QUIZ#5 Definitions(Problem set 5)

Load-Insensitive Algorithm

A link's cost does not explicitly reflect it's current (or recent past) level of congestion.

Nodes

Devices or data points that are part of a larger network.

Graph:

G = (N,E): A set of N nodes and a collection of E edges, where each edge is a pair of nodes from N.

RIP Response Message

a message that contains updated information on the router's table. This is done approximately every thirty seconds.

Bellman-Ford Equation

x (y) = minv {c(x,v) + dv (y)}, where dx is the cost of the least cost path from node x to node y, and where the minv in the equation is taken over all of x's neighbors

Area border routers

(ABR) is a kind of router that is located near the border between one or more Open Shortest Path First (OSPF) areas. It is used to establish a connection between backbone networks and the OSPF areas.

MAC desirable characteristics

1. When only one node has data to send, that node has a throughput of R bps. 2. When M nodes have data to send, each of these nodes has a throughput of R/M bps. This need not necessarily imply that each of the M nodes always has an instantaneous rate of R/M, but rather that each node should have an average transmission rate of R/M over some suitably defined interval of time. 3. The protocol is decentralized; that is, there is no master node that represents a single point of failure for the network. 4. The protocol is simple, so that it is inexpensive to implement

Parity Bit

A bit that acts as a check on a set of binary values, calculated in such a way that the number of 1s in the set plus the parity bit should always be even (or occasionally, should always be odd).

Time Frames

A complete cycle of events within the time division period.

First-hop router

A default router

RIP (Routing Information Protocol)

A distance vector protocol that operates in a manner very close to the idealized DV protocol. Hop Count is used as a cost metric in RIP. A hop is the number of subnets traversed along the shortest path from source router to destination subnet, including the destination subnet.

Framing

A frame consists of a data field, in which the network-layer datagram is inserted, and a number of header fields. The structure of the frame is specified by the link-layer protocol.

Link-layer Frame

A frame is the protocol data unit at the data link layer. Frames are the result of the final layer of encapsulation before the data is transmitted over the physical layer. A frame is "the unit of transmission in a link layer protocol, and consists of a link layer header followed by a packet.

OSPF (Open Shortest Path First)

A link-state protocol that uses flooding of link-state information and a Dijkstra least-cost path algorithm. With OSPF, a router constructs a complete topological map (that is, a graph) of the entire autonomous system, where Dijkstra's algorithm is used to determine a shortest-path tree to all subnets, with itself as the root node. Link costs are determined by the administrator.

Link Access

A medium access control (MAC) protocol specifies the rules by which a frame is transmitted onto the link, which is the sender can send a frame whenever the link is idle.

Carrier Sense Multiple Access (CSMA)

A network protocol that listens to or senses network signals on the carrier/medium before transmitting any data.

Least-cost Path

A path between source and destination that has the least cost

Count-to-Infinity

A problem where the result of bad news about the increase in link cost travels slowly.

MAC protocol

A protocol by which nodes regulate their transmission into the shared broadcast channel.

Path

A sequence of nodes such that each of the pairs are edges in E

Carrier Sense Multiple Access / Collision Detection(CSMA/CD)

A set of rules determining how network devices respond when two devices attempt to use a data channel simultaneously (called a collision).

Successful Slot

A slot in which exactly one node transmits.

Token

A small, special purpose frame that is exchanged among nodes in some fixed order, used in the token-passing protocol

Data Over Cable Service Interface Specification(DOCSIS)

A standard interface for cable modems, the devices that handle incoming and outgoing data signals between a cable TV operator and a personal or business computer or television set.

Routing Tables

A table where each row is a distance vector, specifically, it's own distance vector and that of each of its neighbors.

Poisoned Reverse

A technique to prevent routing loops between two immediately neighboring nodes, where a node advertises that its distance is infinity, as long as it's routed via the neighboring node whose link cost increased.

Interior Gateway Protocols

A type of protocol used for exchanging routing information between gateways (commonly routers) within an autonomous system (for example, a system of corporate local area networks).

MAC Address

A unique identifier assigned to network interfaces for communications at the data link layer of a network segment.

Link-State Algorithm

Algorithms with global state information, specifically, being aware of the cost of each link in the network.

RIP Advertisements

Also known as response messages.

Binary Exponential Backoff

An algorithm that uses feedback to multiplicatively decrease the rate of some process(in this case slot time * 2^r where r is between 0, 1...(2^r -1)), in order to gradually find an acceptable rate.

