Types of routes are the main indicators of routing. Routing Components and Route Determination
Types of routing. Protocol groups.
Implemented on network level networks. The routing protocol is responsible for it. When choosing a routing strategy, different goals can be set, for example:
Minimizing package delivery time;
Minimizing the cost of package delivery;
Ensuring maximum network throughput, etc.
The routing problem is solved router, which is defined as a network layer device that uses one or more metrics to determine the optimal path for network traffic based on network layer information.
Under metric some quantitative characteristics of the path are understood, for example, length, travel time, throughput, etc. Routing algorithms can be:
Static or dynamic;
Single-route or multi-route;
Single-level or hierarchical;
Intra-domain or inter-domain;
Unicast or group.
Static(non-adaptive) algorithms involve preliminary selection of routes and manual entry of them into the routing table. Thus, there should already be pre-recorded information about which port to send the packet with the corresponding address to. Examples: DEC LAT protocol, NetBIOS protocol.
In dynamic protocols, the routing table is updated automatically when the network topology or schedule changes.
Single-route protocols offer only one route for transmitting a packet (which is not always optimal).
Multi-route algorithms offer several routes. This allows information to be transmitted to the recipient via several routes simultaneously.
Networks may have single-level or hierarchical architecture. Accordingly, routing protocols are distinguished. In hierarchical networks, routers top level form a special level of the backbone network.
Some routing algorithms operate only within their domains, i.e. used intradomain routing Other algorithms can work with adjacent domains - this is defined as cross-domain routing
Unicast protocols are designed to transmit information (via one or more routes) to only one recipient. Multicast – capable of transmitting data to many subscribers at once.
There are three main groups of routing protocols depending on the type of algorithm used to determine the optimal route:
Distance vector protocols;
Channel state protocols;
Routing Policy Protocols.
Protocols distance vector- the simplest and most common. These are, for example, RIP, RTMP, IGRP.
Such protocols transmit (send out) data from their routing table (addresses and metrics) to neighbors at a certain frequency. Neighbors, having received this data, make the necessary changes to their tables. Disadvantage: These protocols only work well on small networks. As the size increases, service traffic on the network increases and the delay in updating routing tables increases.
Protocols channel status were first proposed in 1970 by Edsger Dijkstra. Here, instead of broadcasting the contents of routing tables, each router broadcasts a list of routers with which it has connections. direct communication, and a list of those directly connected to it local networks. Such distribution can be carried out either when the state of the channels changes, or periodically. Examples of protocols: OSPF, IS-IS, Novell NLSP.
Protocols politicians(rules) routing most often used on the Internet. They rely on distance vector algorithms. Routing information is obtained from neighboring operators based on specific criteria. Based on this exchange, a list of allowed routes is developed. Examples: BGP and EGP protocols.
Routers. Autonomous systems.
Router is a fairly complex device that is defined as a network layer device that uses one or more metrics to determine the optimal path for network traffic based on network layer information.
When creating them, 3 main architectures are used.
1)Single-processor. Here the processor is assigned the entire range of tasks, including: filtering and transmitting packets; modification of packet headers; updating routing tables; allocation of service packages; formation of control packages; working with the SNMP network management protocol, etc.
However, even powerful RISC processors cannot handle heavy workload processing.
2)Extended single-processor. IN functional diagram The router allocates modules responsible for performing a number of tasks (for example, working with service packages). Each such functional module is equipped with its own processor (peripheral).
3)Symmetric multiprocessor architecture. Here the load is evenly distributed across all processor modules. Each of the modules performs all routing tasks and has its own copy of the routing table. This is the most advanced architecture for routers.
IP routers
IP (Internet Protocol) is currently the most common (on the Internet). The protocol operates at the network layer and it is at this layer that routing decisions are made.
There are 2 approaches to choosing a route:
One-step approach;
Source routing.
At one-hop routing Each router takes part in selecting only one datagram transmission step. Therefore, the routing table line does not indicate the entire route (to the recipient), but only one IP address of the next router. For those addresses that are not in the table, the default router address is used.
Algorithms for constructing tables for one-hop routing can be as follows:
Fixed routing (the table is compiled “manually” by the administrator);
Random routing (the packet is transmitted in any random direction except the original one);
Flood routing (the datagram is transmitted in all directions except the original one);
Adaptive routing (the routing table is periodically adjusted based on network topology information from other routers).
