Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-10-05
2003-11-18
Nguyen, Chau (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S392000, C370S401000
Reexamination Certificate
active
06650621
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to load balancing of IP traffic between more than one route between a node and an IP network. More particularly, the invention relates to such a method as described in the preamble of the independent method claim.
BACKGROUND OF THE INVENTION
IP network technology is presently in widespread use, the Internet being a manifest example of a network realized using Internet Protocol (IP). The IP protocol provides a basic packet data transfer mechanism without error checking, acknowledgments or flow control. Other protocols used in combination with the IP protocol such as the TCP protocol are used to provide a reliable data transmission mechanism with transmission error correction, flow control and many other functions. The IP protocol is defined in the specification RFC 791, and the TCP protocol is defined in the specification RFC 793. An introduction to these protocols is presented in RFC 1180. In the following, a short overview of these protocols are given.
The IP protocol version 4 (IPv4) defined by RFC 791 has a limited address space due to the source and destination addresses being only 32 bits long. The current expansion of the Internet and the development of technology, the address space is filling out quickly. Therefore, version 6 of the IP protocol (IPv6) has been designed. The addresses in IPv6 are 128 bits long, allowing a vastly larger address space. There are also further motivations behind IPv6 and other differences between IPv4 and IPv6. The IPv6 protocol is described in the specification RFC 1883. Some details of the TCP and IP protocols relevant to the present invention are described in the following with reference to
FIGS. 1
,
2
, and
3
.
In the IP protocol, data is transmitted in so called datagrams, which contain a header part and a payload data part.
FIG. 1
shows the structure of an IPv4 header. In the following only some of the header fields are described. A detailed description can be found from the above mentioned RFC 791. The first field, the four bits long version field, contains the version number which for IPv4 is 4. The total length field gives the length of the datagram, header and data part combined, as the number of octets i.e. groups of 8 bits. The source and destination addresses specify the IP address of the sender and the intended receiver. Various options can be specified in the options field, which may vary in length from datagram to datagram. The number of different options specified in the options field may as well vary. The options field is not mandatory, i.e. in some datagrams there may be no options field at all. The padding field is used to ensure that the header ends on a 32 bit boundary. The padding field is filled with zeroes. After the padding field comes the payload data part, whose length can be found out by the recipient of the datagram by subtracting the length of the header from the value of the total length field.
FIG. 2
illustrates the structure of an IPv6 header. The IPv 6 header is simpler than the IPv4 header, allowing faster processing of datagrams in transmission nodes. The first four bits of the header comprise the version field, which for IPv6 contains the value
6
. The payload length field specifies the length of the data part in octets. The next header field specifies the type of any header following this header. The next header may for example be a TCP header in case the IP datagram carries a TCP packet, or an extension header. The source and destination address fields, each consisting of four 32-bit words giving a total of 128 bits for each address, specify the sender and the intended receiver of the datagram. Instead of an options field, inclusion of optional data in the header is provided in IPv6 by so called extension headers. Various extension header types are described in RFC 1883. There may be zero, one or more than one extension headers in an IPv6datagram.
FIG. 3
illustrates the structure of a TCP header. The most relevant fields are described in the following. The other fields in a TCP header are described in the above mentioned RFC 793.
The TCP header indicates a destination port number at the receiving host, to which the packet is directed. The TCP protocol makes it possible for many different services to exist at a single IP address, by introducing the concept of a port. A program can listen to a specific port, and receive any data sent to that port. Conversely, a program can send a packet to a specific port on a distant host. Therefore, the destination port number defines which service or program will receive the packet at the host specified by the IP address. Similarly, the source port number indicates, which service or program sent the TCP packet.
The TCP data octets sent by a host are numbered sequentially. The number of the first octet of data in the data part is included in the TCP header in the sequence number field. Based on this number, the receiving second host can check whether TCP packets have arrived through the transmission network in the right order, and if any packets are missing. The second host conventionally sends an acknowledgment to the first host for each received packet. The acknowledgment message is included in a normal TCP packet sent by the second host to the first host. The acknowledgment is indicated by the ACK flag and the acknowledgment number. The acknowledgment number is the sequence number of the next octet, which the sender of the packet is expecting to receive from the other end. If there is no other data to be sent from the second host to the first host, the payload data part can be empty in such an acknowledgment packet. If the second host is transmitting data to the first host, the acknowledgment can be indicated in the header of a packet containing some payload data. Therefore, the ACK messages do not always add transmission load. If a host does not receive an acknowledgment for some data within a timeout period, the data is retransmitted.
The data part follows the TCP header. The length of the data part is carried by the IP protocol, therefore there is no corresponding field in the TCP header.
Due to the small number of IP addresses available in the IPv4 protocol, a technique known as network address translation (NAT) is used. With NAT, a private network such as the local area network of a company can be connected to the public Internet using only a small number of IP addresses of the public Internet, while allowing almost free use of IP addresses for traffic within the private network. Sessions with nodes in the public Internet are initiated from the private network. The network element connecting the two networks and performing the NAT function stores the source address of the initiating node within the private network, and replaces it by one of the small number of IP addresses of the public Internet. The network element stores the pair of an internal address and a public address, and performs source address translation for packets traversing from the internal node to the public Internet and destination address translation for packets traversing from the public Internet to the internal node. The network element retains the pair of addresses i.e. the binding until the internal node terminates all its connections to the public Internet, whereafter the network element may allocate the public address for use by another node of the internal network. The NAT function may also use the TCP port address in translation, whereby a binding specifies the pairing of an internal IP address and TCP port and an external IP address and a TCP port. Use of TCP ports in translation is used especially in the typical situation, in which the private traffic uses only one IP address of the public Internet. In such a situation, packets belonging to different connections from/to different hosts in the private network are kept separate by using different TCP ports for the connections.
The NAT functionality can also be used to increase the security of the internal network, since the NAT function hides the internal addresses, whereb
Fish Ron
Hyun Soon-Dong
Nguyen Chau
Ronald Craig Fish
Stonesoft Oy
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