Edges

An edge (or link) of a network (or graph) is one of the connections between the nodes (or vertices) of the network.

Routing Administrative Autonomy

An organization should be able to run and administer its network as it wishes, while still being able to connect its network to other outside networks.

Node

Any device that runs a link-layer (i.e., layer 2) protocol. Nodes include hosts, routers, switches, and WiFi access points

Routing Scale

As the number of routers become large, the overhead involved in computing, storing, and communicating routing information (for example LS updates or least-cost path changes) becomes prohibitive.

Network Adapter = NIC(Network Interface Card)

At the heart of the network adapter is the link-layer controller, usually a single, special-purpose chip that implements many of the link-layer services. The NIC is also referred to as an Ethernet card and network adapter. It is an expansion card that enables a computer to connect to a network

Polynomial Codes

CRC codes are also known as polynomial codes.

Dynamic Routing Algorithm

Change the routing paths as the network traffic loads or topology change.

Global Routing Algorithm

Computes the least-cost path between source and destination using complete, global knowledge about the network.

AS (Autonomous Systems)

Consists of a group of routers that are typically under the same administrative control (e.g. operated by the same ISP or belonging to the same company or network)

Point-to-Point Link

Consists of a single sender at one end of the link and a single receiver at the other end of the link.

Multiple access problem

Coordinating the access of multiple sending and receiving nodes to a shared broadcast channel.

CRC(Cyclic Redundancy Checking)

Cyclic redundancy checking is a method of checking for errors in data that has been transmitted on a communications link. A sending device applies a 16- or 32-bit polynomial to a block of data that is to be transmitted and appends the resulting cyclic redundancy code (CRC) to the block. The receiving end applies the same polynomial to the data and compares its result with the result appended by the sender. If they agree, the data has been received successfully. If not, the sender can be notified to resend the block of data.

Destination Router

Default router of the destination host

Source Router

Default router of the source host

Channel Partitioning Protocols

Divide channel into smaller "pieces" (time slots, frequency); allocate piece to node for exclusive use.

Distance Vector Algorithm

Each node maintains a vector of estimates of the costs (distances) to all other nodes in the network

EDC

Error Detection and Correction bits sent and received through a link.

Bit-level error detection

Errors in the received frames are detected by means of Parity Check and Cyclic Redundancy Check (CRC). In both cases, few extra bits are sent along with actual data to confirm that bits received at other end are same as they were sent. If the counter-check at receiver' end fails, the bits are considered corrupted.

Inter-AS Routing Protocol

Handles the two tasks of - obtaining reachability information from neighboring ASs and propagating the reachability information to all routers internal to the AS.

Broadcast link

Has multiple sending and receiving nodes all connected to the same, single, shared broadcast channel.

ARP Packet

Has several fields, including the sending and receiving IP and MAC addresses. Both ARP query and response packets have the same format. The purpose of the ARP query packet is to query all the other hosts and routers on the subnet to determine the MAC address corresponding to the IP address that is being resolved.

BGP Peers

In BGP, pairs of routers exchange routing information over semi-permanent TCP connections using port 179. For each TCP connection, the two routers at the end of the connection are called BGP peers.

Internet Checksum

In checksumming techniques, the d bits of data are treated as a sequence of k-bit integers. One simple checksumming method is to simply sum these k-bit integers and use the resulting sum as the error-detection bits

BGP(Border Gateway Protocol v4)

Is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet.

Speed of Convergence

LS: O(n^2) algorithm requires O(nE) messages. May have oscillations DV: Convergence time varies. May be routing loops. Count-to-infinity problem.

Message Complexity

LS: With n nodes, E links, O(nE) messages sent DV: Exchange between neighbors only. Convergence time varies.

Load-Sensitive Algorithm

Link costs vary dynamically to reflect the current level of congestion in the underlying link.

Multiple same-cost paths

Multiple paths to a destination that have the same cost.

Taking-turns Protocols

Nodes have some mechanism that denotes who's turn it is to send via polling or token passing.

Routing Loop

Packets continue to be routed in an endless circle rather than reaching their destinations.

Slotted ALOHA

Requires that time be segmented into slots of a fixed length exactly equal to the packet transmission time. Every packet transmitted must fit into one of these slots by beginning and ending in precise synchronisation with the slot segments. A packet arriving to be transmitted at any given station must be delayed until the beginning of the next slot.

Robustness

Router malfunctions. LS: Node can advertise incorrect link cost. Each node computes only its own table. DS: DV node can advertise incorrect path cost. Each node's table used by others.