Adaptive routing protocols are most widespread in IP networks. These protocols are: RIP, OSPF, IS-IS, EGP, BGP, etc. At source routing The route selection is made by the end node or the first router along the datagram path. This method has not found widespread use in IP networks, but is widely used in ATM networks (for example, the PNNI protocol).
Autonomous systems
Due to the growth of the Internet, the performance of routers has decreased significantly. The volume of traffic to support routing has increased incredibly and the routing tables have grown in size. In this regard, the Internet was divided into a number of Autonomous Systems (AC) (Autonomous System) (Fig. 7.1.). Each such system is a group of networks and routers managed by an authorized person. This allows the router within each AS to use different routing protocols. Here, dynamic routing protocols are used, defined as a class of IGP protocols (IGP - Interior Gateway Protocol - internal gateway protocol). This class includes the protocols RIP, IS-IS, etc.
For interaction between routers belonging to different ASs, an additional protocol called EGP (external gateway protocol) is used.
RIP protocol
The RIP protocol belongs to the IGP class. The protocol appeared in 1982 as part of the TCP/IP protocol stack. Became the standard routing protocol within an autonomous system. Limitation - the protocol does not support long paths containing more than 15 transitions.
The metric used is the number of hops (that is, the number of routers that a datagram must pass through before reaching the recipient). The path with the fewest hops is always chosen.
Periodically, each router sends route update messages to its neighbors. Such a message contains its entire routing table. This table is first filled with the addresses of those networks to which the router has direct access (see Fig. 7.2.).
Before transmitting information to a neighboring router, the table is adjusted - the number of transitions to the recipient increases by one. Upon receiving such a service message from a neighboring router, the router updates its routing table in accordance with the following rules:
a) If the new number of transitions is less than the old one (for the address specific network) – this entry is entered into the routing table.
b) If the entry came from the router that was the source of the already stored entry, then the new hop count value is entered even if it is greater than the old one.
By default, the interval between sending messages is 30 seconds. If a neighboring router is silent for a long time (more than 180 s), entries related to it are deleted from the routing table (assuming a failure of the line or the router itself).
OSPF protocol
The OSPF (Open Shortest Path First) protocol was adopted in 1991. It is intended for use in large distributed networks. Based on the channel state algorithm. The essence of this1 algorithm is that it must calculate the shortest path. By “shortest” we do not mean the physical length, but the time of information transfer. The router sends queries to its neighbors located in the same routing line to determine the state of the links to and from them. The state of the channel is characterized by several parameters called “metrics”. It could be:
Channel capacity;
Delay of information when passing through this channel, etc. Having summarized the information received, the router communicates it to all neighbors. after that, it constructs a directed graph of the routing domain topology. Each edge of the graph is assigned an evaluation parameter (metric) (Fig. 7.3.).
Then Dijkstra's algorithm is used, which traverses two given nodes with a set of edges with the lowest total cost, i.e. the optimal route is selected. In accordance with this, a routing table is built.
The OSPF protocol belongs to the class of IP protocols and replaces the RIP protocol in large and complex networks. Information about channel status is sent every 30 minutes. Based on these messages, a link state database (Link-State 1 Datadase) is created on each router. This base is the same on all routers in the domain.
Based on this database, the router generates a network topology map and a tree of shortest paths to all possible recipients (see figure). Then a routing table is formed (Table 7.1.). For networks directly connected to the router, the metric is set to zero.
When the state of at least one connected channel changes, the router sends messages to its neighbors. The channel database is adjusted, the shortest paths are calculated, and the routing table is regenerated.
In large networks (with hundreds of routers), the protocol generates a lot of routing information, and the link state database can reach several MB.
Lecture 19 a brief description of protocols
Questions:
1. Routing. Types and algorithms of routing.
2. Dynamic routing protocol RIP.
3. ICMP Control Message Protocol.
4. UDP protocol.
5. TCP protocol.
6. DNS protocol.
7. SNMP network management protocol.
8. Protocols remote control. Telnet protocol.
9. File exchange protocols.
10. SMTP, POP3, IMAP protocol.
11. HTTP protocol.
Routing refers to the movement of information from a source to a destination through an internetwork. Routing is often contrasted with bridging, which, in the popular understanding of this method, performs exactly the same functions. The main difference between the two is that bridging takes place at Layer 2 reference model ISO, while routing occurs at Layer 3. This difference accounts for the fact that routers use logical addresses (such as IP addresses) and bridges use hardware addresses.
