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18 Ιουλ 2012 (πριν από 6 χρόνια και 4 μέρες)

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Network Layer Software
Selamawit Gebre-Amlak
Colorado Technical University
Department of Computer Science
Monday, January 10, 2011



Network Layer Software

The purpose of network layer is to routing packets of information from a source machine
to the target machine. This function of network layer are different than that of data link layers
whose purposes are to route the binary digits from one end of a wire to the other end. Whoever,
the network layer determines the operation of the subnet. Network layer functions also include
logical addressing, routing, datagram encapsulation, fragmentation and reassembly, and error
handling and diagnostics.
Transport Layer
The fourth layer of the OSI Reference Model, the transport layer, is also responsible for
fragmentation and reassembly. There are some transport layer protocols that provide services to
handle flow control and end-to-end error recovery. The Transport layer comprise two port
numbers: a destination port number that identifies the destination application program on the
remote machine and a source port number that identifies the application on the originating
Matter such as, routing of packets through the subnet which allowing it to be connected
to the Internet with a single shared network address. A sublet is a section of a network that shares
a common address component. On TCP/IP networks, subnets are all devices whose IP addresses
have the identical prefix. Without subnets, there might be surplus use of the limited number of
network address get multiple connections to the Internet, one for each of its physically separate
sub-networks. Issues like, congestion control, which might be needed to be adjusting forwarding
rates for data frames to keep traffic levels from overwhelming the network medium and a means
of linking together multiple networks.

Routing Algorithms
Router algorithms can be divided into two major groups, the non-adaptive algorithms and
adaptive algorithms. The performance of a routing environment is an important factor used by
routing algorithm protocol. The best paths for data are decided by the routing algorithm. The
routing algorithm computes the path that would better achieve in transporting the data from the
source to the goal which the router uses.



For example, whereas the RIP is a compelling, “distance vector routing protocol” built
around the Berkely BSD routed application and was made for smaller IP type networks. RIP uses
UDP port 520 for route updates. RIP calculates the best route using hop count. RIP is like most
vector routing protocols which takes certain amount of time to converge. Even though, RIP
requires fewer powers from the central processing unit (CPU) and Random-access memory
(RAM) compared to other routing protocols, RIP still have limitations.
However, RIP uses one type of routing algorithm to help the router move data while the
routing protocol Open Shortest Path First (OSPF) uses another. “Open Shortest Path First (OSPF)
is a popular link-state routing protocol for IP networks. OSPF (Open Shortest Path First), which,
as the name implies, is an open standard routing protocol used to seek out shortest path routes just
like RIP versions but, OSPF is specially designed for large networks.”

Adaptive Algorithms

An adaptive algorithm is does what its name say. It is an algorithm that alters its
performance based on the resources accessible. For instance, stable partition is O(n lg n)
assuming using no additional memory is required, if however it was given O(n) as memory then it
can be O(n). If adaptive algorithm used “Least Mean Square (LMS)” algorithm it can executes
quickly but converges gradually. LMS complexity increases linearly with the number of weights.
The Least mean squares (LMS) algorithms are a class of adaptive filter. They are used to
impersonate a required filter by “finding the filter coefficients that relate to producing the least
mean squares of the error signal.” There is a difference between the desired signal and the actual
signal. Another algorithm that can be used is ’Recursive Least Squares (RLS). Unlike the LMS
algorithm which converges gradually, RLS converges quickly. Its complexity increases
approximately with the square of the number of weights. This algorithm at times could become
problematic and unstable when the number of weights is large.
The Recursive least squares (RLS) adaptive filter is an algorithm which recursively finds
the filter coefficients. The ‘filter coefficients’ reduces a weighted linear least squares outflow task
that of the input signals. Where as the least mean squares (LMS) aims to reduce the mean square
error. In the comparison the input signals for the (RLS) are considered deterministic while for the
(LMS) which also uses equivalent algorithm are considered stochastic. The various types of
signed (LMS) various types of signed algorithms simplify hardware implementation. Both, the
normalized (LMS) as well as variable-step-size LMS algorithms are robust to a range of variety


input signal's statistics, for instance power. The constant modulus algorithm is useful when no
training signal is available. It also performs best for constant modulus digital modulations
techniques such as Phase-Shift Keying (PSK). Binary PSK Carrier using the 180 degree phase
shifts at bit edges.

Non-adaptive Algorithms
In a Non-adaptive Routing Algorithm also known as Dynamic Routing it consults a static
table in order to determine to which computer it should send a packet of data. This is in contrast
to an adaptive routing algorithm which bases its decisions on data which reflects current traffic
conditions. Dynamic routing executes the same task as static routing except it is more robust. In
order for network routes for packets setting, the static routing allows routing tables in specific
routers to be setup in a static manner. If a router on the route goes down the destination may
become unreachable. Dynamic routing allows routing tables in routers to change as the possible
routes change. There are several protocols used to support dynamic routing including RIP and
OSPF mentioned above.
In dynamic routing, it can be done using hop count or tic count. Hop count is how many
routers the message must go through to reach the recipient, while tic count is the time to route in
1/18 seconds (ticks). Even though the dynamic routing protocols do not change how routing is
done they do allow for dynamic altering of routing tables. There are two classifications of
protocols Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP). The Interior
Gateway Protocol (IGP) used to describe the fact that each system on the internet can choose its
own routing protocol. RIP and OSPF are interior gateway protocols. Exterior Gateway Protocol
(EGP) uses two routers of different systems. These two routers are Exterior Gateway Protocol
(EGP) and Border Gateway Protocol (BGP). Border Gateway Protocol (BGP) uses TCP as a
transport protocol. When two systems are using BGP, they establish a TCP connection. The two
systems then send each other their BGP routing tables. BGP uses distance vectoring. The way it
detects failures is by sending periodic messages every 30 seconds. It exchanges information about
reachable networks with other BGP systems including the full path of systems that are between
them. On the other hand, OSPF have routes based on IP type of service (part of IP header
message) such as FTP or Telnet. It support subnets and assigns cost to each interface based on
reliability, round trip time, and the like. it distributes traffic evenly over equal cost routes and
uses multicasting.


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Algorithms for Coverage Control and Space Partitioning in Mobile Robotic Networks,

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Department of Mathematics, State University of New York, College at Geneseo, Geneseo, NY 14454, USA,
Probabilistic Nonadaptive Group Testing in the Presence of Errors and DNA Library Screening,

Hong-Bin Chen, Hung-Lin Fu, Nonadaptive algorithms for threshold group testing,
Department of Applied Mathematics, National Chiao Tung University, Hsinchu, 30050,