Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-10-26
2002-11-26
Olms, Douglas (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S474000
Reexamination Certificate
active
06487217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to the field of computer networking. More particularly, the present invention relates to a method for transmitting delay sensitive information over systems using both Internet Protocol and Frame Relay.
2. The Background Art
Modern computer networks are divided up into layers. Each layer is responsible for providing some service to the layer above it, and may use the services of the layer below it. The International Standards organization (ISO) defined seven layers as a standard for computer networks. This standard is depicted in
FIG. 1
at reference numeral
10
. The layers are defined as follows:
(1) A physical layer, which is responsible for transmitting unstructured bits of information across a link.
(2) A data link layer, which transmits chunks of information across a link.
(3) A network layer, which is responsible for ensuring that any pair of systems in the network can communicate with each other.
(4) A transport layer, which establishes a reliable communications stream between a pair of systems.
(5) A session layer, which offers services above the simple full-duplex reliable communication stream provided by the transport layer.
(6) A presentation layer, which is responsible for providing a means by which applications can agree on representations of data.
(7) An application layer, which runs applications.
An increase in the use of the Internet in the 1970's made it necessary for a standard to be created for communications over the Internet. This was prompted by the fact that the Internet comprises what is essentially a huge number of smaller networks, each of the smaller networks possibly having different standards of communication. Therefore, the Internet Protocol Suite was created to- establish a single standard of communicating over the Internet, while still allowing for individual networks to maintain their own standards of communications within their own networks.
The Internet Protocol Suite is depicted in
FIG. 1
at reference numeral
12
. It comprises several standards for many of the network layers defined by the ISO. The Internet Protocol Suite standard for use with the network layer is called the Internet Protocol (IP), depicted at reference numeral
14
of FIG.
1
. IP provides fragmentation and reassembly of data as well as error reporting and, along with TCP, is the heart of the Internet Protocol Suite.
IP works by splitting up data into IP packets, or chunks of information which contain not only the data to be transmitted but a variety of other information about the data as well. The IP Packet format is depicted in FIG.
2
. The IP packet
20
contains the following fields:
(1) Version
22
, which indicates the version of IP currently used.
(2) IP Header Length (IHL)
24
, which indicates the packet header length in 32-bit words.
(3) Type-of-Service
26
, which specifies how the upper layer protocol wants the packet to be handled.
(4) Total length
28
, which indicates the length in bytes of the entire packet, including the header and data.
(5) Identification
30
, which contains an integer identifying the packet, allowing for packets to be reassembled upon delivery.
(6) Flags
32
, which indicate whether the packet can be fragmented and whether the packet is the last fragment in a series of fragmented packets.
(7) Fragment Offset
34
,
(8) Time-to-live
36
, which maintains a counter which gradually decrements down to zero at which point the packet is discarded, which keeps packets from looping infinitely.
(9) Protocol
38
, which indicates which upper-layer protocol should receive the packet after IP processing is complete.
(9) Header checksum
40
, which helps ensure IP header integrity.
(10) Source address
42
, which specifies the sending node.
(11) Destination address
44
, which specifies the receiving node.
(12) Options
46
, which allows IP to support carious options, such as security.
(13) Data
48
, which contains the information itself.
IP remains the standard for network layer communication over the Internet even today. Additionally, many individual networks have also adopted the IP standard within their own network. IP remains the standard of choice for networks which utilize phone lines or other low speed, low reliability communications mediums, as it was designed with many safeguards to prevent errors.
Additionally, the use of IP packets allows a tremendous flexibility for a system to fragment data and send the packets in an order that maximizes efficiency. For example, if one user is sending an extremely large piece of information, while another was sending an extremely small piece of information, without fragmentation it would be possible for the user sending the extremely small piece of information to encounter an extremely large delay while the large piece of information was transmitted over the network. By fragmenting the large piece of information into packets, however, it is possible for the system to implement a feature wherein access to the bandwidth of the network is rotated evenly from user to user. This would mean that a portion of the large piece of information is sent, then the small piece of information is sent, then the rest of the large piece of information is sent. Thus, routers were designed with just such a feature, where access to the network was cycled between the users in equal doses.
A problem arises, however, in the transmission of voice, audio, video, or other delay sensitive information, over IP. IP was designed for the transmission of data, not voice. When transmitting data, delays, while annoying, normally do not affect the usefulness of the data. Unlike data, however, voice is delay sensitive. When talking on the phone, a delay of even a second between transmission and receipt can interrupt a conversation. In addition, there is a necessity in voice communication for two way simultaneous transmissions. For example, it is quite common for two people to speak at the same time during a conversation. Because of these requirements, it is necessary for voice to have simultaneous or near-simultaneous transmissions. Placing voice transmissions on the same level with data transmissions would result in ineffective voice transmission.
There are other types of delay sensitive information that are sometimes transmitted over networks. These can include such things as real-time video transmissions, interactive video game transmissions, and the like. Delay sensitive information is any information whose usefulness may be diminished significantly by delays in transmission. The main type of delay sensitive information is voice, but the same techniques used to handle voice information may be used to handle other types of delay sensitive information as well.
In order to remedy the problem of transmitting voice sensitive information over IP, two different solutions were developed. In the first, one of the type-of-service bits
26
is used to signify whether the data is delay sensitive or not. Thus, a network device supporting delay-sensitive transmission will look to this bit to determine what precedence to give the data in the queue holding data waiting for transmission over the network.
The second solution developed for the transmission of voice over IP involves the use of a Resource Reservation Protocol (RSVP). In these systems, in order to successfully transmit voice from one node to another, every node in the chain must be one that honors the RSVP system. Then, before transmission occurred, each node in the chain would be contacted and told to reserve a certain amount of bandwidth for the incoming transmission. After each node complied, the conversation could be initiated.
FIG. 3
depicts an example of an IP network
60
. For simplicity, this network
60
may be thought of as the Internet, with node A
62
, node B
64
, node C
66
, and node D
68
. These nodes
62
,
64
,
66
,
68
may be Internet domains, each containing a subnetwork
70
,
72
,
74
,
76
respectively. If a user at node A
62
wanted to engage in a voice conversation
Cisco Technology Inc.
Hanish Marc S.
Olms Douglas
Thelen Reid & Priest LLP
Vanderpuye Ken
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