations, while IPv6 was designed around 128-bit addresses to give every device a globally unique, non-NAT’d address. The distinction matters because it affects address exhaustion, header processing overhead, and whether NAT traversal is required for peer-to-peer connectivity. Comparison Diagram IPv4IPv61921681132 bits · dotted-decimal20010db885a3000000008a2e03707334128 bits · hex colon-notation~4.3 billion addresses~340 undecillion addressesRelative address length32 bits (IPv4)128 bits (IPv6) — 4x longerNAT dependencyIPv4: needs NAT (scarce space)IPv6: end-to-end, no NAT needed Comparison Table Aspect IPv4 IPv6 Address length & notation 32-bit, dotted-decimal (e.g. 192.168.1.1) 128-bit, hexadecimal colon-separated (e.g. 2001:0db8::7334) Address space size ~4.3 billion addresses ~340 undecillion addresses Address assignment Manual configuration or DHCP Stateless Address Autoconfiguration (SLAAC) or DHCPv6 Header structure Variable-length header with options field and checksum Fixed 40-byte header, no checksum, optional extension headers NAT requirement Commonly required due to address scarcity Not needed; supports true end-to-end addressing Broadcast/discovery Uses broadcast (e.g. ARP) for local discovery Broadcast eliminated; uses multicast Neighbor Discovery Built-in security IPsec is an optional add-on IPsec support is part of the core protocol spec Adoption & compatibility Universally supported, legacy infrastructure Growing adoption, requires dual-stack or tunneling for legacy interop Key Differences IPv6 addresses are 128-bit, four times longer than IPv4’s 32-bit addresses, resolving address exhaustion IPv6 removes the need for NAT, restoring true end-to-end connectivity between hosts IPv6 uses a simplified, fixed-length header that speeds up router processing compared to IPv4’s variable header IPv6 replaces ARP broadcasts with Neighbor Discovery multicast for local address resolution When to Use Each IPv4 ...