Gateway Routers

Routers responsible for forwarding packets to destinations outside the AS.

Static Routing Algorithm

Routes change very slowly over time, often as a result of human intervention.

Bit-level error correction

Similar to error detection, except that a receiver not only detects when bit errors have occurred in the frame but also determines exactly where in the frame the errors have occurred.

Pure Unslotted ALOHA

Similar to slotted ALOHA but new arrivals are transmitted immediately (no slots). No need for synchronization and fixed length packets.

Hot-Potato Routing

The AS gets rid of the packet (the hot potato) as quickly as possible (more precisely, as inexpensive as possible), by sending the packet to the gateway router that has the smallest router-to-gateway cost among all gateways with a path to the destination.

eBGP

The TCP connection along with all the BGP messages sent over the connection is called a BGP session. Furthermore, a BGP session that spans two ASs is called an external BGP (eBGP) session.

FEC(Forward Error Correction)

The ability of the receiver to both detect and correct errors

OSPF support for hierarchy

The ability to structure an autonomous system hierarchically; specifically structures called areas. Backbone > Area Border Routers > non-border Routers

Time Slots

The amount of time it takes for a node to broadcast or transmit its signal in its associated time frame.

Decentralized Routing Algorithm

The calculation of the least-cost path is carried out in an iterative, distributed manner. No node has complete information about the cost of all network links.

Link

The communication channels that connect adjacent nodes along the communication path.

Two-Dimensional Parity

The d bits in D are divided into i rows and j columns. A parity value is computed for each row and for each column. The resulting i + j + 1 parity bits comprise the link-layer frame's error-detection bits. The receiver can thus not only detect the fact that a single bit error has occurred, but can use the column and row indices of the column and row with parity errors to actually identify the bit that was corrupted and correct that error!

Polls

The master queries each slave device in turn as to whether it has any data to transmit.

Default Router

The one a host is typically directly attached to.

Shortest Path

The path with the smallest number of links between the source and destination

Polling Protocols

The polling protocol is a master node. It is used to eliminate collisions.It is used to surveys each of the nodes and transfer certain maximum number of data frames. If received message from the master node, then each node will try to transfer the data otherwise, master node sends message asking it to send its data. One node completed successfully then start another transaction by using master node.

Generator

The polynomial that becomes the divisor in a polynomial long division.

Backbone

The primary role of the backbone area is to route traffic between the other areas in the AS.

Undetected Bit Errors

The receiver may be unaware that the received information contains bit errors.

Channel Propagation Delay

The time it takes for a signal to propagate from one of the nodes to another.

Token Passing Protocol

The token passing protocol is not a master node. It is used to transfer data in some fixed order.If any node has the token they send its data. If it is not received destination node then search to go for next node and transfer it. The main disadvantage is, if any node fails, then the entire transfer data will be gone.

ARP

Translates between network-layer addresses (IP) and link-layer addresses (MAC) by referencing the ARP table, which contains mappings of IP and MAC addresses as well as a TTL.

Random Access Protocols

Transmit at full channel data rate R. No coordination among nodes. Two or more transmitting nodes -> "collision". random access MAC protocol specifies: how to detect collisions and how to recover from collisions (e.g., via delayed retransmissions).

Intra-AS Routing Protocol

Used to determine how routing is performed within an autonomous system (AS)

Protocols used in DOCSIS

Uses FDM to divide the downstream (CMTS to modem) and upstream (modem to CMTS) network segments into multiple frequency channels. Each upstream channel is divided into intervals of time (TDM-like), each containing a sequence of mini-slots during which cable modems can transmit to the CMTS. Sends a control message known as a MAP message on a downstream channel to specify which cable modem (with data to send) can transmit during which mini-slot for the interval of time specified in the control message. Cable modems send mini-slot-request frames to the CMTS during a special set of interval mini-slots that are dedicated for this purpose. These mini-slot-request frames are transmitted in a random access manner and so may collide with each other

Link-layer addressing

Uses the MAC address to correctly determine which router in the Autonomous system it needs to be forwarded to.

Reliable Delivery

When a link-layer protocol provides reliable delivery service, it guarantees to move each network-layer datagram across the link without error. A link-layer reliable delivery service can be achieved with acknowledgments and retransmissions.

Collide

When all of the nodes receive multiple frames at the same time.

iBGP

a BGP session between routers in the same AS is called an internal BGP (iBGP) session.