Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1997-03-19
2001-09-18
Marcelo, Melvin (Department: 2663)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S356000, C370S401000
Reexamination Certificate
active
06292479
ABSTRACT:
TECHNICAL FIELD
The present invention relates to telecommunications networks and more particularly to the transport of a voice call through diverse network paths including a switched telephone network and a wide area data internetwork, for example, the Internet. The routing set-up for such call includes conveyance of caller identification information to the destination network to enable provision of caller information based enhanced services to subscribers.
BACKGROUND OF THE INVENTION
Implementation of voice telephone service over a worldwide data network, such as the Internet, offers advantages that are now being explored. The Internet basically comprises several large computer networks joined together over high-speed data links ranging from ISDN to T
1
, T
3
, FDDI, SONET, SMDS, OT
1
, etc.
A computer network is simply a collection of autonomous computers connected together to permit sharing of hardware and software resources, and to increase overall reliability. The qualifying term “local area” is usually applied to computer networks in which the computers are located in a single building or in nearby buildings, such as on a college campus or at a single corporate site. When the computers are further apart, the terms “wide area network” or “long haul network” are used, but the distinction is one of degree and the definitions sometimes overlap.
A bridge is a device that is connected to at least two LANs and serves to pass message frames or packets between LANs, such that a source station on one LAN can transmit data to a destination station on another LAN, without concern for the location of the destination. Bridges are useful and necessary network components, principally because the total number of stations on a single LAN is limited. Bridges can be implemented to operate at a selected layer of protocol of the network.
In operation, computer networks are governed by protocols, i.e., sets of conventions or rules that govern the transfer of data between computer devices. The simplest protocols define only a hardware configuration, while more complex protocols define timing, data formats, error detection and correction techniques, and software structures. Protocols generally are employed in multiple layers. A low-level physical layer protocol assures the transmission and reception of a data stream between two devices. Data packets are constructed in a data link layer. Over the physical layer, a network and transport layer protocol governs transmission of data through the network, thereby ensuring end-to-end reliable data delivery.
The Internet is a collection of networks, including Arpanet, NSFnet, regional networks such as NYsernet, local networks at a number of university and research institutions, and a number of military networks. TCP/IP protocols provide a set of services that permit users to communicate with each other across the entire Internet. The specific services that these protocols provide include file transfer, remote log-in, remote execution, remote printing, computer mail, and access to network file systems.
The basic function of the Transmission Control Protocol (TCP) is to ensure that commands and messages from an application protocol, such as computer mail, are sent to their desired destinations. TCP provides for keeping track of what is sent, and for retransmitting anything that does not get to its destination correctly. If any message is too long to be sent as one “datagram,” it will be split into multiple datagrams and TCP protocol ensures that they all arrive correctly and are reassembled for the application program at the receiving end. Since these functions are needed for many applications, they are collected into a separate protocol (TCP) rather than being part of each application.
The Internet Protocol (IP) provides a basic service to TCP: delivering datagrams to their destinations. TCP in effect hands IP a datagram with an intended destination; IP is unaware of any relationship between successive datagrams, and merely handles routing of each datagram to its destination. If the destination is a station connected to a different LAN, the IP makes use of routers to forward the message.
TCP/IP operates as a five layer protocol, the five layers generally described as follows:
Layer
5
—The Application Layer. Applications such as ftp, telnet, SMTP, and NFS relate to this layer.
Layer
4
—The Transport Layer. In this layer, TCP and UDP add transport data to the packet and pass it to layer
3
.
Layer
3
—The Internet Layer. When an action is initiated on a local host (or initiating host) that is to be performed or responded to on a remote host (or receiving host), this layer takes the package from layer
4
and adds IP information before passing it to layer
2
.
Layer
2
—The Network Interface Layer. This is the network device as the host, or local computer, sees it and it is through this medium that the data is passed to layer
1
.
Layer
1
—The Physical Layer. This is literally the Ethernet or Serial Line Interface Protocol (SLIP) itself.
At the receiving host the layers are stripped one at a time, and their information is passed to the next highest level until it again reaches the application level. If a gateway exists between the initiating and receiving hosts, the gateway takes the packet from the physical layer, passes it through a data link to the IP physical layer to continue. As a message is sent from the first host to the second, gateways pass the packet along by stripping off lower layers, readdressing the lower layer, and then passing the packet toward its final destination.
A router, like a bridge, is a device connected to two or more LANs. Unlike a bridge, however, a router operates at the network layer level, instead of the data link layer level. Addressing at the network layer level may make use of a 32-bit address field for each host, and the address field includes a unique network identifier and a host identifier within the network. Routers make use of the destination network identifier in a message to determine an optimum path from the source network to the destination network. Various routing algorithms may be used by routers to determine the optimum paths. Typically, routers exchange information about the identities of the networks to which they are connected.
When a message reaches its destination network, a data link layer address is needed to complete forwarding to the destination host. Data link layer addresses are 48 bits long and are globally unique, i.e., no two hosts, wherever located, have the same data link layer address. A protocol called ARP (address resolution protocol) obtains a data link layer address from the corresponding network layer address (the address that IP uses). Typically, each router maintains a database table from which it can look up the data link layer address, but if a destination host is not in this ARP database, the router can transmit an ARP request throughout the network that asks a host having the network layer address to supply its data link layer address in a return message. only the addressed destination host responds, and the router is then able to insert the correct data link layer address into the message being forwarded, and to transmit the message to its final destination.
IP routing specifies that IP datagrams travel through internetworks one hop at a time (next hop routing) based on the destination address in the IP header. The entire route is not known at the outset of the journey. Instead, at each stop, the next destination (or next hop) is calculated by matching the destination address within the datagram's IP header with an entry in the current node's (typically but not always a router) routing table.
Each node's involvement in the routing process consists only of forwarding packets based on internal information resident in the router, regardless of whether the packets get to their final destination. IP routing does not alter the original datagram; the datagram source and destination addresses remain unaltered. The IP header always specifies the IP address of the original
Bartholomew Dale L.
Farris Robert D.
Flaherty Stephen J.
Bell Atlantic Network Services Inc.
Lee Chiho Andrew
Marcelo Melvin
McDermott & Will & Emery
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