Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data transfer regulating
Reexamination Certificate
1998-03-30
2001-06-12
Rinehart, Mark H. (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data transfer regulating
C709S235000, C709S240000, C370S418000, C370S429000, C710S053000, C710S054000, C702S187000
Reexamination Certificate
active
06247058
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communication between network nodes. More specifically, the present invention relates a network device that transmits data packets between network segments and time stamps arriving packets to support a variety of packet management functions.
DESCRIPTION OF THE RELATED ART
In the art of computer networking, protocol stacks are commonly used to transmit data between network nodes that are coupled by network media. Network nodes include devices such as computer workstations, servers, network printers, network scanners, and the like. To harmonize the development and implementation of protocol stacks, the International Standards Organization (ISO) promulgated an Open System Interconnection (OSI) Reference Model that prescribes seven layers of network protocols.
FIG. 1
is a block diagram
10
of the OSI Reference Model. The model includes a hardware layer
12
, a data link layer
14
, a network layer
16
, a transport layer
18
, a session layer
20
, a presentation layer
22
, and an application layer
24
. Each layer is responsible for performing a particular task. Hardware layer
12
is responsible for handling both the mechanical and electrical details of the physical transmission of a bit stream. Data link layer
14
is responsible for handling the packets, including generating and decoding of the address used by the hardware protocol and any error detection and recovery that occurred in the physical layer. For example, in an Ethernet network data link layer
14
is responsible for generating and decoding the media access control (MAC) address. Network layer
16
is responsible for providing connections and routing packets in the communication network, including generating and decoding the address used by upper level protocols and maintaining routing information for proper response to changing loads. For example, in the TCP/IP protocol, network layer
16
is responsible for generating and decoding the IP address. Transport layer
18
is responsible for end-to-end connections between nodes in the network and the transfer of messages between the users, including partitioning messages into packets, maintaining packet order and delivery, flow control, and physical address generation. Session layer
20
is responsible for implementing the process-to-process protocols. Presentation layer
22
is responsible for resolving the differences in formats among the various sites in the network, including character conversions, and duplex (echoing). Finally, application layer
24
is responsible for interacting directly with the users. Layer
24
may include applications such as electronic mail, distributed data bases, web browsers, and the like.
Before the ISO promulgated the OSI Reference Model, the Defense Advanced Research Projects Agency (DARPA) promulgated the ARPNET Reference Model. The ARPNET reference model includes four layers, a network hardware layer, a network interface layer, a host-to-host layer, and a process/application layer.
As their names imply, the OSI and ARPNET Reference Models provide guidelines that designers of protocols may or may not choose to follow. However, most networking protocols define layers that at least loosely correspond to a reference model.
In the field of computing, there are many popular protocols used to transmit data between network nodes. For example, TCP/IP, AppleTalk®, NetBEUI, and IPX are all popular protocols that are used to transmit data between servers, workstations, printers, and other devices that are coupled to computer networks.
It is common for several protocols to operate concurrently within a single network node, even if the network node has a single network interface. For example, a typical computer workstation may use TCP/IP to communicate over the Internet, and IPX to communicate with a network server. Likewise, a printer may be configured to receive print jobs using either the AppleTalk® protocol or the NetBEUI protocol. Typically these protocols sit on top of lower level hardware protocols. For example, it is common for two computer systems coupled via an Ethernet network to communicate using the TCP/IP protocol. Generally, a software routine existing at data link layer
14
or network layer
16
routes data packets between the network adapter and the proper protocol stack.
Consider a TCP/IP packet transmitted over an Ethernet network. The Ethernet packet includes a 48-bit media access control (MAC) address that addresses another node on the Ethernet network. The entire Ethernet packet is protected by a cyclic redundancy check (CRC) code that is calculated and stuffed into the Ethernet packet by the sending network adapter, and is used by the receiving network adapter to verify the integrity of the Ethernet packet. If the integrity of the packet cannot be verified, the packet is discarded. Encapsulated within the Ethernet packet is the IP portion of the TCP/IP protocol, which is known in the art as a datagram. The datagram includes a 32-bit IP address and a 16 bit checksum code that protects the IP header. If the integrity of the IP header cannot be verified, the datagram is discarded. The TCP portion of the TCP/IP protocol is encapsulated within the datagram, and has a 16 bit checksum code that protects the TCP header and the contents of the TCP portion of the datagram. If the integrity of the TCP header or the contents of the TCP portion cannot be verified, the datagram is discarded and the sender will retransmit the packet after not receiving an acknowledge datagram from the intended recipient. Note that this packet contains two addresses, the Ethernet address and the IP address. The relationship between these two addresses will be described in greater detail below.
FIG. 2
is a diagram showing a prior art network
26
. Network
26
interconnects network nodes
28
,
30
,
32
,
34
,
36
,
38
,
40
,
42
, and
44
. As described above, the network nodes may be devices such as computer workstations, servers, network printers, network scanners, and the like. For the sake of this discussion, assume that the network nodes are equipped with Ethernet network adapters and transmit data using the TCP/IP protocol. Many networks conform to a series of standards promulgated by the Institute of Electrical and Electronics Engineers (IEEE). This series of standards is known in the art as the IEEE 802 family of standards. The IEEE 802 family of standards are hereby incorporated by reference.
The network nodes are coupled together into LAN segments via hubs. All nodes in a LAN segment are in a common collision domain because each node in a LAN segment receives a signal when another node attempts to transmit a packet, and if two nodes in a LAN segment attempt to transmit a packet at the same time, a collision occurs. The Ethernet protocol includes a retransmission algorithm that minimizes the likelihood that another collision will occur when the two nodes attempt to retransmit their respective packets. In
FIG. 2
, network nodes
28
,
30
, and
32
are coupled together into LAN segment
48
via hub
46
. Likewise, network nodes
34
,
36
, and
38
are coupled together into LAN segment
52
via hub
50
and network nodes
40
,
42
, and
44
are coupled together into LAN segment
56
via hub
54
.
Traditionally, a prior art hub was a network device that served as the central location for attaching wires from network nodes, such as workstations. Early prior art hubs were passive. There was no amplification of the network signals, and the hub simply coupled together the network wiring from the network nodes to form sets of common conductors that interconnected the nodes. On the other hand, repeaters provided amplification of signals between network nodes, thereby allowing a larger number of network nodes to be coupled together into LAN segments. More recently, hubs have begun to incorporate some of the functionality of switches (discussed in greater detail below) and repeaters. Modern hubs are capable of implementing multiple sub-networks such that two or more network nodes coupled to
Erlandson Erik E.
Miller John P.
Hewlett--Packard Company
Kang Paul
Plettner David A.
Rinehart Mark H.
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