Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
2000-09-29
2004-11-23
Olms, Douglas (Department: 2661)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S235000, C370S395210
Reexamination Certificate
active
06822940
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to computer networks, and more specifically, to a method and apparatus for adapting enforcement of network quality of service policies in a network system based on feedback about network conditions.
BACKGROUND OF THE INVENTION
A computer network typically comprises a plurality of interconnected entities that transmit (“source”) or receive (“sink”) data frames. A common type of computer network is a local area network (“LAN”) that generally comprises a privately owned network within a single building or campus. LANs employ a data communication protocol (LAN standard) such as Ethernet, FDDI, or Token Ring, that defines the functions performed by the data link and physical layers of a communications architecture (i.e., a protocol stack), such as the Open Systems Interconnection (OSI) Reference Model. In many instances, multiple LANs may be interconnected by point-to-point links, microwave transceivers, satellite hookups, etc., to form a wide area network (“WAN”), metropolitan area network (“MAN”) or Intranet. These internetworks may be coupled through one or more gateways to the global, packet-switched internetwork generally known as the Internet or World Wide Web (WWW).
Each network entity preferably includes network communication software, which may operate in accordance with Transport Control Protocol/Internet Protocol (TCP/IP). TCP/IP generally consists of a set of rules defining how entities interact with each other. In particular, TCP/IP defines a series of communication layers, including a transport layer and a network layer. At the transport layer, TCP/IP includes both the User Data Protocol (UDP), which is a connectionless transport protocol, and TCP, which is a reliable, connection-oriented transport protocol. When a process at one network entity wishes to communicate with another entity, it formulates one or more messages and passes them to the upper layer of the TCP/IP communication stack. These messages are passed down through each layer of the stack where they are encapsulated into packets and frames. Each layer also adds information in the form of a header to the messages. The frames are then transmitted over the network links as bits. At the destination entity, the bits are re-assembled and passed up the layers of the destination entity's communication stack. At each layer, the corresponding message headers are stripped off, thereby recovering the original message that is handed to the receiving process.
One or more intermediate network devices are often used to couple LANs together and allow the corresponding entities to exchange information. For example, a bridge may be used to provide a “bridging” function between two or more LANs. Alternatively, a switch may be utilized to provide a “switching” function for transferring information, such as data frames or packets, among entities of a computer network. Typically, the switch is a computer having a plurality of ports that couple the switch to several LANs and to other switches. The switching function includes receiving data frames at a source port and transferring them to at least one destination port for receipt by another entity. Switches may operate at various levels of the communication stack. For example, a switch may operate at Layer
2
, which in the OSI Reference Model, is called the data link layer, and includes the Logical Link Control (LLC) and Media Access Control (MAC) sub-layers.
Other intermediate devices, commonly known as routers, may operate at higher communication layers, such as Layer
3
, which in TCP/IP networks corresponds to the Internet Protocol (IP) layer. Conventionally, IP data packets include a corresponding header that contains an IP source address and an IP destination address. Routers or Layer
3
switches may re-assemble or convert received data frames from one LAN standard (e.g., Ethernet) to another (e.g., Token Ring). Thus, Layer
3
devices are often used to interconnect dissimilar subnetworks. Some Layer
3
intermediate network devices may also examine the transport layer headers of received messages to identify the corresponding TCP or UDP port numbers being utilized by the corresponding network entities. Many applications are assigned specific, fixed TCP and/or UDP port numbers in accordance with Request For Comments (RFC)
1700
. For example, TCP/UDP port number
80
corresponds to the Hypertext Transport Protocol (HTTP), while port number
21
corresponds to File Transfer Protocol (FTP) service.
Allocation of Network Resources
A process executing at a network entity may generate hundreds or thousands of traffic flows that are transmitted across a network. Generally, a traffic flow is a set of messages (frames and/or packets) that typically correspond to a particular task, transaction or operation (e.g., a print transaction) and may be identified by various network and transport parameters, such as source and destination IP addresses, source and destination TCP/UDP port numbers, and transport protocol.
The treatment that is applied to different traffic flows may vary depending on the particular traffic flow at issue. For example, an online trading application may generate stock quote messages, stock transaction messages, transaction status messages, corporate financial information messages, print messages, data backup messages, etc. A network administrator may wish to apply a different policy or service treatment (“quality of service” or “QoS”) to each traffic flow. In particular, the network administrator may want a stock quote message to be given higher priority than a print transaction. Similarly, a $1 million stock transaction message for a premium client should be assigned higher priority than a $100 stock transaction message for a standard customer.
Computer networks include numerous services and resources for use in moving traffic throughout the network. For example, different network links, such as Fast Ethernet, Asynchronous Transfer Mode (ATM) channels, network tunnels, satellite links, etc., offer unique speed and bandwidth capabilities. Additionally, the intermediate devices also include specific resources or services, such as a particular number of buffers or priority queues, filter settings, availability of different queue selection strategies, congestion control algorithms, etc.
Individual frames or packets can be marked so that intermediate devices may treat them in a predetermined manner. For example, the Institute of Electrical and Electronics Engineers (IEEE) describes additional information for the MAC header of Data Link Layer frames in Appendix 802.1p to the 802.1D bridge standard.
FIG. 1A
is a partial block diagram of a Data Link frame
100
that includes a MAC destination address (DA) field
102
, a MAC source address (SA) field
104
and a data field
106
. According to the 802.1Q standard, a user_priority field
108
, among others, is inserted after the MAC SA field
104
. The user_priority field
108
may be loaded with a predetermined value (e.g., 0-7) that is associated with a particular treatment, such as background, best effort, excellent effort, etc. Network devices, upon examining the user_priority field
108
of received Data Link frames
100
, apply the corresponding treatment to the frames. For example, an intermediate device may have a plurality of transmission priority queues per port, and may assign frames to different queues of a destination port on the basis of the frame's user priority value.
FIG. 1B
is a partial block diagram of a Network Layer packet
120
corresponding to the Internet Protocol. Packet
120
includes a type_of_service (ToS) field
122
, a protocol field
124
, an IP source address (SA) field
126
, an IP destination address (DA) field
128
and a data field
130
. The ToS field
122
is used to specify a particular service to be applied to the packet
120
, such as high reliability, fast delivery, accurate delivery, etc., and comprises a number of sub-fields. The sub-fields may include a 3-bit IP precedence (IPP) field and three one-bit
Zavalkovsky Arthur
Zlotkin Gilad
Cisco Technology Inc.
Hickman Palermo & Truong & Becker LLP
Nguyen Brian
Olms Douglas
LandOfFree
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