From a commercial point of view, routing only gained popularity in the 1970s.
A routing table is a form of rules by which IP datagrams of this computer sent to the destination address of the datagram. Routing tables are created not only in special devices - routers, but also on each computer. The routing table can be static or dynamic.
The distribution of static routing tables is set by the network administrator before routing begins. It does not change unless the network administrator changes it. Algorithms that use static routes are easy to develop and work well in environments where network traffic is relatively predictable and the network design is relatively simple.
Dynamic routing algorithms adapt to changing network conditions in real time. They do this by analyzing incoming routing update messages. If the message indicates that a network change has occurred, the routing programs recalculate the routes and send new routing adjustment messages. Such messages permeate the network, prompting routers to re-run their algorithms and change routing tables accordingly.
Algorithm for searching a route in a routing table
The table contains entries that consist of a network address field, a network mask field, a gateway address field, a network interface address field, and a metrics field.
When a computer sends a datagram, it first determines whether the recipient's address is on the same branch as the sender's address, if so, then the datagram is sent to the recipient directly. (direct routing) If not, then the routing table is looked up for an entry corresponding to the address destinations (indirect routing).
The search algorithm is as follows. If for any record the bitwise product of the destination IP address and the network mask field matches the value of the network address field, then this datagram will be sent to the gateway corresponding to this record, specified in the gateway address field, via network interface– host of the sender of the datagram to this gateway, specified in the network interface address field.
In the TCP/IP stack, not only routers, but also end nodes make decisions about who to send a packet to for its successful delivery to the destination node, based on the so-called routing tables.
Consider the following example of organizing a small class C network connected to an Internet provider through a router, which at the same time provides communication between these two segments. Let the network number allocated to this organization be 210.20.30, and the Internet gateway address be 210.20.30.254.
Questions:
1. What goods are transported by routes?
2. What is a route called?
3. Positive aspects of routing?
4. Who sets the weight and length standards for block trains and on what do they depend?
Literature:
1. Perepon V.P. "Organization of cargo transportation." Route 2003 (page 114)
Routing shipments from loading points is a highly efficient way to organize freight transportation.
Routing is the subject of a contract for the organization of cargo transportation by rail, therefore only the parties to the contract have the right to determine its content. It may provide for departure routes formed on a railway access track or on railway station, groups of cars for organizing stepped station or section routes, etc.
Each loaded car or group of loaded cars is not sent directly to the destination station, but is included in the train for that direction.
The process of waiting for the required number of cars for a full train is called accumulation . After the accumulation of cars, special trains are organized. This organization is called train formation plan .
According to the conditions of formation, bulk cargo: coal, ore, oil, building materials, etc. transported by routes.
Route - this is a train of a set weight or length, formed by the shipper or the road in accordance with the PTE and the formation plan from cars loaded by one or more shippers at one or more stations, assigned to one unloading station or in a spray with the mandatory release of at least one technical station from processing car traffic.
Routing is one of the effective methods of transporting goods and has the following positive aspects: Sending routes pass through one or more marshalling stations without processing, therefore, the delivery of cargo is accelerated, the work of reforming trains is reduced, the cost of transportation is reduced, the turnover of wagons is accelerated, the need for wagons is reduced, it is better the safety of transported goods is ensured, the competitiveness of goods manufacturers and railway transport increases.
Standards for the weight and length of block trains for roads are established by the Ministry of Transport. This depends on local conditions (terrain, track profile, technical equipment of the site, length of receiving and departure tracks). It is prohibited to change the established standards for the weight and length of routes on roads in the direction of increase, but in the direction of decrease it is possible, but not by more than one car. Established norms of weight and length of routes are announced to shippers.
The railway is obliged to provide wagons primarily for loading to those shippers who send goods along routes; for this purpose, preferential transportation tariffs are provided.
