1.
'Valid' Global Routing State: iff forwarding decisions deliver pkts to dest, no dead ends/loops, goal of rting protocols
2.
Baud rate: number of voltage changes per second Bit rate: number of bit changes per second
3.
Buffer Size: 2TxC in general, (2T x C) / √n for small, O(log W) for tiny, T is RTT, C is capacity, n is #flows, W is window
4.
Classless InterDomain Routing: subnet part of arbitrary length Classful Routing: A/B/C/D/E - 8/16/24
5.
Code Division Multiple Access: unique code per user, all share same frequency but have different 'chipping' sequence to encode data, signal = data X 'chipping' sequence, decoding - inner product of signal & sequence
6.
Cyclic Redundancy Check: detects more errors than parity eg 2 bit, multiplication & binary division, parameterised by n bit divisor P
7.
Data-link Layer: responsibility of transferring datagram from one node to adjacent node over a link
8.
Delivery Tree: set of paths to destination, must cover every node exactly once, spanning tree routed at destination
9.
Destination Based Routing: paths to same destination must coincide once they overlap, unless they never cross
10.
Dynamic Host Configuration Protocol: dynamically get address from server alternative to hard-coded in file. Addresses leased, hosts renew leases, allows reuse of addresses. Dynamic reallocation, can move around
11.
Encoding: encryption, error detection, compression, analog
12.
Error Correction/Detection Advantages & Disadvantages: Correction: + no resend - more check bits, false recovery possible
Detection: + less check bits - resend
13.
Even Parity: add bit such that #1s even, detect 1b errors 2D Bit Parity: detect & correct 1b errors
14.
Forward Error Correction: replace erroneous data by its closest error-free data
15.
Forwarding: 'data plane' directing packet to outgoing link, single router using routing state
16.
Frame: layer-2 packet, encapsulates datagram
17.
Hierarchical Addressing: route aggregation allows efficient advertisement of routing information
18.
Improvements: accountability & anonymity (source address), different packet header at edge/core, payment field
19.
Input Port Queuing: fabric slower than total arrival rate, Head-of-line blocking, front datagram stops others behind
20.
Interface: Connection between host/router & physical link Subnet Mask: Number of bits in subnet part
21.
Internet Control Message Protocol: communicate network level info: errors, echo req/reply, carried in IP datagrams
22.
IP Address: 32-bit identifier for host/router/interface has subnet part then host part, allocated by ICANN
23.
IPv4 Packet: 4b version, 4b header length (#32b words), 8b type of service, 16b total length, 16b identifier (tell which fragments belong together), 3b flags (ReservedF, DontfragF, MoreF - not last), 13b frag offset (part of datagram), 8b time to live (decrement each hop, if 0 discard & send time exceeded msg to src, prevents loops), 8b protocol (TCP=6,UDP=17), 16b header checksum (every router checks), 32b source IP, 32b dest IP, options (trcrt)
24.
IPv6: version, traffic class, flow label, payload length, next header, hop limit, source address, dest address. No fragmentation (end-end), no header len (fixed size), no checksum (other layers), new options - next header (fix size), 64 bit addresses, flow label (resource allocation to flows, handle different types of service)
25.
Link Layer Channel Services: framing, link access (encapsulates datagram into frame + header, trailer; channel access if shared medium, uses MAC addresses in headers for source & dest) reliable delivery between adjacent nodes (little error checking on low bit-error links (fibre, twisted pair) higher error rates for wireless) flow control (pacing between send & receive) error detection (signal attenuation, noise, receiver detects errors - signals for retransmit or drops) error correction (identifies & correct bit errors) half & full duplex (half - both nodes can transmit, not at same time)
26.
Link Layer Implementation: in adaptor (network interface card) attaches to system buses, hard+soft+firmware
27.
Longest Prefix Match: route on entry with highest number of bits from start which match - most specific
28.
Manchester code: transition at period mid-point, low-high if 1, high-low if 0, data xor clock = value, 2 clock/period
29.
Network Address Translation (NAT): all datagrams leaving local network have same NAT IP address but diff port#s, use NAT translation table with map of (sourceIP,port#)(NAT IP, new port#), use for incoming datagrams, outside client cant connect to server behind NAT because must use single visible IP, must statically configure NAT to fix, could use Universal Plug n Play Internet Gateway Device to allow NATed host to learn public IP & add/delete port#s. NAT & FTP have a control channel which violates layers.
30.
Network layer connection service: provided by a virtual circuit - a connection-oriented network
31.
Network layer connectionless service: provided by datagram network, no end-end connection, use addresses, 'elastic' service, no timing req, 'smart' end systems (control/recovery), simple network, non-uniform
32.
Network Service Model: eg guaranteed delivery (with max time), in order delivery, guaranteed min bandwidth etc
33.
Networks: ISPs (backbone/edge), Enterprises (core/edge), Datacenters (top-of-rack/aggregation & core) (+all border)
34.
Noise: no consistency in data Multi-access Schemes: phase / polarisation / spin / CDMA
35.
Non-return-to-zero: 1/0 = high/low, no neutral or rest position
36.
Non-return-to-zero-inverted: transition at clock mid-point if bit is one, no transition is bit is zero
37.
Non-return-to-zero-mark: transition on clock edge if bit is one, no transition is bit is zero
38.
Output Port Queuing: arrival rate via switch > output line speed, can lead to queuing delay or loss (overflow)
39.
Quad-level code: 4 levels, represent 2 bits per period
40.
Relaying: NATed client establishes connection to relay, external client connect to relay, relay bridges pkts between
41.
Route Computation: learn from observation / centralised computation (1 node has entire network map) / pseudo-centralised computation (all nodes have entire network map) / distributed computation (no nodes have entire map)
42.
Routing: 'control plane' computing paths packets will follow, routers communicate, jointly create routing state
43.
Self-learning route computation: topology where loops impossible (eg spanning tree), only 1 path to destinations, use 'learning switches' to discover paths, switches send flood packets to all ports on spanning tree, all nodes covered, switches learn by remembering where flooding packets that arrive at it originated, can use packet source IDs stored with TTL, if unknown destination then forward to all other ports and learn from response
44.
Self-learning route computation algorithm: packet arrives; index table; if entry {if destPort == arrivePort drop else forward } else flood. - requires loop-free topology (spanning tree), slow to react to failure (TTL), little control over paths (no computation)
45.
Source / Destination Routing: paths from 2 sources can be very different, even if they pass through same nodes
46.
Subnet: device interfaces with same subnet part, can physically reach each other without intervening router
47.
Switches: Enterprise/Edge (24-48 ports), Aggregation (192+), Backbone (fewer), Border (very few)
48.
Switching via Bus: input port - output port via shared bus, bus contention, speed limited by bus bandwidth
49.
Switching via Interconnection Network: no bus bandwidth limitations, may fragment datagram into cells
50.
Switching via Memory: direct CPU control, packet copied to memory, then read, 2 bus crossing, limited by mem B
51.
Traceroute: uses TTL + odd port, on expiry ICMP message with name & IP, calc RTTx3, stop on host unreachable msg
52.
Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers
53.
Virtual Circuit: source-dest path, ≈ telephone circuit, setup & teardown, packets carry VC#, router with state for each connection, link & router resources may be allocated to VC giving predictable service, links can change VC#, strict timing & reliability req, guaranteed service, complexity inside network not at end systems.
