HP OpenVMS System Manager's Manual, Volume 2:...

Managing the Local Area Network (LAN) Software

Managing Local Area Networks

Understanding Local Area Networks  

• Ethernet--One of the earliest and the most common LANs. Ethernet can refer to either a general LAN application (for example, Ethernet address) or to the specific CSMA/CD (carrier sense multiple access with collision detection) technology that implements the Intel®, Xerox, and Digital intercompany Ethernet specifications.
  
  The three types of Ethernet LANs are the following:

  Ethernet (IEEE 802.3) with transmission speeds of 10Mbps

  Fast Ethernet (IEEE 802.3u) with transmission speeds of 100Mbps

  Gigabit Ethernet (IEEE 802.3z) with transmission speeds of 1000Mbps

  All three types of Ethernet employ the CSMA/CD protocol and the same frame format and same frame size. Optionally, Gigabit Ethernet allows the use of oversize frames, called jumbo frames.



• FDDI (Fiber Distributed Data Interface) -- Implemented as a dual-ring, token ring LAN.



• Token Ring -- The IEEE 802.5 token passing ring.



• ATM (Asynchronous Transfer Mode) -- The following standards are supported:

  LAN emulation over ATM supports the ATM Forum's LAN Emulation V1.0 (LANE) standard.

  Classical IP over ATM supports the RFC 1577 standard. (DGLTA, DGLPA, DGLPB only)




• Shared memory -- Emulation of Ethernet among Galaxy nodes using shared memory.

LAN Characteristics  

LAN controllers are devices that, along with additional external hardware, implement the Ethernet, FDDI, Token Ring, LAN emulation over ATM or Classical IP (RFC 1577) specifications. A LAN controller and the local system constitute a node. The LAN controller communicates with the local system through the system bus, and with remote systems implementing the Ethernet, FDDI, Token Ring, or LAN emulation over ATM specifications through the communication medium.

The Ethernet specification is described in The Ethernet-Data Link Layer and Physical Layer Specification and specifications available from IEEE. The FDDI specifications are available from ANSI. The Token Ring specifications are available from IEEE. The LAN emulation over ATM specifications are available from the ATM Forum.

Application programs use the LAN driver's QIO and VCI interfaces to perform I/O operations to and from other nodes on the LAN. For information about the QIO and VCI interfaces, refer to the HP OpenVMS I/O User's Reference Manual.

Characteristics of LAN Media provides a brief summary of the differences between the types of LAN media.

Table 1   Characteristics of LAN Media

Media	Speed	Maximum Frame Size	Maximum Cable Lengths1
Ethernet 802.3	10Mbps	1518 bytes	10Base-T - 100 meters 10Base-2 - 185 meters 10Base-5 - 500 meters
Fast Ethernet 802.3u	100Mbps	1518 bytes	100Base-TX--100 meters 100Base-FX--- 2KM
Gigabit Ethernet 802.3z	1000Mbps	1518 or 9018 bytes	1000Base-SX fiber optic - 550 meters 1000BaseT copper UTP--100 meters
FDDI	100Mbps	4495 bytes	UTP - 100 meters Multinode fiber - 2KM
Token Ring 802.5	4 or 16 Mbps	4462 bytes	UTP - 45 meters STP - 110 meters
LAN emulation over ATM	155Mbps or 622Mbps	1516, 4544, or 9234	Multinode fiber - 2KM UTP - 300 meters

Ethernet LANs  

An Ethernet network consists of a set of nodes connected by various types of cables, communicating according to the CSMA /CD protocol. In the simplest form of a network, two systems can be connected by a single cable in point-to-point fashion. More complex configurations add Ethernet switches and hubs to connect more systems.

FDDI LANs  

FDDI uses a dual ring of trees topology. It uses one ring as the primary ring, the other ring as a backup, and the tree configuration for increased flexibility, manageability, and availability.

FDDI networks and Ethernet networks can be combined to form a single extended LAN. This lets applications running on a system connected to FDDI communicate with applications that run on a system connected to Ethernet.

An FDDI concentrator or switch provides for the attachment of FDDI devices such as VAX and Alpha nodes or FDDI-Ethernet bridges to the LAN.

Token Ring LANs   

Token Ring controllers use either shielded or unshielded twisted pairs of wire to access the ring. Note that it is difficult to connect a Token Ring LAN directly bridged to any other type of LAN. However, routing protocols to other LANs allow interconnection.

ATM LANs   

LANs over ATM consist of a connection-oriented network based on cell switching. The OpenVMS ATM network uses AAL5 ATM adaption layer for data transmission.

For LAN emulation over ATM, OpenVMS implements only the LAN emulation client (LEC) and does not implement the LAN emulation server (LES), the Broadcast and Unknown (BUS), or the LAN emulation Configuration Server (LECS). The LES, BUS, and LECS must be provided by some other facility such as the ATM switch. OpenVMS supports eight LAN emulation clients per ATM adapter.

Classical IP over ATM (CLIP) implements a data-link level device that has the same semantics as an Ethernet interface (802.3). This interface is used by a TCP/IP protocol to transmit 802.3 (IEEE Ethernet) frames over an ATM network. The model that OpenVMS follows for exchanging IP datagrams over ATM is based on RFC1577 (Classical IP over ATM).

LAN Addresses  

Nodes on the LAN are identified by unique addresses. A message can be sent to one, several, or all nodes on the LAN simultaneously, depending on the address used.

Upon application, IEEE assigns a block of addresses to a producer of LAN nodes. Thus, every manufacturer has a unique set of addresses to use. Normally, one address out of the assigned block of physical addresses is permanently associated with each controller (usually in read-only memory). This address is known as the hardware or MAC address of the controller. Each controller has a unique hardware address.

A LAN address is 48 bits in length. LAN addresses are represented as six pairs of hexadecimal digits (six bytes) separated by hyphens (for example, AA-01-23-45-67-FF). The bytes are displayed from left to right in the order in which they are transmitted; bits within each byte are transmitted from right to left. In this example, byte AA is transmitted first; byte FF is transmitted last.

A LAN address can be an address of a single node or a multicast address, depending on the value of the low-order bit of the first byte of the address (this bit is transmitted first). The two types of node addresses are:

• Individual or physical address--The unique address of a single node on a LAN. The least significant bit of the first byte of a physical address is 0. (For example, in physical address AA-00-03-00-FC-00, byte AA in binary is 1010 1010, and the value of the low-order bit is 0.)



• Multicast address--A group address that can be recognized by one or more nodes on a given LAN. The least significant bit of the first byte of a multicast address is 1. (For example, in the multicast address 0B-22-22-22-22-22, byte 0B in binary is 0000 1011, and the value of the low-order bit is 1.)
  
  Token Ring devices do not support IEEE 802 standard multicast addresses. They do support functional addresses. A functional address is a locally administered group address that has 31 possible values. Each functional address sets one bit in the third through sixth bytes of the address, and bytes 1 and 2 are 03-00 (C0:00 in bit reversed format). To convert a multicast address to a functional address, use the LANCP command SET DEVICE/MAP.

1	Larger networks can be constructed with hubs, bridges, and switches.

( Number takes you back )

Managing Local Area Networks