The basis for organizing shipping routes is the calendar planning of loading at intermediate stations to different destinations on certain days. Scheduling allows you to organize routes from wagons loaded by several shippers, when the loading size of each of them is insignificant.
Magnitude (and in calculations the following can be accepted:
■ for automated and mechanized hump sorting
stations 1.5-2.2 hours;
■ for non-mechanized stations 2.1-2.8 hours; „|____________ ;:_,___ , t ________ „„..
■ for humpless stations 4.0-5.0 hours.
In addition, when passing jets without processing, it must be taken into account that recycling carriages at stations and pass them without processing The costs are far from the same. Recycling requires sorting tracks, humps, hoods, locomotives, and a large staff of station workers.
Therefore, in order to take into account the economic costs of the options, the concept of the equivalent of car recycling was introduced. Savings from railcar recycling are expressed by the equivalent h in= 1.5-2.5, savings in locomotive hours and crew hours are expressed by h = 0.4-1.5.
Thus, the final formula for calculating the reduced car-hour savings per car is:
All calculations by definition T are conducted at the Ministry of Railways of Russia using electronic computer technology.
3.2. Organization of car flows from loading points
Types of routes, basic routing indicators
On railway networks are allocated several hundred main, decisive stations, at which 70 % loading, and about the same number of stations - 70 % unloading. At loading stations, powerful cargo flows are formed, which are included in the top ten most important cargoes: oil, forestry, coal, ore, construction, chemical and mineral fertilizers, grain, etc. The most effective way organization of car flows is transportation routing. It allows you to speed up the delivery of goods, reduce the need for a working fleet of cars, free passing stations from expensive work on processing cars, and therefore reduce operating costs in the transportation process.
The routes are distinguished:
According to the terms of the organization from the loading points;
■ for its intended purpose;
According to the terms of the application.
According to the conditions of the organization, the following routes are distinguished from the loading points:
Routes are distinguished by destination:
According to the terms of application, the routes are:
A high percentage of coverage by sender routing has such cargo as ore (more than 90%), coal and oil (about 70%), chemical and mineral fertilizers (more than 50%). Grain cargo is poorly routed (about 3 %).
If we analyze the distance traveled, then more than 57% of routes follow short distances(up to 400 km). And routes traveling over distances of more than 1,500 km make up only 10%. The indicated percentages cannot fully characterize the level of routing on the network, because one third of the routes go only to route bases, i.e. into spraying, which is less efficient compared to pure sender routing to the unloading station.
The quality of routing organization is assessed by the following indicator:
as routing level ^, where () m is the mass of goods sent on routes; 0, - total weight of shipped goods.
But it is much more expedient to take the ratio ^-p as the main indicator of the routing level, where 1 M is the average route distance
volume of cargo on shipping routes, km; I is the average distance of cargo, km.
Routing involves two major components: determining optimal routing paths and transporting groups of information (usually called packets) across an internetwork. In this paper, the latter of these two components is called switching. Switching is relatively simple. On the other hand, route determination can be very complex process
Route determination can be based on various indicators (values resulting from algorithmic calculations on a single variable - for example, route length) or combinations of indicators. Software implementations routing algorithms calculate route metrics to determine optimal routes to a destination.
To facilitate the route determination process, routing algorithms initialize and maintain routing tables that contain routing information. Routing information changes depending on the routing algorithm used.
Routing algorithms fill routing tables with a certain amount of information. Destination/Next Hop associations tell the router that a certain destination can be optimally reached by sending a packet to a certain router representing the "next hop" on the way to the final destination. When a router receives an incoming packet, it checks the destination address and tries to associate that address with the next forwarding.
Routing tables may also contain other information. "Indicators" provide information about the desirability of a particular channel or path. Routers compare metrics to determine optimal routes. The indicators differ from each other depending on the routing algorithm used. A number of common indicators will be presented and described later in this chapter.
Routers communicate with each other (and maintain their routing tables) by passing various messages. One type of such message is a "routing update" message. Routing updates typically include all or part of the routing table. By analyzing routing update information from all routers, any one of them can build a detailed picture of the network topology. Another example of messages exchanged between routers is a “link-state announcement.” A link-state announcement informs other routers about the status of the sender's links. Link information can also be used to build a complete picture of the network topology. Once the network topology is understood, routers can determine optimal routes to destinations.
